Decomposition Of Hydroxyapatite Research Articles

Bovine hydroxyapatite/3Y-TZP bioceramic: Aligning 3Y-TZP content with sintering parameters

This study aimed to produces and characterize bovine hydroxyapatite (HA) bioceramic with 3Y-TZP addition and analyze different sintering curves. HA was extracted from bovine bones and nanoparticulated. HA discs (0, 1, 5 and 10 wt% 3Y-TZP) were subjected to uniaxial and isostatic pressing. Dilatometry analysis was performed and the groups were sintered using 3 different firing curves (conventional, 1300 °C; 2-step, 1292 °C; 2-step, 1420 °C). The samples were analyzed by X-ray diffraction (XRD), biaxial flexural strength (BFS), Vickers microhardness (VH) and Field emission scanning electron microscopy (FE-SEM). The dilatometry results signaled the need for sintering optimization in groups added with 3Y-TZP. XRD demonstrated the characteristic crystallographic peaks of HA in the pure groups and with 1% 3Y-TZP, and decomposition of HA into β-TCP and formation of calcium zirconate in the groups with 5 and 10% 3Y-TZP. Considering each composition, the groups of pure HA (131.3 ± 13.5 MPa; 401 ± 12.7 GPa) sintered by the conventional curve and HA+1%3Y-TZP (145 ± 8.6 MPa; 507 ± 47.9 GPa), HA+5%3Y-TZP (68.1 ± 14.2 MPa; 183 ± 9.8 GPa) and HA+10%3Y-TZP (55.6 ± 5.1 MPa; 96.1 ± 7.64 GPa) sintered by the 2-step curve at 1420 °C, combined the best BFS and VH results. The addition of 1 wt% 3Y-TZP and optimization in the sintering process improved the mechanical and microstructural properties of HA bioceramics and maintenance of its crystalline characteristics. Refinement in material processing is necessary for the future use of this bioceramic in dentistry.

Strengthening bio-circularity by reinforcing waste derived triphasic calcium phosphate to fabricate alumina toughened zirconia biocomposite with enhanced bioactivity

Animal waste bone (AWB) is a significant component of food waste, generating millions of metric tons annually and posing environmental and economic challenges due to improper management. Despite its rich bioactive compound content, AWB is underutilized. To address these issues, we propose incorporating waste-derived calcium phosphate phases from AWB into an alumina toughened zirconia (ATZ) composite, forming a Hydroxyapatite/Tricalcium Phosphate/Whitlockite-ATZ biocomposite. The high-temperature treatment during ATZ consolidation promotes Hydroxyapatite (HAp) formation and decomposition of HAp to Tricalcium phosphate (TCP) phases. Trace amounts of magnesium in AWB aid in Whitlockite (Wk) formation. This triphasic material exhibits excellent biocompatibility and osteoconduction, suitable for bone regeneration. ATZ ensures mechanical stability and counters degradation of calcium phosphate phases. Although AWB incorporation reduces mechanical properties, the resulting ATZ-AWB biocomposite meets acceptable biomaterial standards. The present ATZ-AWB biocomposite possess bulk density, apparent porosity, hardness, and bending strength in the range of 3.7–5.2 g/cm3, 3.6–17%, 2–9 GPa and 620–1000 MPa respectively. AWB incorporation enhances bioactivity, as demonstrated by increased apatite layer formation in simulated body fluid (SBF). By fostering bioactivity, this approach not only tackles biocircularity but also offers economically accessible biomaterials, thereby advancing environmental sustainability and socioeconomic progress.

Unraveling the structural complexity of and the effect of calcination temperature on calcium phosphates derived from Oreochromis niloticus bones

