Effects of ions in aqueous media on hydroxyapatite induction by silica gel and its relevance to bioactivity of bioactive glasses and glass-ceramics

In vitro remineralization assessment of enamel subsurface lesions using different percentages of surface reaction-type pre-reacted glass-ionomer containing gum-based material

OBJECTIVE

To identify the remineralization activity of enamel subsurface lesions using different percentages of surface pre-reacted glass-ionomer (S-PRG) filler containing gum-base material.

METHODS

Gum extracts from gum-base materials containing 0wt%, 5wt%, and 10wt% S-PRG filler were prepared as GE0, GE5, and GE10, respectively. A total of 50 bovine enamel specimens were used, and the polished enamel surface of a 3 × 3 mm2 window area was exposed. The specimens were then subjected to a demineralization solution for seven days to create a subsurface enamel lesion. Remineralization was then conducted for seven days using a protocol whereby the specimens were immersed three times a day in prepared gum extracts (0wt%, 5wt%, and 10wt%) and artificial saliva of pH 7 (Control) for 20 min at 37 °C. Thereafter, remineralization assessment was performed by using Swept Source Optical Coherence Tomography (SS-OCT) and micro-computed tomography (μCT). Surface morphology and elemental analysis were conducted by scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDS).

RESULTS

The depths of the demineralized lesions in the GE5 and GE10 groups were significantly lower than those of the Control and the GE0 groups. SEM observations of the enamel surface morphology of the GE5 and GE10 groups indicated remineralization with S-PRG filler-related elements present.

CONCLUSION

The GE5 and GE10 S-PRG filler containing gum-base materials showed significantly improved surface remineralization and reduced demineralization of the enamel lesions. EDS analysis suggested that the released ions from the S-PRG filler might be responsible for surface remineralization.

CLINICAL SIGNIFICANCE

The S-PRG filler containing gum-base material may have a significant remineralization effect and improve the surface morphology of enamel subsurface lesions.

Antibacterial and Cytotoxic Silica-Polycaprolactone-Chlorogenic Acid Hybrids by Sol-Gel Route

Organic-inorganic hybrid materials were synthesized by a sol-gel route, using silicon alkoxide together with low molecular weight polycaprolactone and caffetannic acid. The synthesized hybrids were characterized by scanning Fourier-transform infrared (FTIR) spectroscopy, and their surface morphology was acquired by scanning electron microscopy (SEM) analysis. The hybrids were investigated for their antiradical capacity using the DPPH and ABTS tests, while the Kirby-Bauer test was used to evaluate their effects on the growth of Escherichia coli and Enterococcus faecalis. Furthermore, a biologically active hydroxyapatite layer has been observed to form on the surface of intelligently synthesized materials. The MTT direct test showed that the hybrid materials are biocompatible with NIH-3T3 fibroblast cells, while they were cytotoxic towards colon, prostate, and brain tumor cell lines. These results shed new light on the suitability of the synthesized hybrids in the medical field, thus affording knowledge on the features of the bioactive silica-polycaprolactone-chlorogenic acid hybrids.

Visualizing Different Crystalline States during the Infrared Imaging of Calcium Phosphates

Methods utilizing relatively simple mathematical operations during physical analyses to enable the visualization of otherwise invisible correlations and effects are of particular appeal to researchers and students in pedagogical settings. At the same time, discerning the amorphous phase from its crystalline counterpart in materials is challenging with the use of vibrational spectroscopy and is nowhere as straightforward as in phase composition analytical methods such as X-ray diffraction. A method is demonstrated for the use of first- and second-order differentiation of Fourier transform infrared spectra of calcium phosphates to distinguish their amorphous states from the crystalline ones based on the exact line positioning rather than on comparatively vaguer band broadening and splitting effects. The study utilizes a kinetic approach, focusing on the comparison of spectral features of amorphous precursors annealed in air at different temperatures and aged for different periods of time in an aqueous solution until transforming to one or a mixture of crystalline phases, including hydroxyapatite and α- and β-tricalcium phosphate. One of the findings challenges the concept of the nucleation lag time preceding the crystallization from amorphous precursors as a "dead" period and derives a finite degree of constructive changes occurring at the atomic scale in its course. The differential method for highlighting spectral differences depending on the sample crystallinity allows for monitoring in situ the process of conversion of the amorphous calcium phosphate phase to its crystalline analogue(s). One such method can be of practical significance for synthetic solid state chemists testing for the chemical stability and/or concentration of the reactive amorphous phase in these materials, but also for biologists measuring the maturity of bone and medical researchers evaluating its phase composition and, thus, the state of metabolic and mechanical stability.

Enhancement of osteoblast cells osteogenic differentiation and bone regeneration by hydroxyapatite/phosphoester modified poly(amino acid)

Hydroxyapatite/poly(amino acid) (HA/PAA) has been used to treat a variety of long bone and vertebral bony defects, and a further biocompatibility improvement is a key for better application. Phosphoester (PE) contained materials are highly biocompatible but could hardly treat massive bone defects due to its fast-degradation-derived mechanical instability. To address the problems of the two materials, we have incorporated PE molecule into the main chain of PAA by chemical bonding. As a result, the compressive strength of HA/PAA with 1 wt% and 2.5 wt% PE maintained in the range of 80-150 MPa after soaking in PBS for 12 weeks, which could be attributed to the amplified hydrogen-bonding inside composites. Besides, the PE-containing HA/PAAs with increased hydrophilic function groups (O=P-O bonds and O=P-N), created a more favourable surface for cell adhesion. Meanwhile, compared with HA/PAA, the PE-containing HA/PAAs had a fast minerlization speed and promoted cell osteogenic differentiation. Furthermore, the in vivo study indicated that PE-containing HA/PAAs could facilitate bone formation (4 weeks), and form a complete bone bridging (12 weeks) in a rabbit cranial bone defect. In summary, the HA/PE-m-PAAs possessed good mechanical stability, improved cytocompatibility and osteoconductivity, so the composites have a great potential for massive bone defect treatment.

