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Schematic illustration of the AFM nanoindentation strategy for measuring the Young's modulus (E) of the HAP/Col hydrogels. (a) Fabrication process of the collagen fibers (blue thread) which were mixed with the HAPs (white dot) by stirring at 10,000 rpm. The BMP-2 and neutralization solution were added to the collagen slurry, and the cross-linking process was conducted at 37 °C for 4 h. After that, the HAP/Col hydrogel was incubated in the PBS solution at 37 °C to mimic physiological conditions. (b) Schematic illustration of AFM nanoindentation in the aqueous solution. Pressing the sample with the bead causes the cantilever to deflect and change the degree of reflection of the laser. The detector senses the change in the laser value, which allows the measurement of the surface modulus of the sample. (c) Hertz model for analyzing the E value of the HAP/Col hydrogel. This model is based on the contact between a sphere and a half space, showing the F−D curve-based AFM, which contours the surface of the sample while recording a pixel-by-pixel full F−D curve.
Source publication
Hydroxyapatite nanoparticle-complexed collagen (HAP/Col) hydrogels have been widely used in biomedical applications as a scaffold for controlled drug release (DR). The time-variant mechanical properties (Young’s modulus, E) of HAP/Col hydrogels are highly relevant to the precise and efficient control of DR. However, the correlation between the DR a...
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... used atomic force microscopy (AFM), which is the most versatile and powerful microscopic technology for analyzing samples at the nanoscale. 25−27 Among the various applications of AFM, we operated the nanoindentation test using an AFM cantilever with a 10.8 μm bead (Figure 1). We provided a quantitative analysis of the time-variant nanomechanical behavior of the hydrogels with different HAP concentrations. ...
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... fabricate three-dimensional (3D)-structured hydrogels, we prepared both rat tail-derived collagen type I solution (3.8 mg/mL) and neutralization solution from Advanced BioMatrix (USA). We purchased a recombinant human bone morphogenic protein-2 (rhBMP-2) from Peprotech (USA) and the HAP nanoparticles (<200 nm) from Sigma Aldrich (USA) ( Figure S1, Supporting Information). The ELISA kits (Koma Biotech, South Korea) were used for the rhBMP-2 assay. ...
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... On the other hand, by adding to a neutral solution at 37 °C, the conversion of Lys/Hyl residues located in the nonhelical C-and Ntelopeptides of collagen molecules causes the covalent intermolecular cross-linking of collagens. 33 After cross-linking the HAP/Col hydrogels on a petri dish, we added the PBS (pH 7.4) to analyze the DR at 37 °C, under mimic physiological conditions (Figure 1a). Because the HAP/Col hydrogels were hydrated and degraded with time, the drug was released into the buffer. ...
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... given time points up to 28 days, the release media was sampled and replaced with fresh PBS solution each time. For nondestructive AFM nanoindentation, we used a 10.8 μm polystyrene bead-functionalized AFM cantilever with a spring constant of 0.08 N/m (Figure 1b). As the AFM cantilever was loaded to the gel surface, we could measure the F−D curves of each HAP/Col hydrogel in the PBS solution ( Figure 1c). ...
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... nondestructive AFM nanoindentation, we used a 10.8 μm polystyrene bead-functionalized AFM cantilever with a spring constant of 0.08 N/m (Figure 1b). As the AFM cantilever was loaded to the gel surface, we could measure the F−D curves of each HAP/Col hydrogel in the PBS solution ( Figure 1c). Once an AFM cantilever is indented into the HAP/Col hydrogel, the mechanical contact between the bead and the gel surface causes a deflection of the cantilever. ...
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... deformation of the cantilever created a change in the laser displacement on the position-sensitive detector (PSD), and the result was recorded as the F−D curves. Upon analyzing the F− D curves, we adopted the Hertz model to determine E of the hydrogel (Figure 1c). The model is related to the applied loading force F and the indentation depth or deformation δ (see Experimental method 2.5). ...
