Papers by Author: Masanobu Kamitakahara

Abstract: Octacalcium phosphate (OCP) is regarded as a precursor of hydroxyapatite (HA) which is a main inorganic comstituent of human bones and teeth. OCP is becoming regarded as an important biomaterial. Recently, implanted OCP was found to be converted to apatitic phase in the body and support bone regeneration. Therefore, it is important to reveal the transformation mechanism of OCP to HA for revealing the mechanism of bone formation and for the development of biomedical materials for bone. In this study, we focused on the dissolution of OCP and precipitation of HA. OCP particles were immersed in distilled water at 60 °C. The temporal change of the immersed powders and immersing solution were examined, and the transformation mechanism of OCP to HA was discussed. As there was an unreactive period in the first stage of the transformation, HA crystals seemed to grow easily once HA nuclei were formed. It is speculated that HA nuclei formed on OCP crystals by heterogeneous nucleation, and then HA crystals grow using calcium and phosphoric ions supplied from dissolved OCP.

Abstract: Tricalcium phosphate (TCP) ceramics are useful biodegradable bone-repairing materials. Silicate-containing TCP ceramics are expected to be useful as biodegradable bone-repairing materials which promote the bone regeneration because it has been reported that the silicate promotes bone formation. In the present study, silicate-containing TCP ceramics were prepared through a wet chemical process at the starting compositions from 0 to 0.05 in the Si/(P+Si) molar ratio. The prepared silicate-containing TCP ceramics were characterized and evaluated in vitro. The crystal phase of the products was α-TCP, and the tendency that the lattice constants linearly shifted from 0 to 0.05 in the starting Si/(P+Si) molar ratio was observed. It is speculated that the added silicate was incorporated in the crystal structure of TCP. The pellets were prepared by a sintering process, and soaked in a simulated body fluid (SBF) to estimate their bone-bonding ability. The addition of silicate to TCP promoted to hydroxyapatite formation on the TCP ceramics in SBF. This result implies the high possibility that the silicate addition would promote the bone-bonding ability of the TCP ceramics.

Abstract: Three types of calcium phosphate porous materials were prepared by the applied hydrothermal method. One of them was non-stoichiometric hydroxyapatite (HA) with calcium deficient composition and the others were β-tricalcium phosphate (β-TCP) and HA/β-TCP bi-phase material. Granules with several millimeter in size of calcium deficient HA, β-TCP and HA/β-TCP could be prepared. These granules with porosity over 70 % were composed of rod-shaped particles with aspect ratio about 10. Rod-shaped particles were locked together to make sub-micro-sized pores of about 0.1 to 0.5 µm in size. These materials must be suitable for the bone graft materials and as the scaffolds of cultured bone.

Abstract: Spherical beta-tricalcium phosphate (b-TCP) granules synthesized using a unique dropping slurry method expressed good osteoconductivity with prominent bone apposition and bioresorbability when implanted into the rat femur (Gonda et al., Key Eng. Mater. 361-363:1013-1016, 2008). The spherical b-TCP granules were implanted into the bone defect created in the distal end of the right femur of each 8-week-old female Wistar rat. To analyze performance of the spherical b-TCP granules as bone substitute in the bone with reduction in osteogenic potential, the right sciatic neurectomy was performed after implantation and the right hind limb was kept unloaded for 2 weeks before euthanization. Four weeks after implantation, some spherical b-TCP granules with resorption in part were surrounded by newly formed bone. Eight and 12 weeks after implantation, most of the residual b-TCP granules were embedded in newly formed bone, and total volume of the implant and newly formed bone was more than the other portions of the bone or the bone of control animals. Osteoclast activity in the implanted area was also higher than the other portions of the bone or the bone of control animals. Replacement of the intraosseous residual b-TCP granules for bone progressed at 12 weeks after implantation compared to those at 8 weeks after implantation. These data suggested that the spherical b-TCP granules stimulated osteogenesis and osteoclast activity of the unloaded bone.

