Fibroblast and osteoblast adhesion and morphology on calcium phosphate surfaces

Implant loosening in bone fixation is an unresolved complication associated with internal fixation. It is generally accepted that this problem can be overcome by modifying the implant/bone interface for improved osseointegration. This is achieved, in part, by hydroxyapatite (HA) or tricalcium phosphate coatings. Unfortunately, the benefits of these coatings are constrained by not only the generally low strength of their adhesion to the implant surface but also the limited cohesion within their layers. Anodic Plasma-chemical treatment (APC) has been developed to incorporate electrolytes and produce coatings with various microtopographies and strong adhesion to implants. In this in vitro study fibroblast and osteoblast morphologies and adhesion to various substrates were evaluated using qualitative and quantitative methods. The substrates were Thermanox plastic and commercially pure titanium. The latter were surface-treated using several different methods: conventional anodisation, plasma spraying of HA and anodic plasma-chemical (APC) treatment in an electrolyte solution containing either calcium and phosphate (APC-CaP) or phosphoric acid (APC-P). Both osteoblasts and fibroblasts showed extensive cell spreading, total cell area and greatest amount of adhesion, with defined adhesion patterns on the Thermanox plastic, anodised titanium, and the two APC-CaP substrates. With fibroblasts, almost no cell spreading and very low adhesion, was observed in cells cultured on the APC-P and HA surfaces. The extent of cell spreading correlated with the area of focal adhesions as assessed by the amount of vinculin labelling. The Thermanox plastic, anodised titanium, and the two APC-CaP substrates were the most cytocompatible substrates with regard to this in vitro evaluation.