Plasma protein adsorption on titanium: comparative in situ studies using optical waveguide lightmode spectroscopy and ellipsometry

Blood serum and plasma adsorption combined with antibody techniques was studied at different wall shear rates by means of in situ optical waveguide lightmode spectroscopy (OWLS) using waveguides sputter coated with TiO2. In situ ellipsometry under stagnant flow conditions was used as a reference technique on titanium (Ti) surfaces, which had been sputter coated with TiO2. OWLS experiments at medium or high wall shear rates showed the best reproducibility and the results were quantitatively most similar to those from ellipsometry. Exposure to serum from 15 s to 30 min resulted in increased serum deposition as well as increased, subsequent anti-C3c binding (both ellipsometry and OWLS), but did not show increased amounts of antibodies binding to complement factor 1q (C1q) or IgG. This differs from earlier results [1] using in situ ellipsometry with titanium surfaces covered by a thin natural (thermal) oxide layer, where small but significant amounts of C1q were shown to be present on the surface after short incubation times in serum. Wall shear rates appear to have a significant influence on the magnitude and composition of the protein adlayers. At very low rates (1.5 s(-1)), significantly increased binding of antibodies to complement factor 3c (anti-C3c) on serum-preincubated surfaces was observed. This was coupled with a significantly prolonged lag-time between the initiation of buffer rinsing and the actual removal of material. Factors such as cell geometry, shear rate and viscosity are likely to be the main experimental factors determining the observed kinetics. After incubation in heparinised blood plasma for 3 min, a large subsequent binding of anti-high-molecular-weight kininogen was observed. This indicates a potential intrinsic coagulation activity and is in line with previous ellipsometry/antibody results. The combined OWLS and ellipsometry results show that the two methods agree surprisingly well for the quantitative determinations of protein and antibody adsorption. (C) 1998 Elsevier Science B.V. All rights reserved.