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.