Yan Sun Graduate Student B.A. Physics, B. S. Applied Mathematics, 2006, University of Chicago Cook Hall 2057, 1-7199 yan at northwestern dot edu

Studies of Polymer Interfaces with X-ray Standing Waves

The interaction of proteins with a surface can be reduced or prevented if the surface is grafted with polymers [1,2,3]. This type of polymer brush system is relevant for a variety of industrial and medical applications, including the development of drugs and biomaterials aimed at fighting nonspecific protein adsorption and the health complications associated with it. For example, thrombosis, which is the formation of a clot inside a blood vessel that can lead to stroke and other serious health problems, is attributed to the adsorption of plasma proteins such as fibrinogen to the surface of a foreign material inside a blood vessel. The elimination of protein adsorption can also be important in developing and improving various consumer goods, such as care products for contact lenses that work to prevent the build-up of lysozyme on the surface and thus reduce the need for cleaning the lenses.

The primary technique used in this research is x-ray standing waves (XSW) generated via total external reflection (TER) from an x-ray mirror surface. The goal is to understand the structure, surface, and thermodynamics of the polymer brush system and its ability to protect the underlying substrate. The general setup of the model system (shown in the figure) consists of polyethylene oxide (PEO) chains in an aqueous environment grafted onto a palladium mirror as well as onto a membrane. Bromine marker atoms, which produce a spatially dependent x-ray fluorescence signal, are attached to the end of the PEO chains as well as to free molecular species in solution. The bromine distribution obtained via XSW can reveal information about the conformation of the PEO brushes and their effectiveness in preventing protein adsorption as the distance between the two PEO brush layers is varied.

The XSW experiments are carried out at the Advanced Photon Source at Argonne National Laboratory under the direction of my joint advisor Dr. Jin Wang.

[1] Unsworth, L. D., Sheardown, H., and Brash, J. L. Langmuir 21, 1036-1041 (2005).
[2] Harder, P., Grunze, M., and Dahint, R. J. Phys. Chem. B 102, 426-436 (1998).
[3] Szleifer, I. Biophys J. 72, 595-612 (1997).