Papers by Author: Takahiro Kawai

Abstract: In order to study method for preparing bioactive titanium metal, calcium ions were attempted to be incorporated into the surface of the titanium metal by ion exchange method. Titanium metal was soaked in 5M NaOH solution and 100mMCaCl2 solution and subjected to heat treatment. About 5 atom% of Na was incorporated into the surface of the titanium metal by the NaOH treatment This Na was completely replaced with calcium ion by the CaCl2 treatment and maintained even after the heat treatment. Critical detaching strength of the surface layer to the substrate of NaOH-treated titanium metal was a little increased by the CaCl2 treatment and remarkably increased by the heat treatment. Apatite-forming ability of the NaOH-treated titanium metal in SBF was increased by the CaCl2 treatment, but decreased by the subsequent heat treatment.

Abstract: Apatite formation on polyamide films containing either carboxyl or sulfonic groups was compared in 1.5SBF, whose ion concentrations are 1.5 times those of a simulated body fluid (SBF). The sulfonic groups induced the apatite nucleation earlier than the carboxyl groups. In contrast, the rate of crystal growth depended not on the kind of functional group, but on the degree of supersaturation of the surrounding solution. The more ready association of sulfonic groups with calcium ions may lead to earlier apatite nucleation than that of carboxyl groups. Adhesive strength of the apatite layer to polyamide film containing sulfonic groups was significantly lower than that with carboxyl groups depending on the chemical interactions as well as on the mechanical properties of the polyamide film.

Abstract: Bone morphogenetic protein (BMP) is known as a protein that induces new bone in heterotopic sites. This study was conducted to assess the cell-biological effects of crude porcine BMP and 3 pulp-capping materials by implantation and cell culture methods. The following results were obtained: a new bone site of approx 5mm in diameter were induced in the hind limbs, which confirmed the osteoinductive activity of the crude BMP. The pulp-capping materials hardly influenced the calcification of rat dental pulp (RDP) cells. Our data also suggest that the effect of the crude BMP on the proliferation and calcification depended on its quantity. The finding of a large increase in the ALPase activity and the formation of mineralized nodules caused by the crude BMP , suggests that the crude BMP enhanced the calcification by RDP cells. Consequently, it is quite possible that crude porcine BMP could be used as a pulp-capping material.

Abstract: The aim of this study is evaluate to the cellular viability of elution from the newly developed resin and Osteobond® in vitro. The basis of the newly developed resin are methacryloyloxyethyl methyl succinate and 1,6-Hexanediol dimethacrylate. The basis of Osteobond is methyl methacrylate. The concentrations of basis in each elution were determined by high-performance liquid chromatography (HPLC). Cellular viabilities of L-929 mouse fibroblasts were evaluated by direct cells counting, and then, each IC50 value was calculated. Moreover, patterns of cell death were analyzed using annexin V/propidium iodide staining with the phase-contrast microscope and flow cytometry. The concentration of Osteobond elution was 2.16 mM of MMA, and the newly developed resin elution was 1.02 mM of TA and 1.87 x 10-2 mM of HX. Until 72 hours of incubation, treatment with each elution impaired the viability of L-929 cells in a dose-dependent manner. IC50 value of Osteobond was 6.48 x 10-4 mM of MMA. However, IC50 of the newly developed resin was not calculated. Treatment with Osteobond elution showed more necrotic cells than with the newly developed resin elution. In conclusion, the results demonstrated much more excellent cellular viability of the newly developed resin than that of MMA resin. Thus, it is suggested that the newly developed resin will be more useful as an implantation material for dentistry and orthopaedics.

Abstract: Hybrids consisting of hydroxyapatite and biodegradable polymers are attractive materials for bone repair. We recently developed hydroxyapatite-alginate hybrids through a soaking process of alginate modified with 3-aminopropyltriethoxysilane (APES), ethylenediamine (EDA) and CaCl2 in a solution mimicking body fluid such as SBF, 1.5SBF proposed by Kokubo et al.. In this study, biological behavior of the apatite-alginate hybrid fabricated through modification with APES and CaCl2 were evaluated after implantation in a rat tibia, in comparison with that of alginate gel without hydroxyapatite. The higher degree of calcification was observed for the hydroxyapatitealginate hybrid than the alginate gel without hydroxyapatite. The hydroxyapatite precipitated on and inside alginate allowed the hybrid to show not only osteoconduction but also suitable biodegradation after implantation in bony defect.

Abstract: The purpose of this study was to evaluate the physical properties of the composite membrane before and after soaking in simulated body fluid (SBF) and discuss both degradation and maintenance of their properties. Before and after soaking in SBF, some deposits were found on the preexisted apatite crystals, and Ca and P were mainly detected by energy dispersive X-ray analyzer (EDX). Our results suggest that the composite membrane consisting of apatite and the biodegradable PLGA copolymer would have excellent biocompatibility and maintain adequate physical properties for in vivo use.

Abstract: It is well known that bone morphogenetic protein (BMP) induces bone formation and requires for carriers. Poly-lactic acid / poly-glycolic acid (PLGA) is frequently used as the carriers of BMP. We developed a biodegradable composite PLGA membrane, which was containing oriented needle-like apatite with BMP. The composite membranes were implanted into the thigh muscle pouch of 3-week-old-mice. At 3 weeks after implantation, the implanted area was observed by optical microscopy. The composite membrane containing oriented needle-like apatite with BMP induced new bone formation. It seems that this composite membrane might be a scaffold of BMP and promoting the healing of bone defects.

Abstract: Organic polymer coated with hydroxyapatite (so-called apatite) on its surface is a candidate of new hybrid materials for medical applications since it is expected to show bone-bonding ability and achieve mechanical properties derived from organic substrate. We have shown that some kinds of polyamide films containing carboxyl group or sulfonic group form hydroxyapatite in the simulated body environment, when they are incorporated with calcium chloride. In the present study, the polyamide containing carboxyl groups were modified with silanol groups and its apatite-forming ability was investigated in 1.5SBF, which has ion concentrations 1.5 times those of a simulated body fluid (SBF). It was found that polyamide films modified with silanol groups showed higher ability to induce apatite on its surface in 1.5SBF than the films without the modification, when they were incorporated with calcium chloride.

Abstract: The adhesion of bovine collagen type I, bovine serum albumin, bovine IgG, 1 % and 10 % (v/v) human serum to hydroxyapatite (HA), silicon-substituted hydroxyapatite (Si-HA) and tissue culture plastic were studied. The materials were incubated at 37 °C for 30 minutes, after which the protein solution was removed and analyzed. The adsorbed protein was evaluated by electrophoresis and immunoassay after extraction from the materials. The degree of adhesion was higher for collagen, followed by IgG and albumin on all materials. However there was no difference in the amount of collagen adsorbed onto the surface of each material and this was also the finding with albumin and IgG. These results suggest that the increased bioactivity seen with Si-HA is not due to the degree of protein adhesion, but may possibly be due to changes in the conformation of the bound proteins.