Tissue Engineering and Cardiac Repair
Due to the inability of adult cardiac myocytes to proliferate, spontaneous repair or regeneration of heart muscle is not normally possible. Consequently, pathological events such as myocardial infarction result in permanent damage that often leads to heart failure and death. As a potential therapeutic strategy, stem cells offer great potential due to their ability to differentiate into tissue-specific cell types guided by cues within the local niche microenvironment, possibly providing a cell source for cardiac repair. However, complications including low cell retention and viability, combined with a demanding and evolving post-infarction environment, have impeded the identification of mechanisms governing stem cell based treatments for myocardial infarction, resulting in failed clinical trials. Engineered cardiac tissues offer alternative experimental model systems combining a more physiologic 3D environment than the standard Petri dish, with long-term viability and improved experimental control not possible with natural heart muscle preparations. However, engineered cardiac tissues have been developed primarily for surgical repair applications, rather than as living in vitro systems designed for investigating mechanisms of myocardial injury, repair, and regeneration. Our research involves development of innovative new tools and approaches combining soft lithography, cell patterning, and bioreactor design for tissue and organoid engineering, with the overall objective of improving the understanding and efficacy of novel cell- and gene-therapy based approaches for cardiac repair.
Atomic Force Microscopy and Cell Mechanobiology
The atomic force microscope (AFM) is emerging as a powerful tool in cell biology. Originally developed for high-resolution imaging, the AFM also has unique capabilities as a nano-indenter to probe the dynamic viscoelastic material properties of living cells in culture. In particular, AFM elastography combines imaging and indentation modalities to map the spatial distribution of cell mechanical properties, which in turn re?ect the structure and function of the underlying cytoskeleton. Indeed, many fundamental aspects of cellular function, including shape, deformability, motility, division, adhesion, and differentiation, are critically dependent on the micromechanical properties (e.g., stiffness, nonlinearity, anisotropy, and heterogeneity) of the cell and its extracellular substrate. There is also evidence that the state of health or disease of a cell might be uniquely reflected in its mechanical response. Our research is focused on enhancing and expanding the kinds of measurements that can be obtained from AFM mechanical testing experiments. Computer model simulations are used to help interpret AFM measurements and develop novel experiments. Resulting innovations in probe design, testing protocols, and data analysis have enabled us to distinguish cell phenotypes based on the indentation response, to characterize changes in composite cell material properties by elastographic mapping, to measure the viscoelastic response to unconfined compression for comparing whole-cell properties with local indentation measurements, to monitor the response of vascular cells and tissues to osmotic loading, to reconstruct the timecourse of dynamic stiffness changes in beating cardiomyocytes, to measure substrate-dependent differences in cell stiffness, to map regional meso-scale tissue properties for understanding biomechanical function, and to monitor calcium signaling waves in response to targeted mechanical stimulation of micropatterned cell networks. While our specific interests deal with the mechanobiology of cells and tissues of the cardiovascular system, many of the methods are applicable to a wide range of cell and tissue types. A number of technical and practical hurdles have yet to be overcome before these techniques can be translated for clinical use. However, the future holds great promise for AFM elastography of living cell or tissue biopsies to provide novel biomechanical markers that will enhance patient-specific detection, diagnosis, and treatment of disease.