In the last decades polymer hydrogels have drawn considerable attention as excellent soft materials with a wide variety of applications . Hydrogels are a class of soft polymeric materials that have the ability to hold substantial amount of water, exhibit low interfacial tension, and can exhibit physical properties similar to those of living tissues . Due to their permeability and biocompatibility (because of high water content) they have attracted much attention in the pharmaceutical and biomedical fields as key materials for various applications. Hydrogels are used, e.g. in drug delivery systems, tissue engineering materials, for contact lenses and protein separation, matrices for cell-encapsulation, cosmetic products or wound dressing, enzyme biosensors, chemical valves, metal particle preparation, etc. .