ABSTRACT
This paper reports an active catheter-tip device functionalized by integrating a temperature-responsive smart polymer onto a microfabricated flexible heater strip, targeting at enabling the controlled steering of catheters through complex vascular networks. A bimorph-like strip structure is enabled by photo-polymerizing a layer of poly(N-isopropylacrylamide) hydrogel (PNIPAM), on top of a 20 × 3.5 mm2 flexible polyimide film that embeds a micropatterned heater fabricated using a low-cost flex-circuit manufacturing process. The heater activation stimulates the PNIPAM layer to shrink and bend the tip structure. The bending angle is shown to be adjustable with the amount of power fed to the device, proving the device's feasibility to provide the integrated catheter with a controlled steering ability for a wide range of navigation angles. The powered device exhibits uniform heat distribution across the entire PNIPAM layer, with a temperature variation of <2 °C. The operation of fabricated prototypes assembled on commercial catheter tubes demonstrates their bending angles of up to 200°, significantly larger than those reported with other smart-material-based steerable catheters. The temporal responses and bending forces of their actuations are also characterized to reveal consistent and reproducible behaviors. This proof-of-concept study verifies the promising features of the prototyped approach to the targeted application area.
ABSTRACT
This paper reports the first in vivo testing of a resonant-heating stent toward wireless hyperthermia treatment of in-stent restenosis. The stent, made of gold-coated medical-grade stainless steel, is designed to function as an electrical inductor and forms a radiofrequency (RF) resonant circuit with an integrated capacitor microchip. Upon implantation and deployment with the balloon catheter, the stent device serves as a wireless heater as part of the resonant wireless power transfer system, which allows for the device to produce mild heat only when the stent is resonated with a tuned RF electromagnetic field supplied from the external antenna. The wireless power transmitter includes an independent omnidirectional booster antenna that enhances the power delivery to the implanted stent device. The entire stent device is packaged with 40-µm-thick Parylene C film that is shown to be essential for minimizing electrothermal damping in a conductive liquid like blood. The in vitro tests of the prototype system show a temperature increase of 3.3 °C in the stent device couple in a flow loop of saline pumped at a flow rate relevant to the condition of coronary stenosis. In swine models, the system demonstrates RF heating of the stent devices expanded to different diameters, in live blood stream, achieving temperature rises of up to 2.6 °C in a consistent and repeatable manner. These results bring the technology one step closer toward clinical realization of wireless thermal therapy of in-stent restenosis.