In this study, the interplay between the structural complexity, microstructure, and mechanical properties of calcium phosphates (CaPs) derived from fish bones, prepared at various calcination temperatures, and their corresponding sintered ceramics was explored. Fourier-transform infrared analysis revealed that the calcined powders primarily consisted of hydroxyapatite (HAp) and carbonated calcium hydroxyapatite, with an increasing concentration of Mg-substituted β-tricalcium phosphate (β-TCP) as the calcination temperature was increased. X-ray diffraction patterns showed enhanced sharpness of the peaks at higher temperatures, indicating a larger crystallite size and improved crystallinity. The ceramics exhibited a significantly larger crystallite size and an increased concentration of the β-TCP phase. Rietveld analysis revealed a larger volume of the β-TCP phase in the ceramics than in their calcined powders; this could be attributed to a newly formed β-TCP phase due to the decomposition of HAp. Extended X-ray absorption fine structure analysis revealed the incorporation of Mg in the Ca2 site of HAp, Ca2 site of β-TCP, and Ca5 site of β-TCP, with a higher substitution of Mg in the Ca5 site of β-TCP at elevated temperatures. The mechanical properties of HAp ceramics can be improved by increasing the calcination temperature because of their improved relative density and dense porous structure at elevated temperatures. This comprehensive investigation sheds light on the phase evolution, microstructural changes, and consequential impact on the mechanical properties of CaPs derived from fish bones, thereby facilitating the development of tailored CaP ceramics for biomedical applications.

Synthesis of boronized Ti6Al4V/FHA composites by microwave sintering for dental applications

Boronized Ti6Al4V/FHA composites were prepared by microwave sintering of mixed powders of Ti6Al4V, TiB2, and synthesized fluorine-substituted hydroxyapatite (FHA) with variable compositions at 1050 °C for 30 min. The unique “lens effect” of microwave facilitated the in-situ transformation of nanoscale TiB2 into TiB, serving as the reinforcing phase within the composites. Increasing the theoretical fluorine substitution percentage of FHA from 0% to 50% caused less thermal decomposition of hydroxyapatite during sintering, promoting densification and thereby mechanical properties of the composites. However, elevating the substitution percentage to 100% led to excessive grain growth and FHA agglomeration, deteriorating the composite mechanical performance. The boronized Ti6Al4V/FHA composite produced using FHA with the theoretical fluorine substitution of 50% exhibited the highest compressive strength (397.7 MPa), proper compressive modulus (10.65 GPa) and maximum microhardness (385.3 HV). Furthermore, it showed excellent hydrophilicity and good cell adhesion, confirming its superior bioactivity for dental applications.

Microwave-assisted synthesis of composites based on titanium and hydroxyapatite for dental implantation.

Titanium (Ti) and its alloys are widely used in clinical practice. As they are not bioactive, hydroxyapatite (HA) is commonly used to modify them. This study offered a review of microwave-assisted synthesis of composites based on Ti and HA for dental implantation by exploring their interaction mechanisms with microwave and features of two main techniques, namely microwave coating and sintering, along with current challenges and potential solutions in the field. It was shown that microwave coating enables rapid deposition of HA, but suffers from problems such as uneven coating thickness, poor integrity and unstable composition of the products. They can be solved by creating interlayers, combining the spin coating technique, etc. Unlike microwave coating, microwave sintering can effectively modify the mechanical properties of the composites, despite the shortcomings of excessive elastic moduli and potential HA decomposition. These issues are expected to be addressed by adding alloying elements and employing appropriate materials as space holders and ion-doped HA for sintering.

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.

Influence of Titanium Dioxide Grain Size on Phasic Composition and Lysozyme Adsorption of Hydroxyapatite and Titanium Dioxide Composite Powders—A Thermal Decomposition Study by XRD and SEM Analysis

AbstractBiomedical applications make high demands on the development of novel bioactive materials, which are often based on functionalized calcium phosphates (CaPs). In this study, pure nanoscaled hydroxyapatite (HAp) and modified HAp with titanium dioxide (TiO2) with both nano‐ and microparticles are successfully synthesized from the reactants calcium hydroxide and orthophosphoric acid in a wet chemistry reaction. The obtained powders are sintered in a temperature range of 750 °C–1400 °C to study their thermal decomposition behavior. The phase composition and the surface morphology are characterized using X‐ray diffraction, scanning electron microscopy, and energy dispersive X‐ray spectroscopy with element mapping. Lysozyme adsorption experiments reveal significantly higher adsorption on the samples modified with nanoparticles. Sintered samples modified with both TiO2particle sizes show HAp decomposition to β‐tricalcium phosphate (β‐TCP) as well as the formation of perovskite (CaTiO3) in different portions depending on the TiO2particle size. TiO2nanoparticles support anatase to rutile transformation at lower temperatures than TiO2microparticles. The results show that the examined HAp/TiO2composites may serve as a starter material for tailormade biomaterials with specific composition by variation of the sintering temperature and the TiO2particle size.

