[Show abstract][Hide abstract] ABSTRACT: A new method of force modulation scanning force microscopy (SFM) imaging based on a constant compliance feedback loop is presented. The feedback adjusts the loading force applied by the SFM tip to the surface in order to maintain a constant compliance beneath the tip. The new method, constant compliance force modulation (CCFM), has the advantage of being able to quantify the loading force exerted by the tip onto the sample surface and thus to estimate the elastic modulus of the material probed by the SFM tip. Once the elastic modulus of one region is known, the elastic moduli of other surface regions can be estimated from the spatial map of loading forces using the Hertz model of deformation. Force vs. displacement measurements made on one surface locality could also be used to estimate the local modulus. Several model surfaces, including a rubber-toughened epoxy polymer blend which showed clearly resolved compliant rubber phases within the harder epoxy matrix, were analyzed with the CCFM technique to illustrate the method's application.
[Show abstract][Hide abstract] ABSTRACT: The principles of protein adsorption are briefly reviewed with emphasis on model proteins at model interfaces. Using a data set for protein behavior at the air/water interface, a multi-variate, multi-axes treatment of protein adsorption behavior is developed: the Tatra plot. By the careful placement and scaling of radial axes, representing 12 protein, surface, and interface parameters, one can begin to deduce various correlations between these parameters. The correlations are then used to formulate hypotheses with which to design additional experiments. The treatment is extended to the solid/liquid interface using data available in the literature for model proteins on model solid surfaces. We then present brief discussion of the extension of the technique to more complex surfaces, including means to parameterize solid/liquid interfacial properties, before proceeding to more complex proteins based on a structural domain approach to protein structure and function. A preliminary analysis employing albumin is briefly presented. We move on to protein resistant surfaces based on polyethylene oxide and present a rationale for the properties and behavior of such interfaces, including a preliminary theoretical model which may be useful for the design and optimization of protein resistant surfaces. Finally, we briefly present some preliminary atomic force microscopy studies of immunoglobulins on mica surfaces, demonstrating not only direct imaging of proteins at interfaces in an aqueous environment but, perhaps even more importantly, their manipulation, processing, and ordering.
Full-text · Article · Dec 1992 · Clinical Materials