A novel designed high strength and thermoresponsive double network hydrogels cross-linked by starch-based microspheres

A new kind of nanocomposite double network (DN) hydrogels consisting of starch-based microspheres cross-linked oligo (ethylene glycol) methyl ether methacrylate) (POEGMA) as soft network and diethylene glycol dimethacrylate (DEGMA) cross-linked poly(2-(2-methoxyethoxy) ethyl methacrylate (PMEO2MA) as brittle network (named POEGMA/PMEO2MA DN hydrogels) were synthesized by a two-step free radical polymerization. The chemical structure of DN hydrogels was characterized by 1H NMR, the temperature sensitive properties were measured by the lower critical solution temperature (LCST) tested by UV-Vis spectrophotometer as a function of temperature, the mechanical properties were measured by tensile test. The LCST showed only one transition at 20.2 °C measured by the transmittance variation as a function of the ambient temperature from 5 to 70 °C. The fracture toughness and the hysteresis behaviors were also tested and showed that they were affected by the content of starch-based microspheres cross-linker in the soft POEGMA network, the content of small-molecular cross-linkers and monomer concentration in the brittle PMEO2MA network. They are related to perfect network and physical adherence and entanglements between microspheres and the networks brought by AAS microspheres, the increment of “sacrifice bond” brought by DEGMA and polymer chains entanglement brought by MEO2MA. These studies will provide theoretical support for the future research of DN hydrogel and macromolecular microspheres cross-linked hydrogel.