Cold Spraying of Thick Biomimetic and Stoichiometric Apatite Coatings for Orthopaedic Implants

Ceramic coatings have a long history in the orthopaedic field, with plasma sprayed coatings of hydroxyapatite as leading standard in the manufacturing process; however, these coatings can contain secondary phases resulting from the decomposition of hydroxyapatite at high temperatures, which limit the lifetime of implants and their osseointegration. This work aims to produce coatings that can maximize bone osseointegration of metallic implants. In order to preserve the raw characteristics of hydroxyapatite powders that are thermally unstable, coatings were deposited by cold spray onto Ti6Al4V alloy substrates. In contrast with other thermal spray technologies, this process presents the advantage of spraying particles through a supersonic gas jet at a low temperature. On top of hydroxyapatite, carbonated nanocrystalline apatite was synthesized and sprayed. This biomimetic apatite is similar to bone minerals due to the presence of carbonates and its poor crystallinity. FTIR and XRD analyses proved that the biomimetic characteristics and the non-stoichiometric of the apatite were preserved in the cold spray coatings. The cold spray process did not affect the chemistry of the raw material. The adhesion of the coatings as well as their thicknesses were evaluated, showing values comparable to conventional process. Cold spraying appears as a promising method to preserve the characteristics of calcium phosphate ceramics and to produce coatings that offer potentially improved osseointegration.

Effect of 45S5 bioactive glass on the sintering temperature of titanium-hydroxyapatite composite

Titanium (Ti) is widely known for its good mechanical properties and corrosion resistance. However, it has poor biocompatibility. Hydroxyapatite (HA) is a biocompatible material but has poor mechanical properties. Making Ti-HA composite creates a promising choice of biomaterial in dental and medical applications. However, creating a Ti-HA composite requires sintering at high temperatures which leads to oxidation of Ti. The aim of this study was to reduce the sintering temperature of Ti-HA composite by incorporating 45S5 Bioactive Glass (BG) without compromising the chemical, physical and mechanical properties of the composite. In this study, a Ti-HA-BG composite with wt% of 45-45-10 respectively was produced via powder metallurgy. This was compared with the control composite consisting of 50 wt% Ti- 50 wt% HA. Powders according to the above-mentioned ratio were milled at 200 rpm for 5 hours by using a planetary ball milling machine. Samples were then compacted into cylindrical pellets via uniaxial pressing at 1500 psi and sintered in an atmospheric furnace at 1000 °C, 1100 °C and 1200 °C for 4 hours. Ti-HA and Ti-HA-BG sample characteristics were examined and compared by using Fourier Transformed Infrared Spectroscopy (FTIR), Energy Dispersive X-Ray (EDX) and X-Ray Diffraction (XRD). The density and volumetric expansion of the composites were also measured and compared. Results from XRD data indicate the reduction of oxidation of Ti and decomposition of HA in Ti-HA-BG composite at lower temperature in comparison to Ti-HA composite. The density of Ti-HA-BG composites are higher compared to Ti-HA composite while the volumetric expansion of Ti-HA-BG composites is lesser than Ti-HA composite. Therefore, BG is a low melting point additive that acts as a good sintering aid to effectively lower the sintering temperature while maintaining the desired properties of initial components.

Detonation Spraying of Hydroxyapatite on a Titanium Alloy Implant.

Hydroxyapatite (HA), the major mineral component of tooth enamel and natural bones, is a good candidate for bone tissue engineering. Synthetic HA is used for making coatings on metallic implants intended for medical applications. A HA coating renders the implant biocompatible and osteoinductive. In addition, it improves fixation and the overall performance of the implanted object. In the present work, HA coatings were deposited on a medical titanium alloy implant with mesh geometry and a developed surface by detonation spraying. The feedstock powder was HA obtained by the dry mechanochemical method. Single-phase HA coatings were obtained. The coatings were formed not only on the surfaces normal to the particle flow direction, but also on the sides of the mesh elements. Despite partial melting of the powder, no decomposition of HA occurred. This work demonstrates the prospects of detonation spraying for the production of HA coatings on metallic implants with complex geometries.

