Formation Of Calcium-deficient Hydroxyapatite Research Articles

One and two-step electrodeposition of composite films of calcium-deficient hydroxyapatite matrix with nanoscale Ag- and Zn-based particles

A fundamental study regarding the electrochemical synthesis of composite coatings with application in the orthopaedic field has been conducted. In particular, the electrodeposition of calcium phosphate coatings with Ag nanoparticles (AgNPs) from either a single electrolyte (one-step, 1S) or two electrolytes (two-step, 2S) on a β-Ti alloy (Ti-18Mo-6Nb-4Ta in wt%) was investigated. Pulse current deposition was implemented to produce the composite coatings by the 1S approach from a simple solution containing 42 mM Ca(NO3)2·4H2O, 25 mM NH4H2PO4, and 0.5 mM AgNO3 at 65°C. Meanwhile, the calcium phosphate matrix was also deposited by pulse current, and Ag was afterwards grown by direct current from 0.1 M KNO3 + x mM AgNO3 (x = 5, 10) at 25 °C (2S approach). The Ca/P ratio of the matrix was compatible with the formation of calcium-deficient hydroxyapatite (CDHA). The resulting Ag content in the composites could be varied between 4 and 13 wt% as a function of the working conditions. The 2S-derived coatings produced by electroplating Ag at j = –20.8 mA/cm2 from 0.1 M KNO3 + 10 mM AgNO3 furnished an optimal dispersion of the AgNPs on top of the CDHA matrix, while aggregation and/or dendritic growth was observed in other cases. Glow discharge optical emission spectrometry (GDOES) measurements indicated that a given amount of AgNPs becomes engulfed in the CDHA matrix during the 1S electrodeposition, whereas most of them decorate its outer surface in the 2S-derived coatings. The applicability of the two approaches was extended to the case of zinc oxide. ZnO-containing CDHA coatings in which the Zn element was homogeneously distributed across the film surface were obtained from 42 mM Ca(NO3)2·4H2O, 25 mM NH4H2PO4 and 1 mM Zn(NO3)2·6H2O at 65 °C (1S approach). On the contrary, ZnO-NPs could be clearly observed when deposition from 5 mM KNO3 + 5 mM Zn(NO3)2 was performed at 70 °C on top of previously grown CDHA (2S approach). The results indicated that the percentage and location of the antibacterial element (Ag, Zn) in the calcium phosphate matrix can be tuned on demand to a great extent by electrochemical means.

Solvothermal Synthesis of Calcium Hydroxyapatite via Hydrolysis of Alpha-Tricalcium Phosphate in the Presence of Different Organic Additives

In this study, the effects of sodium lauryl sulfate and various amino acids (DL-aspartic acid, dodecanedioic acid, and suberic acid) on the formation of calcium-deficient hydroxyapatite via hydrolysis of α-tricalcium phosphate (α-TCP) were investigated; moreover, a combined effect of these additives and ethylene glycol as a synthesis medium was also estimated. The hydrolysis reaction was performed in solutions containing different concentrations of additives in aqueous and mixed aqueous–organic media under solvothermal conditions. It was demonstrated that the nature and the concentration of organic additives influence the phase purity and morphology of the final product. Higher concentrations of sodium lauryl sulfate and dodecanedioic acid induced the formation of impurities in addition to hydroxyapatite, while aspartic and suberic acid did not affect the phase purity. The morphology of the samples varied from plate- to rod-like depending on the concentrations of specific organic additive.

Solvothermal Synthesis of Calcium-Deficient Hydroxyapatite via Hydrolysis of α-Tricalcium Phosphate in Different Aqueous-Organic Media

In the present work, the effects of various organic solvents (solvent nature and fraction within the solution) and solvothermal conditions on the formation of calcium-deficient hydroxyapatite (CDHA) via hydrolysis of α-tricalcium phosphate (α-TCP) are investigated. The wet precipitation method is applied for α-TCP synthesis, and the hydrolysis reaction is performed in solutions with different water-to-organic solvent ratios under solvothermal conditions at 120 °C for 3 h and at 200 °C for 5 h. Ethyl alcohol, isopropyl alcohol, and butyl alcohol did not inhibit the hydrolysis of α-TCP, while methyl alcohol and ethylene glycol have a more prominent inhibitory effect on the hydrolysis, hence the formation of single-phased CDHA. From all the solvents analysed, ethylene glycol has the highest impact on the sample morphology. Under certain water to ethylene glycol ratios and solvothermal conditions, samples containing a significant fraction of rods are obtained. However, samples prepared with ethylene glycol are characterised by a particularly low BET surface area.

