Flexible substrate-based thermo-responsive valve applied in electromagnetically powered drug delivery system

This paper presents a novel drug delivery system consisting of an electrolytic pump to drive the drug solution and a flexible substrate-based thermo-responsive valve to control the exit port. An electromagnetic field (60 mT, 450 kHz) is used to wirelessly power both the pump and the valve. The valve model is fabricated out of polydimethylsiloxane, in which a thermo-responsive poly N-isopropylacrylamide hydrogel is filled. This valve can avoid undesired drug diffusion at the outlet of the device over an extended period; it also allows a reverse flow to refill the drug reservoir within a given opening time. This is especially suitable for long-term drug delivery using a solid drug in reservoir approach. When the electromagnetic field is turned on, an electrolytic reaction happens in the actuator which results in an electrolysis-bubble expansion that drives the drug liquid toward the valve. In the meantime, the iron microparticles that are embedded into the PDMS substrate produce heat due to magnetic losses. The heating of the iron powder causes the hydrogel to shrink, resulting in an open valve. When the electromagnetic field is turned off, the bubbles are recombined in the presence of electrolysis catalysts, thereby decreasing the pressure in the actuator. This draws fresh body liquid from outside the device into the drug reservoir to dissolve the remaining solid-form drug before the PNIPAM fully seals the valve. Our experimental results reveal that the system is capable of being repeatedly implemented, and flow is effectively controlled by an external magnetic field strength.