Impacts of chemically different surfaces of implants on a biological activity of fibroblast growth factor-2–apatite composite layers formed on the implants

Abstract

BackgroundImplants coated with fibroblast growth factor-2 (FGF-2)–apatite composite layers were previously reported to enhance soft-tissue formation, bone formation, and angiogenesis around the implants owing to the biological activity of FGF-2. However, it is unclear whether the chemistries of the material and surface of implants have some impact on the retention of the biological activity of FGF-2 in FGF-2−apatite composite layers on them. Since magnitude of the impact should be evaluated for extensive application of the composite layer to coat various implants, following items were examined; (1) surface chemistries of six implants, (2) mitogenic activities of FGF-2 in FGF-2–apatite composite layers on the implants, and (3) improved synthesis method of the composite layer for retention of the mitogenic activity of FGF-2. HypothesisThe biological activity of FGF-2 in the composite layer is affected by the chemistries of the material and surface of implants. Materials and methodsSix commercial products of pins and screws having different surface chemistries were coated with FGF-2–apatite composite layers. The composite layers were quantitatively analyzed for calcium (Ca), phosphorus (P) and FGF-2, and also evaluated the mitogenic activities of FGF-2. Improvement of the synthesis method was then attempted using two pin products. ResultsEach commercial product had a chemically and morphologically characteristic surface. FGF-2–apatite composite layers were formed on all the commercial products. Although the Ca, P, and FGF-2 contents (4.7±0.9μg/mm, 2.2±0.4μg/mm, and 21.1±3.7ng/mm, respectively) and the Ca/P molar ratios (1.69±0.01) of the composite layers were almost the same, rate of retention of the mitogenic activity of FGF-2 in the composite layers significantly decreased on some pin products (3/12–4/12). The decrease in rate of retention of the mitogenic activity of FGF-2 was prevented by a two-step synthesis method to form a composite layer on a precoating with calcium phosphate (9/12–12/12). DiscussionThe chemistries of the implant surfaces had a significant impact on the retention of the mitogenic activity of FGF-2 in the composite layers formed on the implant. The two-step synthesis method was useful to retain mitogenic activity of FGF-2 regardless of the surface chemistries of the implants. The two-step synthesis method has potential to expand the applicability of FGF-2–apatite composite layers to a wider range of implants. Level of evidenceIII, Case control in vitro study.