Katsuo Nakamura

Surface Structure Design and Characterization of Bioabsorbable and Functionally Graded Apatites Originated from Bovine Bone

Abstract. Bioabsorbable and functionally graded apatites (fg-HAp) ceramics were designed using calcined bovine bone (b-HAp) by the partial dissolution-precipitation methods. The fg-HAp ceramics with micro-pores of 10-160 nm had larger specific surface areas (30-40 m2･g-1) than the b-HAp ceramics, although the two HAp ceramics exhibited same macro-pore sizes of 100-600 µm and porosities of 60-80 %. Surface structure of these ceramics was modified by soaking at 309.5 K for 1-90 days in a simulated body fluid (SBF). At 8 days after the soaking, microstructure of the fg-HAp changed from small grains to dense cocoon-like ones by rapid precipitation of HAp microcrystals, while at 14 days, that of the b-HAp was porous urchin-like grains, suggesting that the fg-HAp had higher bone-bonding ability than the b-HAp.

Surface Design and Water Vapor-Adsorption Characteristics of Biomimetic Composite Materials Derived from Salmon Resource

Biomimetic composites of hydroxyapatite (HAp) and collagen with fast bio-absorption and good biocompatibility were designed utilizing salmon bone and skin at 283-293 K and pH 7.5-7.9 by a dissolution-precipitation method. Simultaneously, dissolved-precipitated HAp (dp-HA) was prepared at pH 9-10 using the calcined bone. The HAp/collagen composites (HA-C) were constituted by Ca2+-deficient HAp, I type-collagen and gelatin. At the synthetic temperature of 283 K, collagen fiber and HAp microcrystals were seen, while at 293 K, frock like-agglomerated particles or fiber like-oriented columnar ones were observed depending on the composition ratio (H/C) of HAp to collagen. Specific surface areas and total pore volumes for the HA-C synthesized at 293 K clearly increased with increasing the H/C, although there were micro-and-meso-pores in the pore diameters of 3-30 nm. Concerning water vapor-adsorption isotherms at 298 K for the HA-C powders, hysteresis-curves of the amounts of water vapor adsorbed (V) were recognized in the adsorption-desorption processes. The V values increased with increasing the H/C under the low relative pressures (P/PS) of 0-0.3 that mean monolayer-adsorption of water molecule. However, for H/C=2.2, the V values were the highest under the high P/PS of 0.70-0.90 that mean multilayer-adsorption and the biggest hysteresis-curve was found under the P/PS of 0.45-0.60, suggesting that the HA-C (H/C=2.2) powder not only adsorb water molecule on the surfaces but also absorb one into the crystal structure. Accordingly, the biomimetic HA-C powders will be applied as water-absorbable adsorption materials for cosmetic products or bone-regeneration therapy.

Characterization of Bio-Absorbable and Biomimetic Apatite/Collagen Composite Powders Derived from Fish Bone and Skin by the Dissolution-Precipitation Method

Bio-absorbable and biomimetic composites (HA-C) of hydroxyapatite (HAp) and collagen were designed utilizing salmon bone and skin at 298K and pH 7.5-7.9 by a dissolution-precipitation method. The HA-C powders were consistuted by Ca2+-deficient HAp containing small amounts of Na+ and Mg2+ ions and I type-collagen. Microstructure and surface characteristics of the HA-C powders gradually changed depending on the composition ratio of HAp to collagen (H/C). The HA-C powder of H/C=3.5 had frock like-agglomerated particles consisted of nano-crystals, micro-pore, and meso-pore so that it exhibited high specific surface area (75m2¥g-1) and large total pore volume (0.543 cm3¥g-1). From adsorption isotherms of water vapor at 298K for the HA-C powders, hysteresis - curves of the amounts of water vapor adsorbed were obtained in the adsorption-desorption processes. The amounts of water vapor adsorbed for the H/C=3.5 powder were the highest values under the relative partial pressures of 0.73-0.93. At 2 weeks after implantation of the HA-C powders into the subcutaneous tissue of the back region in rats, collagen was completely bio-absorbed and body fluid permeated into large agglomerated particles, although bio-absorption by multi-giant cell- infiltration was recognized around the surface layers of HAp particles.