Degradable calcium deficient hydroxyapatite/poly(lactic-glycolic acid copolymer) bilayer scaffold through integral molding 3D printing for bone defect repair

A novel method was developed for calcium deficient hydroxyapatite (CDHA) scaffold 3D printing, through which a bilayer scaffold was fabricated by the integral molding of individual CDHA and poly(lactic-glycolic acid copolymer) (PLGA). The hydration reaction of α-tricalcium phosphate (TCP) was utilized to form CDHA, and a mixed solution of gelatin, glycerine and glutaraldehyde was applied as the dispersant and adhesive. The concentration of the glutaraldehyde (1‰(v/v)) and the mixing ratio of α-TCP (0.6, 0.8, 1.0 and 1.2 g ml−1) were studied with regard to the effect on the forming ability of the CDHA ink. The influence of α-TCP proportion (0.6, 0.8, 1.0 and 1.2 g ml−1) on the formation of CDHA was also researched in phase analysis, morphology and compressive strength measurements. The CDHA/PLGA bilayer scaffold was fabricated with a good combination of the two components by 3D printing. The in vitro degradation, cytotoxicity and cell proliferation behavior were studied. Meanwhile, the in-vivo performances in terms of surgical safety, biodegradation and osteogenic capacity were investigated with a cortical bone defect model in a rabbit femur. The results showed that the CDHA/PLGA bilayer scaffold had excellent biocompatibility and no cytotoxicity. The scaffolds were successfully implanted and presented remarkable osteogenic capacity within 6 months through analyses in radiography and histology. In conclusion, the method has a potential clinical application in diverse bone repair practices by varied 3D-printing fabrication.

Antibiotic and anesthetic drug release from double-setting α-TCP cements

The alpha phase of tricalcium phosphate (α-TCP) can form calcium-deficient hydroxyapatite (CDHA), similar to bone hydroxyapatite. α-TCP can be employed as a biocompatible cement and used as a drug vehicle. Double-setting α-TCP cement composed of acrylamide (α-TCP DS) has better mechanical properties than traditional α-TCP cement. However, no studies on the use of α-TCP DS-based systems for drug release have been reported. In this study, we prepared α-TCP- and α-TCP DS-based samples containing gentamicin sulfate, lidocaine hydrochloride, bupivacaine hydrochloride and levobupivacaine hydrochloride. The properties of the samples were characterized, and the use of the samples as vehicles for these drugs was evaluated. The cements were characterized using X-ray diffraction, Fourier transform infrared spectroscopy, mechanical property tests and apparent porosity evaluation. The drug release in vitro was determined using ultraviolet–visible absorption spectroscopy. For statistical analysis, a confidence interval of 95% with a significance level < 5% was used. Neither the hydrogel nor the drugs interfered with the formation of CDHA, but they increased the mechanical strength of the studied cement. The Peppas–Sahlin model described the mechanisms involved in the drug-release kinetics process, revealing that Fickian diffusion was the main drug-release mechanism with a small influence from the Case II mechanism.

Manipulation of Mg2+-Ca2+ Switch on the Development of Bone Mimetic Hydroxyapatite.

Ionic substitution can affect essential physicochemical properties leading to a specific biological behavior upon implantation. Therefore, it has been proposed as a tool to increase the biological efficiency of calcium phosphate based materials. In the following study, we have evaluated the contribution of an important cation in nature, Mg2+, into the structure of previously studied biocompatible and biodegradable hydroxyapatite (HA) nanorods and its subsequent effect on its chemical, morphology, and bone mimetic articulation. Mg2+-substituted HA samples were synthesized by an aqueous wet-chemical precipitation method, followed by an hydrothermal treatment involving a Mg2+ precursor that partially replace Ca2+ ions into HA crystal lattice; Mg2+ concentrations were modulated to obtain a nominal composition similar to that exists in calcified tissues. Hydrothermally synthesized Mg2+-substituted HA nanoparticles were characterized by X-ray powder diffraction, FT-NIR and EDX spectroscopies, field emission scanning and high resolution transmission electron microscopies (FE-SEM, H-TEM). Molecular modeling combining ab initio methods and power diffraction data were also performed. Results showed that Mg2+-substitution promoted the formation of calcium deficient HA (cdHA) where Mg2+ replacement is energetically favored at Ca(1) position in a limited and specific amount directing the additional Mg2+ toward the surface of the crystal. The control of Mg2+ incorporation into HA nanorods gave rise to a tailored crystallinity degree, cell parameters, morphology, surface hydration, solubility, and degradation properties in a dose-replacement dependent manner. The obtained materials show qualities that conjugated together to drive an optimal in vitro cellular viability, spreading, and proliferation confirming their biocompatibility. In addition, an improved adhesion of osteoblast was evidenced after Mg2+-Ca2+ substitution.

