Closed Loop Mechanical Actuation of Cardiac Microtissue

Mechanical forces play a significant role in the maturation and function of stem cell derived cardiac tissue. We present a micromechanical test bed with closed loop actuation to control tissue strain with sub-micron spatial and 10 ms temporal resolution. A hydrogel is self-assembled between two custom elastomer posts, where one post is functionalized with a rare-earth magnet. Opposing it is a spherical pillar top facilitating hydrogel attachment. An anti-Helmholtz coil imposes gradient magnetic fields on the magnet translating to nanoNewton forces and tissue strain. The cardiomyocytes beat spontaneously, imposing another force on the magnet. The magnet position is detected without contact by imbedding a hall sensor. The detected signal is processed by analog filters and phase-sensitive detection. The loop is closed with an Arduino MEGA, which digitizes the signal, performs an algorithm, and drives the coils with an arbitrary analog signal.