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The structure and mechanics of bone
Abstract
The four levels of hierarchy considered in this review are the nanoscale (the mineralised collagen fibre and the extrafibrillar mineral), the microscale (the structure as visible under the microscope), the mesoscale (particularly the relationship between cancellous and cortical bone) and the whole bone scale. The explosion of papers at the nanoscale precludes any settling on one best model. At the microscale the inadequacies of linear elastic fracture mechanics, the importance of R-curves for understanding what is happening to cracks in bone, and the effect of different histological types are emphasised. At the mesoscale the question of whether cancellous bone is anything but compact bone with a lot of holes in it, and the question of whether cancellous bone obeys Wolff's 'law' is discussed. The problem of not damaging bone when examining it with X-rays is mentioned (though not solved). At the whole bone level the relative roles of genetics and the external forces and the question of the way in which bones are loaded, in bending or compression, is raised, and the question of size effects, long underestimated or ignored by the bone community, is discussed. Finally, the question of why there are hierarchies at all in bone is addressed.
... Total fragmentation was only registered on dry specimens (19.53%) (Tables 3 and 4). Different authors state that the hydrated, fresh or dry condition of a bone determines its mechanical properties (Nyman et al. 2006;Currey 2012;Marín-Monfort et al. 2014, and references therein). In mammals, the presence of water affects the mechanical properties of the bone generating more plasticity (Nyman et al. 2006;Marín-Monfort et al. 2014 and references therein). ...
... The mechanical properties of dry bones, by comparison to wet bones are defined by higher stiffness and lower anelastic deformation (Nyman et al. 2006;Currey 2012;Marín-Monfort et al. 2014). Thus, under similar compression conditions, dry bones reach the mechanical failure point faster than hydrated specimens. ...
... Bone is a complex and dynamic tissue that provides mechanical support to the body and plays crucial roles in calcium homeostasis and haematopoiesis [1]. The inorganic phase of bone is primarily composed of calcium phosphates (CaP), predominantly in the form of hydroxyapatite (HAp, Ca10(PO4)6(OH)2) which corresponds to 65 -70% of bone tissue [2]. ...
Chitosan-based scaffolds offer significant potential in tissue engineering and regenerative medicine. Whilst exhibiting great bio-regenerative and biocompatible properties, their mechanical properties remain quite poor. The presented research is focused on the modification of macroporous chitosan scaffolds with various amounts of bioactive ceramics (hydroxyapatite) and its influence on the physical and rheological properties of the composite scaffold. Chitosan/hydroxyapatite composite scaffolds with a highly porous microstructure have been prepared by suspending hydroxyapatite (HAp) particles into the chitosan matrix. According to SEM imaging, homogeneous dispersion of the inorganic phase in a chemically-crosslinked chitosan matrix had been achieved. The obtained composite scaffolds exhibited lower swelling capacity with respect to pure chitosan after 24 h of incubation in Hanks’ balanced salt solution. Rheological measurements show an increase in storage and loss modulus indicating an improvement in mechanical properties under shear stress. Furthermore, no significant change in loss factor (tanδ) was observed indicating no change in composite viscoelastic properties with an increase in HAp content.
... When the size of the unit cells of these materials is not negligible with respect to the overall structure size, geometry of the unit cell affects the overall response. Size effect is observed when the continuum is constituted of granular material, e.g., sandy soil [1], concrete [2], polycrystalline solids [3], ceramics [4], bone [5], liquid crystals, foams [6], magnetic fluids [7], nanomaterials [8] etc. This effect is prominently seen near the crack tip of a composite material, e.g., concrete, where the size of the fracture process zone is not negligible with respect to the size of the material body. ...
... The knee joint experiences load not only from substrate reaction forces, but also from the action of muscles, tendons and ligaments during various locomotor activities. Additionally, soft tissue morphology of the knee joint in extant non-human great apes (hereafter, just 'great apes') differs in the degree to which it provides stability and mobility at different joint angles (Barak et al., 2011;Currey, 2003Currey, , 2012Demes, 2007;Pearson & Lieberman, 2004;Rubin et al., 2002;Ruff et al., 2006;Shaw & Ryan, 2012). In comparison, the human knee joint has several bony and soft tissue features that stabilize the knee especially in a fully extended posture (DeSilva et al., 2018;Haile-Selassie et al., 2012;Harcourt-Smith et al., 2015;Harcourt-Smith, 2016;Lovejoy et al., 2009;Sylvester & Organ, 2010;Sylvester, 2013;Sylvester et al., 2011). ...
Extant great apes are characterized by a wide range of locomotor, postural and manipulative behaviours that each require the limbs to be used in different ways. In addition to external bone morphology, comparative investigation of trabecular bone, which (re‐)models to reflect loads incurred during life, can provide novel insights into bone functional adaptation. Here, we use canonical holistic morphometric analysis (cHMA) to analyse the trabecular morphology in the distal femoral epiphysis of Homo sapiens ( n = 26), Gorilla gorilla ( n = 14), Pan troglodytes (n = 15) and Pongo sp. ( n = 9). We test two predictions: (1) that differing locomotor behaviours will be reflected in differing trabecular architecture of the distal femur across Homo , Pan , Gorilla and Pongo ; (2) that trabecular architecture will significantly differ between male and female Gorilla due to their different levels of arboreality but not between male and female Pan or Homo based on previous studies of locomotor behaviours. Results indicate that trabecular architecture differs among extant great apes based on their locomotor repertoires. The relative bone volume and degree of anisotropy patterns found reflect habitual use of extended knee postures during bipedalism in Homo , and habitual use of flexed knee posture during terrestrial and arboreal locomotion in Pan and Gorilla . Trabecular architecture in Pongo is consistent with a highly mobile knee joint that may vary in posture from extension to full flexion. Within Gorilla , trabecular architecture suggests a different loading of knee in extension/flexion between females and males, but no sex differences were found in Pan or Homo , supporting our predictions. Inter‐ and intra‐specific variation in trabecular architecture of distal femur provides a comparative context to interpret knee postures and, in turn, locomotor behaviours in fossil hominins.
... In human bones, fatigue fractures often occur in military recruits, with 0.91% of male recruits and 1.09% of female recruits suffering fatigue fractures. Between 4.7% and 15.6% of all runners' injuries are stress fractures [10]. Deep learning in neural networks can detect fractures in materials with up to 98% accuracy, according to recent research [11]. ...
Fatigue fractures in materials are the main cause of approximately 80% of all material failures, and it is believed that such failures can be predicted and mathematically calculated in a reliable manner. It is possible to establish prediction modalities in cases of fatigue fractures according to three fundamental variables in fatigue, such as volume, number of fracture cycles, as well as applied stress, with the integration of Weibull constants (length characteristic). In this investigation, mechanical fatigue tests were carried out on specimens smaller than 4 mm2, made of different industrial materials. Their subsequent analysis was performed through precision computed tomography, in search for microfractures. The measurement of these microfractures, along with their metrics and classifications, was recorded. A convolutional neural network trained with deep learning was used to achieve the detection of microfractures in image processing. The detection of microfractures in images with resolutions of 480 × 854 or 960 × 960 pixels is the primary objective of this network, and its accuracy is above 95%. Images that have microfractures and those without are classified using the network. Subsequently, by means of image processing, the microfracture is isolated. Finally, the images containing this feature are interpreted using image processing to obtain their area, perimeter, characteristic length, circularity, orientation, and microfracture-type metrics. All values are obtained in pixels and converted to metric units (μm) through a conversion factor based on image resolution. The growth of microfractures will be used to define trends in the development of fatigue fractures through the studies presented.
... The bone is an important tissue structure that is responsible for movement, protection, and support in the entire body. It has an organic component represented by collagen (types I, III, and IV) and fibrillin and an inorganic component represented by hydroxyapatite [18]. The organic part offers flexibility to the entire structure, and the inorganic part is responsible for strength, summing their action during the presence of the tooth or implant in the alveolar bone (Figure 2). ...
The introduction of composites and dental materials in the implantology field has shown an important increase in the past years. The restorative approaches using dental implants are currently a desirable option for edentulous patients. Since their introduction in dentistry, dental implants have proven to be a reliable option for restabling the functions and esthetics of certain areas. Characteristics such as high biocompatibility, nontoxicity, and high corrosion resistance have been key factors for their worldwide acceptance. In time, researchers aimed to improve their qualities by manufacturing the implants using various materials that could improve the interaction between the bone and implant. Although, until now, dental implant materials were limited to the use of single or coated metals, there are certain limitations that current studies aimed to overcome by introducing a new category, the composite dental implants. With this new category, the mechanical characteristics can be designed in order for their integration and further functions to have a positive outcome. This chapter describes the use of composite dental implants as a restorative prosthetic option, their advantages, and physicochemical and osteointegration properties as future approaches for restorative prosthetic rehabilitation.
... In human bones, fatigue fractures often occur in military recruits, 0.91% of male recruits and 1.09% of female recruits suffer fatigue fractures. Between 4.7% and 15.6% of all runners' injuries are stress fractures (Currey, 2012). ...
Fatigue fractures in materials are the main cause of approximately 80% of all material failures, and it is believed that such failures can be predicted and mathematically calculated in a reliable manner. It is possible to establish prediction modalities in cases of fatigue fracture, according to three fundamental variables in fatigue, such as volume, number of fracture cycles, as well as applied stress, with the integration of Weibull constants (length characteristic). This investigation was carried out mechanical fatigue tests on specimens smaller than 4 mm2 in section of different industrial materials for their subsequent analysis through precision computed tomography in search of microfractures. The measurement of these microfractures, along with their metrics and classifications, was recorded. A convolutional neural network trained with deep learning was used to achieve the detection of microfractures in image processing. The detection of microfractures in images with 480x854 or 960x960 pixels is the primary objective of this network, and its accuracy is above 95%. Images that have microfractures and those that do not are classified by the network. Subsequently, by means of image processing, the microfracture is isolated. Finally, the images that do contain this feature are interpreted by image processing to obtain their area, perimeter, characteristic length, circularity, orientation, and type microfracture metrics. All values will be obtained in pixels and converted to metric units (μm) through a conversion factor based on image resolution.
... While not directly related to free vibration, this information is important for understanding the structural properties of cancellous bone. Some studies utilized nanoindentation tests and determined the mechanical properties of bone such as Young's modulus, hardness, fatigue strength, and flexural modules (Currey, 2012;Currey et al., 2007;Hassenkam et al., 2004). Zysset et al. (1999) used nanoindentation to measure the elastic modulus and hardness of cortical and trabecular bone lamellae in the human femur. ...
Osteoporosis is a skeletal disease characterized by reduced bone mass and microarchitectural deterioration, leading to increased fragility. This study presents a novel three-dimensional poroelastodynamic model for analyzing cancellous bone free vibration responses. The model incorporates the Navier-Stokes equations of linear elasticity and the Biot theory of porous media, allowing the investigation of osteoporosis-related changes. The analysis considers parameters like porosity, density, elasticity, Poisson ratio, and viscosity of bone marrow within the porous medium. Our findings indicate that natural frequencies of cancellous bone play a crucial role in osteoporosis prediction. By incorporating experimental data from 12 mouse femurs, we unveil insights into osteoporosis prediction. Increased porosity reduces bone stiffness, lowering natural frequencies. However, it also increases bone mass loss relative to stiffness, leading to higher frequencies. Therefore, the natural frequencies of osteoporotic bone are always higher than the natural frequencies of normal bone. Additionally, an increase in bone marrow within the pores, while increasing damping effects, also increases natural frequencies, which is another indication of osteoporosis growth in bone. The presence of bone marrow within the pores further influences natural frequencies, providing additional insights into osteoporosis growth. Thinner and smaller bones are found to be more susceptible to osteoporosis compared to larger and bigger bones due to their higher natural frequencies at equivalent porosity levels.