Selective Laser Melting of Ti6Al4V-2%Hydroxyapatite Composites: Manufacturing Behavior and Microstructure Evolution

In this work, selective laser melting of Ti6Al4V (Ti64) and 2 wt.% hydroxyapatite (HA) composites was performed with the purpose of osseointegration enhancement and biological fixation between implants and bone tissue. The microstructural evolution and mechanical properties were analyzed by using X-ray diffraction (XRD), optical microscopy (OM), a scanning electron microscope (SEM) equipped with (EDX) and (EBSD) systems, microhardness, nanoindentation, and tensile testing. The results showed that the Ti64-2%HA composite components exhibited complicated manufacturing behavior, which could be correlated with the decomposition of HA. The microstructure was found to mainly consist of α Ti with a small amount of HA distributed along grain boundaries. Furthermore, the interaction between Ti64 and HA leading to the formation of Ti3P, TixO, P, and CaTiO3 phases, resulted in poor tensile properties, as compared to pure Ti64 components. Conversely, the tensile properties of SLM Ti64-2%HA composite components were significantly higher than human bone reported previously in the literature.

Effect of pH level and calcination on the production of calcium phosphates by acidic route of wet precipitation

Multiphasic calcium phosphate powders were synthesized by the acidic route, using lactic acid as a chelating agent that allows the production of a stable and rich solution of calcium and phosphate ions at room temperature. After pH adjusting, without varying the concentrations of precursor solution, XRD and FTIR analyses showed different CaP phases before and after heat treatment at 1000 °C. At pH 5, brushite plate-like particles were produced, while at higher pH levels (7 to 12) nano-hydroxyapatite particles were formed. After the calcination process, partial and total decomposition of hydroxyapatite in the β-TCP phase was explained by XRF analysis due to the calcium-deficient hydroxyapatite of synthesized samples at pH 7 and 10. This work presents an important method to synthesize any desired CaP phase compositions by varying the pH level and subsequently performing heat treatment, which has a direct effect on morphology, crystallinity, and formation of different CaP powders.

The bioactivity of titanium-cuttlefish bone-derived hydroxyapatite composites sintered at low temperature

ABSTRACT The most limiting features of titanium as a bone substituent are lack of bioactivity and high Young’s modulus. We have prepared titanium-hydroxyapatite (Ti-HAp) composites using titanium hydride as sintering agent to provide titanium sintering at lower temperature and preserve the stability of apatite phase. After low temperature sintering, no hydroxyapatite decomposition was detected. Pure titanium samples sintered in the presence of hydride showed smooth surface indicating good densification at 800°C. Higher HAp content resulted in decreased density and higher porosity due to the formation of micro- and macro-pores caused by the integration of HAp particles into titanium matrix and titanium hydride decomposition. However, Vickers microhardness test showed increased hardness for Ti-HAp composite with 10% of HAp regarding pure Ti. The bioactivity of Ti-HAp composites evaluated in simulated body fluid significantly improved with HAp content. The presence of HAp has lowered the cytotoxic effect of Ti-based composites on Hek293 cells.

Sintering behavior, mechanical properties, and biocompatibility of TiO2–Co-calcium phosphates composites prepared by AROS process

TiO2–Co–hydroxyapatite (TCN–HA) powders, in which TCN prepared by an alloying–recomposition–oxidation–sintering process was mixed with HA (5–40 vol%), were sintered at 1100, 1200, 1300, and 1400 °C. Structural characterization was performed using X-ray diffraction, field-emission scanning electron microscopy, and energy-dispersive spectroscopy. The relative density (RD) of the sintered TCN–20HA increased until 1200 °C, followed by a rapid decrease at temperatures higher than 1300 °C. The density decrease at higher temperatures was related to the release of a large amount of H2O by the decomposition of hydroxyapatite (HA). The flexural strengths and fracture toughness of the TCN–HA samples with HA contents up to 20 vol% and Vickers hardness of all of the samples were higher than those of the pure TCN sample. The enhancements in their mechanical properties could be attributed to the higher densification. In a cytotoxicity test, the viabilities of cells cultured for 2 days on the TCN–HA samples were significantly increased for HA contents up to 20 vol% (p < 0.05). In addition, all of the samples with HA exhibited increased viabilities of cells cultured for 4 days. Therefore, the HA addition is effective for the enhancements in their mechanical properties and cell viability and proliferation with the culture time.

