Slide-Ring Microneedle Hydrogels for Sweat Monitoring Evaluated via a Benchtop Sweat Simulator

Wearable sweat sensors are promising tools for non-invasive biomarker monitoring, but their development is hindered by the lack of standardized testing platforms and human sweat variability. Although hydrogels with high swelling capacity are attractive for sweat collection, poor post-swelling mechanical resistance often limits their application. To overcome this limitation, this study presents a mechanically robust, highly swellable hydrogel featuring surface microneedles (MN) that enhance sweat absorption kinetics through capillary fluid dispersion without microstructural collapse. The microneedle patch incorporates a PDMS-molded hydrophilic copolymer network with PEG-β-cyclodextrin-based pseudopolyrotaxanes as mobile crosslinking junctions to promote stress dissipation and structural integrity. Additionally, a benchtop sweat simulator was developed to deliver synthetic sweat with tunable, reproducible flow rates, compositions, and temporal profiles through a programmable interface. Using colorimetric pH monitoring as a proof-of-concept, the hydrogel demonstrated excellent performance across simulated biological variability, highlighting the vital role of material design in accelerating wearable biosensor translation.