... This study employed scapula bone as autologous bone graft, which is a flat bone type composed of thin outer layers of cortical bone and thicker cancellous bone. Cancellous bone has more cellular components compared to the mineral contents [35,36]. Hence, this may explain the lower mineral density observed in the autologous bone chamber as observed on microCT evaluation. ...
Autologous bone replacement remains the preferred treatment for segmental defects of the mandible; however, it cannot replicate complex facial geometry and causes donor site morbidity. Bone tissue engineering has the potential to overcome these limitations. Various commercially available calcium phosphate-based bone substitutes (Novabone®, BioOss®, and Zengro®) are commonly used in dentistry for small bone defects around teeth and implants. However, their role in ectopic bone formation, which can later be applied as vascularized graft in a bone defect, is yet to be explored. Here, we compare the above-mentioned bone substitutes with autologous bone with the aim of selecting one for future studies of segmental mandibular repair. Six female sheep, aged 7–8 years, were implanted with 40 mm long four-chambered polyether ether ketone (PEEK) bioreactors prepared using additive manufacturing followed by plasma immersion ion implantation (PIII) to improve hydrophilicity and bioactivity. Each bioreactor was wrapped with vascularized scapular periosteum and the chambers were filled with autologous bone graft, Novabone®, BioOss®, and Zengro®, respectively. The bioreactors were implanted within a subscapular muscle pocket for either 8 weeks (two sheep), 10 weeks (two sheep), or 12 weeks (two sheep), after which they were removed and assessed by microCT and routine histology. Moderate bone formation was observed in autologous bone grafts, while low bone formation was observed in the BioOss® and Zengro® chambers. No bone formation was observed in the Novabone® chambers. Although the BioOss® and Zengro® chambers contained relatively small amounts of bone, endochondral ossification and retained hydroxyapatite suggest their potential in new bone formation in an ectopic site if a consistent supply of progenitor cells and/or growth factors can be ensured over a longer duration.
... Throughout millions of years of evolution, an arsenal of natural materials have shown remarkable mechanical properties [2][3][4][5][6]. Their superior mechanical performance is derived [7][8][9], providing fruitful learning resources for the design of structural connections. ...
Structural connections between components are often weak areas in engineering applications. In nature, many biological materials with remarkable mechanical performance possess flexible and creative sutures. In this work, we propose a novel bio-inspired interlocking tab considering both the geometry of the tab head and neck, and demonstrate a new approach to optimize the bio-inspired interlocking structures based on machine learning. Artificial neural networks for different optimization objectives are developed and trained using a database of thousands of interlocking structures generated through finite element analysis. Results show that the proposed method is able to achieve accurate prediction of the mechanical response of any given interlocking tab. The optimized designs with different optimization objectives, such as strength, stiffness, and toughness, are obtained efficiently and precisely. The optimum design predicted by machine learning is approximately 7.98 times stronger and 2.98 times tougher than the best design in the training set, which are validated through additive manufacturing and experimental testing. The machine learning-based optimization approach developed here can aid in the exploration of the intricate mechanism behind biological materials and the discovery of new material designs boasting orders of magnitude increase in computational efficacy over conventional methods.
... Bone is a biological composite structure that provides it with great strength, toughness, and lightweight needed for its mechanical activities. 1 The structure of bone can be investigated by treating demineralized bone since it contains numerous hierarchical levels of structural organization. 2,3 It is required to "soften" these tissues by eliminating the mineralized components due to the particular physical hardness it provides. ...
Background: Bone is a biological complex structure primarily comprising collagen and minerals. It is important to demineralize these mineralized tissues to remove their calcium apatite crystals for analysing the sub-cellular, cellular, and fibrillar architecture. Six demineralizing agents’ efficacy was examined by assessing their duration, ease of handling tissue, staining, and histological criteria. The present study aimed to evaluate six commonly used demineralizing agents to identify the best decalcifying agent. Methods: Twenty resected hard tissue specimens (1 cm × 1 cm x 1 cm) from the archives were used in the study. These segments were decalcified by solutions namely 10% nitric acid, 10% formic acid, 14% ethylene di amine tetra acetic acid (EDTA), a mixture of formic acid and hydrochloric acid (formic + HCL) 4% each, and a mixture of formic acid and nitric acid 4% each (formic + HNO3), 10% formal nitric acid further subjected to radiographic endpoint test. Results: The present study confirmed the fact that samples treated with EDTA showed the best overall impression in terms of tissue integrity and histology followed by 10% formal nitric acid which gave fairly good cellular details and was also rapid in the action. Conclusions: Based on the present study findings, we suggest that 10% formal nitric acid is the better decalcifying agent available, considering time and tissue integrity as two main factors.
... Due to its heterogeneity and anisotropy, the hierarchical structure of natural bone is divided into several different levels, from nano and macro to the level of whole bone [11,13]. In the literature, there is a division into four, seven or nine levels [10,[13][14][15]. The unevenness of the bone structure largely depends on the number of levels in the assessment scale and the level used for analysis. ...
Interest in calcium phosphate cements as materials for the restoration and treatment of bone tissue defects is still high. Despite commercialization and use in the clinic, the calcium phosphate cements have great potential for development. Existing approaches to the production of calcium phosphate cements as drugs are analyzed. A description of the pathogenesis of the main diseases of bone tissue (trauma, osteomyelitis, osteoporosis and tumor) and effective common treatment strategies are presented in the review. An analysis of the modern understanding of the complex action of the cement matrix and the additives and drugs distributed in it in relation to the successful treatment of bone defects is given. The mechanisms of biological action of functional substances determine the effectiveness of use in certain clinical cases. An important direction of using calcium phosphate cements as a carrier of functional substances is the volumetric incorporation of anti-inflammatory, antitumor, antiresorptive and osteogenic functional substances. The main functionalization requirement for carrier materials is prolonged elution. Various release factors related to the matrix, functional substances and elution conditions are considered in the work. It is shown that cements are a complex system. Changing one of the many initial parameters in a wide range changes the final characteristics of the matrix and, accordingly, the kinetics. The main approaches to the effective functionalization of calcium phosphate cements are considered in the review.
... Moreover, low scale tensegrity type systems, possibly multiscale, have been shown to deliver interesting possible applications for isolation based on their intrinsic strongly non linear geometrical properties (De Tommasi, Maddalena, Puglisi, & Trentadue, 2017;De Tommasi, Marano, Puglisi, & Trentadue, 2015;Trentadue, De Tommasi, & Marasciuolo, 2021). Also in nature, hierarchical structures have been recognized at the base of the capacity of dissipation and crush resistance of different biological systems such as bones (Currey, 2012), spider silks (Fazio, De Tommasi, Pugno, & Puglisi, 2022) and nacre (Oaki & Imai, 2005). ...
We propose a new conceptual approach to reach unattained dissipative properties based on the friction of slender concentric sliding columns. We begin by searching for the optimal topology in the simplest telescopic system of two concentric columns. Interestingly, we obtain that the optimal shape parameters are material independent and scale invariant. Based on a multiscale self-similar reconstruction, we end-up with a theoretical optimal fractal limit system whose cross section resembles the classical Sierpi\'nski triangle. Our optimal construction is finally completed by considering the possibility of a complete plane tessellation. The direct comparison of the dissipation per unit volume with the material dissipation up to the elastic limit shows a great advantage: . Such result is already attained for a realistic case of three only scales of refinement leading almost (96%) the same dissipation of the fractal limit. We also show the possibility of easy recovering of the original configuration after dissipation and we believe that our schematic system can have interesting reliable applications in different technological fields. Interestingly, our multiscale dissipative mechanism is reminiscent of similar strategies observed in nature as a result of bioadaptation such as in the archetypical cases of bone, nacre and spider silk. Even though other phenomena such as inelastic behavior and full tridimensional optimization are surely important in such biological systems, we believe that the suggested dissipation mechanism and scale invariance properties can give insight also in the hierarchical structures observed in important biological examples.
... Lamellar bone is the most abundant type in the cortical bones and composed of osteonal tissue. Osteons are cylindrical shaped structural and is composed of concentric lamellar structure ( Figure 1A) (Liu et al., 2017), the diameter ranges from 50 to 500 μm (Currey, 2012), and the lamella thickness is about of 3-7 μm (Giner et al., 2014a). Cortical bone is mainly composed of organic phase (Fratzl and Fratzl, 2010) and inorganic phase, and the organic phase is mainly formed by mineralized collagen fibers (Hamed et al., 2010). ...
Osteons are composed of concentric lamellar structure, the concentric lamellae are composed of periodic thin and thick sub-lamellae, and every 5 sub-lamellae is a cycle, the periodic helix angle of mineralized collagen fibers in two adjacent sub-lamellae is 30°. Four biomimetic models with different fiber helix angles were established and fabricated according to the micro-nano structure of osteon. The effects of the fiber periodic helical structure on impact characteristic and energy dissipation of multi-layer biomimetic composite were investigated. The calculation results indicated that the stress distribution, contact characteristics and fiber failur during impact, and energy dissipation of the composite are affected by the fiber helix angle. The stress concentration of composite materials under external impact can be effectively improved by adjusting the fiber helix angle when the material composition and material performance parameters are same. Compared with the sample30, the maximum stress of sample60 and sample90 increases by 38.1% and 69.8%, respectively. And the fiber failure analysis results shown that the model with a fiber helix angle of 30° has a better resist impact damage. The drop-weight test results shown that the impact damage area of the specimen with 30° helix angle is smallest among the four types of biomimetic specimens. The periodic helical structure of mineralized collagen fibers in osteon can effectively improve the impact resistance of cortical bone. The research results can provide useful guidance for the design and manufacture of high-performance, impact-resistant biomimetic composite materials.
... Here, we define mechanical biomarkers as measures of the mechanical response of bone to external loads. These measures include organ-level mechanical behavior (e.g., stiffness or rigidity) or tissue-level behavior (e.g., stress, load to failure, or strain energy density), and there are several helpful sources describing their derivation in the context of bone [5][6][7]. ...
Purpose of Review
The purpose of this review is to summarize insights gained by finite element (FE) model-based mechanical biomarkers of bone for in vivo assessment of bone development and adaptation, fracture risk, and fracture healing.
Recent Findings
Muscle-driven FE models have been used to establish correlations between prenatal strains and morphological development. Postnatal ontogenetic studies have identified potential origins of bone fracture risk and quantified the mechanical environment during stereotypical locomotion and in response to increased loading. FE-based virtual mechanical tests have been used to assess fracture healing with higher fidelity than the current clinical standard; here, virtual torsion test data was a better predictor of torsional rigidity than morphometric measures or radiographic scores. Virtual mechanical biomarkers of strength have also been used to deepen the insights from both preclinical and clinical studies with predictions of strength of union at different stages of healing and reliable predictions of time to healing.
Summary
Image-based FE models allow for noninvasive measurement of mechanical biomarkers in bone and have emerged as powerful tools for translational research on bone. More work to develop nonirradiating imaging techniques and validate models of bone during particularly dynamic phases (e.g., during growth and the callus region during fracture healing) will allow for continued progress in our understanding of how bone responds along the lifespan.
