Dynamic Protein Adsorption onto Dendritic Polyglycerol Sulfate Self-Assembled Monolayers

Biomaterial surfaces that are in contact with blood are often prone to unspecific protein adsorption and the activation of the blood clotting cascade. Hence, such materials usually must be functionalized with low-fouling or anticoagulant polymer coatings to increase their performance and durability with respect to various applications, for example as implants or in biomedical devices. Many coatings are based on anionic polymers, such as heparin, and are known to have pronounced anticoagulant effects. To assess the ability of a surface to prevent biofouling and to get further insight into its underlying mechanism, studies of the protein adsorption on self-assembled monolayers (SAMs) are often used as a predictive tool. In this article, we synthesized thioctic acid-functionalized dendritic polyglycerol sulfate (dPGS), which is a well-known synthetic heparin mimetic, and immobilized it onto gold model surfaces. The anionic dPGS SAMs were characterized via contact angle measurements and ellipsometry and compared to their neutral dendritic polyglycerol (dPG) counterparts with respect to their single protein adsorption of the two most abundant blood proteins albumin (Alb) and fibrinogen (Fib). In addition, we used QCM-D and ToF-SIMS as complementary techniques to investigate the dynamic, mixed, and sequential adsorption of Alb and Fib. Our results clearly demonstrate an incomplete Vroman effect and indicate the rearrangement of the adsorbed protein layers, which is presumably drive by ionic interactions between the two proteins and the anionic dPGS surface.