Citations
... By embedding these nanoparticles into biodegradable polymers or hydrogels, researchers have been able to fabricate scaffolds that not only support cell growth and tissue formation, but also impart specific biological signals to enhance tissue regeneration. For example, HA nanoparticles have been combined with collagen to create composite scaffolds for bone tissue engineering [64][65][66][67]. These scaffolds not only provide a supportive matrix for cell growth, but also enhance osteogenic differentiation of stem cells, leading to improved bone formation. ...
... Previous studies have revealed that adding of hydroxyapatite nanoparticles in moderate amounts to hydrogels increased the Young's modulus of hydrogels and decelerated the degradation rate. 60 Martincic et al. found lower infection rates in hydroxyapatite collagen hydrogels than alginate agarose hydrogels in the treatment of knee cartilage injuries. 61 The biomimetic mineralization approach is the assembly of nHA onto COL I, a strategy that mimics natural bone at the molecular level. ...
Cartilage regeneration remains difficult due to a lack of blood vessels. Degradation of the extracellular matrix (ECM) causes cartilage defects, and the ECM provides the natural environment and nutrition for cartilage regeneration. Until now, collagen hydrogels are considered to be excellent material for cartilage regeneration due to the similar structure to ECM and good biocompatibility. However, collagen hydrogels also have several drawbacks, such as low mechanical strength, limited ability to induce stem cell differentiation, and rapid degradation. Thus, there is a demanding need to optimize collagen hydrogels for cartilage regeneration. In this review, we will first briefly introduce the structure of articular cartilage and cartilage defect classification and collagen, then provide an overview of the progress made in research on collagen hydrogels with chondrocytes or stem cells, comprehensively expound the research progress and clinical applications of collagen‐based hydrogels that integrate inorganic or organic materials, and finally present challenges for further clinical translation.
... 15 The nanoindentation used in this study is a method of measuring mechanical properties by pressing probes of a certain shape and size into materials. 16 Although traditional nanoindentation techniques were developed for stiff materials, 17 nanoindentation testing of hydrogels, 18 soft tissues, 19 and cells 20 has subsequently attracted substantial attention because of the high spatial resolution nanoindentation allows with local testing of mechanical properties of soft matter that is not possible using macroscale techniques. Over the past decade, despite the challenges encountered with substantial inelastic and associated creep deformation of soft biomaterials, nanoindentation technology, especially utilizing spherical tipped indenters, along with the classic Hertz model has gradually begun to be used for reliable measurement of soft matter. ...
Purpose
To evaluate the regional effects of different corneal cross-linking (CXL) protocols on corneal biomechanical properties.
Methods
The study involved both eyes of 50 rabbits, and the left eyes were randomized to the five intervention groups, which included the standard CXL group (SCXL), which was exposed to 3-mW/cm² irradiation, and three accelerated CXL groups (ACXL1–3), which were exposed to ultraviolet-A at irradiations of 9 mW/cm², 18 mW/cm², and 30 mW/cm², respectively, but with the same total dose (5.4 J/cm²). A control (CO) group was not exposed to ultraviolet-A. No surgery was done on the contralateral eyes. The corneas of each group were evaluated by the effective elastic modulus (Eeff) and the hydraulic conductivity (K) within a 7.5-mm radius using nanoindentation measurements.
Results
Compared with the CO group, Eeff (in regions with radii of 0–1.5 mm, 1.5–3.0 mm, and 3.0–4.5 mm) significantly increased by 309%, 276%, and 226%, respectively, with SCXL; by 222%, 209%, and 173%, respectively, with ACXL1; by 111%, 109%, and 94%, respectively, with ACXL2; and by 59%, 41%, and 37%, respectively, with ACXL3 (all P < 0.05). K was also significantly reduced by 84%, 81%, and 78%, respectively, with SCXL; by 75%, 74%, and 70%, respectively, with ACXL1; by 64%, 62%, and 61%, respectively, with ACXL2; and by 33%, 36%, and 32%, respectively, with ACXL3 (all P < 0.05). For the other regions(with radii between 4.5 and 7.5 mm), the SCXL and ACXL1 groups (but not the ACXL2 and ACXL3 groups) still showed significant changes in Eeff and K.