... Nevertheless, it has been argued that the trajectorial theory applies best to a simply loaded bone like the artiodactyl calcaneus and might be valid in some additional bones (Currey, 1984;Biewener et al., 1996;Skedros and Baucom, 2007). Though the arrangement of trabeculae in the human proximal femur seem to fit the concept of following the lines of principal stress inherent in the T/C paradigm, the underappreciated role of muscle loads and other aforementioned factors support the conclusion that this argument is specious (Currey, 2012). When considering the distinctive arches in the human proximal femur (Fig. 1), perhaps the role of habitual loading in the formation of such architecture is best summed up by the words of P.D.F. ...
The mechanobiology of the human femoral neck is a focus of research for many reasons including studies that aim to curb age-related bone loss that contributes to a near-exponential rate of hip fractures. Many believe that the femoral neck is often loaded in rather simple bending, which causes net tension stress in the upper (superior) femoral neck and net compression stress in its inferior aspect ("T/C paradigm"). This T/C loading regime lacks in vivo proof. The "C/C paradigm" is a plausible alternative simplified load history that is characterized by a gradient of net compression across the entire femoral neck; action of the gluteus medius and external rotators of the hip are important in this context. It is unclear which paradigm is at play in natural loading due to lack of in vivo bone strain data and deficiencies in understanding mechanisms and manifestations of bone adaptation in tension vs. compression. For these reasons, studies of the femoral neck would benefit from being compared to a 'control bone' that has been proven, by strain data, to be habitually loaded in bending. The artiodactyl (sheep and deer) calcaneus model has been shown to be a very suitable control in this context. However, the application of this control in understanding the load history of the femoral neck has only been attempted in two prior studies, which did not examine the interplay between cortical and trabecular bone, or potential load-sharing influences of tendons and ligaments. Our first goal is to compare fracture risk factors of the femoral neck in both paradigms. Our second goal is to compare and contrast the deer calcaneus to the human femoral neck in terms of fracture risk factors in the T/C paradigm (the C/C paradigm is not applicable in the artiodactyl calcaneus due to its highly constrained loading). Our third goal explores interplay between dorsal/compression and plantar/tension regions of the deer calcaneus and the load-sharing roles of a nearby ligament and tendon, with insights for translation to the femoral neck. These goals were achieved by employing the analytical model of Fox and Keaveny (J. Theoretical Biology 2001, 2003) that estimates fracture risk factors of the femoral neck. This model focuses on biomechanical advantages of the asymmetric distribution of cortical bone in the direction of habitual loading. The cortical thickness asymmetry of the femoral neck (thin superior cortex, thick inferior cortex) reflects the superior-inferior placement of trabecular bone (i.e., "trabecular eccentricity," TE). TE helps the femoral neck adapt to typical stresses and strains through load-sharing between superior and inferior cortices. Our goals were evaluated in the context of TE. Results showed the C/C paradigm has lower risk factors for the superior cortex and for the overall femoral neck, which is clinically relevant. TE analyses of the deer calcaneus revealed important synergism in load-sharing between the plantar/tension cortex and adjacent ligament/tendon, which challenges conventional understanding of how this control bone achieves functional adaptation. Comparisons with the control bone also exposed important deficiencies in current understanding of human femoral neck loading and its potential histocompositional adaptations.
... Iron participates in a variety of enzymatic systems in the body, including the enzymes involved in collagen synthesis. In mammals, approximately 28 types of collagen have so far been identified [114]; among these types, the most prevalent is type I collagen that was found in the extracellular matrix (ECM), particularly in tissues such as tendon and bone [115]. Bone is a complex assembly of type I collagen fibers filled in with mineral crystal of hydroxyapatite [116]. ...
Iron is one of the essential mineral elements for the human body and this nutrient deficiency is a worldwide public health problem. Iron is essential in oxygen transport, participates in many enzyme systems in the body, and is an important trace element in maintaining basic cellular life activities. Iron also plays an important role in collagen synthesis and vitamin D metabolism. Therefore, decrease in intracellular iron can lead to disturbance in the activity and function of osteoblasts and osteoclasts, resulting in imbalance in bone homeostasis and ultimately bone loss. Indeed, iron deficiency, with or without anemia, leads to osteopenia or osteoporosis, which has been revealed by numerous clinical observations and animal studies. This review presents current knowledge on iron metabolism under iron deficiency states and the diagnosis and prevention of iron deficiency and iron deficiency anemia (IDA). With emphasis, studies related to iron deficiency and bone loss are discussed, and the potential mechanisms of iron deficiency leading to bone loss are analyzed. Finally, several measures to promote complete recovery and prevention of iron deficiency are listed to improve quality of life, including bone health.
... Biomechanical loading, amongst other factors (e.g., dietary, hormonal, disease) determines bone (micro)morphology (Heaney, 1995;Heaney et al., 2000;Robling et al., 2006). The Mechanostat model (Frost, 1987) builds on stress and strain theory to explain that a minimum effective strain (MES) determines when bone will adapt to function (Currey, 2012;Martin et al., 2015;Sugiyama et al., 2012). Remodelling is stimulated in both underloaded and overloaded bone, but resorption or formation dominate over one another in the respective mechanical states Sugiyama et al., 2012). ...
... Thus, the nitrogen content is about 5.05% and the collagen content is about 27.71wt%. Depending on the species and type of bone, fresh bone contains 20-35% organic matrix, of which~90% is collagen, giving bone a %N of~3.5-4.5% (Brock et al., 2012;Currey 2012;Richter et al., 2022). Kontopoulos et al. (2020) tested 266 human and animal bone samples from 10,000 BC to 1850 AD, and found that the amide I/PO 4 values were lower than 0.2 and the collagen content was lower than 25%. ...
“Applying red” is a common phenomenon observed in Chinese archaeological sites, with the red pigments having been identified as red ochre or cinnabar if ever been scientifically analyzed. However, this is not the case for Tibet. Although a relatively large number of red-painted artifacts have been recovered in Tibet dating from the Neolithic Period to the Tubo Dynasty, little effort has been made on the pigment composition. Recently, nearly one hundred red substances covered shell beads made of the scared chank (Turbinella pyrum), a large conch from the Indian Ocean, were unearthed from the Qulong site (c. 800–500 BC) in the Ngari plateau, western Tibet. This shell beads assemblage represents the largest and most concentrated group of chank shell beads recovered in the Tibetan Plateau and its surrounding regions. It provides a crucial clue for exploring the local “applying red” tradition. In this study, eight shell beads excavated from the Qulong site were examined by the Portable Energy-dispersive X-ray Fluorescence Spectrometer (pXRF), X-ray diffraction (XRD), Fourier Transform infra-red spectroscopy (FTIR), and Laser Raman spectroscopy. The results are as follows: 1) the coloring agent of all red pigments on the shell bead is iron oxide, i.e., red ocher; 2) bone powder that has not been heated to high temperatures (above 600°C) and proteinaceous binders were added to the paint on the outer surface of sample QSM1-11a, but the thin layer on its interior surface was without bone powder; 3) bone powder was not added to the red residues on samples other than QSM1-11a, QSM1-13b, and QSM2-12. This research may reveal the complexity and diversity of the red substances applied to shell beads from Qulong, and shed light on our understanding of human practices and local customs in the Tibetan plateau and the surrounding areas in prehistoric times.
... Bone is made of cancellous and cortical components. Bone density gradually increases from the inner cancellous bone to the outer cortical bone, revealing uneven and porous structure (Hadjidakis and Androulakis, 2006;Currey, 2011;Chen H. et al., 2020). By altering the size and structure of pores in implants, bone-like mechanical characteristics can be achieved (Engh et al., 2003;Niinomi and Nakai, 2011;Manoj et al., 2018;Raffa et al., 2021). ...
Titanium and titanium alloy implants are essential for bone tissue regeneration engineering. The current trend is toward the manufacture of implants from materials that mimic the structure, composition and elasticity of bones. Titanium and titanium alloy implants, the most common materials for implants, can be used as a bone conduction material but cannot promote osteogenesis. In clinical practice, there is a high demand for implant surfaces that stimulate bone formation and accelerate bone binding, thus shortening the implantation-to-loading time and enhancing implantation success. To avoid stress shielding, the elastic modulus of porous titanium and titanium alloy implants must match that of bone. Micro-arc oxidation technology has been utilized to increase the surface activity and build a somewhat hard coating on porous titanium and titanium alloy implants. More recently, a growing number of researchers have combined micro-arc oxidation with hydrothermal, ultrasonic, and laser treatments, coatings that inhibit bacterial growth, and acid etching with sand blasting methods to improve bonding to bone. This paper summarizes the reaction at the interface between bone and implant material, the porous design principle of scaffold material, MAO technology and the combination of MAO with other technologies in the field of porous titanium and titanium alloys to encourage their application in the development of medical implants.
... At the microscale, the mineralized collagen brils are grouped together in a certain direction to form lamellar structure, and the thickness is about of 3-7µm. Further, these lamellae are concentrical surround the haversian canal to compose osteons ) and its diameter ranges from 50 to 500µm (Currey 2012). At the nanoscale, cortical bone is mainly composed of organic phase (Dunlop et al.2010) and inorganic phase, the organic phase is mainly formed by mineralized collagen brils (Hamed et al. 2010). ...
It is found that the osteon is composed of thin and thick lamellae which are periodic and approximately concentric, every 5 lamellae is a cycle, the periodic helix angle of mineralized collagen fibers in two adjacent sub-lamellae is 30°. Four bionic composite models with different fiber helix angles were established and fabricated according to the microstructure of mineralized collagen fibers in osteon. Based on the impact analysis of four kinds of bionic composite models, the effects of the fiber periodic spiral structure on the impact resistance and energy dissipation of multi-layer bionic composite were investigated. The analysis results show that the fiber helix angle affects the impact damage resistance and energy dissipation of multi-layer fiber reinforced composites. Among the four kinds of multi-layer composite models, the composite model with helix angle of 30° has better comprehensive ability to resist impact damage. The test results show that the impact damage area of the specimen with 30° helix angle is smallest among the four types of bionic specimens, which is consistent with the results of finite element impact analysis. Furthermore, in the case of without impact damage, the smaller the fiber helix angle is, the more uniform the stress distribution is and more energy is dissipated in the impact process. The periodic spiral structure of mineralized collagen fibers in osteon are the result of natural selection of biological evolution. This structure can effectively improve the ability of cortical bone to resist external impact. The research results can provide useful guidance for the design and manufacture of high-performance and strong impact resistant bionic composites.
... Bone tissue may undergo biological remodeling through a dynamic process of osteoclast absorption and subsequent osteoblast-induced bone formation [68,[90][91]. Nonetheless, when a big segmental bone defect reaches a crucial size of roughly 10 mm [31], the body is typically unable to complete the self-repairing function. External intervention is necessary to help self-repair by constructing bridges on the bone defect site [92]. ...
Additive manufacturing (AM) is a fast-expanding technology being used to make biomedical implants in a variety of industries. AM has much potential for tailored and customized therapies since each patient is different in general and dental health. It also has a vast and extensive potential for biological mimicry of needed complex states for physiological implants due to its customized design and decreased manufacturing time and cost. AM can produce scaffolds with a tailored exterior form and a porous interior structure, which are crucial for mending extensive segmental bone lesions. Scaffold design, AM, and posttreatments are all part of the scaffold construction process. This research aims to provide a more systematic assessment of the use of various AM processes in the area of biological implants, prosthetics, and scaffolds utilizing different biomaterials, as well as the scope of future research for advancing the field of biomedical using various AM processes.
... For archaeological remains, collagen preservation is typically estimated by measuring the dry weight percentage (%wt) of collagen or by determining the percentage of N (%N) or the atomic C:N of a given collagenous material (49,55,56). Depending on the species and type of bone, fresh bone contains 20 to 35% organic matrix, of which ∼90% is collagen (57,58), giving bone a %N of ∼3.5 to 4.5% (55), and, for humans, a C:N of 3.2 (59). As a general rule, a minimum of 1% collagen, 0.5% N, and C:N values between 2.9 and 3.6 are widely used as a minimum standard for collagen preservation in stable isotope and radiocarbon dating studies (55,59). ...
