A Compliant Micromechanism for Biaxially Stretching Biological Cells

Biological cells are known to respond to mechanical forces. Diverse biological phenomena such as tissue development and cancer are regulated by mechanical forces acting on cells. One such mechanical loading found in various tissues such as alveoli, pericardium, blood vessels, and urinary bladder is biaxial stretching. To study the effect of such a loading pattern, it is necessary to develop mechanical tools that can apply controlled biaxial stretching on cells. Here we present the design for such a device, a compliant micromechanism for biaxially stretching single cells. We first designed a compliant, double-input, biaxial stretching mechanism based on re-entrant structures. Various stretch ratios, defined as the ratio between deformations in orthogonal directions, could be obtained by changing the dimensions of this mechanism. Next, we derived an analytical expression relating the geometric parameters to the stretch ratio. This analytical expression was verified using finite element analysis. By numerically solving this expression, multiple designs for a desired stretch ratio were obtained. Furthermore, we converted our design into a single-input mechanism by coupling the double-input biaxial stretcher to a single-input gripper mechanism. Finally, we demonstrate the functioning of our design using a macroscale, 3D-printed version.