Preparation and properties of self-healable and conductive PVA-agar hydrogel with ultra-high mechanical strength

Developing hydrogels with excellent mechanical properties and functions is important and challenging. Herein, commercial available materials, polyvinyl alcohol (PVA) and agar, are used to synthesize ultra-strong, self-healable and conductive hydrogels by freezing-thawing cycles and soaking in the ammonium sulfate (AS) solution. The relationship between microstructures and mechanical properties of the obtained PVA-Agar hydrogel is analyzed. The results show that the tensile stress and toughness of PVA-Agar precursor hydrogel are only 0.2 MPa and 0.3 MJ/m3, respectively, due to the uneven network with a pore size between 1 and 8 μm and the lower crosslink density of network. After soaking in AS solution, the network becomes dense and uniform with a pore size of 1–3 μm, accompanied by the formation of stronger hydrogen bonds between PVA and agar. As a result, the tensile stress and toughness increase to 18.0 MPa and 42.3 MJ/m3, respectively. Due to the efficient energy dissipation mechanism endowed by dynamic junctions, the hydrogel also has good anti-fatigue property and high self-healing efficiencies (>80%), and the dissipative energy can reach 18.5 MJ/m3, which accounts for 94.9% of the total energy. Furthermore, the hydrogel exhibits electrical conductivity. The full-fledged starting materials, PVA and agar, and easy-operated process, freeze/thaw cycle, provide our method great potentials to scale up and promising applications as a biocompatible and bioactive material.