An Inchworm and Stick-Slip Dual Mode Piezoelectric Linear Actuator for Cell Injection

Cell injection system for biomedical engineering demands that actuators have large stroke, high resolution and speed for cell positioning and injection. Single mode piezoelectric actuators could meet some of these requirements but hardly all. Stick-slip actuator is easy to achieve high-speed operation, but it is prone to setback; The speed characteristics of the inchworm actuator are lower than those of the stick-slip actuator, but the step is more stable and the setback is lower. This study proposes an inchworm and stick-slip dual mode piezoelectric actuator (ISSPA) for cell injection. It integrates two working modes into one actuator and both modes drive the same slider. The stick-slip mode works at high frequency for fast positioning to the cell and the inchworm mode drives the needle to puncture the cell membrane and accurately locates to the specified location. The structure and working principle of the ISSPA are provided. A prototype of the proposed ISSPA is fabricated and experiments are conducted. When the driving voltage of the piezoelectric stack is 100 V and the frequency is 500 Hz, the maximum speed of the ISSPA is 2.287 mm/s in the stick-slip mode. When the driving voltage of the piezoelectric stack is 60 V, the frequency is 3 Hz and the load is 0.5 kg, the minimum step displacement is 57 nm in inchworm mode. Demonstration of cell injection is carried out by using the ISSPA to positioning and puncturing a zebrafish embryo. Fast positioning with the stick-slip mode and accurate puncture with the inchworm mode are achieved with the ISSPA alone, taking 12 seconds for the whole injection process. It could be expected to apply the ISSPA to cells with wide range of diameter, as the frequency of the stick-slick mode and the voltage of the inchworm mode could be well regulated.