Biocoating of Implants with Mediator Molecules: Surface Enhancement of Metals by Treatment with Chromosulfuric Acid

Proteins such as the model protein 125I-ubiquitin and recombinant human bone morphogenetic protein 2 (125I-rhBMP-2) were covalently immobilized on titanium surfaces after reaction of the latter with aminopropyltriethoxysilane (APS) and activation with carbonyldiimidazole (CDI). On titanium powder (grain size ∼ 60 μm, 2400 cm2/g) net amounts of 15–60 ng/cm2 of 125I-ubiquitin could be coupled after correction for ca. 25% non-specifically adsorbed protein. Similarly, normal polished and special surface-enhanced titanium and stainless steel plates (size 1 × 10 × 15 mm) were modified as above and coupled with 125I-ubiquitin and 125I-BMP-2. The surface-enhanced metal plates were prepared by a special chromosulfuric acid treatment, probably leading to an etching of the metal surface and to an increase in the thickness of the metal oxide layer, which produced a strong enhancement of the binding capacity for chemical modification reactions. Dynamic contact angle measurements (Wilhelmy) of the clean surface-enhanced plates yielded an advancing contact angle of 18.0 ° and zero contact angle hysteresis. On such surface-enhanced titanium plates net amounts of 300–500 ng/cm2 of 125I-ubiquitin could be immobilized, values 2–5 fold higher than obtained on normal polished plates. In comparison 60–100 ng/cm2 125I-rhBMP-2 could be immobilized on the oxidized plates. The above technique is being applied as a tool for biocoating bone implants with the aim of constructing bone-cell-reactive interfaces with specific biorecognition properties.