The use of a complex of collagen type I with hydroxyapatite from bone, as a bone implant substitute: an experimental...

A complex composed of bovine collagen type I, extracted from tendons, and hydroxyapatite (HA), was evaluated in two sites: as onlay in the femur and on the periosteal surface of the calvarium of rats. The implants triggered an increasing membranous ossification correlating with implantation time. No enchondral ossification was detected, except in the control group. Osteoblastic cells were seen penetrating implant fragments in which the HA crystals were oriented in the same way as originally in bone. The presence of HA crystals in the cytoplasm of macrophages supports the idea of a cell-directed resorptive process of the implant. We conclude that molecular order and physicochemically driven reactions of HA collagen produce a complex capable of delivering signals to induce ossification under the conditions described in the present study.