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Magneto-mechanical stimulation of bone growth in a bonded array of ferromagnetic fibres
Abstract
A brief experimental and theoretical study is presented into the elastic deformation of bonded arrays of ferromagnetic fibres, when subjected to an external magnetic field. Material made of such fibre arrays is of potential interest for certain biomedical applications, such as prosthetic implants. Externally imposed magnetic fields could be used to generate mechanical strains in surrounding tissue, with possible physiological benefits. It is shown that it should be possible to generate strains within embryonic bone cell networks, forming within such a fibre array, which are sufficient to stimulate enhanced growth. The effects outlined here could thus form the basis of surgical or therapeutic advances.
... An implant coating/scaffold, made of interconnected networks of slender ferromagnetic fibers sintered together at cross-over points, has been developed to promote the growth of healthy peri-prosthetic bone [9,10]. The design draws on the well-known theories of skeletal physiology and the concepts of strain-regulated bone modelling and remodeling [3][4][5]. ...
... Because of shape anisotropy, long fibers magnetize easier along their long axis, as the demagnetizing field is negligible in that direction. To estimate the deformations induced in a ferromagnetic fiber network by application of a magnetic field, an analytical magneto-mechanical model has been developed [9,10]. An important (controllable) design parameter is the fiber segment aspect ratio (the sections between the joints L over the fiber diameter D) as the strain that the fibers can transfer to the in-growing bone is dependent on how much the fibers are able to deflect. ...
... An important (controllable) design parameter is the fiber segment aspect ratio (the sections between the joints L over the fiber diameter D) as the strain that the fibers can transfer to the in-growing bone is dependent on how much the fibers are able to deflect. For metal fiber networks with relatively low fiber volume fraction and slender fiber segments between joints, the macroscopic magneto-mechanical response of such materials can be predicted using an affine model [9,10] based on the deflection of individual fiber segments subjected to a magnetically-induced bending moment. A prosthesis design allowing such an effect to be exploited would involve a circumferentially proximal porous layer, comprising ferromagnetic fibers, bonded to a conventional non-magnetic stem [20]. ...
There is currently an interest in “active” implantable biomedical devices that include mechanical stimulation as an integral part of their design. This paper reports the experimental use of a porous scaffold made of interconnected networks of slender ferromagnetic fibers that can be actuated in vivo by an external magnetic field applying strains to in-growing cells. Such scaffolds have been previously characterized in terms of their mechanical and cellular responses. In this study, it is shown that the shape changes induced in the scaffolds can be used to promote osteogenesis in vitro. In particular, immunofluorescence, gene and protein analyses reveal that the actuated networks exhibit higher mineralization and extracellular matrix production, and express higher levels of osteocalcin, alkaline phosphatase, collagen type 1α1, runt-related transcription factor 2 and bone morphogenetic protein 2 than the static controls at the 3-week time point. The results suggest that the cells filling the inter-fiber spaces are able to sense and react to the magneto-mechanically induced strains facilitating osteogenic differentiation and maturation. This work provides evidence in support of using this approach to stimulate bone ingrowth around a device implanted in bone and can pave the way for further applications in bone tissue engineering.
... An implant coating/scaffold, made of interconnected networks of slender ferromagnetic fibres sintered together at cross-over points, has been developed to promote the growth of healthy peri-prosthetic bone [9,10]. The design draws on the well-known theories of skeletal physiology and the concepts of strain-regulated bone modelling and remodeling [3][4][5]. ...
... Due to shape anisotropy, long fibres magnetize easier along their long axis, as the demagnetizing field is negligible in that direction. To estimate the deformations induced in a ferromagnetic fibre network by application of a magnetic field, an analytical magneto-mechanical model has been developed [9,10]. An important (controllable) design parameter is the fibre segment aspect ratio (the sections between the joints L over the fibre diameter D) as the strain that the fibres can transfer to in-growing bone is dependent on how much the fibres are able to deflect. ...
... An important (controllable) design parameter is the fibre segment aspect ratio (the sections between the joints L over the fibre diameter D) as the strain that the fibres can transfer to in-growing bone is dependent on how much the fibres are able to deflect. For metal fibre networks with relatively low fibre volume fraction and slender fibre segments between joints, the macroscopic magneto-mechanical response of such materials can be predicted using an affine model [9,10] based on the deflection of individual fibre segments subjected to a magneticallyinduced bending moment. A prosthesis design allowing such an effect to be exploited would involve a circumferentially proximal porous layer, comprised of ferromagnetic fibres, bonded to a conventional nonmagnetic stem [20]. ...
There is currently an interest in “active” implantable biomedical devices that include mechanical stimulation as an integral part of their design. This paper reports the experimental use of a porous scaffold made of interconnected networks of slender ferromagnetic fibres that can be actuated in vivo by an external magnetic field applying strains to in-growing cells. Such scaffolds have been previously characterized in terms of their mechanical and cellular responses. In this study, it is shown that the shape changes induced in the scaffolds can be used to promote osteogenesis in vitro. In particular, immunofluorescence, gene and protein analyses reveal that the actuated networks exhibit higher mineralization and extracellular matrix production, and express higher levels of osteocalcin, alkaline phosphatase, collagen type 1a1, runt-related transcription factor 2 and bone morphogenetic protein 2 than the static controls at the 3-week time point. The results suggest that the cells filling the inter-fibre spaces are able to sense and react to the magneto-mechanically induced strains facilitating osteogenic differentiation and maturation. This work provides evidence in support of using this approach to stimulate bone ingrowth around a device implanted in bone and can pave the way for further applications in bone tissue engineering.
... It was difficult to build and develop a model for fibrous porous ceramics due to their complex and disordered network structure. Markaki and Clyne [14,15] developed a model based on the bending behavior of single fiber segment. However, Markaki and Clyne put forward that more systematic and accurate data of fiber network architecture characteristics needed to be acquired. ...
... The contribution of bending to macroscopic deflection was investigated by Markaki and Clyne [14,15]. They derived the axial net strain as: ...
... The plots in Fig. 7b showed the probability distributions of angle (θ) for the three networks and the probability of an isotropic (random) distribution. The probability distribution of the fiber segments orientation P (θ) [28] was given by: (15) where N θi was the number of fibers falling into a bin of width Δθi, centered at θi. Network B was closer to being isotropic, since most fiber segments were found to conform closely to the sin(θ) (random) distribution. The stereogram of network B (Fig. 7b) showed projections that were more random. ...
Accurately establishing the relationship between the network architecture characteristics and performance of fibrous porous ceramics is instructive for structural design and performance control. In the present work, fibrous, high porous (82.87–90.02%), low density (0.247–0.512 g/cm³) and low elastic modulus (50.62–188.56 MPa) mullite ceramics were fabricated by freeze casting. The three dimensional network architectures were characterized by X-ray tomography technique and quantitatively analyzed by 3D image analysis software (imorph, www.imorph.fr). The radius (5.04 µm), types, lengths (64.72–96.49 µm) and orientations (0.87–1.45, anisotropy parameter) of fiber segments in the network architecture were investigated. The extracted results were employed to predict the Young's modulus of the mullite fibrous porous ceramics according to a model based on the bending and axial compression of single fiber segment. The predicted Young's modulus agreed well with the experimental results. The differences of Young's modulus and Poisson ratio between the prediction and the model of Markaki and Clyne were compared. The comparison showed that the difference became larger when the aspect ratio of the fiber segment was less than 6 due to the effect of axial compression. The predicted Poisson ratio had a certain dependence on fiber segment aspect ratio and got close to the constant (1/π) reported by Markaki and Clyne with the increase of fiber segment aspect ratio.
... and f y (x, y) = ∇ y φ(x, y) + ∇ y × A(x, y). (27) In the following section, we equate coefficients of l for l = 0, 1, . . . in (22)(23)(24)(25) to obtain an effective system of PDEs for the zeroth-order displacement field in the homogenized domain Ω H (see Fig. 1). Since we aim at deriving a model that involves macroscale quantities only, it is convenient to define the following cell average operators ...
... Equating coefficients of 0 in (22)(23)(24)(25) yields ...
... whereas equating coefficients of 1 in (22)(23)(24)(25) leads to ...
We derive the new effective governing equations for linear elastic composites subject to a body force that admits a Helmholtz decomposition into inhomogeneous scalar and vector potentials. We assume that the microscale, representing the distance between the inclusions (or fibers) in the composite, and its size (the macroscale) are well separated. We decouple spatial variations and assume microscale periodicity of every field. Microscale variations of the potentials induce a locally unbounded body force. The problem is homogenizable, as the results, obtained via the asymptotic homogenization technique, read as a well-defined linear elastic model for composites subject to a regular effective body force. The latter comprises both macroscale variations of the potentials, and nonstandard contributions which are to be computed solving a well-posed elastic cell problem which is solely driven by microscale variations of the potentials. We compare our approach with an existing model for locally unbounded forces and provide a simplified formulation of the model which serves as a starting point for its numerical implementation. Our formulation is relevant to the study of active composites, such as electrosensitive and magnetosensitive elastomers.
... There have been several previous experimental studies of the mechanical response of stochastic metallic fibre networks made of Cu [4], Ti [5], 20%Cr-80%Ni [6], steel [7][8][9] and stainless steel [10][11][12][13][14][15][16][17][18][19][20][21][22] fibres (in particular 304 [10,11], 316L [12][13][14][15][16][17][18] and 446 [19][20][21][22]). The majority of these studies focused on the effect of fibre size and volume fraction on tensile [4,6,[10][11][12][13][14]17,19], compressive [5,7,13,17,18,[20][21][22], torsional [8,17] and impact [9] responses. ...
... There have been several previous experimental studies of the mechanical response of stochastic metallic fibre networks made of Cu [4], Ti [5], 20%Cr-80%Ni [6], steel [7][8][9] and stainless steel [10][11][12][13][14][15][16][17][18][19][20][21][22] fibres (in particular 304 [10,11], 316L [12][13][14][15][16][17][18] and 446 [19][20][21][22]). The majority of these studies focused on the effect of fibre size and volume fraction on tensile [4,6,[10][11][12][13][14]17,19], compressive [5,7,13,17,18,[20][21][22], torsional [8,17] and impact [9] responses. ...
... There have been several previous experimental studies of the mechanical response of stochastic metallic fibre networks made of Cu [4], Ti [5], 20%Cr-80%Ni [6], steel [7][8][9] and stainless steel [10][11][12][13][14][15][16][17][18][19][20][21][22] fibres (in particular 304 [10,11], 316L [12][13][14][15][16][17][18] and 446 [19][20][21][22]). The majority of these studies focused on the effect of fibre size and volume fraction on tensile [4,6,[10][11][12][13][14]17,19], compressive [5,7,13,17,18,[20][21][22], torsional [8,17] and impact [9] responses. Optimization of their performance clearly requires an understanding of the interplay between processing conditions, network architecture, fibre microstructure and mechanical response characteristics under various types of applied load. ...
In the present paper, highly porous fibre networks made of 316L fibres, with different fibre volume fractions, are characterized in terms of network architecture, elastic constants and fracture energies. Elastic constants are measured using quasi-static mechanical and modal vibration testing, yielding local and globally averaged properties, respectively. Differences between quasi-static and dynamic elastic constants are attributed to through-thickness shear effects. Regardless of the method employed, networks show signs of material inhomogeneity at high fibre densities, in agreement with X-ray nanotomography results. Strong auxetic (or negative Poisson’s ratio) behaviour is observed in the through-thickness direction, which is attributed to fibre kinking induced during processing. Measured fracture energies are compared with model predictions incorporating information about in-plane fibre orientation distribution, fibre volume fraction and single fibre work of fracture. Experimental values are broadly consistent with model predictions, based on the assumption that this energy is primarily associated with plastic deformation of individual fibres within a process zone of the same order as the inter-joint spacing.
