Viscoelastic characterization of cells in microfluidic channels with 3D hydrodynamic focusing

The viscoelastic nature of biological cells has emerged as an increasingly important research subject due to its relevance for cellular functions under physiological and pathological conditions. Advancements in microfluidics have made this technology a promising tool to study the viscoelasticity of cells. However, significant challenges remain, including the complex analysis of stresses acting on cells depending on the channel geometry and the difficulty of keeping cells in the focal plane for imaging. Here, we report a new approach using hyperbolic channels for measuring cell viscoelasticity. A large channel cross section combined with 3D hydrodynamic focusing keeps the stress distribution on the sample simple, while the sample maintains a centered position in the channel. This allowed us to use mechanical calibration particles to characterize the stress curve without having to determine stress contributions from different origins (extension vs shear). It also eliminated the need to quantify the carrier medium's rheology, thus enabling a simpler and faster analysis compared to prior work. Kelvin-Voigt and power-law rheology models were employed to extract the mechanical properties of microgel beads and human leukemia HL60 cells. This new technique offers a robust and scalable method for advancing viscoelastic cell characterization in biophysical studies in health and disease.