Papers by Author: Koji Ioku

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: 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: Since 2001, we have clinically utilized human bone marrow-derived mesenchymal stem cells (MSCs) for bone regeneration. The osteogenic ability of MSCs has been assessed by measurement of alkaline phosphatase activity and calcium deposition. As for the detection of in vitro calcium deposition, we have established the method using calcein, which is a calcium-binding fluorescence material. Using this fluorescence material, we could observe the calcium deposition and then estimate the value of calcium deposition. In this report, we cultured rat MSCs on culture plate as well as transparent β-TCP, and calcium deposition was visualized and quantitated using an image analyzer. After 2 weeks differentiation of rat MSCs to osteoblasts, calcium deposition on β-TCP was observed as a signal of calcium-binding fluorescence. This fluorescence signal was also quantitated with an image analyzer.

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: 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: Newly developed porous β-tricalcium phosphate composed of rod-shaped particles was grafted into distal end of the left femur of female Japan White rabbit. As a control, hydrixyapatite generated in the same size was grafted. In both implants, 350µm in diameter-sized holes were created vertically and horizontally. Three weeks after grafting, margin of the β-tricalcium phosphate was absorbed by osteoclasts and bone formation was seen near the absorbed region. Twenty-four weeks after grafting, more than 80% of the β-tricalcium phosphate was absorbed and newly formed bone was prominently observed. The hydroxyapatite was not remarkably absorbed even 24 weeks after grafting, and newly formed bone was observed only in the holes created in the implants. These results suggest that porous β-tricalcium phosphate composed of rod-shaped particles has highly biodegradable and osteoconductive nature, and appropriate to bone graft substitute.