Tunable Infrared Metasurface on a Soft Polymer Scaffold.

The fabrication of metallic electromagnetic meta-atoms on a soft microstructured polymer scaffold using a MEMS-based stencil lithography technique is demonstrated. Using this technique, complex metasurfaces that are generally impossible to fabricate with traditional photolithographic techniques are created. By engineering the mechanical deformation of the polymer scaffold, the metasurface reflectivity in the mid-infrared can be tuned by the application of moderate strains.

Direct laser writing for cardiac tissue engineering: a microfluidic heart on a chip with integrated transducers.

We have developed a microfluidic platform for engineering cardiac microtissues in highly-controlled microenvironments. The platform is fabricated using direct laser writing (DLW) lithography and soft lithography, and contains four separate devices. Each individual device houses a cardiac microtissue and is equipped with an integrated strain actuator and a force sensor. Application of external pressure waves to the platform results in controllable time-dependent forces on the microtissues. Conversely, oscillatory forces generated by the microtissues are transduced into measurable electrical outputs. We demonstrate the capabilities of this platform by studying the response of cardiac microtissues derived from human induced pluripotent stem cells (hiPSC) under prescribed mechanical loading and pacing. This platform will be used for fundamental studies and drug screening on cardiac microtissues.

Fabrication of multi-material 3D structures by the integration of direct laser writing and MEMS stencil patterning.

The construction of a complex, 3D optical metamaterial challenges conventional nanofabrication techniques. These metamaterials require patterning of both a deformable mechanical substrate and an optically-active structure with ∼200 nm resolution and precision. The soft nature of the deformable mechanical materials often precludes the use of resist-based techniques for patterning. Furthermore, FIB deposition approaches produce metallic structures with considerable disorder and impurities, impairing their optical response. In this paper we discuss a novel solution to this nanofabrication challenge - the integration of direct laser writing and MEMS stencil patterning. We demonstrate a variety of methods that enable this integration and then show how one can produce optically-active, 3D metamaterials. We present optical characterization data on one of these metamaterials to demonstrate the viability of our nanofabrication approach.

Studies of 3D directed cell migration enabled by direct laser writing of curved wave topography.

Cell migration, critical to numerous biological processes, can be guided by surface topography. Studying the effects of topography on cell migration is valuable for enhancing our understanding of directional cell migration and for functionally engineering cell behavior. However, fabrication limitations constrain topography studies to geometries that may not adequately mimic physiological environments. Direct Laser Writing (DLW) provides the necessary 3D flexibility and control to create well-defined waveforms with curvature and length scales that are similar to those found in physiological settings, such as the luminal walls of blood vessels that endothelial cells migrate along. We find that endothelial cells migrate fastest along square waves, intermediate along triangular waves, and slowest along sine waves and that directional cell migration on sine waves decreases as sinusoid wavelength increases. Interestingly, inhibition of Rac1 decreases directional migration on sine wave topographies but not on flat surfaces with micropatterned lines, suggesting that cells may utilize different molecular pathways to sense curved topographies. Our study demonstrates that DLW can be employed to investigate the effects and mechanisms of topography on cell migration by fabricating a wide array of physiologically-relevant surfaces with curvatures that are challenging to fabricate using conventional manufacturing techniques.