Purpose: Type-I collagen, the major structural protein in bone, has beneficial properties regarding bone regeneration. Little is known about the potential effects of collagen coating on orthopedic implants.
Methods: 3 to 6 microg/cm2 of lyophilized type-I collagen was absorbed on titanium rods. Six coated and uncoated pins of 0.9 mm diameter were inserted into the tibia of adult male Wistar rats for 1, 2, 4, 7, 14, and 28 days. Specimens were embedded in methacrylate-based Technovit 9100N resin. From one portion cutting and grinding sections were obtained. The implant was removed from the other half that was depolymerized, sectioned, and mounted for immunohistochemistry.
Results: At day 4, the interface around the collagen-coated implants displayed a granulation tissue with higher numbers of cathepsin D-positive mononucleated cells compared to the uncoated implants (p<0.05). Active osteoblasts, reactive for osteopontin, were increased around the collagen-coated pins at day 4 and 7 (p<0.01). After 28 days of implantation, direct bone contact averaged 74.9% around the collagen-coated implants and 62.1% around uncoated implants (NS). The amount of newly formed bone averaged 76.3% around the collagen-coated pins and 67.8% around the uncoated pins (NS). The histomorphometric findings were confirmed by SRmicroCT in two specimens.
Conclusions: The earlier observation of mononuclear phagocytozing cells and the earlier and higher expression of bone-specific matrix proteins suggest an increased early bone remodeling around titanium pins through collagen coating. A tendency towards increased bone formation was observed around the coated implants.