Increasing Hydroxyapatite Content Research Articles

Preparation and Characterization of Hydroxyapatite Based Composite Material via Cold Sintering Process

This study focuses on the synthesis of hydroxyapatite (HA) from bovine bones through calcination and subsequent combination with Polyvinyl Alcohol (PVA) using the Cold Sintering Process (CSP). The CSP, operating at lower temperatures than conventional methods, aims to preserve the bioactivity and biocompatibility of HA, crucial for biomedical applications. The research investigates the influence of HA composition, sintering temperature, and PVA content on the porosity and compressive strength of the HA-PVA composite. The Hydroxyapatite powder, obtained from calcinated bovine bones, exhibits irregular shapes and sizes with a maximum grain size of 10µm, confirmed by SEM analysis. XRD analysis validates the successful production of Hydroxyapatite, showcasing characteristic peaks. The HA/PVA composite's XRD pattern indicates the dominance of HA, with PVA present as well. The study produces 27 specimens through the CSP, varying HA composition and sintering temperature. Porosity increases with higher HA content and sintering temperature, attributed to the role of PVA in binding HA particles. Compressive strength rises with increased HA content, emphasizing HA's role in enhancing mechanical strength. The presence of porosity is mitigated by a strong bond between HA and PVA, contributing to structural integrity. This research provides insights into tailoring HA-PVA materials for biomedical applications, considering controlled porosity and mechanical strength. The CSP, with its unique advantages, emerges as a promising method for developing customized materials to meet diverse biomedical needs.

Influence of Hydroxyapatite Content on Physical and Rheological Properties of Chitosan-based Scaffold

Chitosan-based scaffolds offer significant potential in tissue engineering and regenerative medicine. Whilst exhibiting great bio-regenerative and biocompatible properties, their mechanical properties remain quite poor. The presented research is focused on the modification of macroporous chitosan scaffolds with various amounts of bioactive ceramics (hydroxyapatite) and its influence on the physical and rheological properties of the composite scaffold. Chitosan/hydroxyapatite composite scaffolds with a highly porous microstructure have been prepared by suspending hydroxyapatite (HAp) particles into the chitosan matrix. According to SEM imaging, homogeneous dispersion of the inorganic phase in a chemically-crosslinked chitosan matrix had been achieved. The obtained composite scaffolds exhibited lower swelling capacity with respect to pure chitosan after 24 h of incubation in Hanks’ balanced salt solution. Rheological measurements show an increase in storage and loss modulus indicating an improvement in mechanical properties under shear stress. Furthermore, no significant change in loss factor (tanδ) was observed indicating no change in composite viscoelastic properties with an increase in HAp content.

Suitability of Gelatin Methacrylate and Hydroxyapatite Hydrogels for 3D-Bioprinted Bone Tissue.

Complex bone defects are challenging to treat. Autografting is the gold standard for regenerating bone defects; however, its limitations include donor-site morbidity and increased surgical complexity. Advancements in 3D bioprinting (3DBP) offer a promising alternative for viable bone grafts. In this experiment, gels composed of varying levels of gelatin methacrylate (GelMA) and hydroxyapatite (HA) and gelatin concentrations are explored. The objective was to increase the hydroxyapatite content and find the upper limit before the printability was compromised and determine its effect on the mechanical properties and cell viability. Design of Experiments (DoE) was used to design 13 hydrogel bioinks of various GelMA/HA concentrations. These bioinks were assessed in terms of their pipettability and equilibrium modulus. An optimal bioink was designed using the DoE data to produce the greatest stiffness while still being pipettable. Three bioinks, one with the DoE-designed maximal stiffness, one with the experimentally defined maximal stiffness, and a literature-based control, were then printed using a 3D bioprinter and assessed for print fidelity. The resulting hydrogels were combined with human bone-marrow-derived mesenchymal stromal cells (hMSCs) and evaluated for cell viability. The DoE ANOVA analysis indicated that the augmented three-level factorial design model used was a good fit (p < 0.0001). Using the model, DoE correctly predicted that a composite hydrogel consisting of 12.3% GelMA, 15.7% HA, and 2% gelatin would produce the maximum equilibrium modulus while still being pipettable. The hydrogel with the most optimal print fidelity was 10% GelMA, 2% HA, and 5% gelatin. There were no significant differences in the cell viability within the hydrogels from day 2 to day 7 (p > 0.05). There was, however, a significantly lower cell viability in the gel composed of 12.3% GelMA, 15.7% HA, and 2% gelatin compared to the other gels with a lower HA concentration (p < 0.05), showing that a higher HA content or print pressure may be cytotoxic within hydrogels. Extrusion-based 3DBP offers significant advantages for bone-tissue implants due to its high customizability. This study demonstrates that it is possible to create printable bone-like grafts from GelMA and HA with an increased HA content, favorable mechanical properties (145 kPa), and a greater than 80% cell viability.