... An analytical magneto-mechanical model has been developed [21] which can be used to estimate the distortions induced in a free-standing porous specimen by application of a magnetic field. The model is based on the deflection of individual fibre segments (between joints) experiencing bending moments as a result of the induced magnetic dipole. ...
... The geometry of such deflections is illustrated in Fig.3. ∆z and ∆r are respectively the relative deflections of the fibre mid-points parallel and normal to the applied field B. The model has been validated by constructing simple fibre assemblies [21]. ...
... However, if it is assumed that, averaged over the volume, constraint effects will cancel out, then the overall deformation can be predicted by summing the contributions from individual segments, taken in isolation. The net axial extension (∆Z/Z) and the net transverse contraction (∆R/R) are predicted [21] to conform to Eqns. (1) and (2) respectively. ...
This work relates to porous material made by bonding together fibres of a magnetic material. When subjected to a magnetic field, the array deforms, with individual fibres becoming magnetised along their length and then tending to line up locally with the direction of the field. An investigation is presented into the concept that this deformation could induce beneficial strains in bone tissue network in the early stages of growth as it grows into the porous fibre array. An analytical model has been developed, based on the deflection of individual fibre segments (between joints) experiencing bending moments as a result of the induced magnetic dipole. The model has been validated via measurements made on simple fibre assemblies and random fibre arrays. Work has also been done on the deformation characteristics of random fibre arrays with a matrix filling the inter-fibre space. This has the effect of reducing the fibre deflections. The extent of this reduction, and an estimate of the maximum strains induced in the space-filling material, can be obtained using a simple force balance approach. Predictions indicate that in-growing bone tissue, with a stiffness of around 0.01-0.1 GPa, could be strained to beneficial levels (~1 millistrain), using magnetic field strengths in current diagnostic use (~1 Tesla), provided the fibre segment aspect ratio is at least about 10. Such material has a low Young's modulus, but the overall stiffness of a prosthesis could be matched to that of cortical bone by using an integrated design involving a porous magneto-active layer bonded to a dense non-magnetic core.
... The base fibers can be flexibly selected to meet various needs, which are made of copper [1], titanium [2], carbon nanotube [3][4][5][6][7], and steel [8]. In particular, a number of stainless steel fibers [9][10][11][12][13][14][15][16] exhibit superior performance such as high temperature resistance, corrosion resistance, high surface to mass ratio and permeability. As the cell size can be accurately controlled with different fibers of diameter ranging from several to several hundred micrometers, they are widely applied in filtration and separation [17], gas infiltration [18], catalyst support [19], biomaterials [11,15], heat transfer [20], and sound absorption [10,21,22]. ...
... In particular, a number of stainless steel fibers [9][10][11][12][13][14][15][16] exhibit superior performance such as high temperature resistance, corrosion resistance, high surface to mass ratio and permeability. As the cell size can be accurately controlled with different fibers of diameter ranging from several to several hundred micrometers, they are widely applied in filtration and separation [17], gas infiltration [18], catalyst support [19], biomaterials [11,15], heat transfer [20], and sound absorption [10,21,22]. In addition, it has been shown that auxetic fiber networks can have various promising mechanical properties over traditional open-cell cellular materials in terms of high specific stiffness and strength, high shear and indentation resistance [13,[23][24][25], larger fracture toughness [26] and enhanced energy absorption properties [27], among others. ...
Sintered metal fiber sheets (MFSs) made by sequential-overlap method are transversely isotropic open-cell cellular materials with paper-like fiber network architectures, which exhibit auxeticity and are promising for various potential applications due to the reentrant micro-structure. The thickness effect on the out-of-plane auxeticity (negative Poisson's ratio) of MFSs samples of 2–20 mm thick subjected to in-plane tensile loading is investigated with digital image correlation technique. Furthermore, the deformation modes of fibers within MFSs during various loading stages are examined with X-ray tomography. It is found that in addition to the straightening of reentrant fibers, fiber layers with defects and joints failure induced slippage between adjacent layers leads to local shear and results in unique umbrella-like local deformation termed umbrella effect, which gradually dominates the auxeticity during tensile loading. Although remarkably increasing lateral deformation, the umbrella effect significantly diminishes the in-plane mechanical performance such as rigidity and strength. In particular, this effect is suppressed by sample thickness: the overall performance tends to stabilize with sample thickness greater than a certain value, provided that the MFS is uniform with all fibers randomly distributed. The finding facilitates wider application of auxetic MFSs with further understanding on the relationship between the thickness effect and performance.
... Therefore, we aim to construct a 3D fibre network reinforced composite. In terms of the fibre network, Clyne et al. have conducted a series of thorough investigations towards bonded metal fibre networks both experimentally and analytically, involving work in the characterisation of the network architecture and capture of independent elastic constants [14][15][16][17][18][19]. Some other research has also been done regarding to the mechanical properties of transversely isotropic fibre networks [20-23], such as metal fibre sintered sheet [24,25]. ...
... Jayanty et al. [10] have fabricated an auxetic stainless steel mat and a composite reinforced by the mat. Clyne et al. [14,15,19] have also included analysis of fibre network composites by introducing a strain https://doi. ...
This research stems from the idea of introducing a fibre-network structure into composites aiming to enhance the stiffness and strength of the composites. A novel new type of composites reinforced by a tranversely isotropic fibre-network in which the fibres are devided into continuous segments and randomly distributed has been proposed and found to have improved elastic properties compared to other conventional fibre or particle composites mainly due to the introduction of cross-linkers among the fibres. Combining with the effects of Poisson's ratio of the constituent materials, the fibre network composite can exhibit extraordinary stiffness. A simplified analytical model has also been proposed for comparison with the numerical results, showing close prediction of the stiffness of the fibre-network composites. Moreover, as a plate structure, the thickness of the fibre network composite is adjustable and can be tailored according to the dimensions and mechanical properties as demanded in industry.
... 23−27 The external applied magnetic field could induce torque magnetic forces into the scaffold that offers mechanical stimulation to the cells, therefore favoring their proliferation and differentiation. 28,29 Under a magnetic field, these scaffolds can be induced to undergo physical changes such as elongation, contraction, or bending. 30−32 These magnetic-sensitive biomaterials are useful in comparison to other stimuli-responsive biomaterials because magnetic stimulation acts at a distance (noncontact force) that is noninvasive and convenient to adapt for therapeutic devices. ...
... Additionally, the external applied magnetic field could induce torque magnetic forces into the scaffold that would presumably be translated into mechanical stimulation to the cells, therefore favoring their proliferation and differentiation. 28,29 2.10. Magnetization of Cells. ...
... This paper relates to an implant device, based on a ferromagnetic material, with the potential to deform in vivo promoting osseointegration through the growth of a healthy periprosthetic bone via a magnetically-induced strain. 3,4 It involves the use of porous magneto-active layers, made of ferromagnetic fibres bonded together, on the surface of prosthetic implants. (Currently, the biological response of such bonded ferromagnetic layers has only been assessed in vitro, see the section on 'Biological Response'.) ...
... Assuming that the fibre becomes fully magnetised along its length, elastic fibre deflections can be predicted analytically 3 and numerically by applying a torque as described in equation (1). Analytically, using standard expressions for cantilever deflection, the relative deflections parallel Dz/z and transverse Dr/r to the applied field (Fig. 4a), at a distance x along the fibre length are given respectively by 3 Dz z~8 ...
Creating 'smart' biomedical devices with the potential for controlled actuation in vivo has been a long-standing scientific pursuit in therapeutic medicine. The present work focuses on a bone regeneration scaffold based on ferromagnetic fibres designed to induce in vivo modelling of in-growing periprosthetic bone by the application of an external magnetic field of clinical magnitude. We present the conceptual basis of such a 'magneto-active scaffold', the properties of prime interest and how these properties can be controlled.
... Total hip replacement using porous metal implant surfaces has been widely implemented surgically for cementless fixation of femoral implants. Porous magneto-active layers, made of slender ferromagnetic fibres, bonded together at cross-over points, have been proposed for use as implant coatings due to their potential to impart mechanical strains in vivo to in-growing bone tissue (1,2). Most ferromagnetic devices are contraindicated for medical resonance imaging due to risks related to movement and dislodgement (3); however, implant fixation using ferromagnetic materials is currently used in several dental systems for removable dental prostheses (4). ...
... (c). However, theoretically the optimal region for transduction of strain to cells in vivo lies within inter-fibre spaces as depicted inFigure 1(a)(2).In this study, it is proposed that the deposition of fibrin at early time points, either as the result of physiological processes or clinical application, would facilitate cell attachment in interfibre regions. This hypothesis was investigated using in vitro cultures of human osteoblasts (HObs). ...
Ferromagnetic fiber networks have the potential to deform in vivo imparting therapeutic levels of strain on in-growing periprosthetic bone tissue. 444 Ferritic stainless steel provides a suitable material for this application due to its ability to support cultures of human osteoblasts (HObs) without eliciting undue inflammatory responses from monocytes in vitro. In the present article, a 444 fiber network, containing 17 vol% fibers, has been investigated. The network architecture was obtained by applying a skeletonization algorithm to three-dimensional tomographic reconstructions of the fiber networks. Elastic properties were measured using low-frequency vibration testing, providing globally averaged properties as opposed to mechanical methods that yield only local properties. The optimal region for transduction of strain to cells lies between the ferromagnetic fibers. However, cell attachment, at early time points, occurs primarily on fiber surfaces. Deposition of fibrin, a fibrous protein involved in acute inflammatory responses, can facilitate cell attachment within this optimal region at early time points. The current work compared physiological (3 and 5 g center dot L-1) and supraphysiological fibrinogen concentrations (10 g center dot L-1), using static in vitro seeding of HObs, to determine the effect of fibrin deposition on cell responses during the first week of cell culture. Early cell attachment within the interfiber spaces was observed in all fibrin-containing samples, supported by fibrin nanofibers. Fibrin deposition influenced the seeding, metabolic activity, and early stage differentiation of HObs cultured in the fibrin-containing fiber networks in a concentration-dependant manner. While initial cell attachment for networks with fibrin deposited from low physiological concentrations was similar to control samples without fibrin deposition, significantly higher HObs attached onto high physiological and supraphysiological concentrations. Despite higher cell numbers with supraphysiological concentrations, cell metabolic activities were similar for all fibrinogen concentrations. Further, cells cultured on supraphysiological concentrations exhibited lower cell differentiation as measured by alkaline phosphatase activity at early time points. Overall, the current study suggests that physiological fibrinogen concentrations would be more suitable than supraphysiological concentrations for supporting early cell activity in porous implant coatings.
... This approach opens up possibilities for utilizing metallic glasses in flexible electronics, where they can be easily shaped, and woven into cellular structures, bundles, textiles, and smart sensors. [22,23] Leveraging their flexibility, magnetic microfibers can be employed to construct magnetic weaves for shields. [3] Furthermore, their unique microstructure and size effects confer excellent structural and functional properties. ...
Thin and flexible materials that can provide efficient electromagnetic interference (EMI) shielding are urgently needed, particularly those that can be rapidly processed and withstand harsh environments. Cobalt-based metallic glasses stand out as prime candidates due to their excellent soft magnetic properties, satisfactory shielding features, and mechanical properties. Herein, a recently developed technique is used to fabricate metallic glass microfibers from Co 66 Fe 4 Mo 2 Si 16 B 12 alloy. The produced microfibers are characterized for their size and uniformity by scanning electron microscopy and their amorphous structure is confirmed by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The cobalt-based metallic glass microfibers show an EMI shielding factor that reaches five in the static regime and obtains an up to 25-fold increase of the attenuation constant in the Ku frequency band. This performance originates from the combination of soft magnetic properties and excellent electrical conductivity. In addition, the flexible microfibers exhibit excellent hardness and elasticity making them suitable for EMI shielding of complex geometries. Their hardness and elastic modulus are measured by nanoindentation to be 11.31 ± 0.60 GPa, and 110.54 ± 11.24 GPa, respectively.
