Yamagishi, K., Zhou, W., Ching, T., Huang, S. Y., Hashimoto, M., Ultra-Deformable and Tissue-Adhesive Liquid Metal Antennas with High Wireless Powering Efficiency. Adv. Mater. 2021, 33, 2008062. https://doi.org/10.1002/adma.202008062
Abstract
Flexible and stretchable antennas are important for wireless communication using wearable and implantable devices to address mechanical mismatch at the tissue–device interface. Emerging technologies of liquid-metal-based stretchable electronics are promising approaches to improve the flexibility and stretchability of conventional metal-based antennas. However, existing methods to encapsulate liquid metals require monolithically thick (at least 100 µm) substrates, and the resulting devices are limited in deformability and tissue-adhesiveness. To overcome this limitation, fabrication of microchannels by direct ink writing on a 7 µm-thick elastomeric substrate is demonstrated, to obtain liquid metal microfluidic antennas with unprecedented deformability. The fabricated wireless light-emitting device is powered by a standard near-field-communication system (13.56 MHz, 1 W) and retained a consistent operation under deformations including stretching (>200% uniaxial strain), twisting (180° twist), and bending (3.0 mm radius of curvature) while maintaining a high quality factor (q > 20). Suture-free conformal adhesion of the polydopamine-coated device to ex vivo animal tissues under mechanical deformations is also demonstrated. This technology offers a new capability for the design and fabrication of wireless biomedical devices requiring conformable tissue-device integration toward minimally invasive, imperceptible medical treatments.
Figure 5 (in paper). Ex vivo demonstrations of the liquid metal antenna using porcine small intestine and heart. A) Schematic illustration of polydopamine (PDA)-coating of the single surface (the side without the microchannel) of the antenna-embedded thin film. B) Images and representative plot of S11 versus frequency of the pristine (left image) and PDA-coated (right image) antenna. Measurements were performed on three different samples for each antenna and similar results were obtained. C) Schematic illustration of the process to attach the antenna to the biological tissue surface with the aid of the water-soluble sacrificial PVA layer. D) Images of the process to attach the antenna to the ex vivo porcine small intestine surface with the aid of the water-soluble sacrificial PVA layer. After the dissolution of the PVA layer, the LEDs were wirelessly turned on by holding the transmission coil (RF power supply: 9 MHz, 1 W) near the antenna. E) Images of the antenna attached to the porcine small intestine while the tissue was stretched (left) and com-pressed (right). LEDs were wirelessly turned on while the tissue was deformed. F) Representative plot of S11 versus frequency of the antenna attached to the porcine small intestine after repeated stretch-compression cycles of the tissue. Measurements were performed on three different samples and similar results were obtained. G) Images of the process to attach the antenna to the ex vivo porcine heart surface (heartbeat was mimicked by applying air pressure via inserted syringe) with the aid of the water-soluble sacrificial PVA layer. After the dissolution of the PVA layer, the LEDs were wirelessly turned on by holding the transmission coil (RF power supply:12 MHz, 1 W) near the antenna. H) Representative plot of S11 versus frequency of the antenna attached to the porcine heart before and after mimicked heartbeats (200 beats at 60 bpm followed by 200 beats at 100 bpm). Measurements were performed on three different samples and similar results were obtained.