Evaluation of composite collagen/hydroxy-apatite implantation and nerve growth factor (NGF) delivery on new bone ingrowth

In this study, a bio-artificial bioresorbable composite consisting of a polymer of collagen/hydroxy-apatite (Col/Hap) enriched with neurotropin - nerve growth factor (NGF), was implanted into the femurs of 73 male Wistar rats, weighing 100-125 g. Implants were left in place for different times, Controls were as follows: a) contralateral femur without any implants; and b) contralateral femur implanted with composite without NGF factor. The rats were euthanized after 1, 10 and 30 days and the implant sites and explants were examined clinically, histologically, by scanning electron microscopy and histomorphometrically. The results show stimulated periosteal and endocortical woven and lamellar bone formation, which yielded increases in bone mass and decreases in bone marrow. The NGF treatment had greater effects in the femur shafts of older male rats than in younger ones. Additionally, we found that NGF increased remodeling activity in the intracortical region and induced an increase of intracortical cavity number and area by the end of the study. Since no similar studies appear to have been carried out, it is difficult to correlate our findings with other studies where neurogenic factors are delivered by complex polymer composites. We believe that this proposed system has great advantages in tissue engineering and is very suitable as a biomaterial for filling irregular defects in orthopaedic and maxillo-facial surgery, bone replacement and fixation, and as a drug delivery device.