The effect of extrusion and injection molding on physical, chemical, and biological properties of PLLA/HAp whiskers composites

This paper deals with physical, chemical and biological properties of polymer-ceramic composites based on poly(l-lactide) (PLLA) with the addition of 10, 20 or 30 % (by weight) of hydroxyapatite (HAp) whiskers, produced by a combination of twin-screw extrusion and injection molding techniques. The materials obtained were tested for morphology (scanning electron microscopy), chemical composition (energy dispersive x-ray spectroscopy, infrared spectroscopy), processing properties (melt flow rates and density), thermal properties (differential scanning calorimetry, thermogravimetry), strength (static tensile test, impact strength) and surface properties (optical profilometry, contact angle measurements). The biological evaluation was performed by in vitro assessment of the manufactured materials’ cytotoxicity, level of colonization by osteo- and fibroblasts and level of adhesion displayed by a microbial pathogen, referred to as the Staphylococcus aureus. The results indicate an influence of the applied processing path on the properties of the filler particles − the apatite whiskers were significantly shortened. On the other hand, we have demonstrated the possibility of obtaining PLLA/HAp composites with good strength parameters, precise geometric shape and slightly improved surface properties. The results of biological evaluation revealed that all of the materials obtained displayed low cytotoxicity and a high level of colonization, irrespective of the content of hydroxyapatite. The only exception was the composite containing 10 % HAp, for which we observed weaker fibroblast adhesion compared to other materials. In turn, the level of colonization by S.aureus grew with the increase in HAp content in polymers. Results of biological evaluation indicate that although obtained polymers display favorable properties in terms of eukaryotic cell adhesion/colonization, they may also provide advantageous surface conditions for bacterial development. Therefore, inclusion of antimicrobial to the materials obtained may be necessary and should be further investigated. Nevertheless, the results obtained certainly provide useful information from the point of view of designing and manufacturing of biocomposites for bone tissue engineering applications.

Insights into nanomechanical behavior of B. mori silk fibroin-hydroxyapatite bio-nanocomposite using MD simulations: Role of varying hydroxyapatite content

Nanocomposite material composed of Bombyx mori Silk Fibroin and hydroxyapatite (B. mori SF-HA) is a potential biomaterial for bone tissue engineering. Here, Bombyx mori Silk Fibroin (B. mori SF) is a flexible and tough organic, polymer phase, and hydroxyapatite (HA) is hard and stiff mineral phase. Knowledge about mechanical deformation behavior together with governing mechanisms, and the role of the two phases (SF and HA phase) and interfacial interactions between them, in B. mori SF-HA biomaterial, at fundamental level is an important factor to consider while developing the tissue grafts. Such nanometer scale behavior is often preferably investigated using molecular dynamics method. Present study aims at understanding the mechanical deformation behavior and associated physical mechanisms in B. mori SF-HA bio-nanocomposite, at nanoscale. For this purpose, computational atomistic models of B. mori SF-HA bio-nanocomposite are developed with varying HA content. Mechanical behavior analysis of these composite models under tensile loading were performed using Molecular Dynamics (MD) simulations. Elastic modulus and tensile strength values in the range of 7–20 GPa and 200–700 MPa, respectively, are obtained for B. mori SF-HA composite, in case of different HA contents, wherein, increased mechanical properties are observed with increase in HA content. Analyses of the deformation trajectories show that the deformation flow behavior in B. mori SF-HA bio-nanocomposites is mainly defined by the soft SF phase. However, energetics analyses show that, the HA phase and SF-HA interfacial interactions also play a considerable role in mechanical performance of B. mori SF-HA bio-nanocomposite. Additionally, interfacial shear strength values in B. mori SF-HA bio-nanocomposite, for different HA contents, have also been obtained. The observations made and insights gained in present work has contribution and impact in gaining an insight into the mechanistic interactions occurring at nanoscale between SF and HA phases in B. mori SF-HA bio-composite.