Human Mesenchymal Stem Cell Combined with a New Strontium-Enriched Bioactive Glass: An ex-vivo Model for Bone Regeneration

A 3D cellular model that mimics the potential clinical application of a biomaterial is here applied for the first time to a bioactive glass, in order to assess its biological potential. A recently developed bioactive glass (BGMS10), whose composition contained strontium and magnesium, was produced in the form of granules and fully investigated in terms of biocompatibility in vitro. Apart from standard biological characterization (Simulated Body Fluid (SBF) testing and biocompatibility as per ISO10993), human bone marrow mesenchymal stromal/stem cells (BM-MSCs) were used to investigate the performance of the bioactive glass granules in an innovative 3D cellular model. The results showed that BGMS10 supported human BM-MSCs adhesion, colonization, and bone differentiation. Thus, bioactive glass granules seem to drive osteogenic differentiation and thus look particularly promising for orthopedic applications, bone tissue engineering and regenerative medicine.

In Vitro Activity Assays of Sputtered HAp Coatings with SiC Addition in Various Simulated Biological Fluids

Considering the requirements of medical implantable devices, it is pointed out that biomaterials should play a more sophisticated, longer-term role in the customization and optimization of the material–tissue interface in order to ensure the best long-term clinical outcomes. The aim of this contribution was to assess the performance of silicon carbide–hydroxyapatite in various simulated biological fluids (Dulbecco’s modified Eagle’s medium (DMEM), simulated body fluid (SBF), and phosphate buffer solution (PBS)) through immersion assays for 21 days at 37 ± 0.5 °C and to evaluate the electrochemical behavior. The coatings were prepared on Ti6Al4V alloy substrates by magnetron sputtering method using two cathodes made of hydroxyapatite and silicon carbide (SiC). After immersion assays the coating’s surface was analyzed in terms of morphology, chemical and phase composition, and chemical bonds. According to the electrochemical behavior in the media investigated at 37 ± 0.5 °C, SiC addition inhibits the dissolution of the hydroxyapatite in DMEM acellular media. Furthermore, after adding SiC, the slow degradation of hydroxyapatite in PBS and SBF media as well as biomineralization in DMEM were observed.

Biodegradable ceramic-polymer composites for biomedical applications: A review

The present work focuses on the state-of-the-art of biodegradable ceramic-polymer composites with particular emphasis on influence of various types of ceramic fillers on properties of the composites. First, the general needs to create composite materials for medical applications are briefly introduced. Second, various types of polymeric materials used as matrices of ceramic-containing composites and their properties are reviewed. Third, silica nanocomposites and their material as well as biological characteristics are presented. Fourth, different types of glass fillers including silicate, borate and phosphate glasses and their effect on a number of properties of the composites are described. Fifth, wollastonite as a composite modifier and its effect on composite characteristics are discussed. Sixth, composites containing calcium phosphate ceramics, namely hydroxyapatite, tricalcium phosphate and biphasic calcium phosphate are presented. Finally, general possibilities for control of properties of composite materials are highlighted.

Inducing bioactivity of dental ceramic/bioactive glass composites by Nd:YAG laser

OBJECTIVES

Aims of this study were to investigate the optimal conditions of laser irradiation of a novel Bioactive Glass/Dental Ceramic-BP67 composite for acceleration of hydroxyapatite-HA formation and to assess cellular responses on the precipitated HA region.

METHODS

BP67 (Bioactive Glass: 33.3%, Dental Ceramic: 66.7%) was fabricated by the sol-gel method. A laser assisted biomimetic-LAB process was applied to BP67 sintered specimens immersed in 1.5-times concentrated simulated body fluid-1.5×-SBF. The effect of various energy densities of pulsed nanosecond Nd-YAG (1064nm) laser and irradiation exposure times (30min, 1 and 3h) were evaluated for HA precipitation. The HA film was characterized by FTIR, XRD, SEM and micro Raman techniques. ICP-AES was used for revealing changes in chemical composition of the 1.5×-SBF during irradiation. Cell viability and morphological characteristics of periodontal ligament fibroblasts-PDLFs, human gingival fibroblasts-HGFs and SAOS-2 osteoblasts on the HA surface were evaluated by MTT assays and SEM.

RESULTS

At optimal energy fluence of 1.52J/cm² and irradiation time for 3h followed by immersion in 1.5×-SBF at 60°C, a dense HA layer was formed on laser-irradiated BP67 within 7 days. The resulting HA film was tightly bonded to the underlying substrate and had mineral composition similar to cementum. MTT assay showed a consistent reduction of cell proliferation on the HA layer in comparison to conventional control ceramic and BP67 for all 3 cell lines studied.

SIGNIFICANCE

These findings suggest LAB is an effective method for acceleration of HA formation on materials with low bioactivity, while cellular responses need further investigation.

Evaluation of the effects of fluoride-releasing varnish on dentin demineralization using optical coherence tomography

Effects of a fluoride-releasing varnish containing surface reaction-type prereacted glass ionomer (S-PRG) filler on dentin demineralization were examined using optical coherence tomography. Bovine incisors that were sliced and treated with undersaturated 0.1 M lactic acid buffer solution (DE group). A thin film of varnish-containing S-PRG filler was applied before demineralization (PRG group). Control was maintained in artificial saliva. Using optical coherence tomography of selected locations on the dentin surface, peak intensity (dB) and width (μm) at 1/e(2) were obtained and integrated values calculated. Although alterations in integrated values were different in each group, there was a slight but not significant increase in those for the control group and a slight but significant increase for the De group. For the PRG group, integrated values were doubled seven days after experiment initiation, followed by a significant increase. Fluoride-releasing varnish containing S-PRG fillers prevented dentin demineralization as detected by optical coherence tomography.

A Dual Role of Graphene Oxide Sheet Deposition on Titanate Nanowire Scaffolds for Osteo-implantation: Mechanical Hardener and Surface Activity Regulator

Scaffold biomaterials with open pores and channels are favourable for cell growth and tissue regeneration, however the inherent poor mechanical strength and low surface activity limit their applications as load-bearing bone grafts with satisfactory osseointegration. In this study, macro-porous graphene oxide (GO) modified titanate nanowire scaffolds with desirable surface chemistry and tunable mechanical properties were prepared through a simple hydrothermal process followed by electrochemical deposition of GO nanosheets. The interconnected and porous structure of the GO/titanate nanowire scaffolds provides a large surface area for cellular attachment and migration and displays a high compressive strength of approximately 81.1 MPa and a tunable Young’s modulus over the range of 12.4–41.0 GPa, which satisfies site-specific requirements for implantation. Surface chemistry of the scaffolds was modulated by the introduction of GO, which endows the scaffolds flexibility in attaching and patterning bioactive groups (such as -OH, -COOH and -NH₂). In vitro cell culture tests suggest that the GO/titanate nanowire scaffolds act as a promising biomaterial candidate, in particular the one terminated with -OH groups, which demonstrates improved cell viability, and proliferation, differentiation and osteogenic activities.