Conclusions
CXL had a significant effect on corneal biomechanics in both standard and accelerated procedures that may go beyond the irradiated area. The effect of CXL in stiffening the tissue and reducing permeability consistently decreased with reducing the irradiance duration.
... As such, our goals were to verify (i) whether the mechanical characterization of the histological specimen would be consistent with the results from conventional histopathological analysis and (ii) whether it could provide abundant information about benign versus malignant epidermal tissues, complementing the traditional histopathological examinations. Atomic force microscopy (AFM) is a multi-functional device that can analyze a sample's morphology, mechanical strength, and surface charge by its nano-scale cantilever [36][37][38][39]. In this report, we demonstrate a robust mechanical characterization of histological specimens using atomic force microscopy (AFM) indentation for discrimination among normal, benign nevus, and melanoma. ...
Melanoma is visible unlike other types of cancer, but it is still challenging to diagnose correctly because of the difficulty in distinguishing between benign nevus and melanoma. We conducted a robust investigation of melanoma, identifying considerable differences in local elastic properties between nevus and melanoma tissues by using atomic force microscopy (AFM) indentation of histological specimens. Specifically, the histograms of the elastic modulus of melanoma displayed multimodal Gaussian distributions, exhibiting heterogeneous mechanical properties, in contrast with the unimodal distributions of elastic modulus in the benign nevus. We identified this notable signature was consistent regardless of blotch incidence by sex, age, anatomical site (e.g., thigh, calf, arm, eyelid, and cheek), or cancer stage (I, IV, and V). In addition, we found that the non-linearity of the force-distance curves for melanoma is increased compared to benign nevus. We believe that AFM indentation of histological specimens may technically complement conventional histopathological analysis for earlier and more precise melanoma detection.
... In addition, HA has biomineralization properties similar to hard tissue; hence, it is currently used in orthopedics and dentistry [2][3][4][5][6]. HA is also used for other biomedical applications such as coating metallic osseous implants, drug delivery, and tissue engineering scaffolds because of its stoichiometric properties that are similar to bone, as well as other advantages such as biocompatibility, intimacy with other biopolymers, and excellence in inducing bone differentiation [7][8][9][10][11][12][13]. Over the past few decades, many researchers have attempted to synthesize the natural forms of HA. ...
... The unit cell of HA has a hexagonal structure according to the lattice parameters (a = 0.95 nm, c = 0.68 nm). The crystal [12]. It should be noted that they first confirmed Young's modulus of single HA nanoparticles. ...
Hydroxyapatite (HA) is one of the most common bioceramics and is abundant in human bones. HA is composed of calcium phosphate, which is prevalent in biomedical processes, particularly bone formation, osteogenesis, and angiogenesis. As HA is one of the core materials that makes up the human body, there has been considerable research on methods of synthesizing HA while changing its properties by substituting various types of metal ions. In particular, previous studies have intensively investigated the size, crystallinities, and morphologies generated using various synthesis methods to change the characteristics of HA by substituting different metal ions. This review summarizes the findings of these studies on HA, including findings on the characteristics of HA in natural bone, methods of synthesizing HA, and findings on metal-ion-substituted HA. Furthermore, the characteristics and applications of HA that were investigated in previous studies are summarized, and the latest trends and perspectives on the future of the field are also presented.
... Moreover, it is shown that composite coatings (samples C and D) are also characterized with greater rate parameters (τ) as compared to polymeric coatings (samples A and B). Thus, it can be concluded that the addition of ceramic leads to the decreased swelling ability of materials and slower liquid medium absorption by composite coatings [15]. from triple degenerate O-P-O bending modes in PO4 3− . ...
... Moreover, it is shown that composite coatings (samples C and D) are also characterized with greater rate parameters (τ) as compared to polymeric coatings (samples A and B). Thus, it can be concluded that the addition of ceramic leads to the decreased swelling ability of materials and slower liquid medium absorption by composite coatings [15]. ...
