Removal of living cells from biosensing surfaces in droplet-based microfluidics using surface acoustic waves

Removal of living biological cells from surfaces is a critical process for many applications in the area of biosensing and lab-on-a-chip. Trypsin is one of the most effective biochemical tools used to cleave the cells proteins that are responsible for bonding cells to surfaces [1]. We propose a method using Rayleigh-type (20MHz) surface acoustic wave (SAW)-based mixing [2] as an accelerator for trypsin mediated removal of living cells from surfaces. In the experiments, a 10 µL droplet of Hank's Balanced Salt Solution (HBSS)-trypsin is placed on a piezoelectric substrate covered with human embryonic kidney cells (HEK293). Using phase contrast microscopy, cells removal time for different acoustic power levels and trypsin concentrations is measured. Results from validation experiments show that a minimum of 180 seconds is necessary to completely release surface-bonded cells covered by the 10µL droplet without the use of SAW (negative control). By using microstreaming flow in the droplets generated by the SAW, cells are released from the surface in less than 8 seconds. This work will contribute to improved lab-on-a-chip devices based on living cell biosensing. [1] K. A. Walsh, Methods in Enzymology (1970), 19, 41-63 [2] A. Renaudin et al., Lab on chip (2010), 10, 111-115