Humidity-Responsive Conductive Hydrogels: A Bio-Based Material for Flexible Electronics

Introduction: The increasing demand for biocompatible and flexible electronic materials has stimulated the research into conductive hydrogels, particularly for biosensors and wearable device applications. Gelatin methacryloyl (GelMA), derived from cold-water fish skin, offers a renewable and biocompatible matrix. This study investigates the synthesis and characterization of GelMA hydrogels loaded with silver nanoparticles (AgNPs) to achieve conductivity, exploring the impact of formulation and environmental factors on material properties.

Methods: GelMA was synthesized and crosslinked using a visible light-activated photoinitiator (BAPO-PEG). AgNPs were incorporated via in situ reduction during crosslinking and by post-crosslinking immersion in silver nitrate solutions. Hydrogel properties were assessed using Fourier-transform infrared spectroscopy (FTIR), photorheology, thermogravimetric analysis (TGA), swelling tests, and electrical conductivity measurements under varying humidity conditions. Piezoresistive behavior was evaluated by measuring current changes under applied compressive strain.

Results: FTIR confirmed successful GelMA synthesis. Photorheology optimized BAPO-PEG concentration for rapid curing. TGA demonstrated thermal stability up to 260-270°C. High water absorption (300%) was observed. In situ AgNP formation delayed gelation, favoring immersion for AgNP incorporation. Electrical conductivity was highly dependent on humidity, with dried samples exhibiting insulating behavior. Conductivity significantly increased with hydration, reaching 6.84 S/m for samples with the highest silver content (GelMA/Ag-50) at 100% relative humidity. Compressive strain enhanced conductivity, indicating piezoresistive properties suitable for sensing applications.

Conclusion: This study demonstrates the successful synthesis of conductive bio-based hydrogels by incorporating AgNPs into a GelMA matrix derived from fish skin gelatin. The resulting materials exhibit tunable electrical properties responsive to humidity and mechanical strain, making them promising candidates for biosensors, humidity sensors, and flexible electronic devices. Further research will focus on optimizing AgNP dispersion and long-term stability for real-world application.