Elastohydrodynamic Relaxation of Soft and Deformable Microchannels

In situ measurement of viscoelastic properties of cellular monolayers via graphene strain sensing of elastohydrodynamic phenomena

Recent advances recognize that the viscoelastic properties of epithelial structures play important roles in biology and disease modeling. However, accessing the viscoelastic properties of multicellular structures in mechanistic or drug-screening applications has challenges in repeatability, accuracy, and practical implementation. Here, we present a microfluidic platform that leverages elastohydrodynamic phenomena, sensed by strain sensors made from graphene decorated with palladium nanoislands, to measure the viscoelasticity of cellular monolayers in situ, without using chemical labels or specialized equipment. We demonstrate platform utility with two systems: cell dissociation following trypsinization, where viscoelastic properties change over minutes, and epithelial-to-mesenchymal transition, where changes occur over days. These cellular events could only be resolved with our platform's higher resolution: viscoelastic relaxation time constants of λ = 14.5 ± 0.4 s-1 for intact epithelial monolayers, compared to λ = 13.4 ± 15.0 s-1 in other platforms, which represents a 30-fold improvement. By rapidly assessing combined contributions from cell stiffness and intercellular interactions, we anticipate that the platform will hasten the translation of new mechanical biomarkers.

2.5D printing of a yield-stress fluid

We report on direct ink writing of a model yield-stress fluid and focus on the printability of the first layer, the one in contact with the supporting substrate. We observe a diversity of deposition morphologies that depends on a limited set of operational parameters, mainly ink flow rate, substrate speed and writing density, and also on material properties (e.g., yield-stress). Among these morphologies, one of them does not depend on fluid properties (as long as the fluid displays some yield-stress) and consists of flat films whose thickness is controllable in a significant range, about $$0.1{-}1$$ 0.1 - 1  mm, and tunable in real time during printing. We thus demonstrate the ability to print films with thickness gradients and prove that the printing fidelity is mainly due to a competition between yield-stress and capillarity.

Dynamics of Compression-Driven Gas-Liquid Displacement in a Capillary Tube

We study two-phase displacement via the steady compression of an air reservoir connected to an oil-filled capillary tube. Our experiments and modeling reveal complex displacement dynamics depending on compression rate and reservoir volume that, for large reservoirs, depend on a single dimensionless compressibility number. We identify two distinct displacement regimes, separated by a critical value of the compressibility number. While the subcritical regime exhibits quasisteady displacement after an initial transient, the supercritical regime exhibits burstlike expulsion.