Examples of suitable base materials are modified or unmodified natural polymers, for example collagen, chitosan, hyaluronic acid and cellulose esters, such as cellulose acetate or cellulose butyrate, modified or unmodified synthetic polymers, for example polyvinyl alcohol, polyhydroxyethyl methacrylate, polyglyceryl methacrylate, and copolymers based on these polymers.