Quantitative screening of engineered implants in a long bone defect model in rabbits

We have standardized a long bone defect model in rabbits to quantitatively compare the bone healing performance of engineered biological implants and have tested the bone healing efficiency of porous cylindrical scaffolds (ø-h, 6-20 mm [diameter 6 mm, height 20 mm] porosity, 70%) that were produced from hydroxyapatite (HA), titanium (Ti), and a novel biodegradable polymer-bioceramic composite (PH70alphaTCP). Scaffolds were perfused with or without 20 x 10(6) rabbit periosteal cells (RPCs) in a bioreactor and implanted in a standardized 2 cm defect in rabbit tibiae. X-rays revealed that new bone had formed at 3 weeks after creation of the defects. At sacrifice after 10 weeks, bone corticalization was observed in the majority of animals. Although PH70alphaTCP scaffolds did not inhibit callus formation, histomorphometric analysis revealed that there was no bone within the biomaterial, in contrast to HA and Ti scaffolds (bone volume ranging from 10% to 25%). We found that Ti and HA scaffold had good osteoconductive properties, but only HA scaffolds seeded with RPCs contributed to long bone mechanical functionality, with the maximum energy and angle being 308% and 155% greater than in control defects without scaffold.