Direct Writing of Elastic Conductors for Three-Dimensional Stretchable Electronics

Skin electronics augment the capability of shareable signals from personal and metabolic activities over communication networks by blurring the physical discontinuity between electronic devices and human skin. With their unique mechanical characteristics, such as lightweight design, softness, and stretchability, skin electronics can be functionalized on various body parts in the form of biosensors, processors, and displays. For high-fidelity operation under these challenging circumstances, the design of skin electronics needs to be tailored elaborately to individuals. However, traditional mask-based lithography primarily optimized for the mass production of standardized, uniform electronics cannot effectively deal with the morphological diversity of the human bodies. Moreover, existing manufacturing processes still lack strategies to implement three-dimensional (3D) structures with soft functional materials such as vertical interconnect accesses (VIAs) and multilayer circuitries that are crucial to the realization of high-performance, multifunctional applications.<br/>Printing technologies have attracted tremendous attention in the realization of customized soft electronics due to their advantages, such as non-vacuum, low-temperature, and non-contact processability. However, most conventional 3D printing processes still deposit one layer at a time, which is unsuitable for complex, filamentary, and omnidirectional wirings (including a z-directional component). In this regard, omnidirectional direct ink writing for self-supporting 3D wirings with elastomer composites has attracted much attention, but the complex composition of their inks that meets apposite rheological properties is a critical bottleneck, resulting in structural collapse and nozzle clogging during extrusion simultaneously. In this presentation, I would like to present our recent results of printing Intrinsically stretchable solid-state elastic conductors into self-supporting 3D geometries. These results promise the design diversity of soft electronics, enabling complex, multifunctional, and tailored human-machine interfaces. Our omnidirectional printing strategies achieve superior viscoelastic properties that provide the structural integrity of printed features, and pseudoplastic and lubrication behaviors that allow great printing stability simultaneously. Freestanding, filamentary, and out-of-plane 3D geometries of intrinsically stretchable conductors are directly written, achieving a minimum feature size &lt;100 μm and excellent stretchability &gt;150%. Particularly, the evaporation of the continuous phase in the emulsion results in microstructured, surface-localized conductive networks, significantly improving their electrical conductivity. To illustrate the feasibility of our approach, we demonstrate skin-mountable electronics that visualize temperature on a matrix-type stretchable display based on omnidirectionally printed elastic interconnects.