Flexible, Structured MWCNT/PDMS Sensor for Chronic Vascular Access Monitoring.

Graft wall pulsation amplitude sensing can provide a measure of functional status, e.g. in hemodialysis access grafts. Current implantable graft monitoring sensors require graft modification and direct bloodstream contact. We propose a new class of piezoresistive flexible pulsation sensors which can be wrapped around the graft to measure wall movement. These sensors must be highly flexible to prevent graft constriction; typical strain sensors are too rigid and the strain sensing range is too limited for this application. We describe a novel additive manufacturing (AM) method for printing polydimethylsiloxane (PDMS) with an internal porous structure, such that material compliance may be tuned anisotropically for a given sensor geometry. Prototype flexible pulsation sensors (FPS) consisting of structured PDMS with an embedded conductive PDMS sensor layer were fabricated and tested. Initial tests demonstrated reliable sensor response to 1-Hz cyclic elongation of 20%, and a sensor gauge factor of 1.0.

A wearable stimulation bandage for electrotherapy studies in a rat ischemic wound model.

The clinical efficacy of electro-therapy in the treatment of chronic wounds is currently debated, and a in-vivo evaluation of stimulation parameters will provide the statistical evidence needed to direct clinical guidelines. A low-cost, wearable electrical stimulation bandage has been developed for use with an established rat ischemic wound model. The bandage consists of a user-programmable stimulator PCB and a plastic bandage with two hydrogel electrodes. The battery-powered bandage may be used for up to seven days between dressing changes, and the stimulator may be reused. The microcontroller-based stimulator uses a boost converter circuit to generate pulses up to 90 V from a 3 V coin cell battery. Consistent operation of the boost converter over the wide input and output voltage ranges is achieved using voltage feedforward and soft-start techniques implemented in firmware. The bandages are laser-cut to shape, and electrical traces are applied using stencils and conductive nickel paint. Both the PCB and electrical traces are encapsulated to protect the animal. The device has been successfully demonstrated using the rat ischemic wound model for a period of seven days, and clinical experiments are ongoing.