Scanning transmission X-ray microscopy (STXM) is being developed as a new tool to study the surface chemical morphology and biointeractions of candidate biomaterials with emphasis on blood compatible polymers. STXM is a synchrotron based technique which provides quantitative chemical mapping at a spatial resolution of 50 nm. Chemical speciation is provided by the near edge X-ray absorption spectral (NEXAFS) signal. We show that STXM can detect proteins on soft X-ray transparent polymer thin films with monolayer sensitivity. Of great significance is the fact that measurements can be made in situ, i.e. in the presence of an overlayer of the protein solution. The strengths, limitations and future potential of STXM for studies of biomaterials are discussed.

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Two different types of low-density detergent-insoluble glycosphingolipid-enriched membrane domain (DIG) fractions were isolated from myelin by extraction with Triton X-100 (TX-100) in 50 mM sodium phosphate buffer at room temperature (20°C) (procedure 1), in contrast to a single low-density fraction obtained by extraction with TX-100 in Tris buffer containing 150 mM NaCl and 5 mM EDTA at 4°C (procedure 2). Procedure 1 has been used in the past by others for myelin extraction to preserve the cytoskeleton and/or radial component of oligodendrocytes and myelin, whereas procedure 2 is now more commonly used to isolate myelin DIG fractions. The two DIG fractions obtained by procedure 1 gave opaque bands, B1 and B2, at somewhat lower and higher sucrose density respectively than myelin itself. The single DIG fraction obtained by procedure 2 gave a single opaque band at a similar sucrose density to B1. Both B1 and B2 had characteristics of lipid rafts, i.e. high galactosylceramide and cholesterol content and enrichment in GPI-linked 120-kDa neural cell adhesion molecule (NCAM)120, as found by others for the single low-density DIG fraction obtained by procedure 2. However, B2 had most of the myelin GM1 and more of the sulfatide than B1, and they differed significantly in their protein composition. B2 contained 41% of the actin, 100% of the tubulin, and most of the flotillin-1 and caveolin in myelin, whereas B1 contained more NCAM120 and other proteins than B2. The single low-density DIG fraction obtained by procedure 2 contained only low amounts of actin and tubulin. B1 and B2 also had size-isoform selectivity for some proteins, suggesting specific interactions and different functions of the two membrane domains. We propose that B1 may come from non-caveolar raft domains whereas B2 may derive from caveolin-containing raft domains associated with cytoskeletal proteins. Some kinases present were active on myelin basic protein suggesting that the DIGs may come from signaling domains. Keywords: caveolin, cerebroside sulfate, cytoskeleton, galactosylceramide, rafts, oligodendrocytes. Extensive studies have demonstrated the existence of lateral membrane domains that contain a specific repertoire of lipids and proteins. These lipid-rich microdomains, or rafts, in the plasma membrane are thought to be formed by the tight packing of the long and highly saturated fatty acids of the sphingolipids and cholesterol and contain GPI-linked and acylated proteins, and certain integral membrane proteins (Brown and

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Core-shell polymer microspheres have been prepared by a two-step precipitation polymerization. These microspheres consist of 3.2 µm polydivinylbenzene-55 (DVB55) cores coated with ∼0.4-0.9 µm wide shells composed of poly(DVB55-co-EDMA), a random copolymer of DVB55 and ethylene glycol dimethyl acrylate (EDMA). The chemical composition, core-shell morphology, and porosity of these structured microspheres have been studied quantitatively with scanning transmission X-ray microscopy (STXM) at a spatial resolution of 100 nm. Images recorded at selected energies through the C 1s absorption region were analyzed using singular value decomposition to obtain quantitative maps of the DVB55 and EDMA components. The EDMA concentration in the shell determined by STXM was found to be in good agreement with that predicted from the comonomer composition over the range of 10-90% EDMA. The precision of chemical quantification at high spatial resolution is shown to be adequate for STXM to be useful in guiding the development of structured polymeric systems for particular applications.