When temporary wireless sensors are used for medical applications, multiple surgeries are needed to install and remove the sensor. If a wholly biodegradable sensor were used, the removal surgery would become unnecessary. To save patients a costly and potentially painful second surgery, Mengdi Luo, Adam Martinez, Chao Song, Florian Herrault, and Mark Allen from the Georgia Institute of Technology explored materials to create an RF biodegradable pressure sensor.
Polyactic acid (PLLA) and polymer liquid crystal (PLC) biodegradable plastics were used to construct the films that operate as the sensor substrate. The conductor materials for the inductor coils and capacitor plates for the sensor were formed from zinc and iron. The coils and plates were electrodeposited on the film using a standard plating bath. The metallic structures and insulating layers were deposited on a flat film that is folded to produce the multi-layer pressure sensor.
Several tests were performed to characterize the biodegradability of the components and the structure. A 0.9% saline solution was used to immerse the metallic pressure-sensor components in a heated mechanical vibration chamber. After a 300-hr. test, the iron oxides were the only remaining material that was not dissolved in the solution. In resonant-frequency testing in saline and air, a similar decline in resonant frequency to increased applied pressure is observed. There is a marked shift in resonant frequency between the air and saline environments. See “A Microfabricated Wireless RF Pressure Sensor Made Completely of Biodegradable Materials,” Journal of Microelectromechanical Systems, Feb. 2014 p. 4.
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