Measurement of single-cell viscoelastic properties using acoustic tweezers

The mechanical property of a cell is a key indicator that shows the pathological characteristics of cells. Cell viscoelasticity is one of the mechanical properties of the cell that exhibits both viscous and elastic characteristics when cell deformation occurs, and a changing acoustic pressure is required when analyzing them. In the measurement of the mechanical properties of cells, acoustic tweezers have been utilized in a non-invasive manner since they have several advantages such as inducing less cell damage and generating high-trapping force compared to optical tweezers. To quantify the viscoelasticity of a cell, a press-focused single-element ultrasound transducer was fabricated. It was used to trap a target cell and then change the deformation by varying trapping forces. The deformation of breast cancer cells at different trapping forces was recorded in a high-speed camera for quantification of cell deformability. Acoustic pressure at different pressures was applied to the cell for quantification of deformation and comparison of metastability. Also, it was found that the amplitude modulated force resulted in a phase delay between applied forces and cell deformation while cell trapping, suggesting that by analyzing the phase delay, the viscosity of the trapped cell can be quantified.