Characteristic and in vitro bioactivity of a microarc-oxidized TiO(2)-based coating after chemical treatment

Microarc oxidation (MAO) was used to prepare a TiO(2)-based coating containing Ca and P on titanium alloy. An alkali treatment was developed to modify the surface of the MAO coating to improve the apatite-forming ability of the coating. The chemically treated MAO coating exhibits a modified layer, with the main constituents being O, Ti, Ca and Na, showing anatase. The modified MAO coating shows a rough and porous morphology containing numerous nanoflakes of approximately 100nm thickness. During the alkali treatment process, P on the surface of the MAO coating shows a main dynamic process of dissolution; however, Ca exhibits a re-deposition process as well as dissolution. The formation of the modified layer could be explained by this mechanism: negatively charged HTiO(3)(-) ions are formed on the MAO coating due to the attack of OH(-) ions on the TiO(2) phase. The HTiO(3)(-) ions could incorporate sodium from the alkali solution and calcium from the alkali solution and MAO coating. The apatite-forming ability of the MAO coating is improved remarkably by the simple chemical treatment, since the surface of the alkali-treated MAO coating could provide abundant Ti-OH groups probably formed by ionic exchanges between (Ca2+, Na+) ions of the alkali-treated MAO coating and H3O+ ions of a simulated body fluid (SBF). Moreover, Ca released from the alkali-treated MAO coating increases the degree of supersaturation of SBF, promoting the formation of apatite. The apatite induced by the alkali-treated MAO coating possesses carbonated structure and pore networks on the nanometer scale.     

Biomimetic deposition of apatite coating on surface-modified NiTi alloy

TiO(2) coatings were prepared on NiTi alloy by heat treatment in air at 300, 400, 600 and 800 degrees C. The heat-treated NiTi alloy was subsequently immersed in a simulated body fluid for the biomimetic deposition of the apatite layer onto the surface of TiO(2) coating. The apatite coatings as well as the surface oxide layer on NiTi alloy were characterized using scanning electron microscopy equipped with energy dispersive spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy. Results showed the samples heat-treated at 600 degrees C produced a layer of anatase and rutile TiO(2) on the surface of NiTi. No TiO(2) was detected on the surface of NiTi after heat treatment at 300 and 400 degrees C by X-ray diffraction, while rutile was formed on the surface of the 800 degrees C heat-treated sample. It was found that the 600 degrees C heat-treated NiTi induced a layer consisted of microcrystalline carbonate containing hydroxyapatite on its surface most effectively, while 300 and 400 degrees C heat-treated NiTi did not form apatite. This was due to the presence of anatase and/or rutile in the 600 and 800 degrees C heat-treated NiTi which could provide atomic arrangements in their crystal structures suitable for the epitaxy of apatite crystals, and anatase had better apatite-forming ability than rutile. XPS and Raman results revealed that this apatite layer was a carbonated and non-stoichiometric apatite with Ca/P ratio of 1.53, which was similar to the human bone. The formation of apatite on 600 degrees C heat-treated NiTi following immersion in SBF for 3 days indicated that the surface modified NiTi possessed excellent bioactivity.     

Surface structure and apatite-forming ability of polyethylene substrates irradiated by oxygen cluster ion beams

Polyethylene (PE) substrates were irradiated at a dose of 1 x 10(15) ions/cm(2) by the simultaneous use of oxygen (O(2)) cluster and monomer ion beams. The acceleration voltage for the ion beams was varied from 3 to 9 kV. Unirradiated and irradiated PE substrates were soaked for 7 days in a metastable calcium phosphate solution (1.5SBF) that had 1.5 times the ion concentrations of a normal simulated body fluid. The irradiated PE substrates formed apatite on their surfaces, irrespective of the acceleration voltage, whereas unirradiated substrates did not form apatite. This is attributed to the formation of functional groups that are effective for apatite nucleation, such as --COOH groups, on the substrate surface by the simultaneous use of O(2) cluster and monomer ion beams. The apatite-forming ability of the irradiated PE substrates was improved greatly by a subsequent CaCl(2) solution treatment. This suggests that Ca(2+) ions introduced on the substrate surface by the CaCl(2) solution treatment accelerated the apatite nucleation. It is concluded that apatite-forming ability can be induced on the surface of PE by the simultaneous use of O(2) cluster and monomer ion beams.     

