Facile fabrication of tough and biocompatible hydrogels from polyvinyl alcohol and agarose

A polyvinyl alcohol (PVA)-agarose (agar) composite hydrogel (M-PVA-agar-60) was developed by simple three cycles of freeze-thawing, followed by successively soaking in ammonium sulfate aqueous solution to induce phase separation and dialyzing against deionized water to remove residual sulfate salts. Due to the synergy of crystalline regions, hydrogen bonding and phase separation domains, the obtained M-PVA-agar-60 hydrogel exhibits excellent mechanical properties (tensile strength = 1.1 MPa, tensile strain = 324% and compressive stress = 12.5 MPa), combined with a high water content of 87.0%. Moreover, the hydrogel hardly expands after immersing in the phosphate-buffered saline aqueous solution at 37°C for a week, and the tensile stress and toughness remain almost the same as their initial values, superior to most reported non-swellable hydrogels. Because of the biocompatible starting materials, absence of toxic chemicals, and dialysis in advance to remove ammonium sulfate, the hydrogel also shows excellent cell compatibility, making it an ideal candidate for tissue engineering materials.