... Thus, metal implants coated with highly porous, bonded ferromagnetic fibers under an external magnetic field enhance implant-host tissue fixation. In this method, the porous coatings were produced by spraying fibers with slow-setting aerosol glue, surface dispersed brazing powder, and then placed in a long quartz tube at 1200°C (105). The coating thus produced high porosities ranging from 70 -90%, with pore size ranging from 100 -300μm. ...
Porous and functionally graded materials have seen extensive applications in modern biomedical devices-allowing for improved site-specific performance; their appreciable mechanical, corrosive, and biocompatible properties are highly sought after for lightweight and high-strength load-bearing orthopedic and dental implants. Examples of such porous materials are metals, ceramics, and polymers. Although, easy to manufacture and lightweight, porous polymers do not inherently exhibit the required mechanical strength for hard tissue repair or replacement. Alternatively, porous ceramics are brittle and do not possess the required fatigue resistance. On the other hand, porous biocompatible metals have shown tailorable strength, fatigue resistance, and toughness. Thereby, a significant interest in investigating the manufacturing challenges of porous metals has taken place in recent years. Past research has shown that once the advantages of porous metallic structures in the orthopedic implant industry have been realized, their biological and biomechanical compatibility-with the host bone-has been followed up with extensive methodical research. Various manufacturing methods for porous or functionally graded metals are discussed and compared in this review, specifically, how the manufacturing process influences microstructure, graded composition, porosity, biocompatibility, and mechanical properties. Most of the studies discussed in this review are related to porous structures for bone implant applications; however, the understanding of these investigations may also be extended to other devices beyond the biomedical field.
... In this regard, the toughness of micro-and nanoscale metallic glass fibers is higher than their bulk form. Additionally, they can be used in many applications because they can be easily formed or woven into cellular structures, bundles, textiles, and smart sensors 11,12 . In fact, there are plenty of work on the fabrication of metallic glass nanofibers but limited research is dedicated to the fabrication of metallic glass microfibers that could be directly utilized or embedded in other applications. ...
Metallic glasses (MG) have attracted much attention due to their superior hardness and good corrosion resistance. However, designing new MG compositions is still a big challenge, and their integration into different systems is limited when they are in the shape of bulk materials. Here, we present a new method for the fabrication of MG in the form of microfibers which could greatly help them to be integrated within different systems. The newly proposed technique has the ability to form MG structure from commercially available alloy compositions thanks to its significantly improved quenching rate(~ 108 K.s−1). In this technique, individual melt droplets are ejected on a rotating wheel forming a thin film which are ruptured upon solidification leading to the formation of MG microfibers. In this regard, we have fabricated microfibers from a commercial DIN 1.4401 stainless-steel which could form a completely amorphous structure confirmed by DSC, XRD, and HRTEM. The fabricated MG microfibers show an increased hardness for more than two-fold from 3.5 ± 0.17 GPa for the as-received stainless-steel to 7.77 ± 0.60 GPa for the amorphous microfibers. Subsequent heat-treatment of the microfibers resulted in a nanocrystalline structure with the presence of amorphous regions when the hardness increases even further to 13.5 ± 2.0 GPa. We propose that confinement of both shear transformation zones and dislocations in the heat-treated MG microfibers plays a major role in enhancing strength.
... [3][4][5] They have significant potential for eventual technological applications in actuators or sensors. 4,6 Such Fe-Pd thin films have been the focus of research primarily for shape memory devices in bioapplications. 7,8 The FSM effect in Fe-Pd alloys originates from the reversible martensitic transformation (MT) from face-centered cubic (fcc) to body-centered tetragonal (bct), which was measured with 0:9 , c=a , 1 9,10 in its equivalent face-centered tetragonal (fct) unit cell, and is generally called "fct" (named "fctI" here) structure since it is close to the fcc one. ...
The effects of local atomic and magnetic configurations on the phase stability and elastic property of the face-centered cubic (fcc) and two body-centered tetragonal [face-centered tetragonal (fctI) and fctII, with 0.9 < c / a < 1 and 0.71 < c / a < 0.9, respectively, in the fct unit cell] phases of Fe 1 − x Pd x ( 0.28 ≤ x ≤ 0.34) shape memory alloys are systematically investigated by using the first-principles exact muffin-tin orbital method in combination with the coherent potential approximation. It is shown that, considering four types of atomic configurations in a fcc unit cell, the two with one random sublattice are both preferable in each x below 300 K. When T = 300 K, the one with three random sublattices also changes to be stabilized for x ≤ 0.30, whereas that with four random sublattices becomes stable in most of these alloys until T ≥ 600 K. Upon tetragonal distortions, in these fully disordered alloys, both the fctI and fctII phases are unstable. The fctI phase is found for 0.29 ≤ x ≤ 0.33, having only the configuration with one random sublattice on the same layer with the Pd site in the unit cell, whereas the fctII phase is obtained for x ≤ 0.30, possessing all the configurations with one, two, and three random sublattices. These results representing the phase diagram of these alloys, their determined equilibrium lattice parameters, and elastic constants of the three phases at 0 K are in line with the experimental and theoretical data, and their estimated structural ( T M) and magnetic ( T C) transition temperatures are also close to the experimental data. Adding 4% magnetic disorder in Fe 0.70 Pd 0.30, the fctII structure is effectively prevented, whereas the thermoelastic martensitic transformation of fcc–fctI can still be retained at 0 K.
... Magnetothermal therapy has a deep penetration within any tissues or organs inside human body. [108] Furthermore, it has been reported that magnetic fields could stimulate cell responses, such as magneto-mechanical stimulation of cell constructs, [109] mechano-sensitive ion channels, [110] magnetic cell seeding, and controlled cell proliferation and differentiation. [111] Hence, biomaterial scaffolds with magnetothermal ability is of great interesting for integrative tumor therapy and bone regeneration. ...
Bone tumors bring great pain to patients, along with a high disability rate and high mortality. Several therapeutic strategies have been applied to treat bone tumors, such as chemotherapy, radiotherapy, and surgical resection. However, these strategies have intrinsic drawbacks, such as the serious side effects of chemotherapy or the necessary reconstructive surgery of surgical resection. To help develop more satisfactory bone tumor treatment strategies, biomaterial scaffolds have been proposed. Biomaterial scaffolds are often applied for repairing bone defects after surgical resection due to their biocompatibility, osteoinductivity, and osteoconductivity as well as excellent physicochemical properties. Simultaneously, the function of bone tumor therapy offers biomaterial scaffolds to eliminate residual tumor cells, thus avoiding tumor recurrence. This review summarizes recent advances in biomaterial scaffolds which are combined with chemotherapy or hyperthermia therapy for treating bone tumors and further bone regeneration. Moreover, the progress in synergistic therapy of bone tumors based on biomaterial scaffolds is also discussed. This review aims to inspire researchers to develop novel fabrication or functionalization strategies for constructing multifunctional biomaterial scaffolds with anti‐tumor properties.
... In fact, under magnetic fields, these scaffolds could provide ondemand release of drugs or biomolecules (i.e., growth factors) inducing osteogenesis and angiogenesis and at the same time magneto-mechanical stimulation on bone cells favoring proliferation, differentiation, and bone healing. The influence of magnetic fields in the cell stimulation has been recently reported including magnetomechanical stimulation of cell constructs (Markaki and Clyne, 2004), mechanosensitive ion channels (Hughes et al., 2008), magnetic cell seeding, and controlled cell proliferation and differentiation (Kanczler et al., 2010). Therefore, the association of magneto-mechanical stimulation and suitable biochemical agents could lead to more efficient treatments for the regeneration of extended bone regions (Xu and Gu, 2014;Kotani et al., 2002). ...
... Strongly bonded assemblies of short ferritic fibers constitute an interesting class of highly porous, permeable materials ( Fig. 5.13). It has been recently proposed that if ferromagnetic fibers are employed, then the material can be actuated by the imposition of a magnetic field [131]. The resultant deformation of the fiber array generates a shape change, which can be predicted for a given fiber orientation distribution and fiber segment aspect ratio. ...
... A porous magneto-active layer, made of slender ferromagnetic fibres bonded together at cross-over points, has been proposed for use as a THR implant coating [9,10]. The purpose of this layer is to grow healthy periprosthetic bone through the application of an external magnetic field of clinical magnitude. ...
Porous coatings on prosthetic implants encourage implant fixation. Enhanced fixation may be achieved using a magneto-active porous coating that can deform elastically in vivo on the application of an external magnetic field, straining in-growing bone. Such a coating, made of 444 ferritic stainless steel fibres, was previously characterised in terms of its mechanical and cellular responses. In this work, co-cultures of human osteoblasts and endothelial cells were seeded into a novel fibrin-based hydrogel embedded in a 444 ferritic stainless steel fibre network. Albumin was successfully incorporated into fibrin hydrogels improving the specific permeability and the diffusion of fluorescently tagged dextrans without affecting their Young’s modulus. The beneficial effect of albumin was demonstrated by the upregulation of osteogenic and angiogenic gene expression. Furthermore, mineralisation, extracellular matrix production, and formation of vessel-like structures were enhanced in albumin-enriched fibrin hydrogels compared to fibrin hydrogels. Collectively, the results indicate that the albumin-enriched fibrin hydrogel is a promising bio-matrix for bone tissue engineering and orthopaedic applications.
... Clyne et coll. [80,81,28] ont développé un modèle analytique simple basé sur la flexion de segments de fibres individuelles inclinées et trouvent un module d'Young de la forme : ...
Ce travail a été réalisé dans le cadre du projet EcOBEx, qui consiste à réduire le bruit du groupe motopropulseur rayonné à l’extérieur par l’ajout d’écrans acoustiques dans le compartiment moteur du véhicule. Les écrans acoustiques sont fabriqués par thermocompression de matériaux poreux uniformes. Les propriétés et l’épaisseur du matériau évoluent en fonction du degré de compression subit par le matériau. L’objectif de ce travail est de proposer des lois pour prédire l’évolution des propriétés des matériaux à partir du taux de compression et de leurs valeurs initiales avant compression. Dans un premier temps, on s’intéresse aux paramètres du modèle de fluide équivalent de Johnson-Champoux-Allard-Lafarge (JCAL) : porosité, résistivité au passage d’air, tortuosité, longueurs caractéristiques visqueuse et thermique, perméabilité thermique statique. Des expressions analytiques sont proposées pour prédire la variation de ces paramètres en fonction de la compression. Elles sont développées à partir d’un modèle de matériaux fibreux à fibres cylindriques où les variations d’orientation des fibres induites par la thermocompression peuvent être prises en compte. Les résultats sont en bon accord avec les mesures effectuées sur deux types de matériaux (mousse à cellules ouvertes et fibreux). Un modèle empirique généralisé est finalement proposé pour la résistivité au passage d’air. Dans un deuxième temps, on s’attache aux paramètres élastiques dont la connaissance est essentielle pour prendre en compte la vibration du squelette. La méthode expérimentale quasistatique est d’abord appliquée pour étudier l’évolution du module de Young par rapport au taux de compression pour les fibres et les mousses. Une loi de puissance est alors proposée pour prédire ces variations. Enfin, une méthode inverse pour estimer les propriétés élastiques d’un matériau poroélastique orthotrope à partir d’une mesure vibratoire d’un écran tricouche thermocomprimé est proposée. Cette méthode permet de caractériser les propriétés élastiques du matériau poreux dans une situation proche de son application réelle.
... It exhibits a number of unique properties such as high specific strength, high specific toughness, high specific surface area, and high permeability. As a result, it is widely used for filtration [1], lightweight sandwich core structures [2,3], fuel cell electrodes [4], biomedical devices [5,6], catalyst supports [7], heat transfer elements [8], and environmental noise control devices [9]. ...