Synergistic effect of silanol group and calcium ion in chitosan membrane on apatite forming ability in simulated body fluid

A chitosan membrane modified with silanol groups and calcium ions on its surface and in its structure, respectively, was newly developed and evaluated for the potential application as a bioactive-guided bone-regeneration membrane. The chitosan membrane, which contained calcium nitrate tetrahydrate, was prepared and further subjected to surface modification with 3-isocyanatopropyl triethoxysilane (IPTS) following hydrolysis with HCl solution. As control, chitosan membranes which contained only calcium nitrate tetrahydrate and modified with only silanol groups were prepared, respectively. Three membranes were exposed to simulated body fluid (SBF) for a period ranging from 3 h to 7 days. The SBF exposure led to the deposition of a layer of apatite crystals on the surface of the chitosan membrane modified with silanol groups and calcium ions, while those modified with only calcium ions or silanol groups did not show the apatite-forming ability. It implies that the silanol groups and calcium ion acted together in a synergistic fashion in the formation of apatite crystals; the silanol groups and calcium ions acted as the nucleation sites and accelerator for the formation of apatite crystals, respectively. Therefore, this new chitosan membrane is likely to have a potential for the application as a bioactive guided bone regeneration membrane because of its apatite-forming ability in the SBF.     

Mechanism and kinetics of apatite formation on nanocrystalline TiO2 coatings: a quartz crystal microbalance study

Apatite (Ca5(PO4)3OH) has long been considered as an excellent biomaterial to promote bone repairs and implant. Apatite formation induced by negatively charged nanocrystalline TiO2 coatings soaked in simulated body fluid (SBF) was investigated using in situ quartz crystal microbalance (QCM), scanning electron microscopy (SEM), Fourier-transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDX) techniques, and factors affecting its formation such as pH, size of TiO2 particles and thickness of TiO2 coatings, were discussed in detail. Two different stages were clearly observed in the process of apatite precipitation, indicating two different kinetic processes. At the first stage, the calcium ions in SBF were initially attracted to the negatively charged TiO2 surface, and then the calcium titanate formed at the interface combined with phosphate ions, consequently forming apatite nuclei. After the nucleation, the calcium ions, phosphate ions and other minor ions (i.e. CO3(2-) and Mg2+) in supersaturated SBF deposited spontaneously on the original apatite coatings to form apatite precipitates. In terms of the in situ frequency shifts, the growth-rate constants of apatite (K1 and K2) were estimated, respectively, at two different stages, and the results were (1.96+/-0.14)x10(-3)s(-1) and (1.28+/-0.10)x10(-4)s(-1), respectively, in 1.5 SBF solution. It was found that the reaction rate at the first stage is obviously higher than that at the second stage.     

Synthesis of osteoconductive organic inorganic nanohybrids through modification of chitin with alkoxysilane and calcium chloride

The so-called bioactive ceramics have been attractive because they spontaneously bond to living bone. Organic-inorganic hybrids consisting of organic polymers and the essential constituents of the bioactive ceramics, i.e., silanol (Si-OH) group and calcium ions (Ca(2+)), are useful as novel bone substitutes, owing to bioactivity and high flexibility. In the present study, organic-inorganic hybrids are synthesized from chitin by modification with glycidoxypropyltrimethoxysilane (GPS) and calcium chloride (CaCl(2)). Their apatite-forming ability is examined in a simulated body fluid (SBF). The prepared hybrids form apatite on their surfaces in SBF within 7 days.     

Mechanism of apatite formation on wollastonite coatings in simulated body fluids

The formation mechanism of apatite on the surface of wollastonite coating was examined. Plasma-sprayed wollastonite coatings were soaked in a lactic acid solution (pH=2.4) to result in the dissolution of calcium from the coating to form silanol (triple bond Si-OH) on the surface. Some calcium-drained samples were soaked in a trimethanol aminomethane solution (pH=10) for 24h to create a negatively charged surface with the functional group (triple bond Si-O(-)). These samples before and after treatment in a trimethanol aminomethane solution were immersed in simulated body fluids (SBF) to investigate the precipitation of apatite on the coating surface. The results indicate that the increase of calcium in the SBF solution is not the critical factor affecting the precipitation of apatite on the surface of the wollastonite coating and the apatite can only form on a negatively charged surface with the functional group (triple bond Si-O(-)). The mechanism of apatite formation on the wollastonite coating is proposed. After the wollastonite coatings are immersed into the SBF, calcium ions initially exchange with H(+) leading to the formation of silanol (triple bond Si-OH) on the surface of the layer and increase in the pH value at the coating-SBF interface. Consequently, a negatively charged surface with the functional group (triple bond Si-O(-)) forms on the surface. Due to the negatively charged surface, Ca(2+) ions in the SBF solution are attracted to the interface between the coating and solution, thereby increasing the ionic activity of the apatite at the interface to the extent that apatite precipitates on the coating surface.     

