Dissolvable material for high-aspect-ratio flexible silicon-microwire penetrations

High-aspect-ratio microwire array devices, which penetrates into a biological tissue, have widely been used in neuroscience, offering in vivo/in vitro electrophysiological stimulation and recording, drug delivery (e.g., DNA), and optogenetics applications. As low invasive and safe penetrations, these microwire devices are required to be further miniaturized and flexibility. However, tissue penetration with such high-aspect-ratio and flexible wires is problematic, because the wire buckles during the penetration. Here, we improve the penetration capability of high-aspect-ratio flexible wires by coating a dissolvable material of “silk fibroin” (Fig.1). The silk-fibroin is a material, which dissolves when the surface contacts with a wet biological tissue, resulting in that embedded wires are appeared and penetrated. We demonstrated the silk fibroin coating over high-aspect-ratio silicon-microwires (~720 μm in length), which was fabricated by vapor-liquid-solid (VLS) growth. The 420-μm-long silicon-wire with a ~200-μm-thick silk film exited the stiffness of 4.03 N/m, which is 72% improved value compared to that of the silicon-wires without silk (2.34 N/m). The effects of the silk support on the wire penetration were confirmed by demonstrating the gelatin penetrations. These results suggest that the numerous high-aspect-ratio flexible bioprobes can be penetrated by using the silk support.