Synthesis And Characterization Of The PH-Sensitive Hydrogels

As a new type of polymer material, hydrogels have a wide application in the areas ofcontrolled drug release and delivery, tissue engineering, enzyme immobilization andother fields because of its soft structure and biocompatibility. Especially, the pH-sensitivehydrogels have been extensively studied in recent years. However, their poor mechanicalproperties and narrow pH-sensitive ranges have severely limited their application.To the poly(mathacrylic acid)(PMAA) hydrogel, in order to overcome the limitation ofpoor mechanical properties, in this study, poly(vinyl acohol)(PVA) was used to modifythe PMAA. The structure, morphology and mechanical properties of these hydrogelsmodified were investigated by Fourier transform infrared (FTIR), Scanning ElectronMicroscope (SEM) and compressing test. The sweeling properties also be studied byswelling experiment.To overcome the limitation of narrow pH-sensitive range, we used n-alkyl methacrylatesto modify methacylic acid in order to synthesize the gels with controlled pH-responsiveranges. The structure, thermal properties of the gels and linear copolymers wereinvestigated by FTIR, Differential Scanning Calorimetry (DSC). The swelling propertieswere also studied.FTIR spectra indicate that there are strong hydrogen bonds between PMAA and PVA.Morphological results show a porous structure of the dry gels, which gives the gels a fastswelling property. Compressing test suggested that the mechanical properties of thehydrogels modified were significantly improved with a slightly decline of thepH-responsive. Swelling experiments shows that with the pH increasing, the swellingratio of the gels first increased and then decreased slightly; with the increase of the ionconcentration, the swelling ratio of the gels first decreased dramatically and then tendedto be steady. When modified with the n-alkyl methacrylates, FTIR spectra indicated thatthe copolymerization between the comonomer and methyl methacrylate did occured. The DSC measurement gave some parameters of the thermal properties of the gels and linearcopolymers. Swelling experiments and suggested that with increasing the fraction ofmodified monomers or the chain length of hydrophobic units, the pH-responsive rangesmoved to the more alkaline pH.Finally, the drug loading and releasing properties were investigated. The releasing resultsshown that the drug release rates were greater in simulated intestinal fluid than in thesimulated gastric. In the same environment, the release rate of small-molecule drug wasfaster than the macromolecular drugs.