Combining collagen and bioactive glasses for bone tissue engineering: a review

Collagen (COL), the most abundant protein in mammals, offers a wide range of attractive properties for biomedical applications which are the result of its biocompatibility and high affinity to water. However, due to the relative low mechanical properties of COL its applications are still limited. To tackle this disadvantage of COL, especially in the field of bone tissue engineering, COL can be combined with bioactive inorganic materials in a variety of composite systems. One of such systems is the collagen-bioactive glass (COL-BG) composite family, which is the theme of this Review. BG fillers can increase compressive strength and stiffness of COL-based structures. This article reviews the relevant literature published in the last 15 years discussing the fabrication of a variety of COL-BG composites. In vitro cell studies have demonstrated the osteogenic, odontogenic, and angiogenic potential of these composite systems, which has been confirmed by stimulating specific biochemical indicators of relevant cells. Bony integration and connective tissue vessel formation have also been studied by implantation of the composites in vivo. Areas of future research in the field of COL-BG systems, based on current challenges, and gaps in knowledge are highlighted.

Mesoporous bioactive glasses: Relevance of their porous structure compared to that of classical bioglasses

In the last decade, the development of third generation bioceramics for Bone Tissue Regeneration has experienced significant progress with the emergence of a new generation of nanostructured materials named mesoporous bioactive glasses (MBG). This new generation of materials, also known as “templated glasses”, presents chemical compositions similar to those of conventional bioactive sol–gel glasses and the added value of an ordered mesopore arrangement. This article shows an indepth comparative study of the ordered porous structures of MBGs compared to conventional glasses (melt and solgel) andhowthese properties influence the bioactivity process. Moreover, the possibility to tailor the textural and structural properties of these nanostructured materials by an exhaustive control of the different synthesis parameters is also discussed. A brief overview regarding the possibility of using these materials as controlled drug delivery systems and as starting materials for the fabrication of 3D scaffolds for bone tissue regeneration is also given.

In vitro bioactivity and antimicrobial tuning of bioactive glass nanoparticles added with neem (Azadirachta indica) leaf powder

Silica and phosphate based bioactive glass nanoparticles (58SiO₂-33CaO-9P₂O₅) with doping of neem (Azadirachta indica) leaf powder and silver nanoparticles were prepared and characterised. Bioactive glass nanoparticles were produced using sol-gel technique. In vitro bioactivity of the prepared samples was investigated using simulated body fluid. X-ray diffraction (XRD) pattern of prepared glass particles reveals amorphous phase and spherical morphology with a particle size of less than 50 nm. When compared to neem doped glass, better bioactivity was attained in silver doped glass through formation of hydroxyapatite layer on the surface, which was confirmed through XRD, Fourier transform infrared (FTIR), and scanning electron microscopy (SEM) analysis. However, neem leaf powder doped bioactive glass nanoparticles show good antimicrobial activity against Staphylococcus aureus and Escherichia coli and less bioactivity compared with silver doped glass particles. In addition, the biocompatibility of the prepared nanocomposites reveals better results for neem doped and silver doped glasses at lower concentration. Therefore, neem doped bioactive glass may act as a potent antimicrobial agent for preventing microbial infection in tissue engineering applications.

Surface characteristics and bioactivity of a novel natural HA/zircon nanocomposite coated on dental implants

The surface characteristics of implant which influence the speed and strength of osseointegration include surface chemistry, crystal structure and crystallinity, roughness, strain hardening, and presence of impurities. The aim of this study was to evaluate the bioactivity and roughness of a novel natural hydroxyapatite/zircon (NHA/zircon) nanobiocomposite, coated on 316L stainless steel (SS) soaked in simulated body fluid (SBF). NHA/zircon nanobiocomposite was fabricated with 0 wt.%, 5 wt.%, 10 wt.%, and 15 wt.% of zircon in NHA using ball mill for 20 minutes. The composite mixture was coated on 316L SS using plasma spray method. The results are estimated using the scanning electron microscopy (SEM) observation to evaluate surface morphology, X-ray diffraction (XRD) to analyze phase composition, and transmission electron microscopy (TEM) technique to evaluate the shape and size of prepared NHA. Surfaces roughness tester was performed to characterize the coated nanocomposite samples. The maximum average R a (14.54 μm) was found in the NHA 10 wt.% of zircon coating. In addition, crystallinity (X c ) was measured by XRD data, which indicated the minimum value (X c = 41.1%) for the sample containing 10 wt.% of zircon. Maximum bioactivity occurred in the sample containing 10 wt.% of zircon, which was due to two reasons: first, the maximum roughness and, second, the minimum crystallinity of nanobiocomposite coating.

Effect of Pre-reacted Glass-ionomer Filler Extraction Solution on Demineralization of Bovine Enamel

Objective

To determine the effect of pre-reacted glass-ionomer (PRG) filler extraction solution on the demineralization of bovine enamel by measuring changes in the ultrasound transmission velocity.

Methods

The specimens were prepared by cutting bovine teeth into enamel blocks. The specimens were immersed in buffered lactic acid solution for 10 minutes twice a day, and then stored in artificial saliva. Other specimens were stored in PRG filler extraction solution for 10 minutes, followed by 10-minute immersion in the buffered lactic acid solution twice a day. The propagation time of longitudinal ultrasonic waves was measured by a pulser receiver. Six specimens were used for each condition, and analyses of variance followed by Tukey tests (α=0.05) were done.

Results

No changes in sonic velocity were found for specimens stored in the PRG filler extraction solution, indicating that the PRG extraction solution had an effect on inhibiting the demineralization of bovine enamel.

Conclusions

The results obtained with the use of an ultrasound measurement technique suggested that PRG filler extraction solution has the ability to prevent demineralization of enamel.

Apatite Nucleation on Low Porosity Silicon in Acellular Simulated Body Fluids

The response of a range of porous Si films to acellular simulated body fluids has been monitored by SEM, EDX and FTIR analyses. Quite low levels of porosity are shown here to induce hydroxyapatite growth both on top of the film, and even on neighbouring areas of bulk Si, which in isolation have no such effect. The in-vitro demonstration of hydroxyapatite nucleation by a porous semiconductor could provide further insight into the phenomenon of bioactivity and help realise a broader range of bioactive materials.

