A Microfabricated Wireless RF Pressure Sensor Made Completely of Biodegradable Materials

A wireless RF MEMS pressure sensor made entirely of biodegradable materials is presented. Such biodegradable sensors may be appropriate for short-term, acute medical implantation applications as they potentially eliminate the need for implant extraction when sensing is no longer required. The biodegradable sensors described here require structural materials for pressure sensing, dielectric materials for insulation, and conducting materials for formation of electrical elements and wireless links. Zinc/iron bilayers were used as the sensor conductor material, and known biodegradable polymers poly-L-lactide and polycaprolactone were used as dielectric and structural materials. Zinc, which otherwise degrades very slowly on its own under biological conditions, is galvanically activated when electrically connected to iron in saline, greatly increasing the total degradation rate of the conductors. To avoid contact of the biodegradable materials with the strong chemicals or solvents that are typically used in conventional MEMS fabrication, embossing, multilayer folding, and lamination were combined with traditional techniques during fabrication. The fabricated sensor was wirelessly tested in both air and 0.9% saline and demonstrated a linear frequency response with external applied pressure. A sensitivity of 39 kHz/kPa was measured in the 0-20 kPa pressure range in air and initially in saline. After immersion in saline for 20 h, the sensor stabilized, remaining stable and functional for 86 h with a sensitivity of -54±4 kHz/kPa.