EFFECT OF CONTROLLED-RELEASE OF PLATELET-DERIVED GROWTH-FACTOR FROM APOROUS HYDROXYAPATITE IMPLANT ON BONE INGROWTH

Platelet-derived growth factor (PDGF) is one of several osteogenic fac tors which affect bone growth and fracture healing. This study examine d the potential of hydroxyapatite (HA) rods with interconnected pores of mean diameter 200 mu m to be used as a matrix for the release of PD GF to enhance bone ingrowth into the implant. In the initial phase of the study the sustained release of PDGF from the HA rods was character ized in vitro for two different PDGF loadings, 10 and 100 mu g per imp lant. The second phase of the study examined bone ingrowth in HA impla nts placed into the medullary canals of rabbit femora. The specimens w ere dumb-bell shaped, with a reduced central diameter so that bone gro wth across a gap could also be determined. Bone ingrowth into HA impla nts was compared with growth into HA implants loaded with 100 mu g of PDGF. Pushout measurements were made of average shear strength across the bone-implant interface and backscatter scanning electron microscop y of thick sections was used to quantify the amount of bone ingrowth i nto the implant. Although greater interfacial shear strength and area of ingrowth were observed, especially across gap sites, in specimens l oaded with PDGF, no difference was statistically significant.