Our team is using carrageenan as a natural polymer for hydrogels. We'd like the surface of our hydrogel to be tough enough to resist minor scratch and tear. As much as possible, we'd like to use biodegradable materials.
you may consider natural plasticizers since they would act as surface modifiers while the surface remains flexible enough and won't tear, how ever double crosslinking would probably work too as Dmitriy Berillo said but acrylamide is not a natural polymer