To optimize the tensile properties of sintered 316L stainless steel fiber felts (SSFFs) which is important for their practical applications, the influence of sintering conditions on the microstructure (fiber ligament, sintering joint) and in turn, the tensile properties was investigated experimentally. It was shown that the tensile strength and tensile elongation of SSFFs were dominated by the tensile properties of the fiber ligaments and the bonding strength of the sintering joints. With the increase of sintering temperature versus holding time, the tensile strength of the fiber ligaments dropped significantly, while the sintering joints grew, producing a higher bonding strength between the fibers, resulting in more fibers being involved in the tensile process. These changes in sintering joints and fiberligamentsfinallyledtoarelativelystaticultimatestrengthofSSFFswithasignificantlyincreased elongation, thus with a large increase in tensile fracture energy. The increase of size of the sintering joints also helped to considerably raise the tensile fatigue limit of 316L SSFFs. This research provides a basis to improve the mechanical properties of sintered 316L SSFFs in industrial production.
... It exhibits a number of unique properties such as high specific strength, high specific toughness, high specific surface area, and high permeability. As a result, it is widely used for filtration [1], lightweight sandwich core structures [2,3], fuel cell electrodes [4], biomedical devices [5,6], catalyst supports [7], heat transfer elements [8], and environmental noise control devices [9]. ...
To optimize the tensile properties of sintered 316L stainless steel fiber felts (SSFFs) which is important for their practical applications, the influence of sintering conditions on the microstructure (fiber ligament, sintering joint) and in turn, the tensile properties was investigated experimentally. It was shown that the tensile strength and tensile elongation of SSFFs were dominated by the tensile properties of the fiber ligaments and the bonding strength of the sintering joints. With the increase of sintering temperature versus holding time, the tensile strength of the fiber ligaments dropped significantly, while the sintering joints grew, producing a higher bonding strength between the fibers, resulting in more fibers being involved in the tensile process. These changes in sintering joints and fiber ligaments finally led to a relatively static ultimate strength of SSFFs with a significantly increased elongation, thus with a large increase in tensile fracture energy. The increase of size of the sintering joints also helped to considerably raise the tensile fatigue limit of 316L SSFFs. This research provides a basis to improve the mechanical properties of sintered 316L SSFFs in industrial production.
... Markak and Clyne [148] showed that magnetomechanical effects could stimulate bone growth in a bonded array of ferromagnetic fibers. Takegami et al. [149] prepared ferromagnetic bone cement by blending magnetite and silica glass powders with resin that could be used for local hyperthermia treatment in the skeletal system. ...
Cancer is one of the leading causes of death worldwide, and unfortunately many cancer treatments have severe side effects. In order to avoid these, recent investigations into new oncological treatments have been carried out. In this context, composite biomaterials have been developed mainly from biopolymers or magnetic hydroxyapatite nanoparticles with the aim of directing and releasing drugs by means of an external magnetic field (hyperthermia). This chapter reviews recent advances in nanoparticle systems for hyperthermia applications with particular emphasis on the heating mechanisms of iron nanoparticles (INPs) and their applications as composite biomaterials.
... [3][4][5] It has turned out to be an excellent candidate for biomedical actuation. 4,6 At high temperature, the parent phase of Fe-Pd possesses face-centeredcubic (fcc) structure, whereas at low temperature, it generally transits to face-centered-tetragonal (fct) or body-centered-cubic (bcc) structure. 7,8 Modeled by the Bain path distortion, 9 the martensitic transformation (MT) from fcc to fct in Fe-Pd alloys was observed in a narrow composition range between 29 and 32 at. ...
The composition-dependent properties and their correlation with the phase stability of Fe75+xPd25−x (−10.0≤x≤10.0) alloys are systematically investigated by using first-principles exact muffin-tin orbitals (EMTO)-coherent potential approximation (CPA) calculations. It is shown that the martensitic transformation (MT) from L12 to body-centered-tetragonal (bct) occurs in the ordered alloys with about −5.0≤x≤10.0. In both the L12 and bct phases, the evaluated a and c/a agree well with the available experimental data; the average magnetic moment per atom increases whereas the local magnetic moments of Fe atoms, dependent on both their positions and the structure of the alloy, decrease with increasing x. The tetragonal shear elastic constant of the L12 phase (C′) decreases whereas that of the bct phase (Cs) increases with x. The tetragonality of the martensite (|1−c/a|) increases whereas its energy relative to the austenite with a negative value decreases with Fe addition. All these effects account for the increase of MT temperature (TM) with x. The MT from L12 to bct is finally confirmed originating from the splitting of Fe 3d Eg and T2g bands upon tetragonal distortion due to the Jahn-Teller effect.
... Thus, the yield strength of the fibre-network materials is critical in these applications. Markaki and Clyne (2004) conducted a magneto-mechanical simulation of bone growth using the ferromagnetic fibre materials and the application of a magnetic field. The concept that a porous and permeable implant could be treated as a scaffold f or tissue growth has been well established ( Hutmacher, 20 0 0 ). ...
Fibre network materials constitute a class of highly porous materials with low density, promising for functional and structural applications; however, very limited research has been conducted, especially on simulation and analytical models. In this paper, a continuum mechanics-based three-dimensional periodic beam-network model has been constructed to describe the stochastic fibre network materials. In this model, the density of the cross-linkers is directly related to the relative density of the fibre network materials, and the cross-linkers are represented by equivalent beam elements. The objective of this work was to delineate the elasto-plastic behaviour of the stochastic fibre network materials. Characteristic stress and strain derived from the total strain energy density have been adopted to reveal the yielding behaviour of the fibre networks. The results indicate that the stochastic fibre network materials are transversely isotropic. The in-plane stiffness and strength are much larger than those in the out-of-plane direction. For the fibre network materials with a small relative density, the relationship between the uniaxial yield strength and the relative density is a quadratic function in the x direction and is a cubic function in the z direction, which agree well with our dimensional analysis and are consistent with the relevant experimental results in literature. The yield surface depends strongly on the relative density and the connection between fibres.
... In fact, under magnetic fields, these scaffolds could provide ondemand release of drugs or biomolecules (i.e., growth factors) inducing osteogenesis and angiogenesis and at the same time magneto-mechanical stimulation on bone cells favoring proliferation, differentiation, and bone healing. The influence of magnetic fields in the cell stimulation has been recently reported including magnetomechanical stimulation of cell constructs (Markaki and Clyne, 2004), mechanosensitive ion channels (Hughes et al., 2008), magnetic cell seeding, and controlled cell proliferation and differentiation (Kanczler et al., 2010). Therefore, the association of magneto-mechanical stimulation and suitable biochemical agents could lead to more efficient treatments for the regeneration of extended bone regions (Xu and Gu, 2014;Kotani et al., 2002). ...
... Previous work has already analysed for this specific material simplified single-fibre geometries under magnetic actuation 15 . Or global values have been predicted analytically for fibre assemblies 41,42 . This present study investigates complete fibre network geometries and analyses the matrix strain on local level. ...
Fibre networks combined with a matrix material in their void phase make the design of novel and smart composite materials possible. Their application is of great interest in the field of advanced paper or as bioactive tissue engineering scaffolds. In the present study, we analyse the mechanical interaction between metallic fibre networks under magnetic actuation and a matrix material. Experimentally validated FE models are combined for that purpose in one joint simulation. High performance computing facilities are used. The resulting strain in the composite’s matrix is not uniform across the sample volume. Instead we show that boundary conditions and proximity to the fibre structure strongly influence the local strain magnitude. An analytical model of local strain magnitude is derived. The strain magnitude of 0.001 which is of particular interest for bone growth stimulation is achievable by this assembly. In light of these findings, the investigated composite structure is suitable for creating and for regulating contactless a stress field which is to be imposed on the matrix material. Topics for future research will be the advanced modelling of the biological components and the potential medical utilisation.
... The integration of open porous structures can be interpreted as a paradigm shift from the conventional cementless femoral stems designed to allow bone on-growth via the use of porous coatings or grit-blasted surfaces (Glassman et al., 2006) to biomimetic femoral stems featuring an open pore architecture and designed for bone ingrowth and lifelong service (Murr, 2017). The biomimetic design should allow mechanical stimulation of the surrounding and ingrowing bone tissue (Simmons et al., 2001;Markaki and Clyne, 2004), and prevent excessive relative motion at the boneimplant interface (Pilliar et al., 1986). ...
Background:
The current total hip prostheses with dense femoral stems are considerably stiffer than the host bones, which leads to such long-term complications as aseptic loosening, and eventually, the need for a revision. Consequently, the lifetime of the implantation does not match the lifetime expectation of young patients.
Method:
A femoral stem design featuring a porous structure is proposed to lower its stiffness and allow bone tissue ingrowth. The porous structure is based on a diamond cubic lattice in which the pore size and the strut thickness are selected to meet the biomechanical requirements of the strength and the bone ingrowth. A porous stem and its fully dense counterpart are produced by laser powder-bed fusion using Ti-6Al-4V alloy. To evaluate the stiffness reduction, static testing based on the ISO standard 7206-4 is performed. The experimental results recorded by digital image correlation are analyzed and compared to the numerical model.
Results & conclusions:
The numerical and experimental force-displacement characteristics of the porous stem show a 31% lower stiffness as compared to that of its dense counterpart. Moreover, the correlation analysis of the total displacement and equivalent strain fields allows the preliminary validation of the numerical model of the porous stem. Finally, the analysis of the surface-to-volume and the strength-to-stiffness ratios of diamond lattice structures allow the assessment of their potential as biomimetic constructs for load-bearing orthopaedic implants.
... Magnetism has been considered positive to the repair of bone tissue which results from the influence on bioelectricity [13][14][15]. However, it is inconvenient and of low efficiency to load a magnet on body. ...
Magnetic field has been considered to have positive effect on growth of bone. Because amagnetic nanoparticle can be regarded as one magnetic dipole, the macroscopic assemblies of magnetic nanoparticles may exhibit magnetic effect on local objects. This paper fabricated macroscopic film of γ-Fe2O3 nanoparticles by layer-by-layer (LBL) assembly on poly-D,L-lactic acid (PLA) scaffold, and studied the magnetic effect of the assembled γ-Fe2O3 nanoparticles film on primary bone marrow cells. The primary bone marrow cells were extracted from a mouse and cultured on the PLA substrate decorated by the film of γ-Fe2O3 nanoparticles after purification. Quantitative PCR (q-PCR) was used to show the cellular effect quantitatively. A just-found magnetosensing protein was employed to verify the magnetic effect of assembled film of nanoparticles on primary cells. It was exhibited that the decoration of nanoparticles enhanced themechanical property of the interface. By acting as the adhesion sites, the LBL-assembled film of nanoparticles seemed beneficial to the cellular growth and differentiation. The expression of magnetosensing protein indicated that there was magnetic effect on the cells which resulted from the assembly of magnetic nanoparticles, implying its potential as a promising interface on scaffold which can integrate the physical effect with good biocompatibility to enhance the growth and differentiation of stem cells. The LBL-assembled film of magnetic nanoparticles may boost the development of novel scaffold which can introduce the physical stimulus into local tissue in vivo.
... The porosity of the implant should be engineered such that it offers a compromise between matching the behavior of surrounding bone, maintaining the mechanical strength of the implant, and providing adequate pore size for bone ingrowth. The first feature should allow ingrowing bone tissue to be mechanically strained at a beneficial level of several millistrains (Simmons et al., 2001;Markaki and Clyne, 2004), prevent excessive shear displacement at the bone-implant interface (Pilliar et al., 1986), and thereby promote new bone formation and differentiation. ...
In the past two decades, a number of porous materials for implant applications have been developed. In this review article, the functional requirements for this class of materials, their manufacturability, morphology and mechanical properties are discussed. A special section is also devoted to modern trends in numerical modeling of these structures. This review article is not meant to be comprehensive; rather, it concentrates on some selected aspects related to the manufacture, characterization and modeling of metallic foams for orthopedic applications.
