Recent advances in soft materials and mechanics activate development of many new types of electrical medical implants. Electronic implants that provide exceptional functions, however, usually require more electrical power, resulting in shorter period of usages although many approaches have been suggested to harvest electrical power in human bodies by resolving the issues related to power density, biocompatibility, tissue damage, and others. Here, we report an active photonic power transfer approach at the level of a full system to secure sustainable electrical power in human bodies. The active photonic power transfer system consists of a pair of the skin-attachable photon source patch and the photovoltaic device array integrated in a flexible medical implant. The skin-attachable patch actively emits photons that can penetrate through live tissues to be captured by the photovoltaic devices in a medical implant. The wireless power transfer system is very simple, e.g., active power transfer in direct current (DC) to DC without extra circuits, and can be used for implantable medical electronics regardless of weather, covering by clothes, in indoor or outdoor at day and night. We demonstrate feasibility of the approach by presenting thermal and mechanical compatibility with soft live tissues while generating enough electrical power in live bodies through in vivo animal experiments. We expect that the results enable long-term use of currently available implants in addition to accelerating emerging types of electrical implants that require higher power to provide diverse convenient diagnostic and therapeutic functions in human bodies.

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Cracks commonly appear in metal patterns when fabricated on native poly(dimethylsiloxane) (PDMS) substrate using general micro-electro-mechanical systems (MEMS) fabrication processes such as lift-off and metal etching. This paper introduces simple, reliable and reproducible fabrication methods to realize crack-free metal patterns on PDMS using intermediate-parylene-deposited PDMS substrate and parylene-filled PDMS substrate. The fabrication parameters of crack-free metal patterning were optimized resulting in reliable and reproducible fabrication outputs. The adhesion of metals on these surface-modified PDMS substrates was evaluated by ASTM tape tests in wet and dry conditions. X-ray photoelectron spectroscopy (XPS) was used to characterize the element composition on the surface of parylene-filled PDMS. The surfaces of native PDMS, parylene-deposited PDMS and parylene-filled PDMS were investigated using scanning electron microscopy (SEM) and XPS for analysis of crack generation during the metal patterning processes. The mechanical properties, such as stress and strain, of native and surface-modified PDMS substrates were measured by standard tension tests. Based on these results, it was concluded that the proposed methods successfully generated reliable crack-free metal patterns based on PDMS substrate using general MEMS technologies, which can be used for various applications such as biomedical devices and flexible electronics.

This study investigates the mechanical and long-term electrical properties of parylene-caulked polydimethylsiloxane (PDMS) as a substrate for implantable electrodes. The parylene-caulked PDMS is a structure where particles of parylene fill the porous surface of PDMS. This material is expected to have low water absorption and desirable mechanical properties such as flexibility and elasticity that are beneficial in many biomedical applications. To evaluate the mechanical property and electrical stability of parylene-caulked PDMS for potential in-vivo uses, tensile tests were conducted firstly, which results showed that the mechanical strength of parylene-caulked PDMS was comparable to that of native PDMS. Next, surface electrodes based on parylene-caulked PDMS were fabricated and their impedance was measured in phosphate-buffered saline (PBS) solution at 36.5 °C over seven months. The electrodes based on parylene-caulked PDMS exhibited the improved stability in impedance over time than native PDMS. Thus, with improved electrical stability in wet environment and preserved mechanical properties of PDMS, the electrodes based on parylene-caulked PDMS are expected to be suitable for long-term in-vivo applications.

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