Papers by Author: Kenichi Shinomiya

Abstract: Hydroxyapatite/hyaluronic acid (HAp/HyA) and hydroxyapatite/chondroitin sulfate (HAp/ChS) microparticles, which show the high adsorption ability of proteins, high biocompatibility and osteoconductivity, are potential scaffolds for a time-controlled BMP release. The present study evaluated the biocompatibility and osteoconductivity of the composites after injection into bone defect. Drilled bone holes were made at tibia and femur of Japanese white rabbits, and HAp/HyA or HAp/ChS was implanted into each bone hole using an injection syringe. After 2 and 4 weeks of implantation, rabbits were sacrificed and histological observations were conducted with HE, TRAP, and ALP staining. Histological observations revealed that HAp/ChS has superior biocompatibility compared with HAp/HyA, and 20% HAp/ChS promotes bone formation as well as osteoblast activities compared with lower ratios of HAp/ChS.

Abstract: In the field of bone tissue engineering using cells combined with scaffolds, it is important to efficiently load cells into porous scaffolds. We devised a novel cell-loading method
into porous beta-tricalcium phosphate (β-TCP) blocks. In this study, we compared this method with two conventional cell-loading methods in terms of cell-loading efficiency and in vivo bone formation capability. Bone marrow stromal cells (BMSCs) were obtained from the femurs of Fisher rats. After about 10 days of culture, BMSCs were harvested and suspended in the plasma of the Fisher rats at a concentration of 2×106 cells/ml. This cell suspension was loaded into porous β-TCP cubes (5×5×5mm) by using three loading methods: a soaking method, a post low-pressure method and a pre low-pressure method (the novel method). These β-TCP cubes were cross-sectioned and stained with toluidine blue and cell-counted. Cell-loading efficiency was significantly higher when using the novel methods. For the study of in vivo bone formation capability, nearly confluent BMSCs were exposed in an osteogenic medium supplemented with 10-7 M dexamethasone, 50µg/ml L-ascorbic acid phosphate and 10mM β-glycerophosphate for 4 days. These osteogenic cells were harvested and suspended in the plasma of the Fisher rats at a concentration of 2×106 cells/ml. This cell suspension was loaded into porous β-TCP cubes (5×5×5mm) by using the three cell-loading methods. Immediately, these β-TCP cubes were implanted at subcutaneous sites in the backs of 7-week-old male Fisher rats and harvested at postoperative 3 and 6 weeks. After cross-sectioning, these sections were stained with hematoxylin and eosin, and the new bone formation area was quantified. Consistent with cell-loading efficiency, in vivo bone formation capability was significantly higher in the novel method at postoperative 6 weeks. We showed the usefulness of the novel cell-loading method in bone tissue engineering.

Abstract: Transplantation surgeries of autologous bone require a second surgery with inherent risks. To avoid these risks, we developed a multi porous implant of hydroxyapatite/collagen composite with desirable biophysical properties (flexibility, elasticity and compression resistance) for use with OP-1 as a graft implant. In this study, we tested the efficacy of this multi porous implant as OP-1 carrier using rabbit posterolateral lumbar fusion model (PLF). PLFs were performed in the following 4 groups of 8 New Zealand white rabbits each: autograft, HAp/Col alone, HAp/Col plus 0.3 mg OP-1, and HAp/Col plus 1.2 mg OP-1. At 5 weeks, fusion masses were analyzed by radiographic and biomechanical tests. Implants consisting of HAp/Col plus OP-1 were more effective than autologous bone in promoting spinal fusion. Low dose and high dose OP-1 were equally effective.