Effect of substrate nature on the electrochemical deposition of calcium-deficient hydroxyapatites

Calcium phosphates were obtained by reducing nitrate ions to produce hydroxide ions on TiO2/stainless steel and TiO2/titanium electrodes. TiO2 coatings on metallic substrates were prepared by sol-gel dip-coating method. The morphology of deposits was observed by FESEM. Chemical nature of calcium phosphate deposits was identified by Raman micro-spectroscopy and FESEM/EDS microanalysis. Electrochemical behavior of nitrate and nitrite reduction on stainless steel and titanium electrodes was studied by linear sweep voltammetry. In addition, voltammetric study of the calcium phosphate electrodeposition on both electrodes was performed. From these measurements was selected the potential to form a calcium phosphate. A catalytic current associated to nitrate reduction reaction was obtained for stainless steel electrode, leading to significant deposition of calcium phosphate. Ca/P ratio for both substrates was less than 1.67. The formation of calcium deficient hydroxyapatite was confirmed by Raman spectroscopy.

Time Dependent Properties of Nanocomposite Hydroxyapatite Based Bone Cements

Calcium phosphate bone cements have gained significant scientific and commercial attention due to their outstanding biological properties. In this work the cement's paste prepared by mixing a-TCP with sodium phosphate solution and the final hardening occurred after immersion in Ringer's solution. Their internal structure evolution from the hydrolysis of a-TCP to the formation of calcium deficient hydroxyapatite was observed my scanning electron microscopy. Time temperature superposition principle was applied in order to investigate their time- and temperature dependent dynamic response. It was found that time temperature superposition can be applied with success and that the material dynamic stiffness is time-and temperature dependent. Also, a nanostructure of hydroxyapatitic platelets and needles evolves within ten days, after specimen immersion for maturing in a Ringer’s solution. The resulting nanostructure was verified by means of scanning electron microscopy and x-ray diffraction techniques.

Reaction kinetics of dual setting α-tricalcium phosphate cements.

Addition of ductile polymers to calcium-deficient hydroxyapatite (CDHA)-forming bone cements based on α-tricalcium phosphate (α-TCP) is a promising approach to improve the mechanical performance of α-TCP cements and extend their application to load-bearing defects, which is else impeded by the brittleness of the hardened cement. One suitable polymer is poly-(2-hydroxyethylmethacrylate) (p-HEMA), which forms during cement setting by radical polymerisation of the monomer. In this study the hydration kinetics and the mechanical performance of α-TCP cements modified with addition of different HEMA concentrations (0-50 wt% in the cement liquid) was investigated by quantitative in situ XRD and four-point bending tests. Morphology of CDHA crystals was monitored by scanning electron microscopy. The hydration of α-TCP to CDHA was increasingly impeded and the visible crystal size of CDHA increasingly reduced with increasing HEMA concentration. Modification of the cements by adding 50 wt% HEMA to the cement liquid changed the brittle performance of the hardened cement to a pseudoplastic behaviour, reduced the flexural modulus and increased the work of fracture, while lower HEMA concentrations had no significant effect on these parameters. In such a composite, the extent of CDHA formation was considerably reduced (34.0 ± 1.8 wt% CDHA with 50 % HEMA compared to 54.1 ± 2.4 wt% CDHA in the reference formed after 48 h), while the general reaction kinetics were not changed. In conclusion, while the extent of CDHA formation was decreased, the mechanical properties were noticeably improved by addition of HEMA. Hence, α-TCP/HEMA composites might be suitable for application in some load-bearing defects and have adequate properties for mechanical treatment after implantation, like insertion of screws.