Abstract: Porous materials of β-tricalcium phosphate (β-Ca3(PO4)2; β-TCP) were prepared from porous hydroxyapatite (Ca10(PO4)6(OH)2; HA) with calcium deficient composition of Ca/P molar ratio of 1.50 synthesized by hydrothermal method. The porous β-TCP was composed of rod-shaped particles of about 10-20 μm in length. Rod-shaped particles were locked together to make micro-pores, and the size of micro-pores formed by tangling of rod-shaped particles was about 0.1-0.5 μm. The particle size and micro-pore size could be controlled by our unique method. It must be suitable for the bone graft material and as the scaffold of cultured bone.

Abstract: A composite layer of fibroblast growth factor-2 (FGF-2) and low-crystalline apatite was formed on an ethylene-vinyl alcohol copolymer specimen using two types of aqueous calcium phosphate solutions supplemented with 10 !g·mL-1 FGF-2; one is a CP solution that is prepared by dissolving chemical reagents into ultrapure water and the other is an RKB solution that can be prepared by mixing clinically approved infusion fluids. In both solutions, a sufficient amount of FGF-2 for new skin tissue formation (1 !g·cm-2) was immobilized on the specimen surface.

Abstract: The present study examined the possibility of using spherical porous granules of hydroxyapatite (HA, Ca10(PO4)6(OH)2) composed of rod-shaped particles as the drug delivery system. The granules composed of rod-shaped HA were successfully prepared by an emulsion method and a hydrothermal treatment. When the rod-shaped granules were soaked in phosphate buffer salines containing lysozyme chloride or albumin, the granules of rod-shaped HA adsorbed more albumin than lysozyme. On the other hand, the HA granules prepared by a normal sintering method adsorbed little lysozyme chloride or albumin. The HA granules composed of rod-shaped particles are expected to be useful as carriers of negatively charged substances.

Abstract: Si-containing tricalcium phosphate (TCP) ceramics are expected to be useful biodegradable bone substitutes that enhance bone regeneration because TCP is a biodegradable ceramic and Si is the trace element that enhances bone formation. We successfully synthesized the Si-containing TCP with different Si contents through a wet process. The Si addition lowered the temperature of phase transition from β-TCP to α-TCP. After the sintering the compacts of Si-containing TCP powders at 1400 oC, the sintered ceramics showed higher density than those of Si-free TCP. The Si addition was effective to promote the sintering of TCP.

Abstract: CaO-SiO2 gels for bioactive organic-inorganic composites were prepared from tetraethoxysilane (TEOS) and calcium nitrate tetrahydrate (Ca(NO3)2⋅4H2O) by a sol-gel method with the addition of the various amount of polyethylene glycol (PEG). The effects of PEG on morphology and bioactivity of the gel were investigated. The samples with the starting compositions of Ca(NO3)2 : TEOS = 30 : 70 in molar ratiowere prepared with or without coexistence of PEG. All the examined gels were obtained as a crack-free bulk bodies after gelation and aging. FT-IR spectra of the prepared gels showed that the gels have similar contents of silanol groups regardless of the amount of PEG. SEM observation showed that the gel consists of aggregates of 2-3 μm spherical particles with a diameter of 2-3 μm when it was prepared with the addition of PEG at a molar ratio of PEG : TEOS = 0.002 : 1, while it consists of aggregates of spherical particles with a diameter of 50 nm at a molar ratio of PEG : TEOS = 0.004 or 0.007 : 1. The size of the CaO-SiO2 powder can be decreased with increasing the amount of the added PEG. All the samples, regardless of the amount of the added PEG, formed apatite on their surfaces in a simulated body fluid (SBF) within 1 d. These results suggest that bioactive fine spherical particles with various size can be obtained through sol-gel processing under co-existence of appropriate amounts of PEG.

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.