... The main objective for designing biocompatible and bioresorbable magnetic scaffolds is the possibility to obtain structures that can be manipulated in situ by applying external magnetic fields. The influence of magnetic fields in the cell stimulation has been recently reported (magneto-mechanical stimulation of cell constructs [3], mechano-sensitive ion channels [4], magnetic cell seeding, and controlled cell proliferation and differentiation) in [5] and [6]. Furthermore, the magnetic field fluxes and gradients generated in the vicinity and inside the scaffold constitute the driving force needed to control specific processes at cell level, allowing magnetic carriers to transport biomolecules and growth factors (VEGF, BMP, etc.) that eventually stimulate bone tissue regenerations and vascular remodeling [7]. ...
The design and fabrication of advanced biocompatible and bioresorbable materials able to mimic the natural tissues present in the human body constitutes an important challenge in regenerative medicine. The size-dependent properties that materials exhibit at the nanoscale as a consequence of their higher surface-to-volume ratio have opened a wide range of opportunities for applications in almost every imaginable field. In this regard, the incorporation of magnetic nanoparticles (MNPs) into biocompatible scaffold formulations provides final materials with additional multifunctionality and reinforced mechanical properties for bone tissue engineering applications. In addition to the biological implications due to their magnetic character (i.e., magnetic stimuli that favor the cell adhesion/proliferation, guiding of growth factors loaded magnetic nanocarriers, etc.), the ability of superparamagnetic scaffolds to simultaneously show magnetic hyperthermia when a dynamic external magnetic field is applied become promising to treat critical bone defects caused by malignant bone cancer through a combined therapy consisting of on demand temperature increase and thermally activated drug delivery. In this paper, we will comment on several different approaches to construct magnetic scaffolds with hyperthermia properties for bone tissue engineering. Experimental details about the design, fabrication and physicochemical characterization of a representative set of magnetic scaffolds have been described, focusing on their hyperthermia properties. The following synthesis procedures to magnetize biocompatible scaffolds reported in this paper covers dip coating of biocompatible gelatin-based scaffolds in aqueous MNPs dispersions, iron doping of the hydroxyapatite (HA) crystal structure, and incorporation of magnetic bioresorbable HA nanoparticles into poly-ε-caprolactone-based polymeric matrices.
... Mandibular distraction osteogenesis on rats at strains of 10-12.5% had high bone apposition rates, at 260 microns/day, and may be ideal for distraction osteogenesis [75]. Similar in concept to distraction osteogenesis, magneto-mechanical stimulation may be another option for inducing bone growth [80]. The results of a theoretical study on the elastic deformation of bonded arrays of ferromagnetic fibers subjected to an external magnetic field show promise for use in biomedical applications. ...
... Strongly bonded assemblies of short ferritic fibers constitute an interesting class of highly porous, permeable materials ( Fig. 5.13). It has been recently proposed that if ferromagnetic fibers are employed, then the material can be actuated by the imposition of a magnetic field [131]. The resultant deformation of the fiber array generates a shape change, which can be predicted for a given fiber orientation distribution and fiber segment aspect ratio. ...
Metals are the materials of choice for many structural implantable device applications and there is not reason to expect a change in the short or probably medium term. Processing-structure relations are described with special emphasis for Ti and Ti-base alloys, austenitic stainless steel, and Co-based alloys, but other metallic materials in use are also presented. Mechanical properties and their relationship with the microstructure are summarised for static and dynamic loads. Chemical properties focus on the corrosion behaviour, nature of the passive films, and the closely related ion release topic. Surface energy and surface charges, which are relevant for the understanding of the biological response, are also revised. A detailed overview of the new family of Ti-base alloys with a lower Young’s modulus, Ni-free Fe-based alloys, nanostructured alloys, biodegradable alloys, and porous metals for the fabrication of scaffolds, is presented.
Weak magnetic fields offer nearly lossless transmission of signals within biological tissue. Magnetic nanomaterials are capable of transducing magnetic fields into a range of biologically relevant signals in vitro and in vivo. These nanotransducers have recently enabled magnetic control of cellular processes, from neuronal firing and gene expression to programmed apoptosis. Effective implementation of magnetically controlled cellular signalling relies on careful tailoring of magnetic nanotransducers and magnetic fields to the responses of the intended molecular targets. This Primer discusses the versatility of magnetic modulation modalities and offers practical guidelines for selection of appropriate materials and field parameters, with a particular focus on applications in neuroscience. With recent developments in magnetic instrumentation and nanoparticle chemistries, including those that are commercially available, magnetic approaches promise to empower research aimed at connecting molecular and cellular signalling to physiology and behaviour in untethered moving subjects. Magnetic nanomaterials can be used to transduce magnetic fields into biologically relevant signals. This Primer describes different magnetic transduction mechanisms, the design of nanotransducers and example applications for studying cell signalling and neuroscience.
This chapter would represent a guide for the reader in the path that goes toward more recent and innovative approaches in bone tissue regeneration.
Starting from an introduction on tissue engineering approaches and an overview on the scaffold fabrication methods and materials, the chapter will first provide concepts related to surface presentation and modification routes, finally approaching to the fascinating field of bioactive magnetic scaffolds. In this context, the basic principles of magnetism and magnetic materials will be reported, starting from a brief hint to current medical applications of magnetism, such as drug and gene delivery, hyperthermia treatment of tumors and radionuclide therapy, magneto-mechanical stimulation or activation of cell-constructs and mechanosensitive ion channels, magnetic cell-seeding procedures, and controlled cell proliferation and differentiation.
The potential to design multifunctional and bioactive 3D structures for in situ and on-demand release of drugs and/or growth factors, as well as for advanced fixation systems, will be highlighted.
Porous coatings on prosthetic implants encourage implant fixation. Enhanced fixation may be achieved using a magneto-active porous coating that can deform elastically in vivo on application of an external magnetic field, straining in-growing bone. Such coating, made of 444 ferritic stainless steel fibres, was previously characterised in terms of its mechanical and cellular responses. In this work, co-cultures of human osteoblasts and endothelial cells were seeded into a novel fibrin-based hydrogel embedded in a 444 ferritic stainless steel fibre network. Albumin was successfully incorporated into fibrin hydrogels improving the specific permeability and the diffusion of fluorescently-tagged dextrans without affecting their Young’s modulus. The beneficial effect of albumin was demonstrated by upregulation of osteogenic and angiogenic gene expression. Furthermore, mineralisation, extracellular matrix production and formation of vessel-like structures were enhanced in albumin-enriched fibrin hydrogels compared to fibrin hydrogels. Collectively, the results indicate that the albumin-enriched fibrin hydrogel is a promising bio-matrix for bone tissue engineering and orthopaedic applications.
Magnetic performances of β-Ti68.75Nb25X6.25 (X=Fe, Mo, Sn, Ta, Zr) alloys were investigated with first-principles method. The results indicate that the alloys of TiNbSn, TiNbTa, and TiNbZr exhibit interestingly strong magnetism. The magnetic properties of the alloys mainly derive from Ti atoms. The X atom modulates the coupling between Ti and Nb producing electrons backward Ti atoms. Such electron transfer induces asymmetry of the d states of Ti atom between spin-up and spin-down channels. Such magnetic properties of β-Ti68.75Nb25X6.25 (X= Sn, Ta, Zr) show great potential in biomedical implants.
A key characteristic of metals is their high thermal and electrical conductivity – due to the presence of free electrons. There are many applications in which these properties are exploited. For example, high thermal conductivity is useful in improving the resistance of materials to thermal shock and avoiding “hot spots” during localized heating. High electrical conductivity is desirable in power transmission lines, electrical and electronic components, and for electromagnetic shielding. A problem commonly arises in situations where such high conductivities need to be combined with good mechanical properties, since conventional strengthening by alloying commonly leads to sharp reductions in these conductivities. Metal matrix composites (MMCs) offer potential for control over property combinations. For example, ceramic reinforcement can strengthen without affecting matrix conductivity, so composite conductivity can remain high. There is thus interest in predicting how conductivity varies with reinforcement properties, volume fraction, aspect ratio, interfacial structure, etc. Combinations of high conductivity with low thermal expansivity confers resistance to distortion under transient heating or cooling conditions. Again, scope for tailoring property combinations is greater for an MMC than with conventional specification of alloy composition and heat treatment.
In this chapter, a brief outline is given of the potential of ferromagnetic fiber networks for usage in delivering in vivo strains to in-growing bone. Beneficial effects on bone-implant bonding can accrue from ferromagnetic fiber networks which deform in vivo via an external magnetic field of clinical magnitude applying therapeutic strains to bone filling the inter-fiber spaces. Simple analytical models based on the torque exerted on a fully-magnetized fiber in conjunction with tomographic data can be used to predict the magneto-mechanical response. In vitro cell culture data have been obtained on both 2D (fully-dense) and 3D (high porous) surfaces to identify an optimum fiber material and establish the surfaces’ ability to support the culture of human osteoblasts and mesenchymal stem cells without inducing toxic or inflammatory responses. Preliminary experimental results on magnetic actuation of ferromagnetic fiber networks suggest an actuation-mediated upregulation of specific genes in the osteogenic lineage together with an increase in protein release.
Successful integration of cementless femoral stems using porous surfaces relies on effective periimplant bone healing to secure the bone-implant interface. The initial stages of the healing process involve protein adsorption, fibrin clot formation and cell osteoconduction onto the implant surface. Modelling this process in vitro, the current work considered the effect of fibrin deposition on the responses of human mesenchymal stromal cells cultured on ferritic fibre networks intended for magneto-mechanical actuation of in-growing bone tissue. The underlying hypothesis for the study was that fibrin deposition would support early stromal cell attachment and physiological functions within the optimal regions for strain transmission to the cells in the fibre networks. Highly porous fibre networks composed of 444 ferritic stainless steel were selected due to their ability to support human osteoblasts and mesenchymal stromal cells without inducing untoward inflammatory responses in vitro. Cell attachment, proliferation, metabolic activity, differentiation and penetration into the ferritic fibre networks were examined for one week. For all fibrin-containing samples, cells were observed on and between the metal fibres, supported by the deposited fibrin, while cells on fibrin-free fibre networks (control surface) attached only onto fibre surfaces and junctions. Initial cell attachment, measured by analysis of deoxyribonucleic acid, increased significantly with increasing fibrinogen concentration within the physiological range. Despite higher cell numbers on fibrin-containing samples, similar metabolic activities to control surfaces were observed, which significantly increased for all samples over the duration of the study. It is concluded that fibrin deposition can support the early attachment of viable mesenchymal stromal cells within the inter-fibre spaces of fibre networks intended for magneto-mechanical strain transduction to in-growing cells.
Ti50Ni49.7Mo0.3, Ti50Ni49.6Mo0.4 and Ti50Ni49.5Mo0.5 alloy fibers were prepared by a melt overflow process. Two-step B2-R-B19′ transformation was observed in the rapidly solidified Ti-Ni-Mo fibers. Upon increasing the Mo-content from 0.3 to 0.5 at.%, the austenite transformation finish temperature (Af) of R → B2 decreased from 43 to −42 °C. Porous shape memory alloy pellets with 75% porosity were fabricated by a vacuum sintering technology, using the alloy fibers. Mechanical properties and shape memory effect of the highly porous Ti50Ni49.6Mo0.4 alloy, of which Af is lower than room temperature, were investigated using a compressive test. The plateau of a stress-strain curve was observed at about 2 MPa and resulted in 5% elongation associated with stress-induced martensitic transformation. It was also found that a recovered strain was 1.8% on heating after the compressive deformation. Because of the high porosity of this specimen, an elastic modulus of 0.91 GPa could be obtained.
The aim of the current work was to examine the human monocyte response to 444 ferritic stainless steel fibre networks. 316L austenitic fibre networks, of the same fibre volume fraction, were used as control surfaces. Fluorescence and scanning electron microscopies suggest that the cells exhibited a good degree of attachment and penetration throughout both networks. Lactate Dehydrogenase (LDH) and TNF-α releases were used as indicators of cytotoxicity and inflammatory responses respectively. LDH release indicated similar levels of monocyte viability when in contact with the 444 and 316L fibre networks. Both networks elicited a low level secretion of TNF-α, which was significantly lower than that of the positive control wells containing zymosan. Collectively, the results suggest that 444 ferritic and 316L austenitic networks induced similar cytotoxic and inflammatory responses from human monocytes.