Strength stability over loading time of zirconia-hydroxyapatite composites

Zirconia (ZrO2) and hydroxyapatite (HAp) are commonly used as materials for medical applications, especially in implants, due to their excellent mechanical properties and bioactive function. Their composites characterize with good mechanical (similar Young's modulus and compressive strength to bone) and biological properties such as: higher bioactivity and biocompatibility. In this paper 3YZrO2 -HAp composites were prepared from the nanometric powders via the wet-mixing process and the pressure-less sintering in the air atmosphere at .1150 °C. Then they were examined in terms of properties. The shrinkage was tested using a dilatometer. The structural properties of the specimens were analyzed by X-ray diffraction, Infrared (MIR) and Raman spectroscopy. The morphology of HAp and the microstructure of the 3YZrO2 -HAp composites were evaluated using TEM and SEM microscopy. The samples’ mechanical properties, such as flexural strength and the Young’s modulus, were measured using the biaxial loading method. The hardness and KIC were examined using the Vickers indentation technique. The mechanical tests showed that all the materials revealed susceptibility to subritical cracking - the higher content of HAp in the composites, the weaker tendency of slow crack growth. The bioactive modifier addition decreased the hardness and KIC of the composites and the other mechanical properties. The microstructure investigation showed that the HAp incorporation into the 3Y-ZrO2 matrix led to higher porosity and the growth of 3Y-ZrO2 grains size, as compared to 3Y-ZrO2 without addition. The XRD results confirmed the MIR and Raman ones. They revealed the HAp decomposition into β-TCP. Additionally, the phase transition of the tetragonal ZrO2(T) into the cubic ZrO2(C) was noted with the increasing HAp content in the composites. The composites’ mechanical properties met the requirements of cancellous bone and may serve as an alternative to biomaterials for bone repair and regeneration processes.

Effect of HA Content on Microstructure and Properties of Ti-27Nb-17Ta-8Zr/HA Composite.

In this paper, Ti-27Nb-17Ta-8Zr/HA series composite materials were prepared by spark plasma sintering (SPS) technology. The medical titanium alloy (Ti-27Nb-17Ta-8Zr) with good mechanical properties, wear resistance, and corrosion resistance was combined with the hydroxyapatite (HA) bioactive ceramic with high biological activity and bone-binding ability. Moreover, the density, microstructure evolution, metal/ceramic reaction, mechanical behavior, in vitro bioactivity, and influencing mechanisms of composite materials with different HA contents were studied. The research results indicate that all biological composite materials are composed of β-Ti solution, α-Ti, and ceramic phases (Ti2O, CaTiO3, CaO, TixPy). With the increase of HA content, the compressive strength and yield strength of the composite material show a trend of first increasing, then decreasing, and then slowly increasing. After soaking in SBF artificial simulated body fluid for 5 days, the deposition of elements such as Ca and P on the surface significantly increased, while elements such as Ti, Nb, Ta, and Zr were evenly distributed in the matrix, demonstrating good in vitro mineralization ability and facilitating the attachment and growth of osteoblasts.

