Engineering Biomaterials that Exhibit Recognition and Specificity
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Mat. Res. Soc. Symp. Proc. Vol. 414 01996 Materials Research Society
assembled molecular structures as guides, templates or supports. To synthesize surfaces precisely engineered to control biological responses, we need analysis methods to guide our synthetic efforts. Surface-localized analytical methods such as electron spectroscopy for chemical analysis (ESCA), secondary ion mass spectrometry (SIMS) and atomic force microscopy (AFM) aid us in optimizing coverage, orientation, precise chemistry and minimization of defects. ESCA provides, for the outermost 10-80A of a material, accurate measurements of stoichiometry, details of functional groups at the surface, thin film thickness, uniformity of coverage and information on functional group orientation [3,4]. SIMS, especially in the static mode, offers detailed molecular information about the outermost 10-15A of a surface, with extremely high analytical sensitivity [5]. Static SIMS also "codes" information about molecular mobility and non-covalent molecular interactions [6,7]. AFM gives information on topography, roughness and defects to the molecular level [8,91. It can provide detail on film thickness and can be used to probe for specific molecular interactions [10,11]. ESCA, SIMS and AFM are only three of many tools that might be applied to understand surface structure. Other methods that will be of value include contact angles (surface wettability and thermodynamics), vibrational spectroscopies applied to surfaces (attenuated total reflectance, infrared absorption reflection) and extended x-ray absorption fine structure (EXAFS) for measuring molecular orientation [12]. General overviews of surface analytical methods are widely available [4,13]. Surfaces that resist protein adsorption and cell attachment A general principle in the design of surfaces engineered to trigger precise biological reactions is that non-specific interactions should be inhibited. Surfaces that resist the adsorption of proteins and the adhesion of cells may serve this purpose. Such surfaces are made in our laboratory by the RF-plasma deposition of PEO-like thin films [14]. The precursor molecules vaporized into the plasma reactor for deposition are dimethyl ethers of oligo ethylene glycols. In particular, triethylene glycol dimethyl ether (triglyme) and tetraethylene glycol dimethyl ether (tetraglyme) have shown promise. In the plasma environment, these molecules deposit onto metal, glass or polymeric surfaces into 50-200A delamination-resistant thin films. By ESCA, these films show considerable PEO character with the majority of the Cls peak representative of structures suggestive of carbons singly bonded to oxygen (there is additional evidence of ether functionality, rather than C-OH). By static SIMS, PEO chains fragments and PEO chain fragments containing methoxy groups are noted. Such surfaces show very low protein adsorption (Table 1), and low levels of attachment of many cell types such as human blood platelets, endothelial cells and Pseudomonas aeruginosa[15].
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Table 1 Adsorpt
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