Design and control of a piezoelectric microgripper for micromanipulation of biological cells

Safe and reliable micromanipulation of biological cells requires microgrippers that combine precise motion, delicate force regulation, and robust control strategies against tissue variability. In this work, we address the challenge of designing and controlling a piezoelectric driven compliant microgripper capable of manipulating biological cells such as embryonic stem cells and oocytes, whose viscoelastic properties and adhesive interactions complicate stable grasping. A compliant amplification mechanism is designed and optimized, and finite element analysis of the optimized microgripper yields a displacement amplification ratio of 25.02 and a first natural frequency of 513.31 Hz, indicating a favorable balance between motion amplification and dynamic performance. Biological cell behavior is represented by a viscoelastic model, while the gripper’s structural dynamics are captured through a hybrid formulation combining rigid body kinematics and Timoshenko beam theory. To regulate displacement and gripping force under contact and non contact conditions, impedance control and hybrid position/force switching control are implemented and compared. The derived analytical models are validated against finite element simulations. Under nominal conditions, both controllers provide satisfactory regulation; however, impedance control exhibits lower sensitivity to tissue stiffness variation, mass estimation uncertainty, and sensor noise, whereas the hybrid scheme is more affected by switching induced transients. The influence of representative piezoelectric hysteresis and creep effects is also investigated through simulation, both individually and simultaneously, and the impedance controller maintains acceptable closed loop performance under the investigated conditions. Additional simulations using human embryonic stem cell properties indicate force regulation in the nano Newton range, while liquid induced added mass and viscous damping have a limited influence within the considered operating regime. The estimated closed loop bandwidths remain below the first structural mode. Overall, the results suggest that integrating compliant design, viscoelastic cell modeling, and impedance based interaction control provides a promising simulation based framework for future biomedical micromanipulation systems.