A comparative study between in vivo bone ingrowth and in vitro apatite formation on Na2O-CaO-SiO2 glasses

This study compared in vivo bioactivity with the in vitro apatite-forming ability of biomaterials. Granules of five kinds of P(2)O(5)-free Na(2)O-CaO-SiO(2) glasses, showing different apatite-forming ability in simulated body fluid (SBF), were implanted into a defect on the femoral condyle of rabbits. Bone ingrowth was evaluated using scanning electron microscopy among five kinds of glasses at 1, 2, 3, 6, and 12 weeks. Quantitative analysis was performed measuring the depth of new bone ingrowth from the periphery. In addition, the total areas of newly formed bone among glass particles were examined at 3 and 6 weeks using confocal laser scanning microscopy (CLSM) after weekly administration of fluorescent calcein. The depth of bone ingrowth among glass particles increased in proportion to their apatite-forming ability in vitro. The CLSM study showed a correlation between the quantities of labeled newly formed bone and in vitro apatite-forming ability. In the P(2)O(5)-free Na(2)O-CaO-SiO(2) glasses, the periods within 3-6 days for inducing apatite in SBF considered a necessary condition to convey bioactivity in vivo, and in vivo evaluations at 2-3 weeks is important to determine this. The in vivo bioactivity was precisely reproduced by apatite-forming ability in SBF. Therefore, evaluating apatite formation in SBF is a good screening test for the in vivo bioactivity of materials, resulting in reduction of the need for animal sacrifices and savings in experimental time.     

UV-enhanced bioactivity and cell response of micro-arc oxidized titania coatings

Using ultraviolet (UV) irradiation of micro-arc oxidized (MAO) titania coating in distilled water for 0.5 and 2h, we have achieved an enhanced bioactivity and cell response to titania surface. The MAO coating appears porous and predominantly consists of nanocrystallized anatase TiO(2). Compared with the MAO coating, the UV-irradiated coatings do not exhibit any obvious change in surface roughness, morphology, grain size and phase component; however, they have more abundant basic Ti-OH groups and become more hydrophilic because the water contact angle decreases significantly from 17.9+/-0.8 degrees to 0 degrees . In simulated body fluid (SBF), bonelike apatite-forming ability is significantly stronger on the UV-irradiated coatings than the MAO coating. SaOS-2 human osteoblast-like cell attachment, proliferation and alkaline phosphatase of the cell are greater on the UV-irradiated coatings relative to the MAO coating. UV irradiation of titania results in the conversion of Ti(4+) to Ti(3+) and the generation of oxygen vacancies, which could react with the absorbed water to form basic Ti-OH groups. The enhanced bioactivity and cell response of the UV-irradiated coatings are proven to result from abundant Ti-OH groups on the coating surfaces. After storing the UV-irradiated coatings in the dark for two weeks, the basic Ti-OH groups on the coatings slightly decrease in amount and can induce apatite formation after a short period of SBF immersion, and show relative long-term stability.     

Formation of bone-like apatite on poly(L-lactic acid) fibers by a biomimetic process.

Bone-like apatite coating on poly(L-lactic acid) (PLLA) fibers was formed by immersing the fibers in a modified simulated body fluid (SBF) at 37 degrees C and pH 7.3 after hydrolysis of the fibers in water. The ion concentrations in SBF were nearly 1.5 times of those in the human blood plasma. The apatite was characterized by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), thin-film X-ray diffraction, and Fourier transform infrared spectroscopy. After 15 days of incubation in SBF, an apatite layer with about 5-6 microm thickness was formed on the surface of the fibers. This apatite had a Ca/P ratio similar to that of natural bone. The mass of apatite coated PLLA fibers increased with extending the incubation time. After 20 days incubation, the fibers increased their mass by 25.8 +/- 2.1%. The apatite coating had no significant effect on the tensile properties of PLLA fibers. In this article, the bone-like apatite coating on three-dimensional PLLA braids was also studied. The motivation for this apatite coating was that it might demonstrate enhanced osteoconductivity in the future studies when they serve as biodegradable scaffolds in tissue engineering.     

