Papers by Author: Shinichi Ogata

Abstract: Electrophoresis can transport ions more rapidly and directionally in a gel. The controlled precipitation of calcium phosphates in an agarose gel was attempted by electrophoresis of calcium and phosphate ions. Wells were prepared on an agarose gel. A CaCl2 solution was placed in wells on the positive side and a Na2HPO4 solution in wells on the negative side. A potential of 100 V was then applied. White precipitates appeared in the gel after 11 min. The white area initially became larger and more intense with increasing time. However, after longer periods, the white area decreased and became weaker, before disappearing after 45 min. Spinous precipitates with a diameter of about 500 nm were obtained when the gels were collected after 20 min. The precipitates were characterized as particles of calcium phosphate.

Abstract: Organic-inorganic hybrids composed of organic polymer and apatite is quite attractive as novel bone-repairing materials since it has mechanical performance analogous to those of natural bone as well as bone-bonding ability, i.e. bioactivity. To fabricate such an apatite-polymer hybrid, biomimetic process has been recently paid much attention. In this process, bone-like apatite is deposited on the surfaces of organic substrates in simulated body fluid (SBF, Kokubo solution) having ion concentrations analogous to those of human extracellular fluid or more concentrated solutions. Previous studies showed that the apatite deposition is triggered by a catalytic effect of carboxyl groups (COOH) on the surfaces of the organic substrates. In this study, we examined apatite deposition on natural polypeptides derived from crops in a biomimetic solution. We selected gluten derived from wheat and zein derived from corn. Both of gluten and zein formed bone-like apatite on their surfaces in a solution that has inorganic ion concentrations 1.5 times those of simulated body fluid, when they were treated with 1 mol/L calcium chloride solution. High content of acidic amino acids such as glutamic acid and aspartic acid in gluten and zein would give large amount of carboxyl groups effective for the apatite nucleation.

Abstract: Our previous study presented that sericin, a kind of silk protein, had high ability of apatite formation under a condition mimicking body environment when the sericin contains high content of β sheet structure. To confirm the effectiveness of β sheet structure on apatite nucleation, we attempted to synthesize of polypeptide containing β sheet structure and investigate apatite formation in 1.5SBF that has 1.5 times the inorganic ion concentrations of human blood plasma. Poly(FEFEFEFG) was synthesized as the polypeptide consisting mainly of β sheet structure. Formation of hydroxyapatite was observed on the film of the poly(FEFEFEFG) after soaking in 1.5SBF within 7 days. We could confirm that β sheet structure was effective even in the synthetic polypeptide.

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 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.

Abstract: Porous a-tricalcium phosphate (a-TCP) ceramics are attractive as a novel bioresorbable material for bone repair, since they can be easily fabricated through conventional sintering of b-TCP at high temperature. However, the solubility of a-TCP is too high to keep its body until the bone defect is repaired completely. Coating of the a-TCP porous body with organic polymer is a way to reduce the degradation rate. In the present study, biodegradation of a-TCP porous body coated with silk sericin was evaluated in vivo. Bone repair at the defect made in rabbit tibia was nearly completed after 4 weeks. Higher density of cortical bone was estimated for a-TCP coated with sericin than for mere a-TCP. The a-TCP porous body coated with sericin is expected as a material that show less degradation than mere a-TCP, and may result in suitable bone repair.

Abstract: Biphasic ceramic consisting of tricalcium phosphate with α- and β -phases (αβ-TCP) is a candidate as biodegradable bone substitutes since its biodegradability may be controlled by the ratio of the phases. In the present study, preparation of porous αβ-TCP body with continuous pores of 10-50 µm in diameter was attempted using additives of Mg, and its in vivo behavior was examined. Powder of β-TCP was mixed with Mg and potato starch to form slurry, followed by loading in polyurethane foam. The sample was fired at 1400°C for 12 hours for sintering process. α-TCP content of the sample decreased with increasing the Mg content, while β-TCP increased. Ceramic body consisting of β-TCP phase was obtained when 1.0 mass% of Mg was added. Porosity of the body decreased with increasing the content of Mg. The αβ-TCP body with 80% porosity was obtained when the content of Mg was 0.1 mass%. The in vivo experiments showed that the rate of degradation of the obtained αβ-TCP was almost same as α-TCP, and much higher than β-TCP.