| AVS 57th International Symposium & Exhibition | |
| Biomaterial Interfaces | Wednesday Sessions |
| Session BI-WeA |
| Session: | Proteins & Peptides on Surfaces |
| Presenter: | E. Hillenmeyer, University of Washington |
| Authors: | E. Hillenmeyer, University of Washington R.A. Penkala, University of Washington W. Thomas, University of Washington D.G. Castner, University of Washington |
| Correspondent: | Click to Email |
von Willebrand Factor (vWF) is a blood-soluble clotting protein responsible for binding platelets through the glycoprotein 1b (GP1b) receptor on the platelet surface. vWF can become activated and bind platelets when bound to exposed collagen in blood vessels or when vWF experiences increased shear.
vWF can also bind platelets when adsorbed to synthetic surfaces and participate in clot formation, which is not desirable for blood-contacting biomaterials. There is evidence that surface properties can influence vWF adsorption. Previous studies showed differences in protein topography (1) and conformation (2) when vWF was adsorbed on mica (1), octadecyltrichlorosilane modified glass (1,2), and collagen VI (2). However, studies were not performed to relate adsorption differences to vWF function.
To more fully characterize the adsorption properties of vWF, we adsorbed the platelet binding domain of vWF (A1 domain) to three surfaces: polystyrene, tissue culture polystyrene, and glass. Protein structure was investigated using x-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectrometry (ToF-SIMS). Protein function was tested by measuring platelet binding in a physiologically relevant flow assay.
Using nitrogen as a marker of protein, XPS showed similar amounts of vWF A1 adsorbed to the three surfaces. However, the flow assay showed significantly different platelet binding to vWF A1 on each surface, as measured by platelet rolling velocity. Rolling velocity was highest on glass, indicating lowest platelet binding. The slowest rolling velocity was observed on polystyrene, indicating the highest level of platelet binding. ToF-SIMS data was analyzed using principle component analysis (PCA). PCA showed separation of the three surfaces with adsorbed vWF A1, indicating conformational differences between the proteins on each surface.
These studies show that surface properties influence structure and function of adsorbed vWF domains. Although there was a similar amount of protein on each surface, protein function was different. Polystyrene, the most hydrophobic of the surfaces, appeared to have the strongest activating effect on vWF. ToF-SIMS studies showed conformational differences, suggesting that conformational differences contribute to the observed functional differences.
Understanding the structure and function of adsorbed vWF gives insight into how vWF behaves on biomaterial surfaces and how this might affect platelet binding. Characterizing vWF adsorption also allows in vitro behavior to be more accurately related to in vivo thrombosis events.