Osteoconduction in keratin-hydroxyapatite composite bone-graft substitutes.

Reconstituted keratin-hydroxyapatite (K-HA) composites have shown potential as nonload-bearing bone graft substitute material. This in vivo study investigated the bone regeneration response of keratin plus 40% HA composite materials in comparison to collagen counterparts and an unfilled defect site. The implantation site was a noncritical size defect created in the long bones (tibia) of sheep, with observations made at 1, 2, 4, 6, 8, and 12 weeks postimplantation. Porous K-HA materials displayed an excellent biocompatibility similar to collagen counterparts; however, the rate of bone regeneration at K-HA implantation sites was markedly slower than that of the collagen or unfilled defect sites. While collagen materials were undetectable by 4 weeks implantation, K-HA composite remnants were present at 12 weeks. However, there is evidence that K-HA implants participated in the natural remodelling process of bone, with bone regeneration occurring via a creeping substitution mechanism. Observations imply that the rate of bone ingrowth into the K-HA defect site was matched with the rate of K-HA resorption. These results suggest that K-HA materials may offer significant benefits as nonload-bearing bone graft substitutes where it is desirable that the degradation of the scaffolding material be well matched with the rate of bone regeneration.