We describe an impedance-based method for cell barrier integrity testing. A four-electrode electrical impedance spectroscopy (EIS) setup can be realized by simply connecting a commercial chopstick-like electrode (STX-1) to a potentiostat allowing monitoring cell barriers cultivated in transwell inserts. Subsequent electric circuit modeling of the electrical impedance results the capacitive properties of the barrier next to the well-known transepithelial electrical resistance (TEER). The versatility of the new method was analyzed by the EIS analysis of a Caco-2 monolayer in response to (a) different membrane coating materials, (b) two different permeability enhancers ethylene glycol-bis(2-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA) and saponin, and (c) sonoporation. For the different membrane coating materials, the TEERs of the standard and new protocol coincide and increase during cultivation, while the capacitance shows a distinct maximum for three different surface materials (no coating, Matrigel ® , and collagen I). The permeability enhancers cause a decline in the TEER value, but only saponin alters the capacitance of the cell layer by two orders of magnitude. Hence, cell layer capacitance and TEER represent two independent properties characterizing the monolayer. The use of commercial chopstick-like electrodes to access the impedance of a barrier cultivated in transwell inserts enables remarkable insight into the behavior of the cellular barrier with no extra work for the researcher. This simple method could evolve into a standard protocol used in cell barrier research.

For successful material deployment in tissue engineering, the material itself, its mechanical properties, and the microscopic geometry of the product are of particular interest. While silk is a widely applied protein-based tissue engineering material with strong mechanical properties, the size and shape of artificially spun silk fibers are limited by existing processes. This study adjusts a microfluidic spinneret to manufacture micron-sized wet-spun fibers with three different materials enabling diverse geometries for tissue engineering applications. The spinneret is direct laser written (DLW) inside a microfluidic polydimethylsiloxane (PDMS) chip using two-photon lithography, applying a novel surface treatment that enables a tight print-channel sealing. Alginate, polyacrylonitrile, and silk fibers with diameters down to 1 μm are spun, while the spinneret geometry controls the shape of the silk fiber, and the spinning process tailors the mechanical property. Cell-cultivation experiments affirm bio-compatibility and showcase an interplay between the cell-sized fibers and cells. The presented spinning process pushes the boundaries of fiber fabrication toward smaller diameters and more complex shapes with increased surface-to-volume ratio and will substantially contribute to future tailored tissue engineering materials for healthcare applications.

Complex‐shaped microgels are promising building blocks for soft metamaterials. Their active and remote orientational control provides significant potential in architecting them in time and space. This work describes the use of magnetically actuable microgels of complex shape for spatio‐temporal flow control and showcases the concept for microfluidic impellers. First, the fabrication of complex‐shaped magnetically actuable poly(ethylene glycol) diacrylate based microgels via stop‐flow lithography is presented. The microgels comprise a pre‐programmed magnetic moment set by pre‐aligned maghemite nanospindles during the fabrication step. This feature allows the microgels to be positioned in a static magnetic field and rotate under application of a rotating external field. The dependence of the magnetic field rotation rate and strength, maghemite content, and microgel shape on the magnetic response of the microgels is comprehensively quantified. Finally, the magnetic complex‐shaped microgels are integrated as actuable impellers in a microfluidic chip. The microgels are positioned in space by polymerizing them around fixed poly(dimethylsiloxane) (PDMS) pillars. Free rotation around the PDMS pillar is achieved due to the oxygen inhibition layer at the chip and pillar surface. The versatility of the fabrication methodology is showcased by the investigation of in‐chip mixing in a microfluidic device consisting of soft responsive impellers.