Induction of bioactivity on silicone elastomer by simultaneous irradiation of oxygen cluster and monomer ion beams

Silicone elastomer substrates were irradiated with acceleration voltages ranging from 3 to 9 kV and doses ranging from 1 x 10(14) to 2.5 x 10(15) ions cm(-2) by the simultaneous use of oxygen cluster and monomer (O(2) CM) ion beams, and then soaking in CaCl(2) solution. The apatite-forming ability of the substrates was examined using a metastable calcium phosphate solution that had 1.5 times the ion concentrations of normal simulated body fluid (1.5SBF). Silicon oxide clusters (SiO(x)) were formed at the silicone elastomer surfaces and the hydrophilicity of the substrates was remarkably improved by the irradiation. The irradiated silicone elastomer substrates formed apatite in 1.5SBF, whereas unirradiated ones did not. These results suggest that irradiation using O(2) CM ion beams is effective for inducing an apatite-forming ability on silicone elastomer substrates.     

In vitro bioactivity and osteoblast response of porous NiTi synthesized by SHS using nanocrystalline Ni-Ti reaction agent

Porous NiTi with an average porosity of 55 vol % and a general pore size of 100-600 microm was synthesized by self-propagating high temperature synthesis (SHS) with the addition of mechanically alloyed nanocrystalline Ni-Ti as the reaction agent. The SHS of porous NiTi using elemental powders was also performed for comparison. To enhance the bioactivity of the metal surface, porous NiTi synthesized by nanocrystalline Ni-Ti was subjected to chemical treatment to form a layer of TiO(2) coating. The porous NiTi with TiO(2) coating was subsequently immersed in a simulated body fluid (SBF) to investigate its apatite forming ability. The effects of the addition of nanocrystalline Ni-Ti as reaction agent and the application of apatite coating on osteoblastic behavior were studied in primary cultures of human osteoblast cells. Results showed that the main phases in porous NiTi synthesized by elemental powders were NiTi, Ti(2)Ni, and unreacted free Ni. By using nanocrystalline Ni-Ti as reaction agent, the secondary intermetallic phase of Ti(2)Ni was significantly reduced and the free Ni was eliminated. TiO(2) coating with anatase phase was formed on the surface of porous NiTi after the chemical treatment. A layer consisting of nanocrystalline carbonate-containing apatite was formed on the surface of TiO(2) coating after soaking in SBF. The preliminary cell culture studies showed that the porous NiTi synthesized with the addition of nanocrystalline Ni-Ti attracted marked attachment and proliferation of the osteoblast cells. This gives the evidence of the potential biomedical applications of the porous NiTi.     

Preparation of bioactive Ti-15Zr-4Nb-4Ta alloy from HCl and heat treatments after an NaOH treatment

Ti-15Zr-4Nb-4Ta alloy does not contain any cytotoxic elements and has a high mechanical strength. Water or HCl and heat treatments were applied to this alloy after NaOH treatment to form a bioactive titanium oxide layer with a nanometer scale roughness on its surface. The nanometer scale roughness was formed on the surface after the first NaOH treatment and remained, even after a subsequent water or HCl and heat treatment. A layer that was mainly composed of anatase was formed on the surface after the heat treatment. Thus, the treated alloy showed a high apatite-forming ability in an SBF, as well as a high scratch resistance. Its high apatite-forming ability was attributed to its positive surface charge. The same alloy subjected to a heat treatment without a water or HCl treatment after the NaOH treatment did not show an apatite-forming ability. This was attributed to a too slow release rate of sodium ions from the surface in an SBF. Ti-15Zr-4Nb-4Ta alloy samples subjected to a water or HCl and heat treatment after the NaOH treatment are expected to be useful as orthopedic and dental implants, since they can form an apatite layer on their surface in a living body and bond to living bone through this apatite layer.     

Apatite-forming ability and mechanical properties of PTMO-modified CaO-SiO2 hybrids prepared by sol-gel processing: effect of CaO and PTMO contents