Study of Correlation between Structure and Shape-Memory Effect/Drug-Release Profile of Polyurethane/Hydroxyapatite Composites for Antibacterial Implants.

The effectiveness of multifunctional composites that combine a shape-memory polyurethane (PU) matrix with hydroxyapatite (HA) as a bioactive agent and antibiotics molecules results from a specific composite structure. In this study, structure-function correlations of PU-based composites consisting of 3, 5, and 10 (wt%) of HA and (5 wt%) of gentamicin sulfate (GeS) as a model drug were investigated. The performed analysis revealed that increasing HA content up to 5 wt% enhanced hydrogen-bonding interaction within the soft segments of the PU. Differential-scanning-calorimetry (DSC) analysis confirmed the semi-crystalline structure of the composites. Hydroxyapatite enhanced thermal stability was confirmed by thermogravimetric analysis (TGA), and the water contact angle evaluated hydrophilicity. The shape-recovery coefficient (Rr) measured in water, decreased from 94% for the PU to 86% for the PU/GeS sample and to 88-91% for the PU/HA/GeS composites. These values were positively correlated with hydrogen-bond interactions evaluated using the Fourier-transform-infrared (FTIR) spectroscopy. Additionally, it was found that the shape-recovery process initiates drug release. After shape recovery, the drug concentration in water was 17 μg/mL for the PU/GeS sample and 33-47 μg/mL for the PU HA GeS composites. Antibacterial properties of developed composites were confirmed by the agar-diffusion test against Escherichia coli and Staphylococcus epidermidis.

Fabrication and Characterization of PCL/HA Filament as a 3D Printing Material Using Thermal Extrusion Technology for Bone Tissue Engineering.

The most common three-dimensional (3D) printing method is material extrusion, where a pre-made filament is deposited layer-by-layer. In recent years, low-cost polycaprolactone (PCL) material has increasingly been used in 3D printing, exhibiting a sufficiently high quality for consideration in cranio-maxillofacial reconstructions. To increase osteoconductivity, prefabricated filaments for bone repair based on PCL can be supplemented with hydroxyapatite (HA). However, few reports on PCL/HA composite filaments for material extrusion applications have been documented. In this study, solvent-free fabrication for PCL/HA composite filaments (HA 0%, 5%, 10%, 15%, 20%, and 25% weight/weight PCL) was addressed, and parameters for scaffold fabrication in a desktop 3D printer were confirmed. Filaments and scaffold fabrication temperatures rose with increased HA content. The pore size and porosity of the six groups’ scaffolds were similar to each other, and all had highly interconnected structures. Six groups’ scaffolds were evaluated by measuring the compressive strength, elastic modulus, water contact angle, and morphology. A higher amount of HA increased surface roughness and hydrophilicity compared to PCL scaffolds. The increase in HA content improved the compressive strength and elastic modulus. The obtained data provide the basis for the biological evaluation and future clinical applications of PCL/HA material.

3D-bioprinted GelMA-gelatin-hydroxyapatite osteoblast-laden composite hydrogels for bone tissue engineering