A Novel Method For Solution Deposition of Hydroxyapatite on to Three Dimensionally Porous Metallic Surfaces: Peri-Apatite Ha

A method for applying HA coatings to metallic surfaces, without the use of high temperature plasma spraying, has been developed. The HA coating is precipitated in an aqueous solution under conditions similar to those occurring in the body during bone formation. This surface mineralization process results in a coating which is highly crystalline and 100% HA. Processing and characterization experimentation and results are included in the paper.

The coating method has the ability to penetrate macroporous (> 100 micron pores) metal structures and coat the undersides and interior surfaces of the areas designed for bone ingrowth on orthopedic devices used for joint replacements. This ability to coat all around a surface is the basis for the name Peri-Apatite HA. Electron microscopy is presented illustrating the coverage and morphology of the coating.

The Peri-Apatite HA coating is currently used on both knee joint replacement and hip joint replacement implants.

Detection of ions released from S-PRG fillers and their modulation effect

The purpose of this study was to analyze the ions released from a surface pre-reacted glass ionomer (S-PRG) filler in distilled water or lactic acid solution. S-PRG filler was mixed with either solution at 1000:1, 100:1, 10:1, and 1:1 ratios by weight. By means of inductively coupled plasma atomic emission spectroscopy and a fluoride electrode, elements released from S-PRG filler were identified to be Al, B, Na, Si, Sr, and F. To investigate the effect of solution pH on ion release, the pH values of the solutions before mixing and after 24 hours' mixing with S-PRG were measured. After 24 hours' mixing, the pH values of solutions at all ratios became more neutral or weakly alkaline regardless of their initial pH levels before mixing. In conclusion, results showed that S-PRG filler released several types of ions, and that ion release was influenced by the mixing ratio of the solution rather than the initial pH of the solution.

Nucleation and growth of biomimetic apatite layers on 3D plotted biodegradable polymeric scaffolds: effect of static and dynamic coating conditions

Apatite layers were grown on the surface of newly developed starch/polycaprolactone (SPCL)-based scaffolds by a 3D plotting technology. To produce the biomimetic coatings, a sodium silicate gel was used as nucleating agent, followed by immersion in a simulated body fluid (SBF) solution. After growing a stable apatite layer for 7 days, the scaffolds were placed in SBF under static, agitated (80 strokes min(-1)) and circulating flow perfusion (Q=4 ml min(-1); t(R)=15s) for up to 14 days. The materials were characterized by scanning electron microscopy/energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy and thin-film X-ray diffraction. Cross-sections were obtained and the coating thickness was measured. The elemental composition of solution and coatings was monitored by inductively coupled plasma spectroscopy. After only 6 h of immersion in SBF it was possible to observe the formation of small nuclei of an amorphous calcium phosphate (ACP) layer. After subsequent SBF immersion from 7 to 14 days under static, agitated and circulating flow perfusion conditions, these layers grew into bone-like nanocrystalline carbonated apatites covering each scaffold fiber without compromising its initial morphology. No differences in the apatite composition/chemical structure were detectable between the coating conditions. In case of flow perfusion, the coating thickness was significantly higher. This condition, besides mimicking better the biological milieu, allowed for the coating of complex architectures at higher rates, which can greatly reduce the coating step.

Functionalization of different polymers with sulfonic groups as a way to coat them with a biomimetic apatite layer

Covalent coupling of sulfonic group (-SO 3H) was attempted on different polymers to evaluate efficacy of this functional group in inducing nucleation of apatite in body environment, and thereupon to design a simple biomimetic process for preparing bonelike apatite-polymer composites. Substrates of polyethylene terephthalate (PET), polycaprolactam (Nylon 6), high molecular weight polyethylene (HMWPE) and ethylene-vinyl alcohol co-polymer (EVOH) were subjected to sulfonation by being soaked in sulfuric acid (H2SO4) or chlorosulfonic acid (ClSO 3H) with different concentrations. In order to incorporate calcium ions, the sulfonated substrates were soaked in saturated solution of calcium hydroxide (Ca(OH)2). The treated substrates were soaked in a simulated body fluid (SBF). Fourier transformed infrared spectroscopy, thin-film X-ray diffraction, and scanning electron microscopy showed that the sulfonation and subsequent Ca(OH)2 treatments allowed formation of -SO3H groups binding Ca2+ ions on the surface of HMWPE and EVOH, but not on PET and Nylon 6. The HMWPE and EVOH could thus form bonelike apatite layer on their surfaces in SBF within 7 d. These results indicate that the -SO3H groups are effective for inducing apatite nucleation, and thereby that surface sulfonation of polymers are effective pre-treatment method for preparing biomimetic apatite on their surfaces.

Hydroxyapatite-Electroplated cp–Titanium Implant and Its Bone Integration Potentiality: An In Vivo Study

PURPOSE

This study was designed to precipitate hydroxyapatite coating on the surface of commercially pure titanium (cpTi) implants using an electroplating technique. After characterization of the hydroxyapatite coating, the bone-implant interface and bone integration of both cpTi and hydroxyapatite-coated implants were assessed.

MATERIALS

Twenty implants were divided equally into 2 main groups (n = 10). Ten cpTi implants were utilized as received, while the others were hydroxyapatite coated and then sterilized. The implants of both groups were inserted in the tibiae of New Zealand rabbits. The purity and crystallinity of the hydroxyapatite coat were characterized using x-ray diffraction. A scanning electron microscope examined the grain morphology. Profilometer evaluated the surface texture before and after sterilization. Histological examination using a scanning electron microscope was performed to qualify osseointegration of the regenerated bone and measure the gap distance at the bone-implant interface.

RESULTS

Pure crystalline hydroxyapatite precipitate of thickness (range 69-78 microm) and rough surface (2.7 +/- 0.2 microm) compared to smooth cpTi (1.3 +/- 0.5 microm). The gamma-radiation sterilization resulted in finer grains and insignificant smoother surface. Histological examination of the cpTi implant exhibited less bone regeneration with few and less dense bone trabeculae, and gap distance was significantly high (1.29 +/- 0.51 microm). Meanwhile, the hydroxyapatite-coated implant showed a recognizable amount of bone regeneration with more and denser bone trabeculae, and gap distance ranged from 0 to 1.32 microm.

CONCLUSIONS

The employed technique provided a thin and uniform pure crystalline hydroxyapatite coating. The characterization of the precipitated film is promising for clinically successful long-term bone fixation.

