Tissue-adhesive hydrogel–MXene biosensor for in situ intraoral TNF-α detection

Mechanical and interfacial characterization of the tissue-adhesive hydrogel (TAH) patch and the assembled TAHM sensor system was performed using a CellScale UStretch device (legacy CellScale platform; now superseded by UniVert. Using the UStretch, the authors quantified tissue adhesion via 90° peel testing following ASTM D6862: porcine skin (and separately porcine gingiva) was adhered to a glass substrate coated with a dried TAH patch, a gentle compressive preload (~5 kPa) was applied for ~5 s to ensure conformal contact, and the assembly was peeled at a constant rate of 1 mm/s while simultaneously translating the stage to maintain a constant 90° peeling geometry; steady-state peel force per unit width was used to compute interfacial toughness, and adhesion time and hydrogel thickness were systematically varied to map adhesion performance. The same UStretch platform was also used to characterize the bulk mechanics of the TAH patch via pure-shear tensile testing on unnotched and notched specimens after controlled rehydration (hydration-time-dependent modulus/stress–stretch behavior and fracture toughness), and to evaluate strain-insensitivity of the biosensor by mounting a sensor on a TAH patch, rehydrating the hydrogel, applying controlled uniaxial stretch magnitudes/frequencies and up to 500 cycles, and recording real-time resistance changes with a DAQ system—demonstrating minimal deformation-induced signal drift (<0.5%) while preserving TNF-α sensing response under strain.