The biomaterial coatings for bone tissue regeneration described in this study promote bioactivity. The ceramic-polymer composite coatings deposited on polylactide (PLA) plates contain polymers, namely polyvinylpyrrolidone (PVP)/polyethylene glycol (PEG), while the ceramic phase is hydroxyapatite (HA). Additionally, collagen (COL) and glutathione (GSH) are components of high biological value. Bone tissue materials requires additionally demanding tribological properties, which are thoroughly described in this research. These findings, presented herein for the first time, characterize this type of highly specific composite coating material and their indicate possible application in bone regeneration implants. Implementation of the collagen in the PVP/PEG/HA composite matrix can tailor demanding tribological performance, e.g., anti-wear and friction reduction. The addition of the ceramic phase in too high a content (15%) leads to the decreased swelling ability of materials and slower liquid medium absorption by composite coatings, as well as strong surface roughening and loosening tribological properties. In consequence, small particles of HA from the very rough composite crumble, having a strong abrasive effect on the sample surface. In conclusion, sample C composed of PVP/PEG/GSH/COL/HA (5%) exhibits high bioactivity, strong mechanical and tribological properties, the highest free surface energy, porosity, and accepted roughness to be implemented as a material for bone regeneration.
... Among them, NP-embedded hydrogel complexes have attracted considerable attention because of the advantages of hydrogels, such as biodegradability, biocompatibility and non-toxicity, which can be combined with the unique properties of NPs [12][13][14][15][16]. For example, Jung et al. demonstrated that the mechanical properties of a collagen hydrogel could be modulated by adding hydroxyapatite NPs [17]. Arno et al. demonstrated improved adhesion and resistance to breakage in calcium alginate hydrogels using poly(L-lactide)-based NPs [18]. ...
Hydrogels containing colorimetric nanoparticles have been used for ion sensing, glucose detection, and microbial metabolite analyses. In particular, the rapid chemical reaction owing to both the hydrogel form of water retention and the sensitive color change of nanoparticles enables the rapid detection of target substances. Despite this advantage, the poor dispersibility of nanoparticles and the mechanical strength of nanoparticle–hydrogel complexes have limited their application. In this study, we demonstrate a milliliter agarose gel containing homogeneously synthesized polyaniline nanoparticles (PAni-NPs), referred to as PAni-NP–hydrogel complexes (PNHCs). To fabricate the optimal PNHC, we tested various pH solvents based on distilled water and phosphate-buffered saline and studied the colorimetric response of the PNHC with thickness. The colorimetric response of the prepared PNHC to the changes in the pH of the solution demonstrated excellent linearity, suggesting the possibility of using PNHC as a pH sensor. In addition, it was verified that the PNHC could detect minute pH changes caused by the cancer cell metabolites without cytotoxicity. Furthermore, the PNHC can be stably maintained outside water for approximately 12 h without deformation, indicating that it can be used as a disposable patch-type wearable biosensing platform.
... The compressive strength of the SNP with a pore size of 30.2 nm was highest compared to the other pellets (Fig. S2). However, both XRD and FTIR spectroscopy analyses indicated a phase transition from HAP to tricalcium phosphate (TCP) beyond the sintering temperature of 500°C; a new peak appeared at 31.1°in the diffraction pattern and 1120 cm − 1 in the IR transmission spectrum (Fig. 3c and d) [67][68][69]71]. As our study focused on the investigation of the effect of natural bone-mimicking nanopores in the HAP scaffold rather than the influence of the phase transition from HAP to TCP, SNPs sintered above 500°C were not analyzed. ...
Background
A considerable number of studies has been carried out to develop alloplastic bone graft materials such as hydroxyapatite (HAP) that mimic the hierarchical structure of natural bones with multiple levels of pores: macro-, micro-, and nanopores. Although nanopores are known to play many essential roles in natural bones, only a few studies have focused on HAPs containing them; none of those studies investigated the functions of nanopores in biological systems.