In vitro apatite formation on polyamide containing carboxyl groups modified with silanol groups

Modification of organic polymer with silanol groups in combination with calcium salts enables the polymer to show bioactivity, that is, the polymer forms apatite on its surface after exposure to body environment. However, how modification with silanol groups influences ability of apatite formation on the polymer substrate and adhesive strength between polymer and apatite is not yet known. In the present study, polyamide containing carboxyl groups was modified with different amounts of silanol groups, and its apatite-forming ability in 1.5SBF, which contained ion concentrations 1.5 times those of simulated body fluid (SBF), was examined. The rate of apatite formation increased with increasing content of silanol groups in the polyamide films. This may be attributed to enhancement of dipole interactions. A tendency for the adhesive strength of the apatite layer on the polyamide film to be decreased with increasing content of silanol groups was observed. This may be attributed to swelling in 1.5SBF and having a high degree of shrinkage after drying. These findings clearly show that modification of organic polymers with the functional groups induces apatite deposition, and also determines the adhesive strength of the apatite layer to the organic substrates.

Preparation of bioactive flexible poly(tetramethylene oxide) (PTMO)-CaO-Ta2O5 hybrids

Poly(tetramethylene oxide) (PTMO)-CaO-Ta2O5 hybrids were prepared by hydrolysis and polycondensation of triethoxysilane-functionalized PTMO (Si-PTMO), tantalum ethoxide (Ta(OEt)5) and CaCl2. In the system CaO-free PTMO-Ta2O5, Si-PTMO/Ta(OEt)5 weight ratios were 30/70, 40/60 and 50/50 (hybrids PT30Ca0, PT40Ca0 and PT50Ca0, respectively). In the system PTMO-CaO-Ta2O5, the Si-PTMO/Ta(OEt)5 weight ratio was 40/60 and CaCl2/Ta(OEt)5 mole ratios were 0.05, 0.10 and 0.15 (hybrids PT40Ca5, PT40Ca10 and PT40Ca15, respectively). Crack-free transparent monolithic hybrids were obtained for all the examined compositions except for PT30Ca0. Even CaO-free hybrids PT40Ca0 and PT50Ca0 formed apatite on their surfaces in a simulated body fluid (SBF) within 14 days. Hybrid PT40Ca0 showed higher mechanical strength, which was increased by soaking in SBF, and larger strain to failure than human cancellous bone. The CaO-containing hybrids showed higher apatite-forming ability than the CaO-free hybrids, and its apatite-forming ability increased with increasing CaO content. Hybrids PT40Ca10 and PT40Ca15 formed apatite within 3 days. The mechanical strength of PT40Ca15 was, however, lower than PT40Ca0 and was decreased by soaking in SBF. Thus obtained flexible bioactive CaO-free PTMO-Ta2O5 hybrids are expected to be useful as bone substitutes.

Strontium-substituted apatite coating grown on Ti6Al4V substrate through biomimetic synthesis

During the last few years Strontium has been shown to have beneficial effects when incorporated at certain doses in bone by stimulating bone formation. It is believed that its presence locally at the interface between an implant and bone will enhance osteointegration and therefore, ensure the longevity of a joint prosthesis. In this study we explore the possibility of incorporating Sr into nano-apatite coatings prepared by a solution-derived process according to an established biomimetic methodology for coating titanium based implants. The way this element is incorporated in the apatite structure and its effects on the stereochemistry and morphology of the resulting apatite layers was investigated, as well as its effect in the mineralization kinetics. By using the present methodology it was possible to incorporate increasing amounts of Sr in the apatite layers. Sr was found to incorporate in the apatite layer through a substitution mechanism by replacing Ca in the apatite lattice. The presence of Sr in solution induced an inhibitory effect on mineralization, leading to a decrease in the thickness of the mineral layers. The obtained Sr-substituted biomimetic coatings presented a bone-like structure similar to the one found in the human bone and therefore, are expected to enhance bone formation and osteointegration.

Novel injectable calcium phosphate/chitosan composites for bone substitute materials

In this study, a novel injectable bone substitute material was developed which consists of chitosan, citric acid and glucose solution as the liquid phase, and tricalcium phosphate powder as the solid phase. This material was moldable because of its paste consistency after mixing. We used four groups of cement to investigate the mechanical properties and biocompatibility of the new biomaterial in vitro, which were named group A (10% citric acid), B (15% citric acid), C (20% citric acid) and D (25% citric acid). The setting times of the cements were 5-30 min. X-ray diffraction analysis showed that the products were hydroxyapatite (HA) and dicalcium phosphate anhydrous. When the concentration of citric acid was increased, the compressive strength of specimen increased. Through the simulated body fluid test, we observed the material was bioactive. Group D could induce Ca and P ions to deposit the surface group D quickly. These results indicated that the concentration of citric acid in the liquid component affected the mechanical properties and bioactivity of cements. The cell cultivation test showed that the cytocompatibility of the new biomaterial was good. The method for preparing the novel bone substitute material is simple. The starting material is more readily available and cheaper than HA, poly(methyl methacrylate), and so on. The cement could have good prospects for medical application.

Bone reconstruction: from bioceramics to tissue engineering

Over the past 30 years, an enormous array of biomaterials proposed as ideal scaffolds for cell growth have emerged, yet few have demonstrated clinical efficacy. Biomaterials, regardless of whether they are permanent or biodegradable, naturally occurring or synthetic, need to be biocompatible, ideally osteoinductive, osteoconductive, integrative, porous and mechanically compatible with native bone to fulfill their desired role in bone tissue engineering. These materials provide cell anchorage sites, mechanical stability and structural guidance and in vivo, provide the interface to respond to physiologic and biologic changes as well as to remodel the extracellular matrix in order to integrate with the surrounding native tissue. Calcium phosphate ceramics and bioactive glasses were introduced more than 30 years ago as bone substitutes. These materials are considered bioactive as they bond to bone and enhance bone tissue formation. The bioactivity property has been attributed to the similarity between the surface composition and structure of bioactive materials, and the mineral phase of bone. The drawback in using bioactive glasses and calcium phosphate ceramics is that close proximity to the host bone is necessary to achieve osteoconduction. Even when this is achieved, new bone growth is often strictly limited because these materials are not osteoinductive in nature. Bone has a vast capacity for regeneration from cells with stem cell characteristics. Moreover, a number of different growth factors including bone morphogenetic proteins, have been demonstrated to stimulate bone growth, collagen synthesis and fracture repair both in vitro and in vivo. Attempts to develop a tissue-engineering scaffold with both osteoconductivity and osteoinductivity have included loading osteoinductive proteins and/or osteogenic cells on the traditional bioactive materials. Yet issues that must be considered for the effective application of bioceramics in the field of tissue engineering are the degree of bioresorption and the poor mechanical strength. The synthesis of a new generation of biomaterials that can specifically serve as tissue engineering scaffolds for drug and cell delivery is needed. Nanotechnology can provide an alternative way of processing porous bioceramics with high mechanical strength and enhanced bioactivity and resorbability.

