Complement deposition from human sera on silicon surfaces studied in situ by ellipsometry. The influence of surface wettability.

Organic material deposition from human sera on silicon dioxide surfaces was studied in situ by means of ellipsometry, an optical method for quantification of thin organic films. The deposition of organic material from sera was followed continuously for 2 h on hydrophobic and hydrophilic silicon surfaces. Both types of surfaces adsorbed organic material and the additional incubation with anti-C3 resulted in further deposition of organic material indicating the presence of C3 in the organic layers. Addition of EDTA in serum or heat inactivation resulted in a decrease of the amount of organic material deposited on the hydrophobic surface as well as in a lack of subsequent anti-C3 deposition on both hydrophilic and hydrophobic surfaces. Preadsorption with immunoglobulin G on the surfaces caused a pronounced increase of the deposition of material from serum as well as of subsequent anti-C3 deposition. Both effects were absent if EDTA was present in the serum. Our results indicate that complement activation and deposition occur by incubation of human sera on hydrophobic and hydrophilic silicon dioxide surfaces, which are two surfaces with very simple and well-defined chemical composition. The degree of the reversibility of the deposition of immunoglobulin G was furthermore larger on hydrophilic silicon.