IntroductionThe treatment of large bone defects remains an area of significant challenge in orthopaedic surgery. In cases where critical-sized defects (CSDs) remain, current treatment options are underwhelming and are often fraught with complications. 3D bioprinting offers a novel solution to CSDs by allowing the placement of osteogenic cells, additive biomaterials and bioactive signaling that mimic native tissue. We describe the suitability of an extrusion-based 3D bioink composed of gelatin methacryloyl (GelMA), gelatin, hydroxyapatite (HA), and osteoblasts for bone tissue engineering. MethodsA MC3T3-E1 Subclone 4 mouse calvarial osteoblast-laden GelMA-gelatin bioink consisting of various concentrations of HA was 3D-bioprinted into porous hydrogel constructs using an in-lab modified BIO-X 3D Bioprinter. The 3D-fabricated constructs were cross-linked via photopolymerization in the presence of Lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP) under UV light (1000 mW/cm2) cultured in complete osteogenic medium. After 1, 14, and 28 days, a cohort of constructs were harvested for analysis. An ALP assay and histological analysis were performed. Cell survivability and proliferation in the composite hydrogels was determined. Real-time polymerase chain reaction (RT-qPCR) was performed to measure expression levels of osteogenic genes bone morphogenetic protein-7 (BMP-7) and Osteocalcin (BGLAP) relative to a housekeeping gene (GAPDH). ResultsThe addition of HA to the bioink significantly decreased swelling from baseline GelMA-Gelatin hydrogels with a slight trend of decreased swelling with increasing HA content. The addition of 5, 10, and 20 mg/mL of HA significantly reduced hydrogel swelling (p ≤ 0.01). There was no difference among the HA groups. Degradation analysis with Type IV collagenase demonstrated that HA significantly decreased hydrogel breakdown in a concentration dependent manner (p ≤ 0.001). Results of the Alamar Blue assay demonstrated significantly increased cell proliferation in all groups at day 28, including the hydrogels without any HA. There was no difference in metabolic activity among the groups (p ≤ 0.01). ALP activity for days 7, 14, and 28 was normalized to Day 1 and found that the addition of 5 mg/mL and 20 mg/mL of HA significantly increased ALP expression at days 7 and 28 (p ≤ 0.05). Live/dead staining at 1, 14, and 28 days after printing showed, in all groups, the majority of the osteoblasts were alive at each time-point. The addition of 20 mg/mL of HA (GG20HA) demonstrated significantly greater BMP7 and BGLAP gene expression at both 14 and 28 days over the hydrogels without HA (p ≤ 0.05). ConclusionIn order for tissue-engineered bone defect repair materials to be successful they need to be biocompatible, biodegradable, similar in strength to bone while allowing for good bone induction, and a three-dimensional porous network structure for host tissue ingrowth. Therefore, 3D bioprinting for bone tissue engineering is an exciting possibility in the treatment of critical-sized bone defects as it presents an opportunity to fulfill these qualities. Although there are many reports on 3D bioprinting of bone-like structures, the ideal bioink(s) for bone tissue regeneration have yet to be discovered. Here we report on the use of a cellular GelMA-gelatin bioink with the addition of HA. In this report we demonstrated the suitability of a GelMA-gelatin-HA bioink for 3D bioprinting of bone tissue engineering applications. The addition of HA to GelMA-gelatin hydrogels significantly (1) decreased hydrogel swelling, (2) improved upon the ability of the hydrogel to resist enzymatic degradation, (3) increased osteoblastic differentiation and mineralization, and (4) increased osteogenic gene expression while maintaining equal cell viability and proliferation to non HA hydrogels. GelMA-gelatin-HA is a promising hydrogel for bone tissue repair.Significance/Clinical Relevance: We demonstrated the suitability of a GelMA-gelatin-HA bioink for 3D bioprinting of bone tissue engineering applications. The addition of HA to GelMA-gelatin hydrogels significantly decreased hydrogel swelling, improved the ability of the hydrogel to resist enzymatic degradation, increased osteoblastic differentiation and mineralization, and increased osteogenic gene expression while maintaining equal cell viability and proliferation to non-HA hydrogels. GelMA-gelatin-HA is a promising hydrogel for bone tissue repair.

Effect of particle size, shape, and weight percentage of hydroxyapatite (HA) on rheological behaviour of polycaprolactone/hydroxyapatite (PCL/HA) composites

The aim of this study is to investigate the influence of hydroxyapatite’s (HA) particle size, shape, and variation of HA weight percentage on the rheological behaviour of polycaprolactone/hydroxyapatite (PCL/HA) composite. The composite was produced by melt blending process using a single screw extruder assisted with an ultrasonic wave with varied HA weight content (0 wt.%, 10 wt.%, 20 wt.%, 30 wt.% and 40 wt.%). Two types of HA were used, which are needle shape (HAN) and irregular shape (HAS). The rheological behaviour of the PCL/HA composite was investigated through the melt flow index (MFI) test at a varied temperature of 100, 110, and 120 °C. The result indicated that an increase of HA content decreases the MFI values of the PCL/HA composite. At similar content of HA, PCL/HAN composite has higher activation energy with lower MFI values compared to PCL/HAS composite. In conclusion, this study concluded that the particle size, shape, and weight percentage of HA significantly affect the rheological behaviour of PCL/HA composites.