Strengthening iron enrichment and dephosphorization of high-phosphorus oolitic hematite using high-temperature pretreatment

The efficient development and utilization of high-phosphorus oolitic hematite is of great strategic significance for the sustainable supply of iron-ore resources in China. In this paper, the mechanism of high-temperature pretreatment for enhancing the effect of iron enrichment and dephosphorization in the magnetization roasting-leaching process was studied by X-ray diffraction (XRD), vibration sample magnetometer (VSM), scanning electron microscopy and energy dispersive spectrometry (SEM-EDS). Compared with the process without high-temperature pretreatment, the iron grade of the magnetic separation concentrate after high-temperature pretreatment had increased by 0.98%, iron recovery rate had increased by 1.33%, and the phosphorus content in the leached residue had decreased by 0.12%. High-temperature pretreatment resulted in the dehydration and decomposition of hydroxyapatite, the dehydration of limonite and the thermal decomposition of siderite, which can produce pores and cracks and weaken the compactness of the ore, improve the magnetization characteristics of roasted ore, and strengthen the iron enrichment and dephosphorization during the magnetization roasting and leaching process.

Indirect selective laser sintering-printed microporous biphasic calcium phosphate scaffold promotes endogenous bone regeneration via activation of ERK1/2 signaling

The fabrication technique determines the physicochemical and biological properties of scaffolds, including the porosity, mechanical strength, osteoconductivity, and bone regenerative potential. Biphasic calcium phosphate (BCP)-based scaffolds are superior in bone tissue engineering due to their suitable physicochemical and biological properties. We developed an indirect selective laser sintering (SLS) printing strategy to fabricate 3D microporous BCP scaffolds for bone tissue engineering purposes. The green part of the BCP scaffold was fabricated by SLS at a relevant low temperature in the presence of epoxy resin (EP), and the remaining EP was decomposed and eliminated by a subsequent sintering process to obtain the microporous BCP scaffolds. Physicochemical properties, cell adhesion, biocompatibility, in vitro osteogenic potential, and rabbit critical-size cranial bone defect healing potential of the scaffolds were extensively evaluated. This indirect SLS printing eliminated the drawbacks of conventional direct SLS printing at high working temperatures, i.e. wavy deformation of the scaffold, hydroxyapatite decomposition, and conversion of β-tricalcium phosphate (TCP) to α-TCP. Among the scaffolds printed with various binder ratios (by weight) of BCP and EP, the scaffold with 50/50 binder ratio (S4) showed the highest mechanical strength and porosity with the smallest pore size. Scaffold S4 showed the highest effect on osteogenic differentiation of precursor cells in vitro, and this effect was ERK1/2 signaling-dependent. Scaffold S4 robustly promoted precursor cell homing, endogenous bone regeneration, and vascularization in rabbit critical-size cranial defects. In conclusion, BCP scaffolds fabricated by indirect SLS printing maintain the physicochemical properties of BCP and possess the capacity to recruit host precursor cells to the defect site and promote endogenous bone regeneration possibly via the activation of ERK1/2 signaling.

Development of Triphasic Hydroxyapatite/(α and β)-Tricalcium Phosphate Based Composites by Sintering Powder of Calcium-Apatite in the Presence of Montmorillonite

In recent years, the development of calcium phosphate/clay composites for bone tissue engineering attracted a lot of interest. In this study, novel bio-composites composed of hydroxyapatite (HAP), α and β-tricalcium phosphate (α, β-TCP) and sodium-montmorillonite (MNa) were developed. The composites were prepared by sintering at 900 °C of calcium-apatite powders in the presence of various amounts of MNa. The calcium-apatite precursors were prepared by the wet precipitation method with two desired Ca/P molar ratios (1.660 and 1.623). Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) were used to characterize the prepared composites. The results showed that during the sintering process, a surface interaction apatite/MNa led to the incorporation of clay ions into the apatite structure resulting in its decomposition and formation of composite ceramics comprising HAP, β and α-TCP. The decomposition of apatite increased with increasing MNa content and with decreasing Ca/P ratio. The decomposition of stoichiometric HAP led to triphasic ceramics with substituted-HAP as the major phase while the decomposition of calcium-deficient HAP led to triphasic ceramics with substituted-α-TCP as the major phase. Combination of MNa–clay phase and substituted-α-TCP can improve both mechanical and biological properties of the prepared composites.