Fluoridation of synthetic apatite: Effect on the formation of calcium-deficient hydroxyapatite and the properties of porous scaffold

Fluoridated apatite (FHA) has been considered as a promising bone substitute substance due to its promoting cell proliferation and osteoblastic activity. This paper reports on the synthesis of FHAs via chemical precipitation at room temperature with different KF additions. The prepared samples were characterized using various characterization methods. Both PO43- and HPO42- ions were found in Fourier transform infrared (FTIR) spectra. X-ray diffraction (XRD) results show that two kinds of CaHPO4•2H2O (DCPD1, DCPD2) mixed with FHA were present in the final products at the lower content of KF addition. However, the amount of DCPD decreased as the increment of KF added, which hints that fluoridation distinctly accelerates the reaction of transforming DCPD into FHA. Meanwhile, 31P magic angle spinning nuclear magnetic resonance (MAS NMR) spectra indicated that the electron density around P nuclei in FHAs changed with F content. The highly interconnected scaffold with small pores nesting inside large ones had been fabricated by using raw FHA powder and behaved in good bioactivity when examined in simulated body fluid (SBF).

Formation of Calcium-Deficient Hydroxyapatite via Hydrolysis of Nano-Sized Pure α-Tricalcium Phosphate

Nano-sized pure α-tricalcium phosphate (α-TCP) fabricated by a novel synthesis approach shows great potential for a faster transformation into calcium-deficient hydroxyapatite (CDHA) than conventionally prepared α-TCP. In this work, amorphous tricalcium phosphate precursors were precipitated and treated with a solvent (water or ethanol), and dried (freeze-dried and oven-dried) before heating at 775 °C. Nanosized α-TCP powders were investigated for their phase composition and crystallinity, particle shape and size, reactivity and cellular biocompatibility. Reaction with water showed faster CDHA formation for freeze-dried powder, at 6 hours, compared to ethanol treated powders, whereas a higher biocompatibility was found for pure α-TCP.

Injectable collagen/α-tricalcium phosphate cement: collagen–mineral phase interactions and cell response

A bone inspired material was obtained by incorporating collagen in the liquid phase of an α-tricalcium phosphate cement, either in solubilized or in fibrilized form. This material was able to set in situ, giving rise to a calcium deficient hydroxyapatite (CDHA)/collagen composite. The morphology and distribution of collagen in the composite was shown to be strongly affected by the collagen pre-treatment. The interactions between collagen and the inorganic phase were assessed by FTIR. A red shift of the amide I band was indicative of calcium chelation by the collagen carbonyl groups. The rate of CDHA formation was not affected when diluted collagen solutions (1 mg/ml) were used, whereas injectability improved. The presence of solubilized collagen, even in low amount (1 %), increased cell adhesion and proliferation on the composites. Still in the absence of osteogenic medium, significant ALP activity was detected both in the inorganic and the collagen-containing cements. The maximum ALP activity was advanced in the collagen-containing cement as compared to the inorganic cement.

Optimization of a biomimetic bone cement: Role of DCPD

We previously proposed a biomimetic α-tricalcium phosphate (α-TCP) bone cement where gelatin controls the transformation of α-TCP into calcium deficient hydroxyapatite (CDHA), leading to improved mechanical properties. In this study we investigated the setting and hardening processes of biomimetic cements containing increasing amounts of CaHPO 4·2H 2O (DCPD) (0, 2.5, 5, 10, 15 wt.%), with the aim to optimize composition. Both initial and final setting times increased significantly when DCPD content accounts for 10 wt.%, whereas cements containing 15 wt.% DCPD did not set at all. Differential scanning calorimetry (DSC), X-ray diffraction (XRD), thermogravimetry (TG) and scanning electron microscopy (SEM) investigations were performed on samples maintained in physiological solution for different times. DCPD dissolution starts soon after cement preparation, but the rate of transformation decreases on increasing DCPD initial content in the samples. The rate of α-TCP to CDHA conversion during hardening decreases on increasing DCPD initial content. Moreover, the presence of DCPD prevents gelatin release during hardening. The combined effects of gelatin and DCPD on the rate of CDHA formation and porosity lead to significantly improved mechanical properties, with the best composition displaying a compressive strength of 35 MPa and a Young modulus of 1600 MPa.

