Akiyoshi Osaka

Apatite deposition on thermally and anodically oxidized titanium surfaces in a simulated body fluid.

By application of a special specimen set-up, thermally oxidized titanium specimen pairs were found able to deposit apatite on the contact surfaces after soaking for 7 days in the simulated body fluid (SBF) of Kokubos recipe. The specimens oxidized at 400 degrees C and 500 degrees C showed the highest ability of apatite deposition. Both increase and decrease in oxidation temperature from this range caused the apatite deposition ability to decrease. The specimen without treatment failed to deposit any apatite. Specimens anodically oxidized in electrolytes of H(3)PO(4), H(2)SO(4) and acetic acid exhibited very low ability of apatite deposition. Furthermore, the specimen thermally oxidized at 400 degrees C was even able to help the surfaces of PTFE and silicone deposit apatite in the PTFE-Ti and silicone-Ti pairs. This in vitro experimental results indicated that the difference in apatite deposition among various titanium oxides does exist and can be distinguished by applying the present specimen set-up. The mechanism of the apatite deposition on the contact surfaces was discussed in relation to the passive dissolution of titanium in SBF. The release of titanium hydroxide and OH(-) ions from the titanium surfaces and their accumulation inside the confined space between the two contact surfaces were suggested to be responsible for the apatite deposition.

The chitosan prepared from crab tendons: II. The chitosan/apatite composites and their application to nerve regeneration

The chitosan tubes derived from crab tendons form a hollow tube structure, which is useful for nerve regeneration. However, in order to use the chitosan tubes effectively for nerve regeneration, there remain two problems to be solved. First, the mechanical strength of the tubes is quite high along the longitudinal axis, but is somewhat low for a pressure from side. Second, the chitosan tube walls swell to reduce the inner space of the tubes in vivo. These two problems limit the clinical use of the chitosan tubes. In this study, to solve the problems, apatite was made to react with the chitosan tubes to enhance the mechanical strength of the tube walls. Transmission electron microscopy showed that apatite crystals were formed in the walls of the chitosan tubes. The c-axis of the crystals aligned well in parallel with chitosan molecules. These results indicate that the apatite crystals grow in the tubes starting from the nucleation sites of the chitosan molecules, probably by forming complexes with amino groups of chitosan and calcium ions. Further, the tubes were thermally annealed at 120 degrees C to prevent from swelling, and simultaneously formed into a triangular shape to enhance the stabilization of the tube structure. By these treatments, the hollow tubes could keep their shape even in vivo after implantation. Animal tests using SD rats further showed that the chitosan tubes effectively induced the regeneration of nerve tissue, and were gradually degraded and absorbed in vivo.

Physical, chemical and in vitro biological profile of chitosan hybrid membrane as a function of organosiloxane concentration

We attempted to prepare chitosan-silicate hybrid for use in a medical application and evaluated the physico-chemical properties and osteocompatibility of the hybrids as a function of gamma-glycidoxypropyltrimethoxysilane (GPTMS) concentration. Chitosan-silicate hybrids were synthesized using GPTMS as the reagent for cross-linking of the chitosan chains. Fourier transform infrared spectroscopy, (29)Si CP-MAS NMR spectroscopy and the ninhydrin assay were used to analyze the structures of the hybrids, and stress-strain curves were recorded to estimate their Youngs modulus. The swelling ability, contact angle and cytocompatibility of the hybrids were investigated as a function of the GPTMS concentration. A certain fraction of GPTMS in each hybrid was linked at the epoxy group to the amino group of chitosan, which was associated with the change in the methoxysilane group of GPTMS due to hybridization. The cross-linking density was around 80% regardless of the volume of GPTMS. As the content of GPTMS increased, the water uptake decreased and the hydrophilicity of the hybrids increased except when the content exceeded amolar ratio of 1.5, when it caused a decrease. The values of the mechanical parameters assessed indicated that significant stiffening of the hybrids was obtained by the addition of GPTMS. The adhesion and proliferation of the MG63 osteoblast cells cultured on the chitosan-GPTMS hybrid surface were improved compared to those on the chitosan membrane, regardless of the GPTMS concentration. Moreover, human bone marrow osteoblast cells proliferated on the chitosan-GPTMS hybrid surface and formed a fibrillar extracellular matrix with numerous calcium phosphate globular structures, both in the presence and in the absence of dexamethasone. Therefore, the chitosan-GPTMS hybrids are promising candidates for basic materials that can promote bone regeneration because of their controllable composition (chitosan/GPTMS ratio).

In vitro apatite deposition on titania film derived from chemical treatment of Ti substrates with an oxysulfate solution containing hydrogen peroxide at low temperature

Abstract Thin titania film consisting of anatase and rutile was deposited on Ti substrates when soaked in a TiOSO 4 /H 2 O 2 solution and aged in hot water. H 2 O 2 corroded the Ti substrates, yielded a porous surface, and kept the solution from peptization. Thicker titania layers were formed in favor of both a greater supersaturation of Ti(IV) in the solution and a higher concentration of hydrated Ti(IV) derived by the corrosion of Ti and the hydrolysis of TiOSO 4 . The effects of aging in hot water were accounted for as they caused structural relaxation of the surface layer involving a rearrangement of Ti–OH and eliminating residual species like peroxide ions. Those titania layers were thus favored to deposit apatite when the Ti substrates were placed under a body environment, i.e. soaked in a simulated body fluid of Kokubos recipe.

