Assessing Structure-Property Relations of Diseased Tissues Using Nanoindentation and FTIR
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Assessing Structure-Property Relations of Diseased Tissues Using Nanoindentation and FTIR Donna M. Ebenstein*, Joan M. Chapman^, Cheng Li^, David Saloner*•, Joseph Rapp°, Lisa A. Pruitt*^ *UCB/UCSF Bioengineering Graduate Group, ^Department of Bioengineering, University of California at Berkeley, Berkeley, CA 94720 • Department of Radiology, °Department of Vascular Surgery, University of California at San Francisco, San Francisco, CA 94143 ABSTRACT Disease processes are often associated with changes in tissue composition. For example, in atherosclerosis lipid and calcification are often found in the artery wall, whereas in healthy arteries the tissue microstructure is dominated by highly organized collagen. Such variations in composition likely result in changes in the material properties of the tissue. However, this relationship has not been fully investigated in atherosclerotic vessels. Using a combination of nanoindentation and spectroscopic techniques, our goal was to assess how changes in tissue composition affect the tissue’s mechanical properties. Fourier Transform Infrared Spectroscopy (FTIR) was used to assess the biochemical composition of the tissue samples, such as the lipid and calcium content of fibrous tissues in diseased arteries. Nanoindentation was used to measure the local mechanical properties of the same tissue samples. This information was then correlated by position in the sample to assess the contributions of different constituents to the overall structure-property relations of these tissues. INTRODUCTION An assessment of structure-property relations for healthy and diseased tissues is essential for accurate modeling of tissues, constructing viable tissue engineered equivalents, and understanding disease progression. Many biological tissues remodel in response to mechanical loading, reorganizing their microstructure and composition in an organized fashion in order to maintain optimal stress levels in the tissue. Disease processes are often associated with changes in tissue composition, which can interfere with the normal balance of tissue remodeling. For example, atherosclerosis is a cardiovascular disease characterized by the accumulation of abnormal constituents such as lipids, calcification, and blood clots in the artery wall. Such variations in composition likely result in changes in the material properties of the tissue. However, these relationships have not been fully investigated. Due to the complex and heterogeneous nature of the diseased tissues bulk tests may not provide sufficient information about the structure-property relations of individual constituents. Rather, micromechanical testing is necessary to isolate the contributions of different constituents to the overall mechanical behavior of the bulk tissue specimen. Our goal was therefore to assess how changes in tissue composition affect atherosclerotic plaque tissue mechanical properties using a combination of nanoindentation and spectroscopic techniques. Local mechanical properties in the heterogeneous tissue samples were mea
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