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

Abstract

Background: Implants 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.

Hypothesis: The biological activity of FGF-2 in the composite layer is affected by the chemistries of the material and surface of implants.

Materials and methods: Six 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.

Results: Each 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).

Discussion: The 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 evidence: III, Case control in vitro study.

Keywords: Apatite; Fibroblast growth factor-2 (FGF-2); Implant surfaces; Mitogenic activity.