Effect of Mercury Column on the Microdynamics of the Piezo-Driven Pipettes

This study is on an interesting phenomenon concerning cellular microinjection procedures which are used for various biomedical applications, and in particular intracytoplasmic sperm injection. Recent years have brought considerable practical improvements in these operations. One of them suggests aspirating a very small quantity of mercury in the injection pipettes prior to piercing into cells. This process is proven to enhance the rate of success considerably. We present a unique study in determining the influence of mercury on the microdynamics of the pipette. The effort contains both numerical simulations and corresponding experimental verification. Ultimately we offer two critical results: (1) The mercury column increases the mass loading and expectedly decreases the natural frequencies of the pipette and (2) The lateral oscillations, which play a destructive role in piercing, are subdued in amplitude due to the mass loading of mercury. Simulation results are presented, which are also verified experimentally using high-speed digital imaging. As a consequence of these findings we also propose some alternative design directions for future microinjection devices.