Collagen peptide mass fingerprinting by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry, also known as zooarchaeology by mass spectrometry (ZooMS), is a rapidly growing analytical technique in the fields of archaeology, ecology, and cultural heritage. Minimally destructive and cost effective, ZooMS enables rapid taxonomic identification of large bone assemblages, cultural heritage objects, and other organic materials of animal origin. As its importance grows as both a research and a conservation tool, it is critical to ensure that its expanding body of users understands its fundamental principles, strengths, and limitations. Here, we outline the basic functionality of ZooMS and provide guidance on interpreting collagen spectra from archaeological bones. We further examine the growing potential of applying ZooMS to nonmammalian assemblages, discuss available options for minimally and nondestructive analyses, and explore the potential for peptide mass fingerprinting to be expanded to noncollagenous proteins. We describe the current limitations of the method regarding accessibility, and we propose solutions for the future. Finally, we review the explosive growth of ZooMS over the past decade and highlight the remarkably diverse applications for which the technique is suited.
... This matrix is primarily made up of inorganic materialhydroxyapatite and other calcium and phosphate salts-as well as organic materials, mainly collagen fibres. These components are what determine the physical properties of the material (Currey 2012;Kendall et al. 2018). Osseous remains recovered in archaeological contexts have been subjected to transformation and degradation mechanisms during the fossilization process. ...
The preparation of samples for traceological analysis is a key methodological aspect in the correct interpretation of use-wear; however, it is often poorly reflected in the archaeological literature. The treatment of osseous tissues is particularly overlooked, and receives even less attention than lithic raw materials. The presence of residues and contaminants on the surface of artefacts can conceal or even be mistaken for use-wear features, thereby affecting their interpretation. Therefore, the objective of this work is to contribute to the systematization of cleaning protocols and the preparation of experimental bone tools for traceological analysis. Through a sequential experiment, we tested the effects of different cleaning agents on experimental samples. Microscopic observation of the samples was complemented with microhardness testing. Our results made it possible to evaluate the cleaning effectiveness of the tested products, to determine how each product affects the bone surface at a microscopic level, and to assess the effects of these products on the treated bone tools in terms of cutting performance.
... Bone tissue can able for biological rebuilding of the mature bone tissue absorption by osteoclasts and new bone for next generation by osteoblasts through a dynamic process [12,13]. ...
Titanium is a most common and best biocompatible material. The demand and application of Ti alloy is increasing rapidly in orthopedics for clinical operations. The porous structures have been designed for bone tissue engineering ororthopedic applications due to its moderate Young's modulus, excellent compressive strength, biocompatibility and sufficient space for cell accommodation. The porous scaffolds with individual complex internal and external shape can be manufactured by additive manufacturing (AM) processes especially selective laser melting (SLM), both of these have great importance for repairing of large sectional bone defects. This advantage makes the SLM process one of the most competitive AM processes used in the biomedical fields. Seven different Ti-6Al-4V porous scaffolds (Diamond, Grid, Cross, Vinties, Tesseract, Star and Octet) of 15 mm cube with 65% porosity were designed using Rhino 6 software and fabricated through SLM using Ti-6Al-4V powders. This work mainly focused on porous scaffolds design and manufacturing by AM particularly SLM, can able to produce scaffolds of nanoscale grains because of its higher heating rate and lower holding time. But this process generally results insufficient compaction where desired function is not achieved. The scaffolds manufactured by SLM have relatively high accuracy of pore structure and low mechanical strength. Grid type structure exhibits lower surface roughness value and better manufacturing ability where error percentage of porosity is lower than the other scaffolds. The process parameters employed in the study like laser power, scanning speed, hatch distancing and layer thickness are the most significant factors that influence the defect behaviour and morphology of the SLM-fabricated samples. Porosity percentage and surface roughness of the scaffold palys a vital role on its desired functions. While the porosity percentage are also effected by input process parameters resulting the variation on effective elastic modulus. The increase in scanning speed leads to elevation of the cooling rate, which results in a finer microstructure. On the other hand, with lower scanning speeds, coarse micrstrucutre is observed.
Functional Bio-based Materials for Regenerative Medicine: From Bench to Bedside explores the use of bio-based materials for the regeneration of tissues and organs. The book presents an edited collection of 28 topics in 2 parts focused on the translation of these materials from laboratory research (the bench) to practical applications in clinical settings (the bedside). Chapter authors highlight the significance of bio-based materials, such as hydrogels, scaffolds, and nanoparticles, in promoting tissue regeneration and wound healing.
Topics included in the book include:
- the properties of bio-based materials, including biocompatibility, biodegradability, and the ability to mimic the native extracellular matrix.
- fabrication techniques and approaches for functional bio-based material design with desired characteristics like mechanical strength and porosity to promote cellular attachment, proliferation, and differentiation
- the incorporation of bioactive molecules, such as growth factors, into bio-based materials to enhance their regenerative potential.
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strategies for the controlled release of molecules to create a favorable microenvironment for tissue regeneration. - the challenges and considerations involved in scaling up the production of bio-based materials, ensuring their safety and efficacy, and obtaining regulatory approval for clinical use
Part 2 covers advanced materials and techniques used in tissue engineering. Topics focus on advanced composite materials for 3D scaffolds and the repair of tissues in different organs such as the heart, cornea, bone and ligaments. Materials highlighted in this part include polyamide composites, electrospun nanofibers, and different bio-based hydrogels.
Functional Bio-based Materials for Regenerative Medicine: From Bench to Bedside is a valuable reference for researchers in biomedical engineering, cell biology, and regenerative medicine who want to update their knowledge on current developments in the synthesis and application of functional biomaterials.
High-performance batteries with various functions are highly expected for building a smart system for the next-generation intelligent equipment. Traditional batteries are faced with great challenges such as adaptability to complex...
Synthetic bone grafting materials play a significant role in various medical applications involving bone regeneration and repair. Their ability to mimic the properties of natural bone and promote the healing process has contributed to their growing relevance. While calcium-phosphates and their composites with various polymers and biopolymers are widely used in clinical and experimental research, the diverse range of available polymer-based materials poses challenges in selecting the most suitable grafts for successful bone repair. This review aims to address the fundamental issues of bone biology and regeneration while providing a clear perspective on the principles guiding the development of synthetic materials. In this study, we delve into the basic principles underlying the creation of synthetic bone composites and explore the mechanisms of formation for biologically important complexes and structures associated with the various constituent parts of these materials. Additionally, we offer comprehensive information on the application of biologically active substances to enhance the properties and bioactivity of synthetic bone grafting materials. By presenting these insights, our review enables a deeper understanding of the regeneration processes facilitated by the application of synthetic bone composites.
Experimental evidence shows that natural bone is piezoelectric, and bioelectric phenomena in natural bone play an essential role in bone development and bone defect repair. Piezoelectric ceramics can deform with physiological movements and consequently deliver electrical stimulation to cells or damaged tissue without the need for an external power source. They exhibit piezoelectricity and good biological properties similar to those of natural bone and have shown great potential in bone tissue engineering. This study aims to present an overview of the relationship between electrical stimulation and bone repair as well as the principle of the piezoelectric effect, emphasizing the material characteristics, research progress and application of piezoelectric ceramics in bone tissue regeneration. The limitations of piezoelectric ceramics in promoting osteogenesis by electrical stimulation were also analysed. Overall, this review comprehensively emphasized the essential characteristics of piezoelectric ceramics and pointed out the new direction for the future development of piezoelectric ceramics.
With the increasing importance of preclinical evaluation of newly developed drugs or treatments, in vitro organ or disease models are necessary. Although various organ-specific on-chip (organ-on-a-chip, or OOC) systems have been developed as emerging in vitro models, bone-on-a-chip (BOC) systems that recapitulate the bone microenvironment have been less developed or reviewed compared with other OOCs. The bone is one of the most dynamic organs and undergoes continuous remodeling throughout its lifetime. The aging population is growing worldwide, and healthcare costs are rising rapidly. Since in vitro BOC models that recapitulate native bone niches and pathological features can be important for studying the underlying mechanism of orthopedic diseases and predicting drug responses in preclinical trials instead of in animals, the development of biomimetic BOCs with high efficiency and fidelity will be accelerated further. Here, we review recently engineered BOCs developed using various microfluidic technologies and investigate their use to model the bone microenvironment. We have also explored various biomimetic strategies based on biological, geometrical, and biomechanical cues for biomedical applications of BOCs. Finally, we addressed the limitations and challenging issues of current BOCs that should be overcome to obtain more acceptable BOCs in the biomedical and pharmaceutical industries.
Objectives:
Recent studies have associated subarticular trabecular bone distribution in the extant hominid first metacarpal (Mc1) with observed thumb use, to infer fossil hominin thumb use. Here, we analyze the entire Mc1 to test for interspecific differences in: (1) the absolute volume of trabecular volume fraction, (2) the distribution of the deeper trabecular network, and (3) the distribution of trabeculae in the medullary cavity, especially beneath the Mc1 disto-radial flange.
Materials and methods:
Trabecular bone was imaged using micro-computed tomography in a sample of Homo sapiens (n = 11), Pan paniscus (n = 10), Pan troglodytes (n = 11), Gorilla gorilla (n = 10) and Pongo sp., (n = 7). Using Canonical Holistic Morphometric Analysis (cHMA), we tested for interspecific differences in the trabecular bone volume fraction (BV/TV) and its relative distribution (rBV/TV) throughout the Mc1, including within the head, medullary cavity, and base.
Results:
P. paniscus had the highest, and H. sapiens the lowest, BV/TV relative to other species. rBV/TV distribution statistically distinguished the radial concentrations and lack of medullary trabecular bone in the H. sapiens Mc1 from all other hominids. H. sapiens and, to a lesser extent, G. gorilla also had a significantly higher trabecular volume beneath the disto-radial flange relative to other hominids.
Discussion:
These results are consistent with differences in observed thumb use in these species and may also reflect systemic differences in bone volume fraction. The trabecular bone extension into the medullary cavity and concentrations beneath the disto-radial flange may represent crucial biomechanical signals that will aid in the inference of fossil hominin thumb use.
This paper aims to investigate the characteristic microstructure-based failure mechanisms observed during the fracture cutting of age-varying bovine cortical bone. To this end, orthogonal cutting experiments are performed on cortical femoral bones harvested from three distinct bovine age groups, viz., young (~1 month), mature (16-18 months) and old (~30 months). Fracture cutting is induced at a depth of cut of 70 μm and a cutting velocity of 800 mm/min by using two distinct tool rake angles of + 20 deg. and 0 deg. The nanoindentation studies and porosity analysis show key differences between microstructural constituents, as a function of age. The high-speed camera images taken during the fracture cutting process provide insight into six dominant microstructure-specific failure mechanisms. These include primary osteonal fracture, woven fracture, and lamellar fracture observed in the plexiform region; and cement line fracture (i.e., osteon debonding), secondary osteonal fracture, and interstitial matrix fracture observed in the haversian regions. In addition to the conventionally reported specific cutting energy metric, a new metric of resultant cutting force per unit crack area and surface integrity are employed here. All cutting responses are seen to be sensitive to age-related microstructural variations and the tool rake angle. In addition to requiring more cutting force, the neutral tool rake angle also results in notable sub-surface damage
Background
There is a genetic component to the minimum effective strain (MES)—a threshold which determines when bone will adapt to function—which suggests ancestry should play a role in bone (re)modelling. Further elucidating this is difficult in living human populations because of the high global genetic admixture. We examined femora from an anthropological skeletal assemblage (Mán Bạc, Vietnam) representing distinct ancestral groups. We tested whether femur morphological and histological markers of modelling and remodelling differed between ancestries despite their similar lifestyles.
