Preparation And Characterization Of Double Network Hydrogel Modified By Polyethylene Glycol And Poly(Vinyl Alcohol)

Hydrogels are environmentally friendly and biocompatible, and have extensive prospect. Double network (DN) hydrogels have improved the mechanical properties of hydrogels further; however it will take long time to prepare the DN hydrogels under rigor experimental environment. According these issues, two-step UV radiation to prepare the DN hydrogels with different light combination is presented. Swelling properties were compared by water-swelling method, the absorptive amount of AM was quantitative analyzed by redox titrations, network's structure was characterized by SEM and TEM, molecular weight of PEG and PVA before and after UV radiation was measured by GPC, mechanical properties of modified DN hydrogels were tested.Swelling dynamics of DN hydrogels modified by PEG or PVA were studied. Swelling rate (SR) of DN hydrogels modified by PEG or PVA were bigger than that of unmodified DN hydrogels, and with the increase of the amount of PEG or PVA, the modified DN hydrogels could absorb more water.The amount of AM in the DN hydrogels (PEG=14.1%) were investigated. The results showed that there were three stages during the process of AM absorption of single network (SN) hydrogels: speed absorption, slow absorption and equilibrium stage. Speed absorption stage was the key point; the amount of AM in the SN hydrogels modified by PEG was twice times than that of unmodified hydrogels.Surface of SN hydrogels and inner structure of DN hydrogels were observed by SEM and TEM. SEM results showed that unmodified SN hydrogels' network was a kind of framework, surface of the framework was smooth with dendritic structure, however the network of SN hydrogels (PEG=14.1%) was loose, the network and meshes were distributed equably, the network of SN hydrogels (PVA=0.82%) was interesting, besides the main network with dendritic structure, tiny network was distributed on the surface of the main network equably and nested in the main network. TEM results showed that the main network of unmodified DN hydrogels were mainly big mesh, the size and distribution of PAM particles were unequal, whereas the main network of DN hydrogels (PEG=14.1%) were smaller than that of the unmodified DN hydrogels, the size and distribution of PAM particles were equal, most of the particles were big size.Molecular weight and distribution of PEG and PVA after UV radiation were studied. After strong UV radiation, molecular weight distribution of PEG became wide, and became wider when adding initiator. After weak UV radiation, part of PEG chain decomposed, and no relevant to initiator. After strong and weak UV radiation, PVA would cross link to each other, molecular weight of PVA after filtration stayed the same.Mechanical properties of DN hydrogels had been characterized. The results showed that under strong-weak UV lights, DN hydrogels of PEG=14.1% showed the best mechanical properties, compressive stress was 22.6 MPa, tensile stress is 0.60 MPa. Under weak-weak UV lights, DN hydrogels of PVA=0.41% showed the best mechanical properties, compressive stress was 21.0 MPa, tensile stress is 0.70 MPa,.The enhanced mechanism of DN hydrogels modified by PEG or PVA was studied. The mechanism of adding PEG's method was two aspects. Firstly, in the synthesis of first network (FN), PEG was the template of the meshes, induced the mesh in the main network, then AM could polymerize in the meshes; Secondly, PEG had induced the two phase aqueous reaction, the size and distribution of PAM particles were equal by two phase aqueous reaction, the mechanical properties of DN hydrogels had been improved. The mechanism of adding PVA's method was that PVA had synthesized tiny network in the first network, the tiny network had nested in the FN like the bone of human, improved the mechanical properties of DN hydrogels.