This is a review of the processing, structure and properties of metals containing a significant volume fraction of distributed internal porosity. These materials serve in a variety of applications, some of which place emphasis on their mechanical properties, while others are driven by transport processes made possible by the accessibility of open pores to the ingress and flow of fluid. Both classes of properties are reviewed after presenting the making and the structure of these materials. Coverage thus includes the processing and structure of highly porous metals, and their properties including conduction, fluid flow, convective heat and mass transfer, thermal expansion, elastic deformation, followed by plasticity, creep, fracture and fatigue.
Fibers of Ti50Ni50, Ti49.75Ni50.25, Ti49.5Ni50.5 and Ti49.25Ni50.75 alloys were prepared by a melt overflow process. The martensitic transformation start temperature (Ms
) of B2
→ B19' in Ti50Ni50 fibers is 52.4 °C. Upon increasing the Ni-content from 50 to 50.75 at%, the Ms
of the B2-B19' transformation keeps decreasing. Cylindrical billets of Ni-rich Ti–Ni alloy with 75% porosity were produced by vacuum sintering
using as-cast alloy fibers. Cyclic compression mechanical testing carried out on the porous specimens revealed shape memory deformation recovery of up to 0.91%, while the superelastic behavior resulted in reversible deformation of up to 4.31%. The permanent plastic strain resulting from the
subsequent three cycles was only 0.78%. Because of the high porosity of the sintered specimen, an elastic modulus of about 3.2 GPa could be obtained.
Ti49.5Ni50.5 shape memory alloy fibers were prepared by a melt overflow process. The martensitic transformation starting temperature of B2 → B19′ in the rapidly solidified fibers was 19 °C. Cylindrical billets of Ni-rich Ti–Ni alloy with 75% porosity were produced by a vacuum sintering technology using as-cast alloy fibers. The mechanical properties and shape memory properties of the highly porous Ti–Ni alloy is investigated using a compressive test. The plateau of the stress–strain curve was observed at about 7 MPa and resulted in 8% elongation associated with stress-induced B2 → B19′ transformation. Because of the high porosity of this specimen, the elastic modulus of about 0.95 GPa could be obtained. It was also found that a recovered strain was 5.9% on heating after the compressive deformation. This recovery of the length is ascribed to the shape memory effect which occurs during the martensitic transformation.
The aim of this work is to improve bone-implant bonding. This can, potentially, be achieved through the use of an implant coating composed of fibre networks. It is hypothesised that such an implant can achieve strong peri-prosthetic bone anchorage, when seeded with human mesenchymal stem cells (hMSCs). The materials employed were 444 and 316L stainless steel fibre networks of the same fibre volume fraction. The present work confirms that hMSCs are able to proliferate and differentiate towards the osteogenic lineage when seeded onto the fibre networks. Cellular viability, proliferation and metabolic activity were assessed and the results suggest higher proliferation rates when hMSC are seeded onto the 444 networks as compared to 316L. Cell distribution was found uniform across the seeded surfaces with 444 showing a somewhat higher infiltration depth.
A facile approach to construct ferroferric oxide/chitosan composite scaffolds with three-dimensional oriented structure has been explored in this research. Chitosan and ferroferric oxide are co-precipitated by using an in situ precipitation method, and then lyophilized to get the composite scaffolds. XRD indicated that Fe3O4 was generated during the gel formation process, and increasing the content of magnetic particles could destruct the crystal structure of chitosan. When the content of magnetic particles is lower than 10%, the layer-by-layer structure and wheel spoke structure are coexisting in the scaffolds. Increasing the content of magnetic particles, just layer-by-layer structure could be observed in the scaffolds. Ferroferric oxide particles were uniformly distributed in the matrix, the size of which was about 0.48 μm in diameter, 2 μm in length. Porosity of magnetic chitosan composite scaffolds is about 90%. When the ratio of ferroferric oxide to chitosan is 5/100, the compressive strength of the material is 0.4367 MPa, which is much higher than that of pure chitosan scaffolds, indicating that the layer-by-layer and wheel spokes complex structure is beneficial for the improvement of the mechanical properties of chitosan scaffolds. However, increasing the content of ferroferric oxide, the compressive strength of scaffolds decreased, because of the decreasing of chitosan crystallization and aggregation of magnetic particles as stress centralized body. Another reason is that the layer-by-layer and wheel spokes complex structure makes bigger contributions for the compressive strength than the layer-by-layer structure does. Three-dimensional ferroferric oxide/chitosan scaffolds could be used as hyperthermia generator system, improving the local circulation of blood, promoting the aggradation of calcium salt and stimulating bone tissue regeneration.
Maintaining bone geometric and structural integrity is a necessity for normal mobility. After fracture, bone disease or other conditions resulting in skeletal loss or compromise, porous materials offer the possibility for near faultless replacement of the normal bone material. Ceramics, and to a lesser extent, metals, are the predominant porous materials currently used in bone engineering. This latter term is used as a blanket term for orthodontics, orthopedics and related fields in which the replacement of bone is either required or selectively chosen. Because bone is a porous material, there is a physiological rationale for the use of porous materials in its replacement. Moreover, porous bone implant material is advantageous for the early incorporation of the implant into or apposed to the bony tissue surrounding it. There is, however, a difference in the size and extent of the bone and implant porosities for optimal bone incorporation of the material. This review intends to clarify both the nature of and reason for this difference. Accordingly, a review of the principal types of porous materials (organics, ceramics, metals, metallorganics and organoapatites and composites) used in bone engineering will be provided. This will springboard a consideration of the important engineering considerations of material property matching, machining and forming, corrosion and biocompatibility, fatigue and lifecycle, coating, and interfacial properties. The importance of matching the porous material to the particular bone engineering application will then be discussed. In providing this review, the authors hope to bring an appreciation of the complexity of the field to the fore, while also demonstrating how much has already been accomplished due to the efforts of many research groups. The ultimate porous bone implant, perhaps, is yet to be designed; however, there is reason to believe that such a material is not long in coming. We hope to demonstrate some possible pathways to this material.
The in vivo remodeling behavior within a bone protected from natural loading was modified over an 8-week period by daily application of 100 consecutive 1 Hz load cycles engendering strains within the bone tissue of physiological rate and magnitude. This load regime resulted in a graded dose:response relationship between the peak strain magnitude and change in the mass of bone tissue present. Peak longitudinal strains below 0.001 were associated with bone loss which was achieved by increased remodeling activity, endosteal resorption, and increased intra-cortical porosis. Peak strains above 0.001 were associated with little change in intra-cortical remodeling activity but substantial periosteal and endosteal new bone formation.
Unlabelled:
In studies on a functionally isolated avian-bone preparation to which external loads could be applied in vivo, we determined the following information. Removal of load-bearing resulted in substantial remodeling endosteally, intracortically, and, to a lesser extent, periosteally. Since the balance of this remodeling was negative, bone mass declined. It therefore appears that functional load-bearing prevents a remodeling process that would otherwise lead to disuse osteoporosis. Four consecutive cycles a day of an externally applied loading regimen that engendered physiological strain magnitudes but an altered strain distribution prevented remodeling and was thus associated with no change in bone mass. A small exposure to, or the first effect of, a suitable dynamic strain regimen appears to be sufficient to prevent the negatively balanced remodeling that is responsible for disuse osteoporosis. Thirty-six 0.5-hertz cycles per day of the same load regimen also prevented intracortical resorption but was associated with substantial periosteal and endosteal new-bone formation. Over a six-week period, bone-mineral content increased to between 133 and 143 per cent of the original value. Physiological levels of strain imposed with an abnormal strain distribution can produce an osteogenic stimulus that is capable of increasing bone mass. Neither the size nor the character of the bone changes that we observed were affected by any additional increase in the number of load cycles from thirty-six to 1800.
Clinical relevance:
The results of this experiment must be considered in relation to the type and duration of the non-physiological loads that were imposed.(ABSTRACT TRUNCATED AT 250 WORDS)
Galileo (1638) observed that "nature cannot grow a tree nor construct an animal beyond a certain size, while retaining the proportions which suffice in the case of a smaller structure". However, subsequent measurement has shown that limb bone dimensions are scaled geometrically with body size (Alexander et al., 1979a), and that the material properties of their constituent bone tissue are similar in animals over a wide range of body weight (Sedlin & Hirsch, 1966; Yamada, 1970; Burstein et al., 1972; Biewener, 1982). If, as suggested in previous scaling arguments (McMahon, 1973; Biewener, 1982), vigorous locomotion involved the same proportional forces over a wide range of animal size, this would create a paradox since large animals would be in far greater danger of skeletal failure than small ones. However, in vivo strain gauge implantations have shown that, during high speed running, axial force as a proportion of body weight (G) in the limb bones of animals decreases as a function of body size from 6.9 G in a 7 kg turkey to 2.8 G in a small (130 kg) horse. Estimates of axial force in larger animals suggest that this is further reduced to 0.8 G in a 2500 kg elephant. Nevertheless, it appears that, regardless of animal size or locomotory style, the peak stresses in the bones of these animals are remarkably similar. Therefore, throughout the range of animals considered (350 times differences in mass), we suggest that similar safety factors to failure are maintained, not by allometrically scaling bone dimensions, but rather by allometrically scaling the magnitude of the peak forces applied to them during vigorous locomotion.(ABSTRACT TRUNCATED AT 250 WORDS)
We have studied damage to the tibial articular surface after replacement of the femoral surface in dogs. We inserted pairs of implants made of alumina, titanium and polyvinyl alcohol (PVA) hydrogel on titanium fibre mesh into the femoral condyles. The two hard materials caused marked pathological changes in the articular cartilage and menisci, but the hydrogel composite replacement caused minimal damage. The composite osteochondral device became rapidly attached to host bone by ingrowth into the supporting mesh. We discuss the clinical implications of the possible use of this material in articular resurfacing and joint replacement.
During life, bone is continually optimized for its load-bearing role by a process of functionally adaptive (re)modelling. This process, which is more active in growing bone, is dominated by high-magnitude, high-rate strains, presented in an unusual distribution. Adaptation occurs at an organ level, involving changes in whole bone architecture and bone mass. The repetitive coordinated bone loading associated with habitual activity may have little role in the preservation of bone mass, and may even reduce the osteogenic potential of an otherwise highly osteogenic stimulus. Cells of the osteocyte/osteoblast network are best placed to appreciate mechanical strain. Among the strain-related responses they show, is a reduced rate of apoptosis. This may serve to regulate and target osteoclast activity. A more complete understanding of the stimuli and pathways involved in both the physiology and pathology of this structural homeostatic mechanism will allow the design of more appropriate exercise regimens and targeted pharmacological interventions to limit morbidity and mortality by reducing bone fragility.
Biphasic calcium phosphate (BCP) bioceramics belong to a group of bone substitute biomaterials that consist of an intimate mixture of hydroxyapatite (HA), Ca(10)(PO(4))(6)(OH)(2), and beta-tricalcium phosphate (beta-TCP), Ca(3)(PO(4))(2), of varying HA/beta-TCP ratios. BCP is obtained when a synthetic or biologic calcium-deficient apatite is sintered at temperatures at and above 700 degrees C. Calcium deficiency depends on the method of preparation (precipitation, hydrolysis or mechanical mixture) including reaction pH and temperature. The HA/beta-TCP ratio is determined by the calcium deficiency of the unsintered apatite (the higher the deficiency, the lower the ratio) and the sintering temperature. Properties of BCP bioceramics relating to their medical applications include: macroporosity, microporosity, compressive strength, bioreactivity (associated with formation of carbonate hydroxyapatite on ceramic surfaces in vitro and in vivo), dissolution, and osteoconductivity. Due to the preferential dissolution of the beta-TCP component, the bioreactivity is inversely proportional to the HA/beta-TCP ratio. Hence, the bioreactivity of BCP bioceramics can be controlled by manipulating the composition (HA/beta-TCP ratio) and/or the crystallinity of the BCP. Currently, BCP bioceramics is recommended for use as an alternative or additive to autogeneous bone for orthopedic and dental applications. It is available in the form of particulates, blocks, customized designs for specific applications and as an injectible biomaterial in a polymer carrier. BCP ceramic can be used also as grit-blasting abrasive for grit-blasting to modify implant substrate surfaces. Exploratory studies demonstrate the potential uses of BCP ceramic as scaffold for tissue engineering, drug delivery system and carrier of growth factors.