Methods
Static histomorphometry data collected from subperiosteal cortical bone of the femoral midshaft, and gross morphometric measures of femur robusticity, were studied in 17 individuals from the Mán Bạc collection dated to 1906 to 1523 cal. BC. This assemblage represents agricultural migrants with affinity to East Asian groups, who integrated with the local hunter-gatherers with affinity to Australo-Papuan groups during the mid-Holocene. Femur robusticity and histology data were compared between groups of ‘Migrant’ (n = 8), ‘Admixed’ (n = 4), and ‘Local’ (n = 5).
Results
Local individuals had more robust femoral diaphyses with greater secondary osteon densities, and relatively large secondary osteon and Haversian canal parameters than the migrants. The Migrant group showed gracile femoral shafts with the least dense bone made up of small secondary osteons and Haversian canals. The Admixed individuals fell between the Migrant and Local categories in terms of their femoral data. However, we also found that measures of how densely bone is remodelled per unit area were in a tight range across all three ancestries.
Conclusions
Bone modelling and remodelling markers varied with ancestral histories in our sample. This suggests that there is an ancestry related predisposition to bone optimising its metabolic expenditure likely in relation to the MES. Our results stress the need to incorporate population genetic history into hierarchical bone analyses. Understanding ancestry effects on bone morphology has implications for interpreting biomechanical loading history in past and modern human populations.
Facile surgical delivery and stable fixation of synthetic scaffolds play roles just as critically as degradability and bioactivity in ensuring successful scaffold-guided tissue regeneration. Properly engineered shape memory polymers (SMPs) may meet these challenges. Polyhedral oligomeric silsesquioxanes (POSSs) can be covalently integrated with urethane-crosslinked polylactide (PLA) to give high-strength, degradable SMPs around physiological temperatures. To explore their potential for guided bone regeneration, here we tune their hydrophilicity, degradability, cytocompatibility, and osteoconductivity/osteoinductivity by crosslinking star-branched POSS-PLA with hydrophilic polyethylene glycol diisocyanates of different lengths and up to 60 wt % hydroxyapatite (HA). The composites exhibit high compliance, toughness, up to gigapascal storage moduli, and excellent shape recovery (>95%) at safe triggering temperatures. Water swelling ratios and hydrolytic degradation rates positively correlated with the hydrophilic crosslinker lengths, while the negative impact of degradation on the proliferation and osteogenesis of bone marrow stromal cells was mitigated with HA incorporation. Macroporous composites tailored for a rat femoral segmental defect were fabricated, and their ability to stably retain and sustainedly release recombinant osteogenic bone morphogenetic protein-2 and support cell attachment and osteogenesis was demonstrated. These properties combined make these amphiphilic osteoconductive degradable SMPs promising candidates as next-generation synthetic bone grafts.
It has been suggested that adverse changes in bone quality due to the accumulation of advanced glycation end-products (AGEs) may play a role in the increased skeletal fragility. These non-enzymatic glycation mediated crosslinks are caused due to the presence of sugars in the extracellular space and can be induced in-vitro. AGEs exist naturally in bone, but with diseases such as type-2 diabetes, they are found at higher levels. While previous studies have examined the relationships between AGE accumulation and some mechanical properties, there is a lack of understanding of how AGE accumulation affects the fracture mechanics behaviour of bone tissue at fall-related loading rates. The objective of this study was to investigate the relationship between AGE accumulation and the fracture mechanics of cortical bone tissue. An in vitro glycation model was used to simulate diabetic conditions in twenty anatomically adjacent pairs of bone from a single bovine femur, which reduced the possibility of inter-specimen variability. Mechanical characterisation was carried out using 3-point bend, fracture toughness and nanoindentation testing, while bone composition was analysed by quantifying the accumulation of fluorescent AGEs. Under three-point bend testing, it was found that the yield stress, ultimate flexural strength, and secant modulus of the glycated samples were significantly higher than the controls. Furthermore, fracture toughness testing showed that the critical fracture toughness was increased by 16% in glycated samples compared to controls. These results provide no evidence that AGEs alone play a role in bone fragility at fall-related loading rates, with AGE accumulation actually found to enhance several pre- and post-yield properties of the tissue.
The external morphology and microanatomy of 32 partial and complete Hyperodapedon premaxillae was examined to assess their functional attributes. This revealed morphological correlates for innervation of Hyperodapedon premaxillae in the form of posteriorly opening enlarged neurovascular foramina associated with several grooves, and a prominent neurovascular sulcus. Scanning electron microscopy shows numerous small, circular foramina in clusters along the lateroventral surface towards the anterior tip and along the ventral edge, often in a preferred orientation. These are found associated with high rugosity along the elongated anterolateral depression, and were related to nutrient supply and/or part of the neurovascular system. Selected premaxillae show extremely high bone compactness indices (especially at the anterior end) suggesting specialized osteosclerotic conditions, and dense and compact bone microstructure with almost no clear transition between the outer compact cortex and inner core. With ontogeny, the premaxillae became lateromedially thickened by deposition of lamellar zonal bone, and highly vascularized and dense from intense Haversian remodelling, suggesting pachyosteosclerosis of the premaxillae. Other characteristic features include profuse open vascular channels or a frayed margin at the anteroventral tip, and dense bundles of long and wavy extrinsic fibres. These features, along with high bone compactness, decrease posteriorly towards the naris. It is proposed that the Hyperodapedon premaxillae were covered by keratinized epithelium or rhamphotheca at the anterior end, and had heightened sensory capabilities that aided foraging for mussels and other invertebrates in soft sediments under shallow water. Such enhanced sensory capability is reported for the first time in an early‐diverging archosauromorph.
Over the years, we have seen how, thanks to experimentation on animal models, the foundations have been laid in the field of implantology. In most cases, studies related to the bone scale are carried out on the species that are most similar in their movements and behavior to humans. The femur has been selected as the reference bone for our test, selecting as animals to experiment with the goat breed, the bovine breed and the porcine breed for their similarity to the human body, obtaining specimens of the cortical part of the bone. Destructive bending tests will be carried out in the same way on each of the femur fragments of each animal. When interpreting the results, we will be guided by taking sections of the transverse and longitudinal part of the bone, performing the tests in both cases inside the femur, and once the results have been obtained, we will proceed to their subsequent evaluation. We relate the bone resistance of the samples to the effect of an oncological drug, Altan Zolendronic Acid 4 mg/ 100 ml solution for perfusion EFG, administered in cases of bone metastasis.
Polymethyl methacrylate (PMMA) bone cements are used as “glue” between orthopedic/orthodontic implants and bone, since they can be modeled and easily applied by the surgeon, while being chemically and biologically stable for many years after surgery. In this research, Y2O3 powder was added to commercial PMMA bone cement to produce a composite resin, which was then characterized and tested in vitro to evaluate the cell proliferation and the quality of osteoblastic bone formed in vitro on the composite. Biological assays showed an increase in cell proliferation on the Y2O3-PMMA composite as compared to the pristine sample. Alizarin Red staining (ARS) showed the amount of bone formed on a composite PMMA resin was about 30% higher than that on the pristine PMMA bone cement reference. The quality of bone tissue was evaluated using Raman spectroscopy, showing the bone tissue formed on the composite had a better degree of mineralization and a higher maturity as compared to the tissue grown on the control sample. These preliminary results suggest that Y2O3 plays a biologically active role in bone growth and Y2O3-composites are affordable, superior candidates as bone cement materials.
Finite element analysis (FEA) is no longer a new technique in the fields of palaeontology, anthropology, and evolutionary biology. It is nowadays a well-established technique within the virtual functional-morphology toolkit. However, almost all the works published in these fields have only applied the most basic FEA tools i.e ., linear materials in static structural problems. Linear and static approximations are commonly used because they are computationally less expensive, and the error associated with these assumptions can be accepted. Nonetheless, nonlinearities are natural to be used in biomechanical models especially when modelling soft tissues, establish contacts between separated bones or the inclusion of buckling results. The aim of this review is to, firstly, highlight the usefulness of non-linearities and secondly, showcase these FEA tool to researchers that work in functional morphology and biomechanics, as non-linearities can improve their FEA models by widening the possible applications and topics that currently are not used in palaeontology and anthropology.
In order to acquire satisfactory load-bearing bone substitute, a series of high performance biobased liquid crystal copolyesters derived from 4-hydroxybenzoic acid (HBA), phloretic acid (HPPA), vanillic acid (VA) and lactic acid (LA) were designed and prepared via “one-pot” melt polymerization method in this work. The structure and properties of the copolyesters were fully investigated by experimental measurements and molecular simulation. The copolyesters showed relative low melting temperatures (176-229°C) and controllable crystallinity (15.3-36.5%), due to the increased molecular chain mobility caused by LA units and the multi-component copolymerization effect. Broad temperature range of nematic liquid crystal phase, good thermal stability as well as shear shinning and viscous melt flow behavior were observed for the copolyesters, indicating they had excellent melt processing ability. As compared with polyetheretherketone (PEEK) materials, the copolyesters exhibited better mechanical properties and hydrophilicity, which of the tensile strength and water contact angle were in range of 95 to 175MPa and 72.5 to 84.8o, respectively, ascribing to the combination effect of its liquid crystal nature and chemical structure. In addition, the cytotoxicity test showed the copolyesters have good biocompatibility. It is shown that the unique combination of potential biodegradability, excellent mechanical properties, hydrophilicity and biocompatibility of the copolyesters make them prospective and suitable for application in load-bearing bone repair area.
▪ Abstract The term bone refers to a family of materials, all of which are built up of mineralized collagen fibrils. They have highly complex structures, described in terms of up to 7 hierarchical levels of organization. These materials have evolved to fulfill a variety of mechanical functions, for which the structures are presumably fine-tuned. Matching structure to function is a challenge. Here we review the structure-mechanical relations at each of the hierarchical levels of organization, highlighting wherever possible both underlying strategies and gaps in our knowledge. The insights gained from the study of these fascinating materials are not only important biologically, but may well provide novel ideas that can be applied to the design of synthetic materials.
Gao et al. (PNAS, 100, 5597–5600 (2003)) have argued that load-bearing mineralized hard tissues, including bones, shells, and teeth, are nanocomposites,
in which the mineral phase has nanoscale dimensions that ensure optimum strength and flaw tolerance. In particular, it has
been claimed that the thickness of these brittle building blocks, being smaller than a critical size, h*, of the order of tens of nanometers, renders them insensitive to the presence of crack-like flaws and enables them to achieve
near-theoretical strength, which is why Nature employs nanoscale features in mineralized biological composites. We find this
point of view, which Gao et al. and others have quoted in subsequent publications and presentations, unpersuasive and present
several counterexamples which show that biological structures, as a result of being comprised of relatively fragile constituents
that fracture at stress levels several orders of magnitude smaller than the theoretical strength, adopt various strategies
to develop mechanical responses that enable them to mitigate catastrophic failure. Nanoscale structural features are not a
result of an innate resistance to very high stresses.
The mechanical properties and the possible biological use of the extremely dense bone of the rostrum of the toothed whale Mesoplodon densirostris were studied. Bone tissue has three main components: mineral, organic material and water, the organic material being mainly collagen. To demonstrate where the rostrum lies in respect to its mineralization and comparatively to other tissues, an ethylenediaminetetraacetic acid (EDTA) was used to dissolve the mineral and to calculate the three weight fractions. The rostrum appears to be at the every end of a process that both in ontogeny and phylogeny tends to remove water and collagen in favor of the mineral.
