Migration and 3D Traction Force Measurements inside Compliant Microchannels.

Cells migrate in vivo through channel-like tracks. While polydimethylsiloxane devices emulate such tracks in vitro, their channel walls are impermeable and have supraphysiological stiffness. Existing hydrogel-based platforms address these issues but cannot provide high-throughput analysis of cell motility in independently controllable stiffness and confinement. We herein develop polyacrylamide (PA)-based microchannels of physiological stiffness and prescribed dimensions for high-throughput analysis of cell migration and identify a biphasic dependence of speed upon confinement and stiffness. By utilizing novel four-walled microchannels with heterogeneous stiffness, we reveal the distinct contributions of apicolateral versus basal microchannel wall stiffness to confined versus unconfined migration. While the basal wall stiffness dictates unconfined migration, apicolateral stiffness controls confined migration. By tracking nanobeads embedded within channel walls, we innovate three-dimensional traction force measurements around spatially confining cells at subcellular resolution. Our unique and highly customizable device fabrication strategy provides a physiologically relevant in vitro platform to study confined cells.

Tunable optical chirality in a metamaterial platform with off-resonantly coupled metal-dielectric components.

Here we present a tunable chiral metamaterial platform that incorporates both metal and dielectric components, where the sign and magnitude of the circular dichroism (CD) response depend on the refractive index of the dielectric component. Using finite-difference time-domain simulations, we show that non-resonant scattering interactions between the components of the system reverse the sign of the CD signal by changing the dissymmetry in absorption of circularly polarized light by the individual plasmonic components of the system. The platform exhibits tunable CD signal regardless of the shape and dimension of the dielectric scatterer, and the magnitude of the CD signal is enhanced by improving the scattering cross section of the dielectric structure. Finally, we show that the structure can be modified to incorporate other materials without diminishing the reversal in dissymmetry in transmission. These results indicate that controlled, off-resonant interactions between different materials in chiral metamaterials may be used to create tailored and tunable chiral platforms.