IN-VITRO EVALUATION OF A NEW INJECTABLE CALCIUM-PHOSPHATE MATERIAL

The purpose of this study was to develop an injectable bone substitute (IBS) for percutaneous orthopedic surgery. The multiphasic material u sed was composed of a 2% aqueous solution of methylhydroxypropylcellul ose (MHPC) and biphasic calcium phosphate (BCP, 60% hydroxyapatite and 40% beta-tricalcium phosphate) in which MHPC served as the carrier fo r 80-200 mu m of BCP granules. The best BCP/polymer ratio was determin ed by the rheological properties and higher BCP content of the materia l. Steam sterilization was more effective than gamma irradiation in ma intaining the stability of the mixture and conserving its physiochemic al and mechanical properties. The in vitro biocompatibility of the com posite was checked by direct-contact cytotoxicity and cell-proliferati on assays. A preliminary in vivo test was performed in the rabbit usin g intraosseous implantations in the femoral epiphysis. Histological an alysis was done after 1, 2, 4, and 10 weeks. Bone ingrowth into the IB S, in close association with BCP granules, was observed after 1 week a nd increased regularly from the surface inward at 2, 4, and 10 weeks. At the same time, smaller BCP granules (less than 80 microns in diamet er) were degraded and resorbed. This injectable biomaterial proved sui table for cavity filling. The water solubility and viscosity of the po lymer allow cells to recolonize, with in situ bonding of the mineral p hase. (C) 1998 John Wiley & Sons, Inc.