Design and Fabrication of a Compliant Micromechanism Amenable for Biaxial Stretching of Single Cells

Biological cells are exposed to a variety of mechanical stimuli from their environment. Cells convert these mechanical stimuli to specific biochemical signals through a process known as mechanotransduction, which is necessary for proper functioning of cells. Biaxial stretching is one such stimuli observed in tissues such as lung alveoli, pericardium, blood vessels and urinary bladder. To study the effect of biaxial stretching on cell function, or any other mechanotransduction process, it is essential to develop tools capable of manipulating cells in the respective deformation mode. Here, we report the design, fabrication and actuation of a compliant micromechanism for in-plane, biaxial stretching of single cells. Our device is an amalgam of a gripper mechanism and an auxetic structure, which can be actuated using a mechanical probe. Cells can be stretched equibiaxially or with any non-equibiaxial stretch ratio, by altering the mechanism geometry. The device is made of SU-8 (a polymeric epoxy-based negative photoresist) using a two-layer lithography process. Since SU-8 is transparent and biocompatible, we can attach cells to the device and continuously image the cells during stretching. By growing NIH 3T3 cells (mouse fibroblasts) on our mechanism, we show that our device is biocompatible.