Nucleation and Growth of Bone-Like Apatite on Surfaces of Metals, Ceramics and Polymers in Simulated Body Fluids

The biomimetic approach of mineralization in vitro is adopted to investigate systematically the nucleation and growth of bone-like apatite on the surface of biomaterials such as bioceramics, metals and polymers, and those chemically surface-treated. The simulated environment is kept isothermic at the human body temperature of 36.5C with three kinds of simulated physiological fluids. The experimental results show that (1) inherent properties of biomaterials determine their bioactivity and the different crystalline structure of same materials results in the difference in bioactivity; (2) the bioactivity can effectively be improved by the surface treatment of biomaterials via chemical methods and by the addition of bioactive particles in a polymer matrix; (3) the bone-like apatite, nucleated and grown in the simulated body fluid with the same ion concentrations to that of the human plasma, possesses the same composition, structure and morphology despite of matrixes; (4) the difference in bioactivity with biomaterials is indicated by the different time for bone-like apatite to nucleate and to grow on their surfaces.

Ammonium hexafluorosilicate increased acid resistance of bovine enamel and dentine

Although diamine silver fluoride (AgF: (NH3)2AgF) stains teeth black, it is known as a very effective agent to prevent the dental caries progress. In order to find another fluoride that has a similar anticariogenic effect without changing tooth color, we prepared ammonium hexafluorosilicate (SiF: (NH4)2SiF6), in which the silver of AgF is replaced with silicon. In this study, the anticariogenic effect of SiF was evaluated using bovine teeth. Fluoride solutions, SiF, AgF, acidulated phosphate fluoride (APF), and sodium fluoride (NaF), were applied to bovine enamel and dentine blocks, and the depth of demineralization was measured after exposure to a demineralizing solution for 24 h. Also, fluoride was applied to a simulated dentine caries specimen to evaluate the caries progress-preventing ability. For the dentine specimens, mineral loss (Delta Z) was also measured with microradiography. We found that SiF treated enamel showed better acid resistance than specimens treated with NaF or APF. AgF treated enamel also showed similar acid resistance, but was stained black. SiF and AgF treated caries-affected dentine showed reduced demineralization when exposed to a demineralization solution for 24 h. Mineral loss (Delta Z) was reduced to 85% and 75%, respectively. Although the acid resistance of the SiF treated teeth was inferior to that of the AgF treated teeth, we consider that SiF has good potential as anticariogenic agent, since it increased acid resistance without changing tooth color.

Effect of bioactive ceramic dissolution on the mechanism of bone mineralization and guided tissue growthin vitro

A major objective of this research work was to evaluate the effect of bone cells on the dissolution-precipitation reaction in vitro. Rat bone marrow stem cells were seeded on silica-calcium phosphate nano composite (SCPC) with different chemical compositions and crystalline structures. Measurements of the Ca, P, Si, and Na concentrations in the tissue culture media using inductively coupled plasma indicated that bone marrow stem cells attached to the surface of SCPC did not affect the dissolution behavior of the material. However, bone marrow stem cells interfered with the back precipitation reaction and inhibited the formation of a calcium phosphate (Ca-P) layer on the material surface. Scanning electron microscope-energy-dispersive X-ray analyses showed that, in the absence of cells, a Ca-P layer formed on the material surface because of the dissolution-precipitation reaction. Bone cells attached to SCPC that contains high silica content absorbed significantly higher concentrations of medium Ca than cells attached to SCPC that contains low silica content. In conjunction with the absorption of high Ca concentration, attached bone marrow stem cells produced calcified nodules and mineralized extracellular matrix, indicating osteoblastic differentiation. Results of the study strongly suggest that the mechanism of bone mineralization at the interface with bioactive ceramics is mainly cell mediated and is enhanced by the absorption of critical concentrations of dissolved Ca and P. The silicon-rich phase also provided a guided cell adhesion and tissue growth in vitro. The enhanced bioactivity reactions and strong stimulatory effect on bone cell function are attributed to the modified crystalline structure of the SCPC material.

Nano-scale study of the nucleation and growth of calcium phosphate coating on titanium implants

The nucleation and growth of a calcium phosphate (Ca-P) coating deposited on titanium implants from simulated body fluid was investigated by using atomic force microscopy (AFM) and environmental scanning electron microscopy (ESEM). Forty titanium alloy plates were assigned into two groups. One group with a smooth surface having a maximum roughness R(max) < 0.10 microm (s-Ti6Al4V) and a group with a rough surface with an R(max) < 0.25 microm (r-Ti6Al4V) were used. Titanium samples were immersed in SBF concentrated by five (SBF x 5) from 10 min to 5 h and examined by AFM and ESEM. Scattered Ca-P deposits of approximately 15 nm in diameter appeared after only 10 min of immersion in SBF x 5. These Ca-P deposits grew up to 60-100 nm after 4 h on both s- and r-Ti6Al4V substrates. With increasing immersion time, the packing of Ca-P deposits with size of tens of nanometers in diameter formed larger globules and then a continuous Ca-P film on titanium substrates. A direct contact between the Ca-P coating and the Ti6Al4V surface was observed. The Ca-P coating was composed of nanosized deposits and of an interfacial glassy matrix. This interfacial glassy matrix might ensure the adhesion between the Ca-P coating and the Ti6Al4V substrate. In the case of s-Ti6Al4V substrate, failures within this interfacial glassy matrix were observed overtime. Part of the glassy matrix remained on s-Ti6Al4V while part detached with the Ca-P film. The Ca-P coating detached from the smooth substrate, whereas the Ca-P film extended onto the whole rough titanium surface over time. In the case of r-Ti6Al4V, the Ca-P coating covered evenly the substrate after immersion in SBF x 5 for 5 h. The present study suggested that the heterogeneous nucleation of Ca-P on titanium was immediate and did not depend on the Ti6Al4V surface topography. The further growth and mechanical attachment of the final Ca-P coating strongly depended on the surface, for which a rough topography was beneficial.

