Papers by Author: Giichiro Kawachi

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: Globular-shaped beta-tricalcium phosphate (β-TCP) granules were synthesized using a unique dropping slurry method and the biological response was analyzed by implantation into the rat femur. Two kinds of globular-shaped β-TCP granules, composed of either rod-shaped particles or conventional non-rod-shaped particles were synthesized, implanted into the left femurs of 8-week-old female Wistar rats, and analyzed histologically. Commercially available β-TCP granules composed of conventional non-rod-shaped particles were also implanted as a control experiment. Four weeks after the operation, part of each implant was already resorbed and the resorbed area was replaced by newly formed bone tissue and bone marrow. Eight weeks after the operation, the resorption and replacement were advanced in each implant. At 12 weeks after the operation, residual globular-shaped β-TCP granules composed of rod-shaped particles were resorbed into compact petrotic bone tissue almost completely. The formation of less compact petrotic bone tissue was observed in specimens implanted with globular-shaped β-TCP granules composed of conventional non-rod-shaped particles. Commercially available β-TCP granules composed of conventional non-rod-shaped particles were mostly resorbed into trabecular bone and the formation of compact petrotic bone tissue was rarely observed. These data suggested that both the unique spherical shape and microstructure of β-TCP particles affected bone-forming activity after the operation.

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: 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: Micrometer-sized hydroxyapatite (HA) with rod-shape was prepared to investigate protein adsorption onto its crystal face, through hydrothermal processing. Adsorption of Bovine serum albumin (BSA) and Lysozyme from chicken egg white (LSZ) on rod-shaped HA crystals with approximately 50 μm in length and 1 μm thickness was examined in phosphate buffer solution. The amount of adsorbed BSA was decreased with increasing phosphate concentration in the examined solution. Adsorption of LSZ was increased with increasing phosphate concentration in the buffer solution up to 50 mmol/L (mM), while it was remarkably decreased when the phosphate concentration reached approximately 100 mM. These phenomena lead to understanding of chromatographic characters of HA for separation of acidic and basic proteins.

Abstract: After hydrothermal treatment of tricalcium phosphate (TCP), calcium deficient hydroxyapatite (HA) with much amount of a-surface (h00) was obtained. It was considered that c-surface of HA had larger surface tension than that of a-surface, therefore HA crystals elongated along c-axis of <001> directions. By using hydrothermal treatment, difference of surface tension was affected crystal growth of HA. The adsorption property of HA will be controlled by designing of HA morphology, because different crystal surfaces have different properties.

Abstract: Porous granules of β-tricalcium phosphate (β-Ca3(PO4)2; β-TCP) were prepared from porous hydroxyapatite granules with calcium deficient composition synthesized by hydrothermal method. The β-TCP granules were 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 granule size, particle size, and micro-pore size could be controlled by our unique method. The porous granules of β-TCP must be suitable for the bone graft material and for scaffold of cultured bone.

Abstract: Porous apatite carrier with high selectivity of adsorption was prepared by using hydrothermal method. α-TCP as the starting material was changed into hydroxyapatite at the temperature above 120 °C for the period over 3 h under saturated vapor pressure. Porous apatite carriers were composed of rod-shaped crystals with non-stoichiometric hydroxyapatite composition. Since HA crystals had rod like shape, the area of a-surface was larger than that of c-surface. This carrier had higher selectivity for bovine serum albumin (acidic protein) than lysozyme chloride (basic protein). This material must be suitable as scaffold for cultured bone, for bone graft material and for drug delivery system (DDS).

Abstract: Porous sheets of hydroxyapatite (Ca10(PO)4(OH)2; HA) with about 50 µm to 1 mm in thickness and porous HA granules of about 50 µm to 1 mm in size with tailored crystal surface were prepared by the hydrothermal vapor exposure method at the temperatures above 105 °C under saturated vapor pressure of pure water. Porous HA sheets with about 75 % porosity prepared at 120 °C were composed of rod-shaped crystals of about 30 µm in length. Porous HA granules prepared at 160 °C were also composed of rod-shaped crystals of about 20 µm in length with the mean aspect ratio of 30. These crystals were elongated along the c-axis. Rod-shaped HA crystals were locked together to make micro-pores of about 0.1 µm in size. Both of materials were nonstoichiometric HA with calcium deficient composition. These materials must have the advantage of adsorptive activity, because they had large specific crystal surface and much micro-pores.

Abstract: Porous plates of hydroxyapatite (Ca10(PO4)6(OH)2; HA) with about 0.5 to 5 mm in thickness and porous HA granules of about 40 µm to 1 mm in size with tailored crystal surface were prepared by the hydrothermal vapor exposure method at the temperatures above 105 °C under saturated vapor pressure of pure water. Porous HA plates with about 75 % porosity prepared at 120 °C were composed of rod-shaped crystals of about 20 µm in length. Porous HA granules prepared at 160 °C were also composed of rod-shaped crystals of about 20 µm in length with the mean aspect ratio of 30. These crystals were elongated along the c-axis. Rod-shaped HA crystals were locked together to make micro-pores of about 0.1 to 0.5 µm in size. Both of materials were nonstoichiometric HA with calcium deficient composition. These materials must have the advantage of adsorptive activity, because they had large specific crystal surface and much micro-pores.