High-resolution visual-tactile integrated measurement device for local adhesion strength of hydrogel surfaces

Hydrogels find extensive applications across various fields, making the quantitative characterization of their mechanical properties a critical area of research. However, due to their complex surface morphology and the coexistence of solid and liquid phases, accurately measuring their adhesion strength presents substantial challenges. This study proposes a visual-tactile adhesion measurement (VTAM) device that utilizes the principle of contact light leakage to capture morphological information of adhesive regions. Multi-angle asynchronous illumination techniques are employed to enhance the image contrast of the fiber-optic endoscope, achieving pixel-level resolution (50 $\mu$m) in the extraction of adhesive regions. Combined with a 0.1 mN high-resolution push–pull force gauge, the VTAM device enables precise measurement of adhesion strength, with a measurement resolution better than 0.3 kPa and a relative error of less than 3%. A comparative analysis between the VTAM device and texture analyzers on hydrogels with varying surface wrinkles reveals the importance of accurate contact area assessment in adhesion strength measurement and demonstrates how surface morphology enhances wet adhesion performance. Furthermore, dry adhesion experiments at varying probe unloading speeds explore the relationship between adhesion strength and peeling rates, revealing a peak adhesion strength as peeling rates increase. This study provides an effective method for measuring adhesion strength in soft materials with complex morphologies.