The hydrogel's equilibrium water content is 20-95% with its aqueous composition containing 0-1 M sodium or potassium phosphate, 0-1 M sodium chloride, 0-1 M potassium chloride, 0-2 M lactic acid, surfactant such as 0-1 M Triton X-100, Tween 80 or sodium lauryl sulfate, and any other biocompatible components.