Frequency-selectable wireless actuation of hydrogel using micromachined resonant heaters toward implantable drug delivery applications

This paper describes a wireless actuation technique for microdevices that are controlled with radiofrequency magnetic fields, targeting at the application to implantable drug delivery devices. A thermoresponsive hydrogel serves as the actuator that is driven by the passive resonant circuit that effectively generates heat only when the field frequency is tuned to the resonant frequency of the circuit, inducing bulk squeezing of the material for drug release. The heater devices are microfabricated to have the resonant frequencies of 30-100 MHz, which are coupled with the hydrogel photo-patterned on the devices. The fabricated heaters provide temperature increase of up to 20degC at their resonances in a wireless set-up, causing ~40% shrinkage of the hydrogel. The frequency-defined release of a test solution is experimentally demonstrated using a fabricated device, which is shown to exhibit an active frequency range of ~2 MHz.