This work focuses on basic research into a P/M processed, porous-surfaced and functionally graded material (FGM) destined for a permanent skeletal replacement implant with improved structural compatibility. Based on a perpendicular gradient in porosity the Young's modulus of the material is adapted to the elastic properties of bone in order to prevent stress shielding effects and to provide better long-term performance of the implant-bone system. Using coarse Ti particle fractions the sintering process was accelerated by silicon-assisted liquid-phase sintering (LPS) resulting in a substantial improvement of the neck geometry. A novel evaluation for the strength of the sinter contacts was proposed. The Young's modulus of uniform non-graded stacks ranged from 5 to 80 GPa as determined by ultrasound velocity measurements. Thus, the typical range for cortical bone (10-29 GPa) was covered. The magnitude of the Poisson's ratio proved to be distinctly dependent on the porosity. Specimens with porosity gradients were successfully fabricated and characterized using quantitative description of the microstructural geometry and acoustic microscopy.
We have studied damage to the tibial articular surface after replacement of the femoral surface in dogs. We inserted pairs of implants made of alumina, titanium and polyvinyl alcohol (PVA) hydrogel on titanium fibre mesh into the femoral condyles.
The two hard materials caused marked pathological changes in the articular cartilage and menisci, but the hydrogel composite replacement caused minimal damage. The composite osteochondral device became rapidly attached to host bone by ingrowth into the supporting mesh.
We discuss the clinical implications of the possible use of this material in articular resurfacing and joint replacement.
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Porous titanium-nickel shape memory alloys (TiNi SMA) can be fabricated using special engineering technique. This material is a whole porous material with interconnected pores. This porous TiNi SMA retains the unique properties of solid TiNi SMA. Its porosity and pore size can be controlled. Its application to orthopaedic field is very expected especially in bone substitute and bone implant and so on. The purpose of this study was to evaluate bone tissue response and histocompatibility of porous TiNi SMA in vivo. Thirty block implants (5 mm×5 mm×7 mm) of porous TiNi SMA were prepared. Analysis of pore structure of the implant was performed using Hg-porosimetry and scanning electron microscope. Fifteen New Zealand white rabbits were used. Sterile porous TiNi SMA implant was implanted in the defects of proximal tibia metaphysis. Limbs of five rabbits were harvested respectively at 2, 4 and 6 weeks post implantation. Each specimen was embedded in PMMA. Embedded specimen was sectioned into 300 \\micron thickness with isomet-diamond saw. Quantitative histomorphometric analysis was performed within the each implant. The pore sizes of porous TiNi SMA were 323±89 \\micron. Porosity was 55.3±6.7%. No apparent adverse reactions such as inflammation and foreign body reaction were noted on or around all implanted porous TiNi SMA blocks. Bone ingrowth was found in the pore space of all implanted blocks. The percent bone ingrowth into the pore space of porous TiNi SMA increased over time. At six week post-implantation, bone ingrowth into pore in TiNi SMA block was very excellent (at 6 week, 78.3±9.7%). This percent bone ingrowth was much higher than that of other porous materials. This in vivo response of porous TiNi SMA observed in this study opens to the possibility that porous TiNi SMA could be used as an ideal bone substitute.
The mechanical properties of metal fibre porous structures were studied in the light of their potential application as surface
coatings of implants. Stainless steel AISI 316 L fibres with diameters of 50 and 100μm were compacted and sintered. The variation
of the modulus of elasticity with density, as obtained in tension, corresponds closely with theoretical models. The ultimate
failure of the tensile specimens proceeds through the fibres, and not through the sinter bonds, except at lower densities.
Differences in yield strength between 50 and 100 μm fibre tensile specimens are explained on the basis of the onset of plastic
deformation of the individual fibres. Upon compression the modulus of elasticity is nearly 10 times smaller than in tension.
This result is due to the different deformation patterns of the fibres in compression and tension.
The pitting corrosion, crevice corrosion and accelerated leaching of iron, chromium and nickel of super-ferritic and duplex stainless steels, and for effective comparison the presently used 316L stainless steel, have been studied in an artificial physiological solution (Hank's solution) by the potentiodynamic anodic polarization method. The results of the above studies have shown the new super-ferritic stainless steel to be immune to pitting and crevice corrosion attack. The pitting and crevice corrosion resistances of duplex stainless steel were found to be superior to those of the commonly used type 316L stainless steel implant materials. The accelerated leaching study conducted for the above alloys showed very little tendency for the leaching of metal ions when compared with 316L stainless steel. Thus the present study indicated that super-ferritic and duplex stainless steels can be adopted as implant materials due to their higher pitting and crevice corrosion resistance.
Many biological processes are affected by electromagnetic fields. Hence incremental internal fields generated by external magnetic fields can be expected to affect that biology. With some exceptions, most of the present interest in the effects of exogenous static and low-frequency magnetic fields centres on three intensity regions. (1) There are concerns that 50-60 Hz power distribution fields as small as 0.2 µT, may affect the health of populations. (2) ac fields that are larger than 1 mT (and usually smaller than 100 mT) with frequencies of a few kHz or less may have therapeutic value with respect to the healing of bone fractures and soft-tissue injuries. (3) The very large slowly varying fields of the order of 2 T used in magnetic resonance imaging might affect the physiology of the patients.
Magnetic fields interact with biological systems through forces on the electrical currents associated with physiological functions and through the torques exerted on the magnetic moments of biologically important molecules and the electrons that play a role in the binding of geminate radicals. The torques that the Earth's magnetic field applies to the ferrimagnetic domains of biologically formed magnetite affects the biology of species in several different phyla and may have consequences in humans. Low-frequency magnetic fields also induce electric fields through the Faraday effect that may have biological consequences. For either the direct magnetic fields or the magnetically induced electric fields to affect the biology of living systems, the interactions with such systems must generally be larger then the interactions with endogenous physiological and thermal noise. This constraint seems to exclude the possibility that the environmental fields less than 1 µT from the electric power distribution system affect health and places important constraints on the minimal fields that can be expected to have therapeutic value.
Studies performed at tissular (three-dimensional, 3-D) or cellular (two-dimensional, 2-D) levels showed that the loading pattern plays a crucial role in the osteoblastic physiology. In this study, we attempted to investigate the response of a 3-D osteoblastic culture submitted to either no external stress or static or dynamic stresses. Rat osteosarcoma cells (ROS 17/2.8) were embedded within collagen type I lattices and studied for 3 weeks. Entrapment and proliferation of cells within the hydrated collagen gel resulted in the generation of contractile forces, which led to contraction of the collagen gel. We used this ability to evaluate the influence of three modes of mechanical stresses on the cell proliferation and differentiation: (1) the freely retracted gels (FRG) were floating in the medium, (2) the tense gels (TG) were stretched statically and isometrically, with contraction prevented in the longitudinal axis, and (3) the dynamic gels (DG) were floating gels submitted to periodic stresses (50 or 25 rpm frequency). Gels showed maximum contraction at day 12 in 50 rpm DG, followed by 25 rpm DG, then FRG (88%, 81%, 70%, respectively) and at day 16 in TG (33%). The proliferation rate was greater in TG than in FRG (+52%) but remained low in both DGs. Gel dimensions were related to the collagen concentration and on a minor extent to cell number. Cells in DG appeared rounder and larger than in other conditions. In TG, cells were elongated and oriented primarily along the tension axis. Scanning electron microscopy (SEM) showed that tension exerted by cells in TG led to reorientation of collagen fibers which, in turn, determined the spatial orientation and morphology of the cells. Transmission electron microscopy (TEM) performed at maximum proliferation showed a vast majority of cells with a distended well-developed RER filled with granular material and numerous mitochondria. Alkaline phosphatase activity peaked close to the proliferation peak in FRG, whereas in TG, a biphasic curve was observed with a small peak at day 4 and the main peak at day 16. In DG, this activity was lower than in the two other conditions. A similar time course was observed for alkaline phosphatase gene expression as assessed by Northern blots. Regardless of the conditions, osteocalcin level showed a triphasic pattern: a first increase at day 2, followed by a decrease from day 4 to 14, and a second increase above initial values at day 18. Microanalysis-x indicated that mineralization occurred after 14 days and TEM showed crystals within the matrix. We showed that static and dynamic mechanical stresses, in concert with 3-D collagen matrices, played a significant role on the phenotypic modulation of osteoblast-like cells. This experimental model provided a tool to investigate the significance and the mechanisms of mechanical activity of the 3-D cultured osteoblast-like cells.
In recent years magnetic retention has gained increasing popularity in dental practice. This investigation compared the corrosion resistance of the palladium-cobalt ferromagnetic alloy (constituent of the keeper cemented on the abutment teeth) coupled with the samarium-cobalt magnets embedded in the removable part of the denture. The behavior of three couples (cobalt-palladium, cobalt-palladium/titanium, and cobalt-palladium/palladium) has been studied. The magnets, because of their poor corrosion resistance, are encapsulated in various materials. To simulate clinical conditions, characterized by the continuous movement of the keeper with respect to the magnet, the experiments were conducted in artificial saliva under intermittent and continuous wear.
Pd-based alloys are major alternatives to gold-based alloys for PFM applications. In electrolytes simulating oral fluids, these alloys exhibit electrode behavior similar to passivity of active metals, i.e., a potential region of almost constant current density up to a critical potential, above which the current increases. The objective of this study was to correlate the electrode behavior with the results of solution analyses and changes in the surface composition of the alloys. Binary alloys Pd-15 wt% Cu and Pd-19 wt% Co, as well as the pure components, were examined. Corrosion potentials vs. time, potentiodynamic anodic polarization curves, polarization resistances vs. time, and potentiostatic anodic charges were measured with synthetic saliva used as the electrolyte. The concentrations of Pd, Cu, and Co in the solution after various exposures were determined by atomic absorption. The surfaces of the alloys were examined by x-ray photoelectron spectroscopy before and after the exposures. The results show that selective dissolution of the less-noble components occurred on the surfaces of both alloys for all the exposures, leaving the surfaces highly enriched in Pd. This enrichment contributed to the potential changes and the passive-type behavior. Copper dissolved more than cobalt at longer exposures and higher potentials, in spite of its higher nobility. Dissolution of cobalt seemed to be limited by the formation of a surface film, which may be related to the transition character of this element.
The properties of an alloy with 65% Pd, 30% Co and 5% Ga have been investigated with consideration to the requirements of a ceramic fusing alloy. The composition of the alloy was at the outset chosen because of a reasonably low melting point of 1200°C. The mechanical properties were found to be satisfactory (σ0.2≈ 530 MPa, total elongation ≈5%). The bond strength between the alloy substrate and the ceramic were measured in 4 point bending to be at least 36 MPa. The fractures occurred in the epoxy glue of the particular bend specimen construction, and the strength was regarded as adequate. During the oxidation procedure prior to ceramic veneering, a dark oxide film consisting of predominantly of CoO was formed. The use of a gold coating agent instead of preoxidation caused an equally high bond strength to the ceramic. The coefficient of thermal expansion was measured to be 14.4 10−6/°C, which can be considered to be adequate and close to that of most dental ceramics for veneering. The castability was found to be satisfactory. The only detected drawback of the alloy was a definite tendency to absorb carbon when melted in a graphite crucible.
