UC Berkeley

Myocardial infarction, commonly known as a heart attack, is caused by the blockage of blood flow to heart, resulting in the death of cardiomyocytes, or heart muscle cells. Scar tissue formation occurs in the area of the damage due to the heart's inability to regenerate myocardial tissue. Therefore, regeneration of myocardial tissue through the use of synthetic scaffolds requires strategies to promote cardiomyocyte attachment while minimizing proliferation of the fibroblast cells that contribute to scar tissue. Previous studies have demonstrated that a synthetic platform consisting of an array of microscale polydimethylsiloxane (PDMS)-based pillars ("micropegs") can accomplish both of these goals, but the mechanism through which this occurs has remained a mystery.

In this work the interaction between microtopographical cues and both fibroblasts and cardiomyocytes is further explored. It is shown that a fibroblast that is attached to a micropeg is less likely to proliferate than ones on a flat surface, but this difference can be partially abrogated in the presence of drugs that inhibit cell contractility. The cells also show increased adhesion to the micropegs as opposed to flat surfaces, as demonstrated by measurements of the dynamics of deadhesion from the surface and changes in expression of specific mechanotransductive genes. Together, these data support a model in which microtopographical cues alter the local mechanical microenvironment of cells by modulating adhesion and adhesion-dependent mechanotransductive signaling, thereby leading to a reduction in proliferation capability.

The research focus then shifts to the use of microtopographical cues to control cardiomyocyte adhesion and organization. Cardiomyocytes cluster around and interact with the full length of the micropegs, exhibiting three-dimensional organization on a two-dimensional surface. By controlling the diameter and spatial arrangement of the micropegs, the degree of clustering can be regulated. The expression of functional markers N-cadherin and connexin 43 also exhibit a dependence on the spatial arrangement of the micropegs. The preference of cardiomyocytes for three-dimensional adhesion is further investigated in the final part of the thesis. By isolating cardiomyocytes in PDMS microwells, the cells are presented with the option of attaching to a vertical wall or a flat space. The cells demonstrate a preferential attachment to the side walls and corners of the microwell. Introduction of the myosin inhibitor blebbistatin reduces the percentage of cells attached to these side walls. Cells attached to a side wall also are less likely to proliferate, similar to the behavior of fibroblasts attached to micropegs. Taken together, these data indicate that incorporation of microtopographical features into cardiac tissue engineering scaffolds can be used to control the adhesion and organization of cardiomyocytes while simultaneously limiting the formation of scar tissue.