Comparison of the release of growth hormone from hydroxyapatite, heat-treated hydroxyapatite, and fluoroapatite coatings on titanium.

Hydroxyapatite (HA), heat-treated hydroxyapatite (HAH), and fluorapatite (FA) coatings on titanium were loaded with human growth hormone (GH), and the subsequent release was monitored in vitro. The amount of GH released was significantly increased from the HA coating that had received a post-plasma-spraying heat treatment prior to incorporation of the growth hormone. Scanning electron microscopy was used to assess the surfaces of the ceramic coatings prior and postincubation with GH. Surface changes were observed on the HA and HAH coatings but not on the FA coatings after incubation with GH. Osteoblast-like cells were grown on the coatings and maintained in culture. Scanning electron microscopy was used to study the morphology of the cells and the interaction of the cells with the ceramic coatings. We used thymidine uptake and DNA content to determine the relative rates of cell division on the different coatings; the optimum rate of cell proliferation was observed on the HAH coating loaded with 0.1 IU/mL GH.