Effects of spinal implant stiffness and removal/retention on bypassed bone mineral density and column/fusion stiffness were studied in dogs.
After facet fusion and bicortical peripedicle screw placement, one group of eight dogs received 6.35 mm and another 4.76 mm rod instrumentation at L3-L5. At 12 weeks, four in each group had implants removed. Bone mineral density was analyzed by dual energy x-ray absorptiometry at 1 to 24 weeks. Axial compressive stiffness of the L3-L5 construct, spinal column, fused facets, and instrumentation were measured. Percent load through the vertebral column was predicted.
Five observations were made for this canine model. First, stiffer implants resulted in more bypassed bone mineral loss at 6 and 12 weeks, plateauing and not different at 24 weeks. Second, after implant removal, a significant and similar rebound in bone mineral density occurred. Third, 4.76 mm rod instrumentation (initially 71% load through column) resulted in stiffer posterior fusions and vertebral columns than 6.35 mm rod instrumentation (initially 57% load through column). Fourth, marked stiffening of the anterior-middle columns (apparently disks) occurred. Fifth, percent load borne by the vertebral column increased with time.
There appears to be a range of percent load through the vertebral column that creates optimum fusion/column stiffening while limiting bone stress shielding effects. The 6.35 mm rod constructs were predicted to allow greater than 70% axial load through the adult human thoracic/lumbar spine, implying biologic responses similar to 4.76 mm rods in dogs.
Ferromagnetic materials with low Curie temperatures are being investigated for use as interstitial implants for fractionated hyperthermia treatment of prostatic disease. Previous investigations of the system have utilized alloys, such as NiCu, with inadequate corrosion resistance, requiring the use of catheters for removal of the implants following treatment or inert surface coatings which may interfere with thermal characteristics of the implants. We are evaluating a palladium-cobalt (PdCo) binary alloy which is very similar to high palladium alloys used in dentistry. Electrochemical corrosion tests and immersion tests at 37 degrees C for both NiCu and PdCo alloy samples in mammalian Ringer's solution were performed. Long-term corrosion rates are 5.8 x 10(-5) microm per year (NiCu) and 7.7 x 10(-8) microm per year (PdCo) from average immersion test results, indicating higher corrosion resistance of PdCo (P < 0.02); immersion corrosion rates were much lower than initial corrosion rates found electrochemically. Both alloys had significantly lower corrosion rates than standard surgical implant rates of 0.04 microm per year (P < 0.001 for both alloys). Scanning electron microscopy illustrates changes in the NiCu alloy surface due to pitting corrosion; no difference is observed for PdCo. The data indicate that the PdCo alloy may be suitable as a long-term implant for use in fractionated hyperthermia.
Simple NaOH and heat treatments provided a Ti-15Mo-5Zr-3Al alloy with a bioactive graded surface structure of an amorphous sodium titanate, where the sodium titanate on the top surface gradually changed into the alloy substrate through titanium oxide. The sodium titanate was free of alloying species of Mo, Zr and Al, since almost all of them were released from the surface of alloy during the first NaOH treatment. The sodium titanate transformed into a hydrated titania via Na+ ion release to induce a bone-like apatite formation on the alloy substrate in a simulated body fluid (SBF). The alloying species neither were released into the SBF nor affected the apatite formation. In the process of apatite formation, the graded surface structure developed into one where the apatite on the top surface gradually changed into the alloy composition through hydrated titania and titanium oxide. It is expected that this graded structure will lead to a strong interfacial bonding strength between the apatite layer and the alloy substrate, thereby providing a tight integration of the alloy with living bone through the apatite layer.
The osteogenic activity of porous titanium fiber mesh and calcium phosphate (Ca-P)-coated titanium fiber mesh loaded with cultured syngeneic osteogenic cells was compared in a syngeneic rat ectopic assay model. In 30 syngeneic rats, (Ca-P)-coated and non-coated porous titanium implants were subcutaneously placed either without or loaded with cultured rat bone marrow (RBM) cells. Fluorochrome bone markers were injected at 2, 4, and 6 weeks. The rats were sacrificed, and the implants were retrieved at 2, 4, and 8 weeks post-operatively. Histological analysis demonstrated that none of the (Ca-P)-coated and non-coated meshes alone supported bone formation at any time period. In RBM-loaded implants, bone formation started at 2 weeks. At 4 weeks, bone formation increased. However, at 8 weeks bone formation was absent in the non-coated titanium implants, while it had remained in the (Ca-P)-coated titanium implants. Also, in (Ca-P)-coated implants more bone was formed than in non-coated samples. In general, osteogenesis was characterized by the occurrence of multiple spheres in the porosity of the mesh. The accumulation sequence of the fluorochrome markers showed that the newly formed bone was deposited in a centrifugal manner starting at the center of a pore. Our results show that the combination of Ti-mesh with RBM cells can indeed generate bone formation. Further, our results confirm that a thin Ca-P coating can have a beneficial effect on the bone-generating properties of a scaffold material.
Musculoskeletal tissue, bone and cartilage are under extensive investigation in tissue engineering research. A number of biodegradable and bioresorbable materials, as well as scaffold designs, have been experimentally and/or clinically studied. Ideally, a scaffold should have the following characteristics: (i) three-dimensional and highly porous with an interconnected pore network for cell growth and flow transport of nutrients and metabolic waste; (ii) biocompatible and bioresorbable with a controllable degradation and resorption rate to match cell/tissue growth in vitro and/or in vivo; (iii) suitable surface chemistry for cell attachment, proliferation, and differentiation and (iv) mechanical properties to match those of the tissues at the site of implantation. This paper reviews research on the tissue engineering of bone and cartilage from the polymeric scaffold point of view.
Revision cases of total hip implants are complicated by the significant amount of bone loss. New materials and/or approaches are needed to provide stability to the site, stimulate bone formation, and ultimately lead to fully functional bone tissue. Porous bioactive glasses (prepared from 45S5 granules, 45% SiO2, 24.5% Na2O, 24.5% CaO, and 6% P2O5) have been developed as scaffolds for bone tissue engineering and have been studied in vitro. In this study, we investigated the incorporation of tissue-engineered constructs utilizing these scaffolds in large, cortical bone defects in the rat simulating revision conditions. With implantation times of 2, 4, and 12 weeks the results were compared to those using the bioactive ceramic scaffold alone. Two tissue-engineered constructs were studied: osteoprogenitor cells that were either seeded onto the scaffold prior to implantation ("primary") or those that were culture expanded to form bonelike tissue on the scaffold prior to implantation ("hybrid"). Defects treated with the hybrid had the greatest amount of bone in the available pore space of the defect over all other groups at 2 weeks (p < 0.05). For both the primary and hybrid groups, woven and lamellar bone was present along the interface of the scaffold and the host cortex and within the porous space of the scaffold at 2 weeks. By 4 weeks, very uniform, lamellar bone was present throughout the scaffold for both tissue-engineered groups. The amount of bone significantly increased over time for all groups while the bioactive ceramic gradually resorbed by 40% at 12 weeks (p < 0.05). Structural properties of the treated long bones improved over time. Long bones treated with the hybrid had an early return in torsional stiffness by 2 weeks. Both tissue-engineered constructs achieved normal torsional strength and stiffness by 4 weeks as compared to the scaffold alone, which achieved this by 12 weeks. Porous, surface modified bioactive ceramic is a promising scaffold material for tissue-engineered bone repair.
The clinical study conducted was a prospective, randomized, double-blind, placebo-controlled trial.
The purpose of this study was to evaluate the effect of combined magnetic fields on the healing of primary noninstrumented posterolateral lumbar spine fusion.
Combined magnetic fields, a new type of biophysical stimulus, have been shown to act by stimulating endogenous production of growth factors that regulate the healing process. This is the first placebo-controlled study to assess the effect of an electromagnetic stimulus on primary noninstrumented posterolateral lumbar spine fusion surgery as well as the first evaluation of combined magnetic fields as an adjunctive stimulus to lumbar spine fusion.
This multicenter investigational study was conducted at 10 clinical sites under an Investigational Device Exemption from the United States Food and Drug Administration. Eligible patients had one-level or two-level fusions (between L3 and S1) without instrumentation, either with autograft alone or in combination with allograft. The combined magnetic field device used a single posterior coil, centered over the fusion site, with one 30-minute treatment per day for 9 months. Randomization was stratified by site and number of levels fused. Evaluation was performed 3, 6, and 9 months after surgery and 3 months after the end of treatment. The primary endpoint was assessment of fusion at 9 months, based on radiographic evaluation by a blinded panel consisting of the treating physician, a musculoskeletal radiologist, and a spine surgeon.
Of 243 enrolled patients, 201 were available for evaluation. Among all patients with active devices, 64% healed at 9 months compared with 43% of patients with placebo devices: a significant difference (P = 0.003 by Fisher's exact test). Stratification by gender showed fusion in 67% of women with active devices, compared with 35% of those with placebo devices (P = 0.001 by Fisher's exact test). By contrast, there was not a statistically significant effect of the active device in this male study population. In the overall population of 201 patients, repeated measures analyses of fusion outcomes (by generalized estimating equations) showed a main effect of treatment, favoring the active treatment (P = 0.030). In a model with main effect and a time by treatment interaction, the latter was significant (P = 0.024), indicating acceleration of healing. Performed in the full sample of 243 patients, results of the intent-to-treat analysis were qualitatively the same as in the evaluable sample of 201 patients.
This investigational study demonstrates that combined magnetic field treatment of 30 min/d increases the probability of successful spine fusion, and statistical analysis using the generalized estimating equations model suggests an acceleration of the healing process. This is the first randomized clinical trial of noninstrumented primary posterolateral lumbar spine fusion, with evaluation by a blinded, unbiased panel. This is the first double-blind study performed to date assessing noninstrumented fusion outcome with extremely critical radiographic criteria. The lower overall fusion rates in this study are attributed to the high-risk patient group with an average age of 57 years, the use of noninstrumented technique with posterolateral fusion only, and the reliance on extremely critical radiographic and clinical criteria and blinded panel for fusion assessment without surgical confirmation.
In conclusion, the adjunctive use of the combined magnetic field device was statistically beneficial in the overall patient population, as has been shown in previous studies of adjunctive bone growth stimulation for spine fusion. For the first time, stratification of fusion success data by gender demonstrated that the female study population responded positively to the adjunctive combined magnetic field treatment, with no statistically significant effect observed in the male study population. Adjunctive use of the combined magnetic field device significantly increased the 9-month success of radiographic spinal fusion and showed an acceleration of the healing process.
The induction of bone formation to an intentional orientation is a potentially viable clinical treatment for bone disorders. Among the many chemical and physical factors, a static magnetic field (SMF) of tesla order can regulate the shapes of blood cells and matrix fibers. This study investigated the effects of a strong SMF (8 T) on bone formation in both in vivo and in vitro systems. After 60 h of exposure to the SMF, cultured mouse osteoblastic MC3T3-E1 cells were transformed to rodlike shapes and were orientated in the direction parallel to the magnetic field. Although this strong SMF exposure did not affect cell proliferation, it up-regulated cell differentiation and matrix synthesis as determined by ALP and alizarin red stainings, respectively. The SMF also stimulated ectopic bone formation in and around subcutaneously implanted bone morphogenetic protein (BMP) 2-containing pellets in mice, in which the orientation of bone formation was parallel to the magnetic field. It is concluded that a strong SMF has the potency not only to stimulate bone formation, but also to regulate its orientation in both in vitro and in vivo models. This is the first study to show the regulation of the orientation of adherent cells by a magnetic field. We propose that the combination of a strong SMF and a potent osteogenic agent such as BMP possibly may lead to an effective treatment of bone fractures and defects.
Strong static magnetic field Corrosion analysis of NiCu and PdCo thermal seed alloys used as interstitial hyperthermia implants
- H Kotani
- H Kawaguchi
- T Shimoaka
- M Iwasaka
- S Ueno
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