100 m Long Thermally Drawn Supercapacitor Fibers with Applications to 3D Printing and Textiles.

Supercapacitor fibers, with short charging times, long cycle lifespans, and high power densities, hold promise for powering flexible fabric-based electronics. To date, however, only short lengths of functioning fiber supercapacitors have been produced. The primary goal of this study is to introduce a supercapacitor fiber that addresses the remaining challenges of scalability, flexibility, cladding impermeability, and performance at length. This is achieved through a top-down fabrication method in which a macroscale preform is thermally drawn into a fully functional energy-storage fiber. The preform consists of five components: thermally reversible porous electrode and electrolyte gels; conductive polymer and copper microwire current collectors; and an encapsulating hermetic cladding. This process produces 100 m of continuous functional supercapacitor fiber, orders of magnitude longer than any previously reported. In addition to flexibility (5 mm radius of curvature), moisture resistance (100 washing cycles), and strength (68 MPa), these fibers have an energy density of 306 µWh cm-2 at 3.0 V and ≈100% capacitance retention over 13 000 cycles at 1.6 V. To demonstrate the utility of this fiber, it is machine-woven and used as filament for 3D printing.

Structured multimaterial filaments for 3D printing of optoelectronics.

Simultaneous 3D printing of disparate materials; metals, polymers and semiconductors with device quality interfaces and at high resolution remains challenging. Moreover, the precise placement of discrete and continuous domains to enable both device performance and electrical connectivity poses barriers to current high-speed 3D-printing approaches. Here, we report filaments with disparate materials arranged in elaborate microstructures, combined with an external adhesion promoter, to enable a wide range of topological outcomes and device-quality interfaces in 3D printed media. Filaments, structured towards light-detection, are printed into fully-connected 3D serpentine and spherical sensors capable of spatially resolving light at micron resolution across its entire centimeter-scale surface. 0-dimensional metallic microspheres generate light-emitting filaments that are printed into hierarchical 3D objects dotted with electroluminescent pixels at high device resolution of 55 µm not restricted by surface tension effects. Structured multimaterial filaments provides a path towards custom three-dimensional functional devices not realizable by existing approaches.

Designable 3D Microshapes Fabricated at the Intersection of Structured Flow and Optical Fields.

3D structures with complex geometric features at the microscale, such as microparticles and microfibers, have promising applications in biomedical engineering, self-assembly, and photonics. Fabrication of complex 3D microshapes at scale poses a unique challenge; high-resolution methods such as two-photon-polymerization have print speeds too low for high-throughput production, while top-down approaches for bulk processing using microfabricated template molds have limited control of microstructure geometries over multiple axes. Here, a method for microshape fabrication is presented that combines a thermally drawn transparent fiber template with a masked UV-photopolymerization approach to enable biaxial control of microshape fabrication. Using this approach, high-resolution production of complex microshapes not producible using alternative methods is demonstrated, such as octahedrons, dreidels, and axially asymmetric fibers, at throughputs as high as 825 structures/minute. Finally, the fiber template is functionalized with conductive electrodes to enable hierarchical subparticle localization using dielectrophoretic forces.

Microfluidics in structured multimaterial fibers.

Traditional fabrication techniques for microfluidic devices utilize a planar chip format that possesses limited control over the geometry of and materials placement around microchannel cross-sections. This imposes restrictions on the design of flow fields and external forces (electric, magnetic, piezoelectric, etc.) that can be imposed onto fluids and particles. Here we report a method of fabricating microfluidic channels with complex cross-sections. A scaled-up version of a microchannel is dimensionally reduced through a thermal drawing process, enabling the fabrication of meters-long microfluidic fibers with nonrectangular cross-sectional shapes, such as crosses, five-pointed stars, and crescents. In addition, by codrawing compatible materials, conductive domains can be integrated at arbitrary locations along channel walls. We validate this technology by studying unexplored regimes in hydrodynamic flow and by designing a high-throughput cell separation device. By enabling these degrees of freedom in microfluidic device design, fiber microfluidics provides a method to create microchannel designs that are inaccessible using planar techniques.

Template-assisted fabrication of salt-independent catalytic tubular microengines.

A simplified template-assisted layering approach for preparing catalytic conical tube microjet engines based on sequential deposition of platinum and gold on an etched silver wire template followed by dicing and dissolution of the template is described. The method allows detailed control over the tube parameters and hence upon the performance of the microengine. The recoiling bubble propulsion mechanism of the tubular microengine, associated with the ejection of internally generated oxygen microbubbles, addresses the ionic-strength limitation of catalytic nanowire motors and leads to a salt-independent movement. Similar rates of bubble generation and motor speeds are observed in salt-free and salt-rich media (at elevated ionic-strength environments as high as 1 M NaCl). Plating of an intermediate nickel layer facilitates a magnetically guided motion as well as the pickup and transport of large (magnetic) "cargo". Surfactant addition is shown to decrease the surface tension and offer a more frequent formation of dense smaller bubbles. The new and improved motor capabilities along with the simple preparation route hold great promise for using catalytic micromotors in diverse and important applications.