Modeling and optimization of combustion synthesis for hydroxyapatite production

In this study, the combustion synthesis of hydroxyapatite was studied and optimized under controlled experimental conditions. The hydroxyapatite content, crystallinity and crystallite size were monitored under changes in type of fuel, pH or red/ox ratio, muffle temperature, and reaction time. The products were characterized by X-ray diffraction, refinement of crystalline phases by the Rietveld method, scanning electron microscopy, and infrared spectroscopy with the Fourier transform. The decomposition of hydroxyapatite, which was the major phase, produced beta tricalcium phosphate in all samples, as indicated by their diffractograms. Infrared spectroscopy analysis revealed the presence of b-type carbonate groups in the structure; thus, the synthesized compound has the following chemical formula: Ca10-x (PO4)6-x (CO3)x (OH)2-x, where 0 < x < 2, which corresponds to carbonated hydroxyapatite (CHAp). The combustion process was modeled using a first-degree polynomial, and we found that the interaction between time and temperature to be the most influential parameter. Optimization indicated that processing conditions at 650 °C for 30 min, using urea at pH = 2 and ϕe = 1.134, produced the best result in terms of HAp composition, yielding 89.25% wt.

Preparation of silicon coated-carbon fiber reinforced HA bio-ceramics for application of load-bearing bone

To facilitate the optimal application of carbon fiber (CF) reinforced hydroxyapatite (HA) bio-ceramics as load-bearing bone substitutes, we adopted the magnetron sputtering method to prepare a Si coating on CF surface and then prepared Si-coated CF (Si-CF) with controllable alignment reinforced HA composites via pressureless and hot-press sintering. CFs were evenly distributed in the HA matrix according to the designed layers and alignment states using a special mold and technology. The results showed that uniform and continuous Si coatings with a thickness of approximately 0.2 μm covered the surface of CF. The bending strength of three-layer Si-CF reinforced HA (3Si-CF/HA) bio-ceramics fabricated by pressureless sintering was 33 MPa, which is 45% higher than that of three-layer CF reinforced HA (3CF/HA) bio-ceramics. Three-layer Si-CF reinforced HA bio-composites fabricated by hot-press sintering (H/Si-CF/HA) had a bending strength of 80.9 MPa, which is more than five times that of 3CF/HA bio-ceramics. The corresponding fracture toughness of H/Si-CF/HA was 2.53 MPa m1/2, which is 27.14% higher than that of 3Si-CF/HA composites. Compared with CF reinforced by HA, Si-coated CF could reduce the contact between CF and the O2 produced by the decomposition of HA. The chemical reaction between Si and O2 produces SiO2. The barrier layer provided by the Si and SiO2 coatings can prevent oxidative damage of CF during sintering and maintain the original reinforcing and toughening effects of CF. Axial pressure strengthened the bond between CF and the HA matrix in the H/Si-CF/HA composites sintered at high temperature. The pores and activated grain boundaries of the composites were reduced, and their degree of densification was improved. Therefore, the bending strength and fracture toughness of H/Si-CF/HA composites were improved and are able to satisfy the requirements of load-bearing bones.

Structure, mechanical and bioactive properties of nanostructured hydroxyapatite/titania composites prepared by microwave sintering

In order to improve the properties of hydroxyapatite (HA), HA/TiO2 composites with different TiO2 addition contents were prepared by microwave sintering. Effects of sintering temperature and TiO2 addition on phase composition, microstructure, mechanical properties and bioactivity were investigated. HA/TiO2 mixtures were prepared by the hydrolysis of tetrabutyl titanate (TBT) in HA particles suspension, which presented high specific surface areas and amorphous TiO2 phase. Compared to no phase change for pure HA, TiO2 addition promoted the HA decomposition by their mutual chemical reactions depending on the sintering temperature and TiO2 content. The sintering behavior of HA/TiO2 composites was also discussed in term of sintering temperature and TiO2 addition content. Ti atoms were uniformly dispersed in the HA/TiO2 composites with the formation of gradual Ti rich particles. TiO2 addition enhanced the sintering ability of HA powders, and HA/TiO2 composites exhibited densifications and fine grains at elevated temperature due to the nanosized raw powders and limited atomic diffusions induced by short sintering durations and byproduct suppressions. The sintering temperature can play a great effect on the microhardness and elastic modulus. New apatite was formed on the surfaces of HA/TiO2 composites after immersion in simulated body fluid, which indicates high bioactivities for composites prepared by microwave sintering.