Development of Bacterial Cellulose Nanocomposites

ABSTRACTThe development of synthetic materials with inherent bone properties would allow the safe restoration of bone function and reduce current risks associated with the use of grafts. This study investigated the development of bacterial cellulose–hydroxyapatite composite (CdHA-BC) as a potential bone substitute material. Composites of bacterial cellulose (BC) and oxidized, degradable, cellulose (OBC) were mineralized by sequential incubation in calcium chloride and aqueous sodium phosphate to form a calcium deficient hydroxyapatite (CdHA). The CdHA produced in BC and OBC is similar in morphology and chemistry to the hydroxyapatite found in natural bone. The formation of CdHA is supported by XRD, and EDS results. The CdHA-BC and CdHA-OBC composites degrade in a simulated aqueous physiological environment.

Effect of ammonium carbonate on formation of calcium-deficient hydroxyapatite through double-step hydrothermal processing

Double-step hydrothermal processing is a process where powder compacts of calcium phosphates are exposed to vapor of solvent solution, followed by being immersed in the solution. In the present study, we investigated the effects of ammonium carbonate on formation of calcium-deficient hydroxyapatite (CDHA) through double-step hydrothermal processing. The synthesized CDHA has high crystallinity when the solution has relatively low concentration of the ammonium carbonate ranging from 0.01 to 0.25moldm(-3). Carbonate content in the prepared samples were distinctly increased with increasing the concentration of ammonium carbonate to indicate formation of carbonate-containing calcium-deficient hydroxyapatite (CHAp) with low crystallinity. Morphology of the CHAp formed on the compacts varied progressively from rods and rosette-like shape to irregular shape with increase in the initial concentration of the ammonium carbonate in the solution. Application of ammonium carbonate in the double-step hydrothermal processing allows fabrication of irregular-shaped CDHA containing carbonate ions in both phosphate and hydroxide site, with low crystallinity, when the initial concentration of ammonium carbonate was 0.5moldm(-3) and more.

ChemInform Abstract: Kinetics of Hydroxyapatite Formation at Low Temperature.

The influence of temperature on the kinetics of formation of calcium-deficient hydroxyapatite by an acid-base reaction has been determined. Calcium-deficient hydroxyapatite is compositionally similar to bone apatite. Reactants used in this study were tetracalcium phosphate, a calcium phosphate more basic than hydroxyapatite, and dicalcium phosphate, which is more acidic than hydroxyapatite. The kinetics of hydroxyapatite formation are initially controlled by the surface areas of the reactants; however, eventually the rate of hydroxyapatite formation becomes diffusionally controlled. The origin of diffusion control appears to be associated with the epitaxial formation of hydroxyapatite on the surface of the dicalcium phosphate reactant. The microstructure of hydroxyapatite formed at 5°, 15°, and 25°C were generally similar and are characterized by the formation of a porous acicular product which covers the surfaces of the reactants. The microstructure of the hydroxyapatite formed at 38°C was distinct from this and exhibited a pseudomorphic relationship with the dicalcium phosphate reactant. Seeding with hydroxyapatite accelerated the initial reaction but did not appear to have major long-term effects on the fractional degree of reaction or on microstructural development. Reaction was also accelerated in a neutral salt solution of high ionic strength.

Apatite formation in composites of α-TCP and degradable polyesters

The objective of this study was to investigate the conversion of α-Ca3(PO4)2 (α-TCP) in composite bone cements based on a water-degradable polyester matrix as a function of the polymer formulation and the α-TCP filler content. Cross-linkable dimethacrylates of ε-caprolactone/D,L-lactide co-polymer or of ε-caprolactone/glycolide co-polymer were mixed with hydroxyethyl-methacrylate, a photo-initiator and α-TCP to obtain composites with a filler content of 80 or 40 wt% α-TCP. The disk shaped composite samples were set by visible light irradiation and immersed in HEPES at 37°C. At selected times the samples were removed from the solution and analysed with X-ray diffractometry and infrared spectroscopy. Conversion of α-TCP into calcium-deficient hydroxy-apatite (CDHAp) was observed for all composites, but the reaction was not completed after 8 weeks immersion. The conversion rate of α-TCP and the crystallinity of the formed apatite apparently were not affected by the type of polyester used, but significantly depended on the α-TCP content of the composites. An increase of the amount of α-TCP in the composite resulted in a slower formation of CDHAp with a higher crystallinity.

