Direct Transfer Printing of Water Hydrolyzable Metals onto Silk Fibroin Substrates through Thermal‐Reflow‐Based Adhesion

In recent years, the use of biopolymers as interface materials between inorganic electronics and biological tissues has increased, which has necessitated the integration of micro‐ and nanofabrication techniques with these unconventional materials. This combination has led to devices with intriguing operational characteristics such as so‐called “transient” bioresorbable devices. Here, a method is investigated which leverages the thermal reflow characteristics of non‐beta‐sheet crystallized silk fibroin protein films to transfer print electronic components onto bioresorbable silk substrates. This is accomplished by applying heat and pressure to the interface of the silk and fabricated components, leading to reflow of the silk and transfer of the components from a silicon carrier wafer onto silk. We demonstrate application of this for both traditional (Au) and highly labile transient metals (Mg), over large areas with single micrometer resolution, all while retaining functionality of the transferred components. Additionally, it is shown how control over the reflow characteristics of silk through the process parameters can lead to both water‐stable and water‐soluble device outcomes and retain the efficacy of entrained biological dopants within the silk substrate matrix. Through these means, this method has the potential to improve the number of fabrication options for devices at the biotic/abiotic interface.