Physico-chemical properties and biocompatibility of in situ-hardening polylactide/nano hydroxyapatite composite for bone substitute

Polylactide (PLA) and hydroxyapatite (HA) composite is a promising material for biomedical applications. The bioresorbability and adequate strength of PLA in combination with the bioactivity of HA clearly provide prospective properties for resorbable bone substitute. The material, however, requires to be shaped prior to surgery, which impedes its practical use, particularly in complex shaped bone defects. In this study, a novel combination of star-shaped and linear PLA powder with various amounts of nano HA, and triethylene glycol dimethacrylate liquid was developed as an in situ forming cement for bone substitute. The effects of different amounts of initiator (0.5 and 1 wt%) and nano HA powder (5, 10, and 15 wt%) on various properties of the composite cement, including handling properties, degree of conversion, gel fraction, residual monomer toxicity and osteoblast differentiation were studied. The in vitro degradation was also examined in terms of weight and mechanical loss. The results demonstrated that the amount of initiator had a great effect on the handling properties of the cement, however, the HA content did not have any significant effect. The increasing HA content slowed down the degradation rate of the cement. All cement formulations in this study exhibited good network forming and ability to induce osteoblast differentiation with negligible residual monomer release to harm cells. The optimal cement formulation was found to be at 15 wt% HA, which allowed for in situ hardening with satisfactory biocompatibility and mechanical support for bone regeneration during deterioration.

Effect of hydroxyapatite content and particle size on the mechanical behaviors and osteogenesis in vitro of polyetheretherketone–hydroxyapatite composite

AbstractPoly‐ether‐ether‐ketone (PEEK) possesses excellent biocompatibility and similar elastic modulus as bones but suffers from poor osseointegration; usually, the addition of hydroxyapatite (HA) is considered as an effective way to improve the osseointegration of PEEK implant interface. To investigate the effect of HA content and particle size on the mechanical behaviors and osteogenesis in vitro of PEEK‐HA composites, the PEEK‐HA specimens with variable HA content and particle size have been fabricated by powder mixing‐heat press method and characterized by mechanical and biological tests. The results showed that the tensile/bending strength and elongation at break of PEEK‐HA are significantly impaired as the increasing HA amount, but the modulus improves. The compressive strength and modulus are improved as the increasing amount of HA. The PEEK‐HA with smaller HA particle size possesses higher‐performance tensile/bending and lower‐performance compressive properties. In osteogenesis tests in vitro, the results reveal that the cells amount attached on the substrate rises and the cells flatten more evenly with numerous cytoplasmic processes on greater area with the increasing HA content and decreasing particle size. The PEEK‐HA group that HA content is 20 wt% and particle size is 20 nm exhibits optimal‐performance osteogenesis in vitro, while maintaining sufficient mechanical properties.

