Usefulness of a novel hydroxyapatite fiber as a scaffold of stem cells for bone regeneration in spinal fusion surgery

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Spinal fusion was conducted in rats using apatite fiber mesh (AFM) loaded with rhBMP-2. The percentage of fusion rate was 100% and concluded that AFM might be effective as a bone substitute in spinal fusion operation. However, as AFM was fragile, we needed to operate carefully on handling. In order to enhance the mechanical properties, we have developed chelete-setting apatite cement using hydroxyapatite particles surfaced-modified with inositol phosphate (IP_6-HAp). The aim of this study is to develop IP_6-HAp as a material for bone grafting. In 2006 and 2007, we have done some studies listed below.1. MC3T3-E1 cells were seeded and cultured on IP_6-HAp. After cell culture, the cell number attached on them was counted to examine initial cell-attachment efficiency and cell proliferation.2. IP_6-HAps were implanted into tibiae of rabbits, together with a control of Biopex[○!R]-R (PENTAX Corporation, Japan). Within 24 weeks after implantation, the rabbits were sacrificed to retrieve the specimens with the surrounding bone for histological evaluation.In experiment 1, The MC3T3-E1 cells cultured on IP_6-HAp showed lower cell attachment and cell proliferation than the control (polystyrene 12-wells plate);. However, cell morphology observed by SEM showed that cells on IP_6-Hap nearly attained to be confluent for 7 days. These results demonstrate that IP_6-Hap have noncytotoxicity.In experiment 2, mature bone was seen to have formed around the surface of the IP_6-HAps as compared with Biopex[○!R]-R. The newly-formed bone was in close contact with the cement surface, without any sign of intervening fibrous tissue layer. This result indicates that IP_6-HAp has an excellent osteoconductivity to living bone.These results have shown that IP_6-HAp has noncytotoxicity. Furthermore, the hard tissue response of IP_6-HAp is shown to be similar to that of Biopex[○!R]-R. Thus, we conclude that IP_6-HAp is useful as a material for novel bone grafting.