Study of the reactivity and in vitro bioactivity of Sr-substituted α-TCP cements

In this study the effect of strontium substitution on the hydrolysis of alpha -tricalcium phosphate (alpha-TCP) toward the formation of calcium deficient hydroxyapatite (CDHA) was investigated. For that purpose substituted alpha-TCP powders with 1, 5 and 10 mol% Sr substitution for Ca were synthesized by reacting at 1500 degrees C stoichiometric amounts of CaCO(3), SrCO(3), and Ca(2)P(2)O(7), followed by rapid quenching in air. XRD analysis of the powders revealed the presence of alpha-TCP (traces of beta-TCP) with enlarged unit cell volume at increased Sr contents, indicating the incorporation of Sr in the crystal structure. Strontium was also incorporated in the apatite phase as revealed by XRD analysis of the set cements. The hydrolysis of milled alpha-SrTCP powders and a pure alpha-TCP (control) was monitored by isothermal calorimetry and the compressive strength of set cements was tested. The results showed a decrease in the reactivity with increasing Sr content and similar final mechanical strength within the Sr series, though lower than the control. The in vitro bioactivity of the set cements after soaking in simulated body fluid for 4 weeks was also tested. The formation of a bone-like apatite layer on the surface of the set cements indicated a potential in vivo bioactivity.

Calcium‐deficient hydroxyapatite‐PLGA composites: Mechanical and microstructural investigation

The microstructural and mechanical properties of composites composed of calcium deficient hydroxyapatite (CDHAp) and poly(lactide-co-glycolide) (PLGA) have been investigated. The composites were formed by hydrolysis of α-tricalcium phosphate (α-TCP) to CDHAp in pressed precomposite compacts of α-TCP-PLGA-NaCl. The differences in hydrolysis of α-TCP-PLGA-NaCl for two compositions of 80:10:10 wt % and 60:20:20 wt %. were monitored by isothermal calorimetry and X-ray diffraction. The microstructural evolution and variance in final composite microstructure after hydrolysis at 37°C, 45°C, and 56°C were examined by scanning electron microscopy. HAp–PLGA composite formed from the α-TCP-PLGA-NaCl (80:10:10) precomposites at 37°C developed a tensile strength of 13.3 ± 0.9 MPa, a flexural strength of 24.8 ± 1.7 MPa, and Young's modulus of 2.8 ± 0.3 GPa. These values were 12.00 ± 0.2 MPa, 36.1 ± 2.1 MPa, and 5.5 ± 0.8 GPa for the precomposite composition 60:20:20. All these mechanical properties showed a variation with hydrolysis temperature and composition. The differences in mechanical properties were related to the final microstructures of the composites, which are governed by the morphological changes in the polymer structure at its glass transition temperature and the extent of cement-type formation of CDHAp by hydrolysis of α-TCP. © 2000 John Wiley & Sons, Inc. J Biomed Mater Res, 51, 726–734, 2000.

Calcium-deficient hydroxyapatite-PLGA composites: mechanical and microstructural investigation.

The microstructural and mechanical properties of composites composed of calcium deficient hydroxyapatite (CDHAp) and poly(lactide-co-glycolide) (PLGA) have been investigated. The composites were formed by hydrolysis of alpha-tricalcium phosphate (alpha-TCP) to CDHAp in pressed precomposite compacts of alpha-TCP-PLGA-NaCl. The differences in hydrolysis of alpha-TCP-PLGA-NaCl for two compositions of 80:10:10 wt % and 60:20:20 wt %. were monitored by isothermal calorimetry and X-ray diffraction. The microstructural evolution and variance in final composite microstructure after hydrolysis at 37 degrees C, 45 degrees C, and 56 degrees C were examined by scanning electron microscopy. HAp-PLGA composite formed from the alpha-TCP-PLGA-NaCl (80:10:10) precomposites at 37 degrees C developed a tensile strength of 13.3 +/- 0.9 MPa, a flexural strength of 24.8 +/- 1.7 MPa, and Young's modulus of 2.8 +/- 0.3 GPa. These values were 12.00 +/- 0.2 MPa, 36.1 +/- 2.1 MPa, and 5.5 +/- 0.8 GPa for the precomposite composition 60:20:20. All these mechanical properties showed a variation with hydrolysis temperature and composition. The differences in mechanical properties were related to the final microstructures of the composites, which are governed by the morphological changes in the polymer structure at its glass transition temperature and the extent of cement-type formation of CDHAp by hydrolysis of alpha-TCP.