Method
We developed a simple yet powerful method to introduce nanopores into alloplastic HAP bone graft materials in large quantities by simply pressing HAP nanoparticles and sintering them at a low temperature.
Results
The size of nanopores in HAP scaffolds can be controlled between 16.5 and 30.2 nm by changing the sintering temperature. When nanopores with a size of ~ 30.2 nm, similar to that of nanopores in natural bones, are introduced into HAP scaffolds, the mechanical strength and cell proliferation and differentiation rates are significantly increased. The developed HAP scaffolds containing nanopores (SNPs) are biocompatible, with negligible erythema and inflammatory reactions. In addition, they enhance the bone regeneration when are implanted into a rabbit model. Furthermore, the bone regeneration efficiency of the HAP-based SNP is better than that of a commercially available bone graft material.
Conclusion
Nanopores of HAP scaffolds are very important for improving the bone regeneration efficiency and may be one of the key factors to consider in designing highly efficient next-generation alloplastic bone graft materials.
... In addition, the continuous stiffness measurement (CSM) method in nanoindentation has proven pivotal in probing sophisticated nanomechanical properties, such as the local strain-rate sensitivity [13,14] and creep stress exponent [15,16]. Furthermore, hydrogels and cellulose-based nanocomposites are being increasingly used for controlled drug delivery purposes where nanoindentation can be applied to correlate the changes in mechanical properties to the amount of drug loaded [17]. Nanoindentation is highly beneficial during the pre-formulation phase of drug development where, in spite of having a finite supply of active pharmaceutical ingredients (APIs), it becomes possible to study the effect of drug composition on the mechanical performance of the manufactured tablets in a high throughput manner due to the small volumes of material involved ($1 lm 3 ) and nearly nondestructive nature [18]. ...
Mechanical properties play a central role in drug formulation development and manufacturing. Traditional characterization of mechanical properties of pharmaceutical solids relied mainly on large compacts, instead of individual particles. Modern nanomechanical testing instruments enable quantification of mechanical properties from the single crystal/particle level to the finished tablet. Although widely used in characterizing inorganic materials for decades, nanomechanical testing has been relatively less employed to characterize pharmaceutical materials. This review focuses on the applications of existing and emerging nanomechanical testing methods in characterizing mechanical properties of pharmaceutical solids to facilitate fast and cost-effective development of high quality drug products. Testing of pharmaceutical materials using nanomechanical techniques holds potential to develop fundamental knowledge in the structure–property relationships of molecular solids, with implications for solid form selection, milling, formulation design, and manufacturing. We also systematically discuss pitfalls and useful tips during sample preparation and testing for reliable measurements from nanomechanical testing.
... Atomic force microscopy (AFM) is a multi-functional device that can analyze a sample's morphology, mechanical strength, and surface charge by its nano-scale cantilever [36][37][38][39]. In this report, we demonstrate a robust mechanical characterization of histological specimens using atomic force microscopy (AFM) indentation for discrimination among normal, benign nevus, and melanoma. ...
Melanoma is visible unlike other types of cancer, but it is still challenging to diagnose correctly because of the difficulty in distinguishing between benign nevus and melanoma. We conducted a robust investigation of melanoma, identifying considerable differences in local elastic properties between nevus and melanoma tissues by using atomic force microscopy (AFM) indentation of histological specimens. Specifically, the histograms of the elasticity of melanoma displayed multimodal Gaussian distributions, exhibiting the heterogeneous mechanical properties, in contrast with the unimodal distributions of elasticity in the benign nevus. We identified this notable signature was consistent regardless of blotch incidence by sex, age, anatomical site (e.g., thigh, calf, arm, eyelid, and cheek), or cancer stage (I, IV, and V). In addition, we found that the non-linearity of the force-distance curves for melanoma is increased compared to benign nevus. We believe that AFM indentation of histological specimens may technically complement conventional histopathological analysis for earlier and more precise melanoma detection.