Biodegradable polymer composites with osteogenic potential

The aim is to study the basic physico-mechanical properties of hydroxyapatite (HA) composites (up to 25–50 wt%) with polylactide (PLA-HA) and poly(e-caprolactone) (PCL-HA) prepared by melt compounding, as well as the osteogenic potential of PLA-HA in vivo . Materials and methods . All biodegradable polymer composites were prepared by hot melt compounding and studied by dielectric spectroscopy in frequency domain, optical microscopy, X-ray diffraction analysis and tensile tests. An ability of PLA-5 wt% HA composites prepared by 3D-printing to induce bone tissue growth in vivo was detected with the help of ectopic subcutaneous test in inbred mice. Results. Values of the real part of complex permittivity of PLA-HA and PCL-HA composites are increased by 15–30% compared to those for initial PLA and PCL, while tand loss factor does not exceed 0.02 for PLA-based composites and 0.2 for PCL-based composites. The crystallinity degree of PLA-HA composites is increased by 3 and 6 times with an increase of HA content from 25 to 50 wt% respectively compared to the indicator for PLA. The crystallinity degree of PCL-HA composites with 25 wt% HA is increased by 2 times compared to the value for PCL. It is due to the fact that HA powder particles play the role of additional nucleation centers. For all this, mechanical strength of composites diminished statistically. Even lowest HA content (5 wt%) in PLA-HA composites prepared by 3D-printing increased the incidence of ectopic osteogenesis by 40%. Conclusion. Designed biodegradable composites have a potential of practical use for bone tissue engineering.

Fabrication, characterization, dielectric properties, thermal stability, flame retardancy and transport behavior of chlorinated nitrile rubber/hydroxyapatite nanocomposites

This work focused on the preparation of chlorinated nitrile rubber (Cl-NBR)/hydroxyapatite (HA) nanocomposites by an open two-roll mixing mill. The formation of nanocomposites was characterized by Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The dielectric properties and flame retardancy of polymer nanocomposites were analyzed with special attention to the loading of HA nanoparticles. Diffusion and permeation properties of petroleum solvents through the prepared Cl-NBR/HA composites were also investigated in detail as a function of filler content, different temperatures and nature of solvent. The incorporation of HA in Cl-NBR has been endorsed by FTIR analysis. The XRD showed the crystalline peaks of HA in the polymer chain. SEM images revealed that the nanoparticles were uniformed distributed in the polymer network with spherically shaped particles. TGA results indicated that the thermal stability of nanocomposites was remarkably higher than the pure Cl-NBR and the thermal stability increases with the loading of nanoparticles. The dielectric study observed a decreasing dielectric constant with increasing frequency, and the maximum property was obtained for 7 phr HA filling in Cl-NBR. The flame resistance of the polymer composites was greatly enhanced by the incorporation of nanoparticles. The diffusion, sorption and permeation constants were found to decreased with increase in HA content. The solvent uptake decreases with the size of the penetrant molecules, and the mechanism of transport of Cl-NBR composite was anomalous in nature. The enthalpy and entropy changes of the nanocomposites were analyzed from the diffusion data. The composite containing 7 phr HA sample showed higher dielectric properties and better solvent resistance properties.

In Vitro Bioactivity Study of Thermoplastic Starch/Bentonite/Hydroxyapatite Composites for Biomedical Applications

Potato starch composites film incorporating hybrid bentonite and hydroxyapatite (HA) were investigated as novel biomaterial for potential biomedical applications. The selected potato starch/bentonite composites were prepared using different ratios of HA (1, 5 and 10 wt%) through solution casting technique. The in vitro bioactivity of potato starch composites film and neat potato starch film to be used as a control were evaluated through immersion in simulated body fluid (SBF) at 37°C for 14 days. The composites films were also subjected to characterization such as morphology, pH evaluation and biodegradability analyses following immersion in SBF. The obtained results showed that the incorporation of HA into starch/bentonite composites improves the bioactivity of the starch hybrid composites by formation of apatite layer on the surface. Increasing HA content in the composite is directly proportional to the quantity of the apatite formed on the scaffolds indicating active surface interactions between the composites and SBF. Furthermore, increasing HA content contributes also to lowering biodegradability of the composite decreases.