Advanced bioceramic composite for bone tissue engineering: Design principles and structure-bioactivity relationship

The synthesis of a new resorbable porous bioactive silica-calcium phosphate composite (SCPC) that can be used as a tissue-engineering scaffold for bone regeneration is described. The effects of chemical composition and thermal treatment on crystallization and the mechanism of phase transformation in SCPC were evaluated. In the silica-rich samples, beta-rhenanite (beta-NaCaPO(4)) and alpha-cristobalite (SiO(2)) were the dominant phases after treatment at 800 degrees C. On the other hand, in the calcium phosphate-rich samples, calcium pyrophosphate (Ca(2)P(2)O(7)) was formed in addition to beta-rhenanite and alpha-cristobalaite. X-ray diffraction analyses showed a shift in the 2 theta value of the main peak(s) of all phases indicating the formation of solid solutions. Phase transformation reactions were accompanied by a loss of water molecules that contributed to the formation of pores in the size range 10-300 microm. All SCPC samples adsorbed a significantly higher quantity of serum protein than bioactive glass (p < 0.0001). In addition, the silica-rich SCPC adsorbed a significantly higher amount of serum protein than the calcium phosphate-rich samples (p < 0.003). While the crystallization of amorphous silica into L-quartz significantly inhibited serum protein adsorption, the transformation of L-quartz into alpha-cristobalite solid solution (ss) significantly enhanced protein adsorption. On the other hand, in conjunction with the transformation of brushite (CaHPO(4)) into pyro- and tri-calcium phosphates, there was a significant decrease in protein adsorption. However, as pyro- and tri-calcium phosphates transformed into beta-rhenanite, by thermal treatment, protein adsorption increased markedly. Critical-size bone defects grafted with silica-rich SCPC were filled with new bone and contained minimal residues of the graft material. Bone defects grafted with bioactive glass enhanced new bone formation, however, with very limited resorption. The enhanced resorption of SCPC in vivo correlates well with the higher rate of silica dissolution from SCPC than bioactive glass. The facilitated Si dissolution was associated with rapid bone regeneration in defects grafted with SCPC. The enhanced bioactivity properties of the SCPC are due to its chemical composition, modified crystalline structure, and high porosity. The new SCPC may be used for a wide variety of applications in the field of bone reconstruction including tissue-engineering scaffolds for cell and drug delivery.

A new quantitative method to evaluate the in vitro bioactivity of melt and sol-gel-derived silicate glasses

Two melt-derived glasses (45S5 and 60S) and four sol-gel glasses (58S, 68S, 77S, and 91S) have been synthesized. The activation energy for the silicon release was determined, and a very close correlation was observed between this value and published results of the bioactive behavior of the glasses. This relationship can be explained in terms of the influence of chemical composition, textural properties, and structural density on the silanol group formation and silicon dissolution. These measurements provide a quantitative method to evaluate the in vitro bioactivity of SiO(2)-based glasses. Preliminary studies suggest an activation energy gap (Ea) of 0.35-0.5 eV as a boundary between bioactive and nonbioactive glasses.

Bonelike apatite formation on ethylene-vinyl alcohol copolymer modified with silane coupling agent and calcium silicate solutions

An ethylene-vinyl alcohol copolymer (EVOH) was treated with a silane coupling agent and calcium silicate solutions, and then soaked in a simulated body fluid (SBF) with ion concentrations approximately equal to those of human blood plasma. A smooth and uniform bonelike apatite layer was successfully formed on both the EVOH plate and the EVOH-knitted fibers in SBF within 2 days. Part of the structure of the resulting apatite-EVOH fiber composite was similar to that of natural bone. If this kind of composite can be fabricated into a three-dimensional structure similar to natural bone, the resultant composite is expected to exhibit both mechanical properties analogous to those of natural bone and bone-bonding ability. Hence, it has great potential as a bone substitute.

In situ study of partially crystallized Bioglass and hydroxylapatite in vitro bioactivity using atomic force microscopy

The present work investigates, in situ, the in vitro bioactivity of partially crystallized 45S5 Bioglass (BG) as a function of immersion time in a simulated body fluid (SBF) using atomic force microscopy (AFM). The results obtained for the crystallized BG were compared to those of hydroxyapatite c- and a-faces. The calcium phosphate layer grows on the crystallized 45S5 B by multiple two-dimensional nucleation and fusion of these two-dimensional islands, which is essentially the same mode as for the hydroxyapatite c-face. The surface of the crystallized 45S5 BG was almost fully covered with a dense and compact calcium phosphate layer after 24 h. The calcium phosphate formation on the crystallized BG arises from a low surface energy of the surface layer and/or an effect of the layer to lower the resistance when the growth units of calcium phosphate incorporate into the growing island. These results indicate that the crystallized 45S5 BG is suitable to be used as a filler for polymeric matrix bioactive composites, as it maintains a high bioactivity associated with a stiffer behavior (as compared to standard BG).

In vitro behavior of silicate glass coatings on Ti6A14V

The in vitro response in simulated body fluid (SBF) of silicate glass coatings on Ti6A14V was evaluated. Glasses belonging to the SiO2-CaO-MgO-Na2O-K2O-P2O5 system were used to prepare 50-70 m thick coatings on Ti6Al4V, employing a simple enameling technique. Glasses with silica content higher than 55 wt% can be used to prepare coatings that do not crack or delaminate and exhibit good adhesion to the alloy. It has been found that coatings with silica content lower than 60 wt% are more susceptible to corrosion and precipitate carbonated hydroxyapatite on their surface during in vitro tests. However, these coatings have a higher thermal expansion than the metal and are under tension. After 2 months in SBF cracks grow in the coating that reach the glass/metal interface and initiate delamination. Glasses with silica content higher than 60 wt% are more resistant to corrosion and have lower thermal expansion. These coatings do not crack but they do not precipitate apatite even after 2 months in SBF.

Functionalization of synthetic polymers for potential use as biomaterials: selective growth of hydroxyapatite on sulphonated polysulphone

A novel composite made of biocompatible synthetic polymer (Sulphonated Polysulphone, SPSPH) which may be easily fabricated in various shapes and synthetic hydroxyapatite (HAP) was prepared. The preparation was done by the spontaneous precipitation of HAP in aqueous suspensions of the polymer particles. The time the precipitation process was allowed to proceed was used to regulate the inorganic content of the composite. The preparation thus obtained, in addition to its effectiveness in inducing HAP formation, could be easily fabricated in various shapes, including films. The SPSPH-HAP composite films, surface area totaling ca. 30 cm2 induced the exclusive formation of HAP with rates proportional to the solution supersaturation. No induction times preceded the formation of HAP. Kinetics analysis with respect to HAP yielded an apparent order of precipitation of 6.0+/-0.4, suggesting polynuclear growth with the formation of nuclei above nuclei. The surface energy calculated from the rates of crystal growth on the polymeric substrate gave for HAP the value of 185 mJ m(-2) of order of magnitude typical for crystalline solids.

