A 3D-printed microdevice for dielectrophoretic torque-driven rotation of dielectric microspheres to support...

Precise control of microscale object rotation is essential for numerous biomedical and microelectromechanical applications. For example, somatic cell nuclear transfer for aquatic biomedical models such as zebrafish faces significant technical challenges, particularly in egg trapping and alignment of an injection needle with the micropyle. In this study, we developed a 3D resin-printed microdevice to achieve frequency-selective electrorotation of dielectric microspheres using a quadrupole electrode configuration driven by phase-shifted alternating current (AC). Theoretical analysis based on the Clausius-Mossotti factor, which governs the polarization of a particle concerning its surrounding environment, highlights the critical role of its imaginary component in the induced dipole moment from the AC field that generates torque. Simulations conducted in COMSOL Multiphysics confirmed the formation of symmetric torque-driven rotation without significant micro-scale object translation. The frequency response of angular velocity exhibited a unimodal profile, with a peak near 4 MHz corresponding to maximum torque efficiency. Experimental validation using 700 μm polystyrene microspheres in Dulbecco's Phosphate Buffered Saline demonstrated consistent clockwise rotation, with a peak angular velocity of 8.1° s^-1 observed at 900 kHz and 16 Vp-p. Although the experimental peak angular velocity occurred at a lower frequency than the theoretical maximum, the rotational trend followed the polarization relaxation behavior captured by $Im\left(K_{cm}\right)$ . Parameter studies further revealed that increasing microscale object permittivity amplified torque generation, while higher medium permittivity reduced it, underscoring the tunability of electrorotation via dielectric properties. This work demonstrates a robust and scalable platform for manipulating large microscale objects. It lays the foundation for future applications involving biologically relevant objects, such as eggs of biomedical research models.