The Effect of Hydroxyapatite Prepared by In Situ Synthesis on the Properties of Poly(Vinyl Alcohol)/Cellulose Nanocrystals Biomaterial

Polyvinyl alcohol/cellulose nanocrystals (CNC) and hydroxyapatite (HA) (PCH) were combined using an in situ method to fabricate porous scaffolds. CNC was extracted from sugarcane bagasse and the effect of HA on PVA/CNC composites was varied with 0, 0.5, 1 and 3 wt%. The scanning electron microscopy images of the PCH composites showed interior pores with pore channels, while the energy dispersive spectroscopy (EDS) results confirmed the increased HA content in the nanocomposite with a Ca/P ratio of 1.67. Porosity and the equilibrium swelling ratio were slightly affected by the HA content. The Fourier transform infrared spectra supported the EDS results by identifying significant peaks belonging to the HA curves of the PCH composites. The crystallinity revealed decreased crystal regions at higher HA content, whereas the mechanical behavior showed the improvement at 0.5 wt% of HA. Cytotoxicity with L929 demonstrated the compatibility of the PCH composites, with 85 ± 0.92% cell viability.

The influence of hydroxyapatite content on properties of poly(L-lactide)/hydroxyapatite porous scaffolds obtained using thermal induced phase separation technique

In the research we obtained porous scaffolds based on poly(L-lactide) and synthetic hydroxyapatite (HA) using thermal induced phase separation technique (TIPS) supported by salt leaching process (SL). The obtained series of composite foams differ in hydroxyapatite content (10, 25, 50, 75, 90 wt% of the HA in PLLA/HA systems). The investigated scaffolds porosity ranged from 88 to 98%, density from 0.024 to 0.140 g/cm3. Water contact angle measurements indicated more hydrophilic scaffold surface with increasing hydroxyapatite content in the composites. Thermogravimetric analysis revealed higher thermal stability of all composites comparing to neat PLLA, indicated presence of ∼3 wt% residual sodium chloride in the scaffolds. Differential scanning calorimetry analysis showed nucleation effect of hydroxyapatite and higher crystallinity of PLLA in the composites as compared to the neat PLLA. The above tests were supplemented with compressive strength measurements, which showed an increase in the Young’s modulus and compressive stresses values parallelly with the increase of the filler content. Proliferation tests of MC3T3-E1 mouse calvaria pre-osteoblast cells indicated directly proportional relationship between hydroxyapatite content and cells proliferation rate.

Studies of Poly(L-lactic acid)/Hydroxyapatite Composites Through DSC and XRD

Poly(L-lactic acid) (PLLA) is important and biodegradable semi-crystalline polymer with promising application in industry. To estimate the effect of synthesized hydroxyapatite (HA) on the performance of PLLA, differential scanning calorimeter (DSC) and X-ray diffraction (XRD) were employed to investigate the crystallization of PLLA/HA composites. DSC showed that HA could accelerate the crystallization of PLLA, and the relationship between HA content and nucleation effect was not linear. However, 10 wt% HA had the best crystallization nucleation effect for PLLA. XRD analysis further confirmed the nucleation effect of HA, and there existed an interesting fact that the intensity of characteristic peak of PLLA/HA after isothermal became weak with an increase of HA content. XRD measurement for PLLA/0.5%HA after different isothermal temperatures showed that the crystallization temperature played important role in crystallization of PLLA.

Biomimetic hydroxyapatite/gelatin composites for bone tissue regeneration: Fabrication, characterization, and osteogenic differentiation in vitro

Herein, we prepared a series of novel hydroxyapatite (HA) nanowire and gelatin composite films with varying HA to gelatin ratios, attempting to simulate the major features of the natural extracellular matrix of bone. The results showed that the ratio of HA nanowires to gelatin had a great influence on the physicochemical and biological properties of the composites. The morphology of the HA/gelatin 7/3 composite film had a fibrous and porous architecture, while the 5/5 and 3/7 samples led to the formation of non-porous rough surfaces. Additionally, an increase in HA content enhanced the composite mechanical properties, with a maximum tensile strength of 114 ± 8 MPa, respectively. The HA/gelatin composite films exhibited good cell adhesion and proliferation. Osteogenic differentiation of mouse bone marrow mesenchymal stem cells on the 7/3 composite film was superior to that of the remaining films, as evident by alkaline phosphatase activity, calcium deposition, and gene expression. Thus, the HA/gelatin 7/3 composite film prepared herein has potential as a bone substitute for bone repair and regeneration.