This article reviews current work on the strength and toughness of bone, its mechanisms of fracture and its ability to repair
and adapt its structure. These properties are affected at all size levels, from the nanostructure of collagen molecules and
mineral crystals, through the microstructure of osteons and trabeculae, up to the macroscopic shape and density variations
that occur at the level of a whole bone.
We present quantum mechanical calculations using density functional theory and semiempirical methods, and molecular mechanics (MM) calculations with a Tersoff–Brenner potential that explore the role of vacancy defects in the fracture of carbon nanotubes under axial tension. These methods show reasonable agreement, although the MM scheme systematically underestimates fracture strengths. One- and two-atom vacancy defects are observed to reduce failure stresses by as much as ∼26% and markedly reduce failure strains. Large holes – such as might be introduced via oxidative purification processes – greatly reduce strength, and this provides an explanation for the extant theoretical–experimental discrepancies.
Mineralized biological materials such as bone, sea sponges or diatoms provide load-bearing and armor functions and universally feature structural hierarchies from nano to macro. Here we report a systematic investigation of the effect of hierarchical structures on toughness and defect-tolerance based on a single and mechanically inferior brittle base material, silica, using a bottom-up approach rooted in atomistic modeling. Our analysis reveals drastic changes in the material crack-propagation resistance (R-curve) solely due to the introduction of hierarchical structures that also result in a vastly increased toughness and defect-tolerance, enabling stable crack propagation over an extensive range of crack sizes. Over a range of up to four hierarchy levels, we find an exponential increase in the defect-tolerance approaching hundred micrometers without introducing additional mechanisms or materials. This presents a significant departure from the defect-tolerance of the base material, silica, which is brittle and highly sensitive even to extremely small nanometer-scale defects.
Our bones are full of cracks, which form and grow as a result of daily loading activities. Bone is the major structural material in our bodies. Although weaker than many engineering materials, it has one trick that keeps it ahead - it can repair itself. Small cracks, which grow under cyclic stresses by the mechanism of fatigue, can be detected and removed before they become long enough to be dangerous. This article reviews the work that has been done to understand how cracks form and grow in bone, and how they can be detected and repaired in a timely manner. This is truly an interdisciplinary research field, requiring the close cooperation of materials scientists, biologists and engineers.
Bone strains are the most important factors for osteogenic adaptive responses. During the past decades, scientists have been trying to describe the relationship between bone strain and bone osteogenic responses quantitatively. However, only a few studies have examined bone strains under physiological condition in humans, owing to technical difficulty and ethical restrictions. The present paper reviews previous work on in vivo bone strain measurements in humans, and the various methodologies adopted in these measurements are discussed. Several proposals are made for future work to improve our understanding of the human musculoskeletal system. Literature suggests that strains and strain patterns vary systematically in response to different locomotive activities, foot wear, and even different venues. The principal compressive, tension and engineering shear strain, compressive strain rate and shear strain rate in the tibia during running seem to be higher than those during walking. The high impact exercises, such as zig-zag hopping and basketball rebounding induced greater principal strains and strain rates in the tibia than normal activities. Also, evidence suggests an increase of tibia strain and strain rate after muscle fatigue, which strongly supports the opinion that muscle contractions play a role on the alteration of bone strain patterns.
Nanocrystals of apatitic calcium phosphate impart the organic-inorganic nanocomposite in bone with favorable mechanical properties. So far, the factors preventing crystal growth beyond the favorable thickness of ca. 3 nm have not been identified. Here we show that the apatite surfaces are studded with strongly bound citrate molecules, whose signals have been identified unambiguously by multinuclear magnetic resonance (NMR) analysis. NMR reveals that bound citrate accounts for 5.5 wt% of the organic matter in bone and covers apatite at a density of about 1 molecule per (2 nm)(2), with its three carboxylate groups at distances of 0.3 to 0.45 nm from the apatite surface. Bound citrate is highly conserved, being found in fish, avian, and mammalian bone, which indicates its critical role in interfering with crystal thickening and stabilizing the apatite nanocrystals in bone.
Physical cues, such as extracellular matrix stiffness, direct cell differentiation and support tissue-specific function. Perturbation of these cues underlies diverse pathologies, including osteoarthritis, cardiovascular disease and cancer. However, the molecular mechanisms that establish tissue-specific material properties and link them to healthy tissue function are unknown. We show that Runx2, a key lineage-specific transcription factor, regulates the material properties of bone matrix through the same transforming growth factor-β (TGFβ)-responsive pathway that controls osteoblast differentiation. Deregulated TGFβ or Runx2 function compromises the distinctly hard cochlear bone matrix and causes hearing loss, as seen in human cleidocranial dysplasia. In Runx2+/⁻ mice, inhibition of TGFβ signalling rescues both the material properties of the defective matrix, and hearing. This study elucidates the unknown cause of hearing loss in cleidocranial dysplasia, and demonstrates that a molecular pathway controlling cell differentiation also defines material properties of extracellular matrix. Furthermore, our results suggest that the careful regulation of these properties is essential for healthy tissue function.
Load-bearing biological materials such as shell, mineralized tendon and bone exhibit two to seven levels of structural hierarchy based on constituent materials (biominerals and proteins) of relatively poor mechanical properties. A key question that remains unanswered is what determines the number of hierarchical levels in these materials. Here we develop a quasi-self-similar hierarchical model to show that, depending on the mineral content, there exists an optimal level of structural hierarchy for maximal toughness of biocomposites. The predicted optimal levels of hierarchy and cooperative deformation across multiple structural levels are in excellent agreement with experimental observations.
We assessed the hydration state of antlers and its effect on antler mechanical properties compared with wet femur. Red deer antlers were removed from the head at various times, from a few days after velvet shedding till late in the season, and weighed weekly until after casting time. Antlers cut just after losing their velvet lost weight rapidly in the first few weeks, then settled down and changed weight very little, the latter changes correlating with air relative humidity. Antlers cut later showed little weight change at any time. The water content of cortical and trabecular parts of the contralateral antler was assessed after cutting. Most of the weight loss was from the cancellous, not the cortical, part of the antler. Wet and dry specimens from the antlers, and wet specimens from deer femora, were tested mechanically. Compared with wet bone, wet antler had a much lower modulus of elasticity and bending strength, but a higher work to fracture. Compared with wet bone, dry antler showed a somewhat lower Young's modulus, but a considerably higher bending strength and a much higher work to fracture. The impact energy absorption of dry antler was much greater than that of wet bone. In red deer, the antler is effectively dry during its use in fights, at least in southern Spain. In addition, dry antler, compared with ordinary bone, shows mechanical properties that suit it admirably for its fighting function.
Natural materials such as bone, tooth, and nacre are nanocomposites of proteins and minerals with superior strength. Why is the nanometer scale so important to such materials? Can we learn from this to produce superior nanomaterials in the laboratory? These questions motivate the present study where we show that the nanocomposites in nature exhibit a generic mechanical structure in which the nanometer size of mineral particles is selected to ensure optimum strength and maximum tolerance of flaws (robustness). We further show that the widely used engineering concept of stress concentration at flaws is no longer valid for nanomaterial design.
Wolff’s law is generally considered to be a philosophical statement to the effect that, over time, the mechanical load applied to living bone influences the structure of bone tissue. But Wolff’s claim was beyond the philosophical statement; his claim was that it was rigorous or mathematical law. From the 19th to the 20th century many argued that the rigid or “mathematical” form of Wolff’s law of trabecular architecture, that promulgated by Wolff, is not valid. That view is endorsed here. The law compares things that appear to be similar but are not, namely, stress trajectories in a homogeneous isotropic elastic material and the trabecular architecture of cancellous bone-this comparison is referred to here as the false premise.
This is a comprehensive and accessible overview of what is known about the structure and mechanics of bone, bones, and teeth. In it, John Currey incorporates critical new concepts and findings from the two decades of research since the publication of his highly regarded The Mechanical Adaptations of Bones. Crucially, Currey shows how bone structure and bone's mechanical properties are intimately bound up with each other and how the mechanical properties of the material interact with the structure of whole bones to produce an adapted structure. For bone tissue, the book discusses stiffness, strength, viscoelasticity, fatigue, and fracture mechanics properties. For whole bones, subjects dealt with include buckling, the optimum hollowness of long bones, impact fracture, and properties of cancellous bone. The effects of mineralization on stiffness and toughness and the role of microcracking in the fracture process receive particular attention. As a zoologist, Currey views bone and bones as solutions to the design problems that vertebrates have faced during their evolution and throughout the book considers what bones have been adapted to do. He covers the full range of bones and bony tissues, as well as dentin and enamel, and uses both human and non-human examples. Copiously illustrated, engagingly written, and assuming little in the way of prior knowledge or mathematical background, Bones is both an ideal introduction to the field and also a reference sure to be frequently consulted by practicing researchers.
Arguments related to the dependence of the strength of solids on mechanics or to the geometry of material are discussed. Scaling laws on the strength of solids usually ignore geometry and are studied by applying mechanics, fracture mechanics for elasto-brittle materials or strain-gradient plasticity for elasto-plastic materials. It is shown that scaling laws are connected to the geometrical and multiscale character of the domain in which the energy exchange occurs. It was found that energy dissipation take place not over a euclidean domain but on a fractal domain, which is always included within euclidean surfaces and volumes.
The recent rewriting of the Bažant’s size effect law (Morel, 2008) which has suggested the existence of an additional asymptotic regime for intermediate structure sizes is now compared to numerical simulations of fracture of geometrically similar notched structures of different sizes extending over 2.4 decades. The quasibrittle fracture behavior is simulated through cohesive zone model (bilinear softening) using a constant set of cohesive parameters whatever the specimen size D is. The R-curves resulting from the load–displacement responses are estimated and appear as size-independent. On this basis, the different asymptotic regimes expected for the size effect on fracture properties at peak load such as the relative crack length, the resistance to crack growth and the nominal strength are shown in fair agreement with the size effect observed on the results obtained from numerical simulations.
Engineering structures must be designed for an extremely low failure probability such as 10⁻⁶, which is beyond the means of direct verification by histogram testing. This is not a problem for brittle or ductile materials because the type of probability distribution of structural strength is fixed and known, making it possible to predict the tail probabilities from the mean and variance. It is a problem, though, for quasibrittle materials for which the type of strength distribution transitions from Gaussian to Weibullian as the structure size increases. These are heterogeneous materials with brittle constituents, characterized by material inhomogeneities that are not negligible compared to the structure size. Examples include concrete, fiber composites, coarse-grained or toughened ceramics, rocks, sea ice, rigid foams and bone, as well as many materials used in nano- and microscale devices.
After a synthesis on some recent data on the biology of bone tissues senso lato, this paper focuses on the limits of known variability of bone regarding its amount of mineralisation (maximal and minimal) and on the underlying control mechanisms. Two models of hypermineralised bones are reviewed among cetaceans: the rostrum of the ‘beaked whale’ Mesoplodon and the tympanic bulla of the dolphin Delphinus. In the first case, hypermineralisation is reached lately through an ultrastructural specialization of the secondary osteons. In the second case, hypermineralisation starts at once, during foetal life, through a specialization of the primary osteons. In both cases, ultrastructural peculiarities of collagen fibrillogenesis are demonstrated. Diameter and spacing of the fibrils leave an exceptional empty space available for mineral deposition. Conversely, hypomineralisation is observed on the model of the Teleost scale. The basal plate of the scale is made of a regular ‘biological plywood’ of densely packed collageneous fibres. The mineral is laid down mostly in the interfibrillary spaces. All such tissue modulations seem to be rigorously controlled by details of the osteoblast biosynthetic activities. In a given situation, osteoblasts may express only a subset of molecules from their potential complete biosynthetic repertoire. The debate now centres on how osteoblasts acquire positional information to express this subset. To cite this article: L. Zylberberg, C. R. Palevol 3 (2004).
