Soft X-ray Spectromicroscopy of Proteins on Patterned Polymer Films

Abstract

Synthetic biomaterials are widely used in medical applications. Their biocompatibility is believed to be related to first interactions with proteins. Thus, quantitative techniques which provide information on the spatial distribution of adsorbed proteins are of interest. In this work, two soft X-ray spectromicroscopy techniques, scanning transmission x-ray microscopy (STXM) and photoemission electron microscopy (X-PEEM), were used for the determination of the preferred sites of interaction of blood proteins on phase segregated polymer films. These techniques are advantageous due to their high chemical speciation, which is provided by near edge X-ray absorption fine structure (NEXAFS) spectroscopy, and their high spatial resolution of ~50 nm for STXM and ~100 nm for XPEEM. STXM, X-PEEM and atomic force microscopy (AFM) were used to characterize thin film polymer blends of polystyrene (PS) and poly(methylmethacrylate) (PMMA). PEEM was used to map the adsorption of fibrinogen (Fg) on this surface from both isotonic, buffered, and low ionic strength, unbuffered aqueous solutions at varying fibrinogen concentrations. STXM was used to locate human serum albumin (HSA) and Fg on microtomed sections of polyurethanes containing copolymer filler particles. The results shown in this thesis demonstrate for the first time that STXM and X-PEEM have the capability to simultaneously locate and detect both adsorbed proteins at the submonolayer level, and the underlying polymer phases, and to map the protein distribution relative to the polymer phases. The STXM measurements are quantitative and can be carried out in the presence of an overlayer of the protein solution.