Microporosity affects bioactivity of macroporous hydroxyapatite bone graft substitutes

This paper describes an investigation into the influence of microporosity on early osseointegration within porous hydroxyapatite scaffolds. Two batches of phase pure porous hydroxyapatite were produced with total porosities of approximately 80%, but with varied levels of microporosity such that the strut porosity of the two batches were 10 and 20%. Cylindrical specimens 4.5mm in diameter were implanted in the distal femur of 6 month New Zealand White rabbits and retrieved for histological and histomorphometric analysis at 1 and 3 weeks. Optical microscopy demonstrated variation in the degree of capillary penetration and bone morphology within scaffolds at I and 3 weeks, respectively. Moreover, histomorphometry demonstrated that there was significantly more bone ingrowth within HA80-2 scaffolds and that the rate of bone formation within these scaffolds was significantly faster. These results indicate that the bioactivity of porous hydroxyapatite scaffolds may be improved by increasing the level of microporosity within the ceramic struts.