Abstract
Advanced Materials Technologies 2019, 4, 1900528
Thermoresponsive Transient Radio Frequency Antennas: Toward Triggered Wireless Transient Circuits
Zhang X, Weber CM, Bellan LM
While implantable medical devices offer tremendous potential for treating a myriad of diseases and disorders, there are many situations in which such devices are only needed for short time periods, with extended presence or surgical removal leading to a host of undesired complications. To address this concern, researchers are working to develop implantable circuitry that eventually disintegrates. Prior work in this area leveraged known bioresorbable materials, but the lifetime of circuits formed from such materials is determined upon fabrication, and on-demand, triggered disintegration is not possible. To better match the lifetime of an implanted device to the status of the condition it is monitoring or treating, it would be advantageous to be able to noninvasively trigger disintegration at a particular time, avoiding situations in which the device lifetime is either too short or too long. Thus, to enable implantable circuitry with wireless capabilities that can disintegrate upon external stimuli, thermoresponsive transient RF antennas are formed that exhibit stable wireless response in warm aqueous environments but disintegrate and irreversibly lose functionality when cooled below a critical temperature. Antennas are formed by embedding patterned networks of silver nanowires in a thermoresponsive polymeric binder, which maintains network conductivity in warm solution but disintegrates and releases the nanowires when solution temperature drops. Mild sintering enhances electrical properties of the conductive nanowire network and antenna response while maintaining the capability for disintegration. To reduce the undesired effects of swelling, devices are sandwiched between two parylene films. These thermoresponsive transient devices represent an important step toward the realization of wireless medical implants whose disintegration can be triggered at any time by an external cooling stimulus.