Geometry optimization of printed piezoresistive sensors for catheter monitoring

An increasing number of biomedical applications would benefit to implement printed piezoresistive sensors for improving device performance and sensor integration. In specific, in urinary catheters used to address urinary incontinence and retention, the implementation of piezoresistive sensors would allow to monitor the deformation along the process of insertion, allowing to reduce or even eliminate some of the inconveniences of this type of procedures. This works reports the development of composite inks based on poly(D,L-lactide-co-glycolide) (PDLG) 50/50 with 2% of multiwalled carbon nanotubes and the development by spray printing of piezoresistive sensors with two types of geometry: square and zig zag shape. The spray printed sensors demonstrate a Gauge factor in the range 0.8 to 1.2 for the zig-zag geometry and 0.3 to 1.1 for the rectangular geometry. A theoretical study was performed to evaluate the stress on the piezoresistive sensors and predict the mechanical behavior of the developed geometries proving that, when strain is applied in the longitudinal way, the rectangular geometry presented double the stress value in relation to the zig zag one. Finally, the zig zag geometry was selected for a proof of concept using a KUKA LBR iiwa 7R800 robot, proving the suitability of the developed sensors for applications. Overall, this work demonstrates that the implementation of piezoresistive sensors based on natural polymers in a zig zag geometry is a suitable approach for urinary catheter deformation monitoring. • Sustainable piezoresistive composites were prepared by spray-printing technique. • The effect of geometry on the electric and piezoresistive response of PDLG composites has been evaluated. • The piezoresistive response is characterized by a maximum GF ~1.2 in the PDLG composite with zig-zag geometry. • This environmentally friendly polymer-based nanocomposites with zig-zag geometry exhibit excellent response in a biomedical catheter.