Crystal Orientation of Hydroxyapatite Induced by Ordered Carboxyl Groups

Hydroxyapatite (HAp) crystals were grown from simulated body fluid (SBF) onto the arachidic acid monolayers with carboxyl groups, which were prepared by the Langmuir-Blodgett (LB) method on substrates. From X-ray diffraction patterns, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and infrared spectra, it was concluded that the crystalline phase nucleated on the LB monolayers was HAp, which was induced by the monolayer because no crystalline materials were grown on substrates without a monolayer. According to SEM and TEM observations, HAp precipitates were hemispherical aggregates consisting of the plate-like crystallites whose specific {100} surfaces were well developed. The HAp crystallites were preferentially oriented with their c-axes in a specific direction parallel to the substrate near the inorganic/organic interface, which suggests the control of the crystallographic orientation in HAp by the aligned carboxyl groups in the LB monolayer. Copyright 2001 Academic Press.

Processing and properties of sol-gel bioactive glasses

Melt derived 45S5 Bioglass(R) has been studied for more than 25 years. Bioglass(R) has excellent biocompatibility, and its surface reactivity has contributed to its clinical success over the past 10 years. Recently, porous bioactive glasses have been derived through sol-gel processing in an attempt to increase the specific surface area, and, thus, the surface reactivity and degradability of the material. This allows the material to be replaced ultimately by natural tissue while it stimulates bone regeneration. In this work, the processing and properties of these sol-gel bioactive glasses are discussed, and a new drying method and treatment is described to make homogeneous particulate and monoliths on a production scale.

In vivo comparison of bioactive glass particles in rabbits

Bioglass particles of the compositions 45s5, 52s and 55s were implanted in the distal femoral epiphysis of rabbits. Animals were sacrificed at 7, 28, and 84 d postoperatively and specimens investigated using light microscopy and histomorphometry. Bone bonding occurred in a zentripetal fashion and fastest for 45s5. Bone formation was hampered at the core of the implantation bed where bone bonding showed a peak at 28d and diminished at 84d (except for 55s). This went along with a significant increase in numerous multinuclear giant cells (MNGC). Implantation model, particle size and surface-area-to-volume ratio are discussed as possible parameters determining bone regeneration.

Effects of amelogenin on the transforming surface microstructures of Bioglass in a calcifying solution

Topographies of a bioactive glass (45S5 type Bioglass(R)) during 0-4 h of immersion in a supersaturated calcifying solution (SCS) and the SCS containing recombinant porcine amelogenin rP172 (SCS(rP172)) were observed by atomic force microscopy. Other techniques including X-ray diffraction, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, and transmission electron microscopy were used for some complementary microstructural investigations. The smooth Bioglass surface changed to be very rough after 0.5 h of SCS immersion because of glass network dissolution. Spherical silica-gel particles with diameters of 150-300 nm consisting of substructures of 20-60 nm across had formed on the sample surfaces after 1 h of SCS immersion. The chemisorption of amorphous calcium phosphate and crystallization of nanophase apatite were seen to occur epitaxially on the silica-gel structures during 1-4 h of SCS immersion. During the first 0.5 h of SCS(rP172) immersion, more than 95% of rP172 protein in solution was adsorbed onto the sample surfaces and generated spherical assemblies of 10-60 nm diameters. During 0.5-4 h of SCS(rP172) immersion, the protein assemblies of rP172 remarkably induced the formation of orientated silica-gel plates (approximately 100-nm wide and 50-nm thick) and subsequently of long and thin apatite needle crystals. The recombinant amelogenin rP172-modulated apatite crystals resembled those formed in the early stage of tooth enamel biomineralization, suggesting the functional roles of amelogenins during the oriented growth of enamel crystallites and a great potential for amelogenins in applications designed to fabricate enamel-like calcium phosphate biomaterials.

Temporal zeta potential variations of 45S5 bioactive glass immersed in an electrolyte solution

45S5 bioactive glass (BG) is a bioactive material known to bond to bone in vivo through a surface calcium phosphate (Ca-P) layer. The goal of this study was to address the importance of BG surface charge in the bioactive response by examining the relationship between charge variations and the formation of the surface Ca-P layer. The zeta potential of BG in an electrolyte solution (TE) was measured by particle electrophoresis, and the formation of a Ca-P layer was characterized using SEM, EDXA, and FTIR. Si, Ca, and P solution concentrations also were determined. The initial BG surface was negatively charged, and two sign reversals were detected during 3 days of immersion. The first, from negative to positive after 1 day, is attributed to the adsorption of cations at the BG surface, and the second reversal was due to the precipitation of phosphate ions from solution. A strong correlation was found between the formation of a Ca-P layer and BG surface zeta potential variations. The dynamic shift in zeta potential from an initially negative surface to a positively charged surface directly corresponded with the formation of an amorphous Ca-P layer. In addition, when the glass surface matured into a crystalline Ca-P layer, it was associated with a reversal from a positive to a negative surface. Future work will focus on the effects of protein adsorption on BG surface charge and Ca-P layer formation kinetics as well as on cellular response to a changing BG surface.

Apatite formation on ethylene-vinyl alcohol copolymer modified with silanol groups

The surfaces of ethylene-vinyl alcohol copolymer (EVOH) substrates were modified with silanol (Si-OH) groups, and their apatite forming ability was examined in a simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma or in a solution with ion concentrations 1.5 times those of SBF (1.5SBF). The surface modification of EVOH was carried out by reacting 3-isocyanatopropyltriethoxysilane, followed by hydrolysis of the ethoxysilyl groups into Si-OH groups. However, no apatite formation was observed on the EVOH substrate thus modified, even after 3 weeks in SBF and 1.5SBF. The Si-OH modified EVOH substrate was further modified by hydrolysis and polycondensation of tetraethyoxysilane (TEOS). It was found that the apatite forms on the TEOS-modified substrate within 3 weeks in 1.5SBF. These results suggest that the presence of a large amount of Si-OH groups (i.e., a cluster of Si-OH groups) on the substrate is prerequisite to apatite formation in the body environment. Apatite-EVOH composites prepared by this process might be useful as hard tissues substitutes.