Transparent monolithics of triethoxysilane end-capped poly(tetramethylene oxide) (Si-PTMO)-modified CaO-SiO2 hybrids were successfully synthesized by hydrolysis and polycondensation of Si-PTMO, tetraethoxysilane (TEOS) and calcium nitrate. As for the samples with varying (Ca(NO3)2)/(TEOS) molar ratios under constant ratio of (Si-PTMO)/(TEOS) of 2/3 in weight. the apatite-forming ability in a simulated body fluid (SBF) which is indicative of bioactivity. remarkably increased with increasing CaO content, although the tensile strength and Young's modulus decreased. The hybrid with (Ca(NO3)2)/(TEOS) = 0.15 in mol formed an apatite on its surface within only 1 day. For this series of samples, the strain at failure which is a measure of capability for deformation of material, was found to be about 30% and almost independent of CaO content. As for the samples with varying (Si-PTMO)/(TEOS) weight ratios under constant ratio of (Ca(NO3)2)/(TEOS) of 0.15 in mol, the strain at failure increased with increasing Si-PTMO content, but the apatite-forming ability, tensile strength and Young's modulus decreased. Thus, the synthesis of the hybrids exhibiting both high apatite-forming ability and high extensibility can be achieved by selecting suitable CaO and Si-PTMO contents. These new kind of hybrid materials may be useful as bioactive bone-repairing materials.     

Mechanism of bonelike apatite formation on bioactive tantalum metal in a simulated body fluid.

Development of tantalum metal with bone-bonding ability is paid much attention because of its attractive features such as high fracture toughness, high workability and its achievement on clinical usage. Formation of bonelike apatite is an essential prerequisite for artificial materials to make direct bond to living bone. The apatite formation can be assessed in vitro using a simulated body fluid (SBF) that has almost equal compositions of inorganic ions to human blood plasma. The present authors previously showed that the apatite formation on tantalum metal in SBF was remarkably accelerated by treatment with NaOH aqueous solution and subsequent firing at 300 degrees C, while untreated tantalum metal spontaneously forms the apatite after a long soaking period. The purpose of the present study is to clarify the reason why the NaOH and heat treatments accelerate the apatite formation on tantalum metal. X-ray photoelectron spectroscopy was used to analyze changes in surface structure of the tantalum metal at an initial stage after immersion in SBF. Untreated tantalum metal had tantalum oxide passive layer on its surface, while amorphous sodium tantalate was formed on the surface of the tantalum metal by the NaOH and heat treatments. After soaking in SBF, the untreated tantalum metal sluggishly formed small amount of Ta-OH groups by a hydration of the tantalum oxide passive layer on its surface. In contrast, the treated tantalum metal rapidly formed Ta-OH groups by exchange of Na+ ion in the amorphous sodium tantalate on its surface with H3O+ ion in SBF. Both the formed Ta-OH groups combined with Ca2+ ion to form a kind of calcium tantalate, and then with phosphate ion, followed by combination with large amount of Ca2+ ions and phosphate ions to build up apatite layer. The formation rate of Ta-OH groups on the treated tantalum metal predominates the following process including adsorption of Ca2+ ion and phosphate ion on the surface. It is concluded that the acceleration of the apatite nucleation on the tantalum metal in SBF by the NaOH and heat treatments was attributed to the fast formation of Ta-OH group, followed by combination of the Ta-OH groups with Ca2+ and phosphate ions.     

Controlled release of strontium ions from a bioactive Ti metal with a Ca-enriched surface layer

A nanostructured sodium hydrogen titanate layer ∼1 μm in thickness was initially produced on the surface of titanium metal (Ti) by soaking in NaOH solution. When the metal was subsequently soaked in a mixed solution of CaCl₂ and SrCl₂, its Na ions were replaced with Ca and Sr ions in an Sr/Ca ratio in the range 0.18–1.62. The metal was then heat-treated at 600 °C to form strontium-containing calcium titanate (SrCT) and rutile on its surface. The treated metal did not form apatite in a simulated body fluid (SBF) even after 7 days. When the metal formed with SrCT was subsequently soaked in water at 80 °C, the treated metal formed bone-like apatite on its surface within 1 day in SBF since the Ca ions were partially replaced with H₃O⁺ ions. However, it released only 0.06 ppm of Sr ions even after 7 days in phosphate-buffered saline. When the metal was soaked after the heat treatment in 1 M SrCl₂ solution instead of water, the treated metal released 0.92 ppm of Sr ions within 7 days while maintaining its apatite-forming ability. The Ti formed with this kind of bioactive SrCT layer on its surface is expected to be highly useful for orthopedic and dental implants, since it should be able to promote bone growth by releasing Sr ions and tightly bond to the bone through the apatite formed on its surface.     

