Fabrication of biocompatible and biodegradable cloth-based sweat sensors using polylactic acid (PLA) via stencil transparent film-printing

Cloth-based sensors are gaining attention for creating microfluidic wearable sensors for continuous monitoring of sweat biomarkers because of their flexibility, low cost, and natural hydrophilicity making them suitable for integration into everyday products. Here, we present a novel, low-cost and simple fabrication approach to create a cloth-based sensor ready for use as a sweat sensor while being environmentally friendly using biocompatible and biodegradable material, polylactic acid (PLA), and a stencil transparent film-printing method. The method provided high-resolution structures with narrowest hydrophilic channels and hydrophobic barriers measuring 1.90 ± 0.34 mm and 1.23 ± 0.14 mm, respectively. Various designs for detecting sweat biomarkers, including pH, lactate, and chloride, were generated by simply adjusting the stencil transparent film designs. For pH detection, a square-shaped cloth-based sensor was constructed and different natural indicators was used as biocompatible and non-toxic reagents to measure pH providing the detection in the pH range of 1-14. In lactate determination, an enzymatic assay with nanoceria as colorimetric probes was used in a spot format, offering a lactate detection range of 2.5-25 mM, effectively distinguishing between normal and abnormal muscle fatigue patients at a cut-off level of 12.5 mM sweat lactate. For chloride, a distance-based format was employed using the reverse Mohr titration assay, resulting in a detection range of 10-100 mM. Finally, the analysis of lactate and chloride in artificial sweat was successfully demonstrated yielding the recovery in the acceptable range demonstrating accurate measurements of the fabricated cloth-based sensors.