Wirelessly activated thermo-responsive polymers for implantable drug delivery and centrifugal microfluidic device applications

Abstract

Thermo-responsive polymers have a great potential to be used in various types of microdevices. Besides being low cost, lightweight, and easy to process, the material properties can be easily tuned by altering the polymer chemistry and structure. These preferences have resulted in their application in many fields, including those in biomedical. Nevertheless, their advantages have not been fully exploited. For instance, most of the actuation mechanisms typically by increasing materials temperature using Joule heating which requires wired interfaces, thus restricting their applications where access and space are crucial. This thesis reports a novel technique for the wireless control of thermo-responsive polymers microactuators and microvalve. The wireless control of thermo-responsive polymers utilizes a radiofrequency magnetic field wireless heating of planar inductor-capacitor circuit to directly heat the actuator/valve, without the use of additional circuits is demonstrated. To function as a cantilever type microactuator, a shape-memory polymer bonded directly with a heater is fabricated. The actuation range of 140 µm as the tip opening distance is achieved at device temperature 44 ºC in 30 s using 0.05 W radio frequency (RF) power. An application of a drug delivery device integrated with the proposed actuator is demonstrated. The actuator is successfully operated in water through wireless activation diffusing acidic solution with an average release rate of 0.172 µL/min. Wireless actuated microvalve using paraffin wax for the centrifugal microfluidic compact disc is also presented and evaluated. Experimental characterization shows a valve operated within ~ 100 s of activation using RF power of 1 W that provides a temperature increase up to 42 ºC at a disc rotation speed of 200 rpm. The presented RF wireless control scheme of thermo-responsive polymer would provide an opportunity to extend further their potential of application beyond this report.