The chitosan prepared from crab tendon I: the characterization and the mechanical properties

Crystalline chitosan was prepared from crab tendon consisting mainly of chitin, including various proteins and calcium phosphates. The crab tendon has high mechanical properties due to its aligned molecular structure. Crab tendon components, i.e. proteins and calcium phosphates, were removed by deacetyl treatment using 50wt% NaOH aqueous solution at 100 degrees C, and a subsequent ethanol treatment. As judged from microscopic observations using an optical polarizer, the treated chitosan remained intact regarding its aligned molecular structure, and had a high tensile strength of 67.9+/-11.4MPa. The tensile strength was further enhanced to 235+/-30MPa by a thermal treatment at 120 degrees C, corresponding to the formation of the intermolecular hydrogen bonds.

The effect of citric acid addition on chitosan/hydroxyapatite composites

Abstract Chitosan/hydroxyapatite (HAp) composites have been prepared using a co-precipitation method. According to TEM observations, chitosan molecules formed nano-particles of 250×50 nm in size with small HAp crystals. The particles aggregated and the precipitates were reached a maximal size (17 μm) at a chitosan content of 25 wt.%, where the ζ-potential was around zero. This means that the precipitate size increased with a decrease in ζ-potential, i.e. electrostatic repulsion between the nano-particles. The precipitate size decreased at chitosan contents higher than 25 wt.% with excess chitosan molecules covering the nano-particles, resulting in a repulsion force between positively charged particles. When citric acid was added to a suspension of chitosan/HAp composite, the precipitates increased in size. Although, when citric acid was added to a pure HAp suspension, the citric acid showed no effect on the size. This finding suggests that citric acid affects chitosan rather than the HAp, through the formation of an ionic complex. This size effect has been found at citric acid contents lower than 3 wt.%. The precipitates have been compressed into a cylindrical shape under a uni-axial pressure, the compressive strength increased with increasing citric acid content. The composition of the maximal compressive strength agreed well with that of the maximal precipitate size.

Preparation of alginic acid layers on stainless-steel substrates for biomedical applications

This study is concerned with the blood compatibility of alginic acid layers immobilized on gamma-aminopropyltriethoxysilane (gamma-APS)-grafted stainless-steel (SUS316L). The surfaces were characterized with contact angle measurement and X-ray photoelectron spectroscopy (XPS). The blood compatibility was evaluated in terms of platelet adhesion and blood clotting time. An in vitro platelet adhesion assay indicated that only a small number of platelets adhered to substrate surfaces modified with gamma-APS and subsequently with alginic acid. Moreover, alginic-acid-immobilized SUS316L substrates had little effect on the blood clotting time. This indicated that alginic-acid-immobilized SUS316L substrates do not adsorb some blood-clotting proteins or factors, or stimulate them.

Synthesis of PDMS-based porous materials for biomedical applications

Polydimethylsiloxane (PDMS) and tetraethoxysilane (TEOS)-based porous organically modified silicates (ORMOSILs) for biomedical applications were synthesized through a sol-gel process, using sucrose particles as templates. These materials were characterized by 29Si CP-MAS NMR spectroscopy, thin film X-ray diffraction, and scanning electron microscopy. Their bioactivity was evaluated using a simulated body fluid (SBF) of Kokubo recipe. These materials had a bimodal porous structure with pores of 300–500 μm and 10–50 μm in diameter. NMR showed that the silanol groups of the PDMS chain cross-linked to silica derived from the hydrolysis and condensation of TEOS. The samples containing Ca(II) exhibited apatite deposition on the pore walls within 3 days in SBF.

Effect of spatial design and thermal oxidation on apatite formation on Ti–15Zr–4Ta–4Nb alloy

Apatite formation on the surface of titanium and its alloys is effective for inducing osteoconductivity when implanted in bony defects. The aim of this study was to investigate the effects of thermal oxidation on apatite formation in macro-grooves on Ti-15Zr-4Ta-4Nb. Thermal oxidation at 500 and 600 degrees C in air led to modification of the Ti-15Zr-4Ta-4Nb surface to rutile phase titanium oxide. Ti-15Zr-4Ta-4Nb thermally oxidized at 500 degrees C in air showed no changes in metallographic structure, but not at 600 degrees C. After soaking in a simulated body fluid for 7days, the formation of apatite could be observed on the internal surfaces of macro-grooves 500mum deep and wide on Ti-15Zr-4Ta-4Nb thermally oxidized at 500 and 600 degrees C in air. These results indicate the potential for osteoconductivity of Ti-15Zr-4Ta-4Nb without changing its metallographic structure, by fabricating only the macro-grooves, i.e., spatial design, and by performing thermal oxidation at 500 degrees C.

Preparation of nanometer-scale rod array of hydroxyapatite crystal.

Fabrication of nano- or micro-structured scaffolds to mimic structural and three-dimensional details of natural bone or teeth has been the subject of much interest, and this study proposes a new strategy for self-assembling one-dimensional hydroxyapatite (HAp) nanorods into organized superstructures. A nanometer-scale rod array of HAp having preferred orientation to the c-axis was successfully prepared simply by soaking calcium-containing silicate glass substrates in Na(2)HPO(4) aqueous solution at 80 degrees C for various periods. Those HAp rods grew perpendicularly to the glass surface, and the crystallites covered the glass surface uniformly, resulting in a dental enamel-like rod array structure consisting of pine-leaf-like structure units.