在动态模拟体液中致密CaP陶瓷表面形貌对类骨磷灰石层形成的影响研究

磷酸钙陶瓷植入体内后其表面类骨磷灰石层的形成是诱导成骨的先决条件。本实验在模拟体液 (Simu-lated body fluid,SBF)以人体骨骼肌组织的正常生理流率 (2 ml/ 10 0 m l· min)下 ,研究在动态 SBF中致密磷酸钙陶瓷表面形貌对类骨磷灰石层形成的影响。结果表明 :在生理流速条件下 ,材料的粗糙表面有利于类骨磷灰石层的形成 ,加大 SBF中 Ca2 +、HPO4 2 -离子浓度 ,类骨磷灰石层的形成速度加快。本研究进一步证实了材料的几何形貌对类骨磷灰石形成的影响 ,加深了对磷酸钙陶瓷在体内诱导成骨机理的理解     

The effect of temperature and initial pH on biomimetic apatite coating

Bone-like apatite coatings were prepared using a biomimetic method in a simulated body fluid (SBF). The effect of initial pH values and immersing temperatures on biomimetic apatite coating formation was studied. Three different temperatures were used in this study: 24 (room temperature), 40, and 60 degrees C. At each temperature, SBF solutions with three different initial pHs were chosen: low, medium, and high. The total inorganic carbon (TIC) content and pH-time profile of each coating system were recorded during the coating formation. The apatite coatings were characterized using X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), and Fourier transform infra-red (FTIR). It has been found that SBF temperature has a great effect on the bicarbonate decomposition rate. The bicarbonate ions tend to decompose faster as the temperature increases. The decomposition of bicarbonate ions results in a pH increase in the SBF. With different initial SBF pHs, the decomposition of different amounts of bicarbonate ions is required to reach the critical pH range of apatite formation. With different amounts of bicarbonate ions in the SBF, the surface morphology of the biomimetic apatite coating formed is different. Therefore, the initial pH of the SBF solution plays a vital role in controlling the surface morphology of the biomimetic apatite coating. Also, it was found that as the SBF temperature increased, the critical pH range at which biomimetic apatite coating forms decreased. The critical pH range for the SBF prepared at 24, 40, and 60 degrees C was 6.65-6.71, 6.55-6.65, and 6.24-6.42, respectively.     

Characterisation of a duplex TiO2/CaP coating on Ti6Al4V for hard tissue replacement

An initial TiO(2) coating was applied on Ti6Al4V by electrochemical anodisation in two dissimilar electrolytes. The secondary calcium phosphate (CaP) coating was subsequently applied by immersing the substrates in a simulated body fluid (SBF) with three times concentration (SBFx3), mimicking biomineralisation of biological bone. Electrochemical impedance spectroscopy and potentiodynamic polarisation assessments in SBF revealed that the anodic TiO(2) layer is compact, exhibiting up to four-folds improvement in in vitro corrosion resistance over unanodised Ti6Al4V. X-ray photoelectron spectroscopy analysis indicates that the anodic Ti oxide is thicker than air-formed ones with a mixture of TiO(2-x) compound between the TiO(2)/Ti interfaces. The morphology of the dense CaP film formed, when observed using scanning electron microscopy, is made up of linked globules 0.1-0.5microm in diameter without observable delamination. Fourier transform infrared spectrometry with an attenuated total internal reflection analysis revealed that this film is an amorphous/poorly crystallised calcium-deficient-carbonated CaP system. The calculated Ca:P ratios of all samples (1.14-1.28) are lower than stoichiometric hydroxyapatite (1.67). These results show that a duplex coating consisting of (1) a compact TiO(2) with enhanced in vitro corrosion resistance and (2) bone-like apatite coating can be applied on Ti6Al4V by anodisation and subsequent immersion in SBF.     

Effect of acidic degradation products of poly(lactic-co-glycolic)acid on the apatite-forming ability of poly(lactic-co-glycolic)acid-siloxane nanohybrid material

The effect of poly(lactic-co-glycolic) acid (PLGA) degradation products on the apatite-forming ability of a PLGA-siloxane nanohybrid material were investigated. Two PLGA copolymer compositions with low and high degradability were used in the experiment. The PLGA-siloxane nanohybrid materials were synthesized by end-capping PLGA with acid end-groups using 3-isocyanatopropyl triethoxysilane following the sol-gel reaction with calcium nitrate tetrahydrate. Two nanohybrid materials that had different degradability were exposed to simulated body fluid (SBF) for 1-28 days at 36.5 degrees C. The low degradable PLGA hybrid showed apatite-forming ability within 3 days of incubation while the high degradable one did not within 28 days testing period. The results were explained in terms of the acidity of the PLGA degradation products, which could directly influence on the apatite dissolution.