Electronic structure calculations based on density functional theory are employed to investigate the effect of substitutional fluoride ions on the local ordering of hydroxy groups in hydroxyapatite. The calculated structural parameters of the two end-member minerals are in good agreement with the experimental hexagonal structures. Electronic density contour plots show the apatite structure to be an ionic crystal, where the phosphate and hydroxy groups behave like polyanions. The calculations on hydroxyapatite identified the oxygen and hydrogen positions of the hydroxyl groups in the crystal structure to be well-defined, alternating in a column in the c-direction. Any disorder within the OH− columns carries an energetic cost of 0.22 eV per OH− but comparison with the fully ordered monoclinic phase of hydroxyapatite shows that ordering between the columns has no energetic advantage. We therefore predict that the experimentally found oxygen
and hydrogen disorder is due to the presence in the crystal of differently oriented locally ordered domains, giving rise to the average partial occupancy which is found in crystallographic studies.
Mineralized collagen fibrils are highly conserved nanostructural building blocks of bone. By a combination of molecular dynamics simulation and theoretical analysis it is shown that the characteristic nanostructure of mineralized collagen fibrils is vital for its high strength and its ability to sustain large deformation, as is relevant to the physiological role of bone, creating a strong and tough material. An analysis of the molecular mechanisms of protein and mineral phases under large deformation of mineralized collagen fibrils reveals a fibrillar toughening mechanism that leads to a manifold increase of energy dissipation compared to fibrils without mineral phase. This fibrillar toughening mechanism increases the resistance to fracture by forming large local yield regions around crack-like defects, a mechanism that protects the integrity of the entire structure by allowing for localized failure. As a consequence, mineralized collagen fibrils are able to tolerate microcracks of the order of several hundred micrometres in size without causing any macroscopic failure of the tissue, which may be essential to enable bone remodelling. The analysis proves that adding nanoscopic small platelets to collagen fibrils increases their Young's modulus and yield strength as well as their fracture strength. We find that mineralized collagen fibrils have a Young's modulus of 6.23 GPa (versus 4.59 GPa for the collagen fibril), yield at a tensile strain of 6.7% (versus 5% for the collagen fibril) and feature a fracture stress of 0.6 GPa (versus 0.3 GPa for the collagen fibril).
The attachment of single ions to putative adsorption sites in the tails of collagen fibers is investigated by means of molecular dynamics simulations and discussed with respect to the very early steps of apatite/collagen biomineral formation. Our studies clearly demonstrate an increased flexibility of the tails of the triple-helical collagen protein. Apart from the termini of the backbone, several side chains were also observed to be freely accessible to ion attachment from aqueous solution. The teleopeptide was systematically scanned for suitable adsorption sites for calcium, phosphate and fluoride ions. Association of these ions was then explored from potential of mean force calculations. The resulting energy profiles reveal a variety of favorable protein-ion bonds and hint at the suitability of the collagen tails to promote apatite aggregation.
Data on the compressive properties of cancellous bone cubes with a large range of densities (relative densities compared with compact bone of 0.04–0.60) show that the exponent relating the Young's modulus to the density is close to quadratic and that it is improbable that the material Young's modulus of our specimens was less than 8 GPa, and was probably considerably higher.
Comparative microstrain measurements of the elastic deformation of tibia compact bone sections taken from 1-, 3- and 12-month-old rabbits, revealed an increase in the elastic modulus from 15.1 to 27.6 GN m–2 with age. This result was correlated with observations of the porosity and hydroxyapatite percentages of the compact bone and the implications for a collagen/hydroxyapatite composite were examined.
The mechanical properties of biological materials have been the focal point of extensive studies over the past decades, leading
to formation of a new research field that intimately connects biology, chemistry and materials science. Significant advances
have been made in many disciplines and research areas, ranging throughout a variety of material scales, from atomistic, molecular
up to continuum scales. Experimental studies are now carried out with molecular precision, including investigations of how
molecular defects such as protein mutations or protein knockout influence larger length- and time-scales. Simulation studies
of biological materials now range from electronic structure calculations of DNA, molecular simulations of proteins and biomolecules
like actin and tubulin to continuum theories of bone and collagenous tissues. The integration of predictive numerical studies
with experimental methods represents a new frontier in materials research. The field is at a turning point when major breakthroughs
in the understanding, synthesis, control and analysis of complex biological systems emerge. Here we provide a brief perspective
of the state of this field and outline new research directions.
The interactions between mineral and collagen phases in the ultrastructural level play an important role in determining the mechanical properties of bone tissue. Three types of mineral-collagen interaction (i.e., ionic interactions, hydrogen/van der Waals bonds, and van der Waals/viscous shear in opening/sliding mode, respectively) have been simulated in this study, using cohesive zone-modeling techniques. Considering the inhomogeneity of bone, a probabilistic failure analysis approach has been also employed to account for the effect of mineral-collagen interfacial behavior on microdamage accumulation in lamellar bone tissues. The results of this study suggested that different interfacial behaviors cause different types of microdamage accumulation. The ionic interactions between the mineral and collagen phases lead to the formation of linear microcracks, while the van der Waals/viscous shear interactions may facilitate the formation of diffuse damage. In the case of hydrogen/van der Waals bonds, a transitional behavior of microdamage accumulation in bone was observed. The findings of this study may help in understanding the mechanisms of mineral-collagen interactions and its effects on the failure mechanism of bone.
This review attempts to show the bone community that there are many ways of being a 'bone', and that the range of mechanical properties of bone material is much greater than is conventionally thought to be the case. However the structure-function relationships have in many cases hardly moved beyond mere assertion. There is a pressing need for an examination of some material properties of a whole variety of bones, always using exactly the same testing method, for instance nanoindentation of wet material, so that firm comparisons can be made.
In situ mechanical testing coupled with imaging using high-energy synchrotron X-ray diffraction or tomography is gaining in popularity as a technique to investigate micrometer and even sub-micrometer deformation and fracture mechanisms in mineralized tissues, such as bone and teeth. However, the role of the irradiation in affecting the nature and properties of the tissue is not always taken into account. Accordingly, we examine here the effect of X-ray synchrotron-source irradiation on the mechanistic aspects of deformation and fracture in human cortical bone. Specifically, the strength, ductility and fracture resistance (both work-of-fracture and resistance-curve fracture toughness) of human femoral bone in the transverse (breaking) orientation were evaluated following exposures to 0.05, 70, 210 and 630 kGrays (kGy) irradiation. Our results show that the radiation typically used in tomography imaging can have a major and deleterious impact on the strength, post-yield behavior and fracture toughness of cortical bone, with the severity of the effect progressively increasing with higher doses of radiation. Plasticity was essentially suppressed after as little as 70 kGy of radiation; the fracture toughness was decreased by a factor of five after 210 kGy of radiation. Mechanistically, the irradiation was found to alter the salient toughening mechanisms, manifest by the progressive elimination of the bone's capacity for plastic deformation which restricts the intrinsic toughening from the formation "plastic zones" around crack-like defects. Deep-ultraviolet Raman spectroscopy indicated that this behavior could be related to degradation in the collagen integrity.
While there are a growing number of increasingly complex methodologies available to model geometry and material properties of bones, these models still cannot accurately describe physical behaviour of the skeletal system unless the boundary conditions, especially muscular loading, are correct. Available in vivo measurements of muscle forces are mostly highly invasive and offer no practical way to validate the outcome of any computational model that predicts muscle forces. However, muscle forces can be verified indirectly using the fundamental property of living tissue to functional adaptation and finite element (FE) analysis. Even though the mechanisms of the functional adaptation are not fully understood, its result is clearly seen in the shape and inner structure of bones. The FE method provides a precise tool for analysis of the stress/strain distribution in the bone under given loading conditions. The present work sets principles for the determination of the muscle forces on the basis of the widely accepted view that biological systems are optimized light-weight structures with minimised amount of unloaded/underloaded material and hence evenly distributed loading throughout the structure. Bending loading of bones is avoided/compensated in bones under physiological loading. Thus, bending minimisation provides the basis for the determination of the musculoskeletal system loading. As a result of our approach, the muscle forces for a human femur during normal gait and sitting down (peak hip joint force) are obtained such that the bone is loaded predominantly in compression and the stress distribution in proximal and diaphyseal femur corresponds to the material distribution in bone.
There is an ongoing discussion on how bone strength could be explained from its internal structure and composition. Reviewing recent experimental and molecular dynamics studies, we here propose a new vision on bone material failure: mutual ductile sliding of hydroxyapatite mineral crystals along layered water films is followed by rupture of collagen crosslinks. In order to cast this vision into a mathematical form, a multiscale continuum micromechanics theory for upscaling of elastoplastic properties is developed, based on the concept of concentration and influence tensors for eigenstressed microheterogeneous materials. The model reflects bone's hierarchical organization, in terms of representative volume elements for cortical bone, for extravascular and extracellular bone material, for mineralized fibrils and the extrafibrillar space, and for wet collagen. In order to get access to the stress states at the interfaces between crystals, the extrafibrillar mineral is resolved into an infinite amount of cylindrical material phases oriented in all directions in space. The multiscale micromechanics model is shown to be able to satisfactorily predict the strength characteristics of different bones from different species, on the basis of their mineral/collagen content, their intercrystalline, intermolecular, lacunar, and vascular porosities, and the elastic and strength properties of hydroxyapatite and (molecular) collagen.
A general methodology for predicting the conditions for the formation of plate-shaped structures by precipitation has been developed. The method has been applied for understanding the morphology of hydroxyapatite formed under different synthetic conditions. Morphology diagram has been developed in the form of pH-T diagrams to predict regions where plate-shaped hydroxyapatite is expected to form. The validity of the morphology diagram has been tested by critical experiments carried out at different conditions coupled with detailed microstructural analysis. Different morphologies ranging from single crystalline sheets, rods to equiaxed particles of hydroxyapatite are achieved by tuning the driving force of the precipitation reactions by varying the parameters such as pH and temperature in the absence of capping/surfactant agents. The synthesis and analysis presented here have important implications for understanding the plate-shaped morphology of apatite crystals that exist in the bone.
Femoral stress fractures tend to occur at the neck, medial proximal-shaft, and distal-shaft. The purpose of this study was to determine the internal femoral forces and moments during running. It was expected that larger loads would occur at these common sites of femoral stress fracture.
Ten subjects ran at their preferred running speed over a force platform while motion capture data were collected. Static optimization in conjunction with a SIMM musculoskeletal model was used to determine individual muscle forces of the lower extremity. Joint contact forces were determined, and a quasi-static approach was used to calculate internal forces and moments along a centroid path through the femur.
The largest mean peak loads were observed at the following regions: anterior-posterior shear, 7.47 bodyweights (BW) at the distal-shaft (posteriorly directed); axial force, 11.40BW at the distal-shaft (compression); medial-lateral shear, 3.75BW at the neck (medially directed); anterior-posterior moment, 0.42BWm at the proximal-shaft (medial surface compression); torsional moment, 0.20BWm at the distal-shaft (external rotation); medial-lateral moment, 0.44BWm at the distal-shaft (anterior surface compression).
