Mapping Elastic Properties of Complex Biological Tissue

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Most biological tissues are rather complex structures with inhomogeneities in material properties and structure at micro- and nanoscopic scales. Detailed characterization of the structure and function of tissues would be served by mapping elastic properties of the tissue with microscopic resolution. The atomic force microscope (AFM) is an ideally suited tool for constructing such maps by doing nano-indentation tests at a large set of points throughout a domain of interest on the tissue and using appropriate mathematical models to extract the desired elastic parameters at each point. Such procedure typically requires analysis of hundreds or thousands of data sets. Without automation, this is a very tedious process which is hindering its use for detailed mapping of elastic properties of biological tissue such as cartilage. We have built a powerful automation tool that allows routine elasticity mapping at any resolution. The goal is twofold: First we want to investigate and compare the elastic properties of natural and tissue-engineered cartilage and other polymer gel-like tissues at the microstructure level. At the same time we investigate simpler artificial gels to which we add ever more complexity (adding various molecular components and various inhomogeneities) and use the AFM in conjunction with macroscopic and osmotic measurements in an effort to elucidate the factors determining the elastic behavior of such tissues. Second, development of the automation software for elastic map construction will create a tool that can and will be used widely by intramural collaborators in a variety of projects, such as the one with NIDCD collaborators on investigating the elastic properties of the tectorial membrane in the inner ear, and the measurement of material properties of supported lipid bilayers.