The mechanical loading environment of the femur during running appears to explain well the redundancy in femoral stress fracture location. We observed the largest internal loads at the three femoral sites prone to stress fracture.
The normal pattern of surface strain produced in the distal third of sheep tibiae was determined by attaching rosette strain gauges to the cranial (anterior), medial, and caudal (posterior) cortices of the tibia. The strain data showed that during locomotion the cranial (longitudinally concave) cortex was the tension surface and the caudal (longitudinally convex) cortex was the compression surface. (This relationship between bending and curvature is the reverse of that which occurs in the radius of the same species).The principal strain directions remained almost constant throughout the main strain period of each stride and were practically unaffected by the speed of locomotion. On neither the cranial nor the caudal surface of the tibia was the larger principal strain aligned along the long axis of the bone. On the cranial surface it formed a proximal and lateral angle of 29 degrees with this axis and on the caudal surface, a similar angle of 23 degrees. This strain pattern is consistent with a loading regimen of craniocaudal bending and torque. The mean peak principal strain on the cranial and caudal surfaces of the bone during walking in five sheep was +709 and -666 microstrain, respectively (ratio, 1.07 to one). In eight sheep the mean thickness of the cranial cortex was 3.0 millimeters and of the caudal cortex, 2.87 millimeters (ratio, 1.03 to one). The directions of secondary osteons in the cranial and caudal cortices of the tibia in these eight sheep were shown to lie between the direction of the long axis of each bone and that of the larger principal strain in that cortex during locomotion. Determinations of the transverse axes of the proximal and distal joint surfaces of the tibia in adult sheep and in sheep in late fetal life showed that during postnatal development the distal end of the bone rotates internally some 14 degrees with respect to the proximal end. The limited strain data available from the tibia of a human suggest that the tibial torque during locomotion is in the same direction in both sheep and humans. The developmental rotation of the tibia in these species, however, is in the opposite direction.
The use of a tranversely isotropic model is tested for the elastic behavior of bovine and human bone and the five independent constants of this model are determined. The accuracy of the model is tested for eight cases by comparing the off-axis modulus predicted by a rotation of stiffness matrix with an experimentally determined off-axis modulus. Ultimate properties are presented for bovine and human bone for tension, compression, and torsional loads. A Hankinson type failure criterion is proposed for off-axis ultimate stress and this predicted value compared with experimental values for nine cases.
In this study the yield behavior of cortical bone was determined under combined loading conditions involving tension, compression and torsion. The axis of each test sample coincided with the long bone axis. To minimize viscoelastic behavior, tests were conducted using an effective strain rate in the range of 0.01-0.06 s-1. Experimental yield loci for bovine and human cortical bone were determined using a strain offset technique to determine the 'common yield point' for combined loading. Several failure criteria which have been used for composite materials were examined for applicability to the experimental results. Data were obtained for bovine and human tibial and femoral bone. The Tsai-Wu criterion was in best agreement to the test data, although Hill's criterion could describe the individual compression-torsion or tension-torsion regimes with good accuracy.
Neutron diffraction measurements have been made of the equatorial and meridional spacings of collagen in fully mineralized mature bovine bone and demineralized bone collagen, in both wet and dry conditions. The collagen equatorial spacing in wet mineralized bovine bone is 1.24 nm, substantially lower than the 1.53 nm value observed in wet demineralized bovine bone collagen. Corresponding spacings for dry bone and demineralized bone collagen are 1.16 nm and 1.12 nm, respectively. The collagen meridional long spacing in mineralized bovine bone is 63.6 nm wet and 63.4 nm dry. These data indicate that collagen in fully mineralized bovine bone is considerably more closely packed than had been assumed previously, with a packing density similar to that of the relatively crystalline collagens such as wet rat tail tendon. The data also suggest that less space is available for mineral within the collagen fibrils in bovine bone than had previously been assumed, and that the major portion of the mineral in this bone must be located outside the fibrils.
The aim of this research was to test the hypothesis that the intact femur is loaded predominately in compression. The study was composed of two parts: a finite element analysis of the intact femur to assess if a compressive stress distribution could be achieved in the diaphyseal region of the femur using physiological muscle and joint contact forces; a simple radiological study to assess the in vivo deflections of the femur during one legged stance. The results of this investigation strongly support the hypothesis that the femur is loaded primarily in compression, and not bending as previously thought. The finite element analysis demonstrated that a compressive stress distribution in the diaphyseal femur can be achieved, producing a stress distribution which appears to be consistent with the femoral cross-sectional geometry. The finite element analysis also predicted that for a compressive load case there would be negligible deflections of the femoral head. The radiological study confirmed this, with no measurable in vivo deflection of the femur occurring during one legged stance.
Acoustic microscopy (30-60 microm resolution) and nanoindentation (1-5 microm resolution) are techniques that can be used to evaluate the elastic properties of human bone at a microstructural level. The goals of the current study were (1) to measure and compare the Young's moduli of trabecular and cortical bone tissues from a common human donor, and (2) to compare the Young's moduli of bone tissue measured using acoustic microscopy to those measured using nanoindentation. The Young's modulus of cortical bone in the longitudinal direction was about 40% greater than (p<0.01) the Young's modulus in the transverse direction. The Young's modulus of trabecular bone tissue was slightly higher than the transverse Young's modulus of cortical bone, but substantially lower than the longitudinal Young's modulus of cortical bone. These findings were consistent for both measurement methods and suggest that elasticity of trabecular tissue is within the range of that of cortical bone tissue. The calculation of Young's modulus using nanoindentation assumes that the material is elastically isotropic. The current results, i.e., the average anisotropy ratio (E(L)/E(T)) for cortical bone determined by nanoindentation was similar to that determined by the acoustic microscope, suggest that this assumption does not limit nanoindentation as a technique for measurement of Young's modulus in anisotropic bone.
The bones of vertebrates are all made from the same basic material, despite a huge variation in size from one species to another. This introduces a problem: large structures are more prone to fatigue failure (stress fracture) than smaller structures made of the same material. This implies that bones in larger animals cannot withstand as much stress in daily use as bones in smaller animals. In fact, this is not the case, because all bones experience approximately the same stresses and strains in use. This implies a variation in the underlying material: bone material in large animals must have superior fatigue properties to offset the disadvantages of size. This hypothesis is tested here by reference to fatigue data from the literature, taken from a range of animals from cows to mice. Fatigue strength was plotted as a function of stressed volume and modelled mathematically using a Weibull distribution. This shows a general tendency for fatigue strength to reduce as volume increases. But when the volume effect is taken into account, there remains a tendency for bones from smaller animals to have lower fatigue strength. This can be modelled by a simple variation in one of the parameters in the Weibull equation, which defines the intrinsic fatigue strength of the material. When extrapolated to the size of the whole bone for each animal, all bones were found to have the same fatigue strength. This resolves the anomaly and implies a complex system in which the underlying structure of bone varies with animal size in order to cancel out scaling effects.
Trabecular bone is a complex material with substantial heterogeneity. Its elastic and strength properties vary widely across anatomic sites, and with aging and disease. Although these properties depend very much on density, the role of architecture and tissue material properties remain uncertain. It is interesting that the strains at which the bone fails are almost independent of density. Current work addresses the underlying structure-function relations for such behavior, as well as more complex mechanical behavior, such as multiaxial loading, time-dependent failure, and damage accumulation. A unique tool for studying such behavior is the microstructural class of finite element models, particularly the "high-resolution" models. It is expected that with continued progress in this field, substantial insight will be gained into such important problems as osteoporosis, bone fracture, bone remodeling, and design/analysis of bone-implant systems. This article reviews the state of the art in trabecular bone biomechanics, focusing on the mechanical aspects, and attempts to identify important areas of current and future research.
Knowledge of kinetics of fatigue crack growth of microcracks is important so as to understand the dynamics of bone adaptation, remodeling, and the etiology of fatigue-based failures of cortical bone tissue. In this respect, theoretical models (Taylor, J. Biomech., 31 (1998) 587-592; Taylor and Prendergast, Proc. Instn. Mech. Engrs. Part H 211 (1997) 369-375) of microcrack growth in cortical bone have predicted a decreasing microcrack growth rate with increasing microcrack length. However, these predictions have not been observed directly. This study investigated microcrack growth and arrest through observations of surface microcracks during cyclic loading (R=0.1, 50-80MPa) of human femoral cortical bone (male, n=4, age range: 37-40yr) utilizing a video microscopy system. The change in crack length and orientation of eight surface microcracks were measured with the number of fatigue cycles from four specimens. At the applied cyclic stresses, the microcracks propagated and arrested in generally less than 10,000 cycles. The fatigue crack growth rate of all microcracks decreased with increasing crack length following initial identification, consistent with theoretical predictions. The growth rate of the microcracks was observed to be in the range of 5x10(-5) to 5x10(-7)mmcycle(-1). In addition, many of the microcracks were observed not to grow beyond 150 microm and a cyclic stress intensity factor of 0.5MNm(-3/2). The results of this study suggest that cortical bone tissue may resist fracture at the microscale by deceleration of fatigue crack growth and arrest of microcracks.
An understanding of the evolution of toughness is essential for the mechanistic interpretation of the fracture of cortical bone. In the present study, in vitro fracture experiments were conducted on human cortical bone in order to identify and quantitatively assess the salient toughening mechanisms. The fracture toughness was found to rise linearly with crack extension (i.e., rising resistance- or R-curve behavior) with a mean crack-initiation toughness, K0 of approximately 2 MPa square root m for crack growth in the proximal-distal direction. Uncracked ligament bridging, which was observed in the wake of the crack, was identified as the dominant toughening mechanism responsible for the observed R-curve behavior. The extent and nature of the bridging zone was examined quantitatively using multi-cutting compliance experiments in order to assess the bridging zone length and estimate the bridging stress distribution. Additionally, time-dependent cracking behavior was observed at stress intensities well below those required for overload fracture; specifically, slow crack growth occurred at growth rates of approximately 2 x 10(-9) m/s at stress intensities approximately 35% below the crack-initiation toughness. In an attempt to measure slower growth rates, it was found that the behavior switched to a regime dominated by time-dependent crack blunting, similar to that reported for dentin; however, such blunting was apparent over much slower time scales in bone, which permitted subcritical crack growth to readily take place at higher stress intensities.
Lamellar bone is common among primates, either in the form of extended planar circumferential arrays, or as cylindrically shaped osteons. Osteonal bone generally replaces circumferential lamellar bone with time, and it is therefore of much interest to compare the mechanical properties and fracture behavior of these two forms of lamellar bone. This is, however, difficult as natural specimens of circumferential lamellar bone large enough for standard mechanical tests are not available. We found that as a result of treatment with large doses of alendronate, the lateral sides of the diaphyses of baboon tibia contained fairly extensive regions of circumferential lamellar bone, the structure of which appears to be indistinguishable from untreated lamellar bone. Three-point bending tests were used to determine the elastic and ultimate properties of almost pure circumferential lamellar bone and osteonal bone in four different orientations relative to the tibia long axis. After taking into account the differences in porosity and extent of mineralization of the two bone types, the flexural modulus, bending strength, fracture strain and nominal work-to-fracture properties were similar for the same orientations, with some exceptions. This implies that it is the lamellar structure itself that is mainly responsible for these mechanical properties. The fracture behavior and morphologies of the fracture surfaces varied significantly with orientation in both types of bone. This is related to the microstructure of lamellar bone. Osteonal bone exhibited quite different damage-related behavior during fracture as compared to circumferential lamellar bone. Following fracture the two halves of osteonal bone remained attached whereas in circumferential lamellar bone they separated. These differences could well provide significant adaptive advantages to osteonal bone function.