Department Of Polymethyl Methacrylate Hydrogel Synthesis, Characterization And Drug Release Applications

Polymer intelligent hydrogels have attracted considerable attention in recent years for their potential applications in biomedical and biotechnological fields, including chemical machines, artificial muscles, controlled drug delivery, tissue engineering, chemical sensors, biosensors and separation of film, etc. These investigations are significativel in both academic and application fields. To some specific drugs, they must be released to a specific diseased region, such as stomach, intestine, colon, etc. One example is the change in pH values from the gastrointestinal tract to the small intestine, namely, from an acid pH to a neutral or slightly basic pH environment. This physiological change plays an important role in selective absorption of drugs. Therefore, pH-sensitive hydrogels, as specific drug carriers, have attracted much attention and have presented a promising and immeasurable prospect recently. However, some of their potential applications are hindered by their low mechanical strength. So acrylonitrile (AN) and carbon nanotubes(CNTs) are used to design and prepared hydrogels to greatly improve mechanical strength of poly(methacrylic acid) (PMAA) hydrogels.In the first part of this paper, novel polyelectrolyte hydrogels based on methacrylic acid (MAA) and AN were prepared. The effect of pH and ionic strength of buffer solutions on the swelling behavior of the hydrogels, state of water, mechanical properties, release of a model drug were studied. In the second part, a pH-sensitive hybrid hydrogel as an environmental-response nanometer-controlled drug delivery system, was prepared based on MAA, N,N-methylene bisacrylamide (NNMBA) and multi-walled carbon nanotubes (MWCNTs) by means of an in-situ free radical cross-linking polymerization avenue. The mechanical behavior and swelling properties of these hydrogels with various contents and particle sizes of MWCNTs were investigated.(1) A pH-sensitive copolymer hydrogel was constructed and developed based on both MAA and AN monomers. The structures of the sensitive hydrogels were characterized by a Fourier transformed infrared spectroscopy (FTIR). The swelling behavior of the hydrogels in different pH values and ionic strength of buffer solutions indicated that the hydrogels were strikingly sensitive to various pH and ionic strength surroundings. The swelling ratios of gels that were incubated in stimulated gastric fluids (SGF, pH 1.4) are lower than those in stimulated intestinal fluids (SIF, pH=7.4). Scanning electron microscope (SEM) observations revealed that the network topology of hydrogels is also presented larger and more patulous mesh sizes in SGF than in SIF. A dynamic mechanical analyzer (DMA) showed that the addition of AN has notably improved the compression mechanical properties of the control sample, the blank PMAA hydrogel. With an increase in AN concentrations, the ability for the copolymers to resist compression deformation enhanced in distilled water and the compress strains almost have the same values in SIF environments. The state of water and the amount of freezing water, non-freezing water were analyzed and quantitatively determined by a differential scanning calorimetry (DSC). The controlled release examination based on theophylline as the model drug exhibited that the release rate in distilled water was faster than that in SIF or SGF, and the introduction of the AN decreased the theophylline release rates in both SIF and SGF surroundings. Furthermore, the release rate variation in SIF was notably larger than that in SGF.(2) A novel pH-sensitive hybrid hydrogel, as an environmental-response nanometer-controlled drug delivery system, was prepared and developed based on MAA, NNMBA and MWCNTs by means of an in situ free radical cross-linking polymerization process. The mechanical behavior and swelling properties of these hydrogels with various contents and particle sizes of MWCNTs were investigated. The characterization of structures and morphologies of the hybrid hydrogels was conducted on the FTIR and SEM. The experimental results revealed that pH response of PMAA/MWCNT hybrid hydrogels was strikingly superior to those of pure PMAA hydrogels. Their equilibrium swelling was maintained at a higher level within an explored range of pH values. The FTIR and SEM findings testified that PMAA networks closely covered the MWCNTs and a MWCNT-well-dispersed hybrid hydrogel was formed. Particle diameters of MWCNTs had an important impact on compression mechanical intensities of the hydrogels. The swelling rate of the hybrid hydrogel in the presence of MWCNTs was obviously faster than that of pure PMAA hydrogels. The nature of polyelectrolytes and a non-electrostatic interaction between polyelectrolytes and MWCNTs were adopted to interpret the above swelling behavior and mechanical properties. These materials are expected to be adopted as excellent candidates in oral drug controlled release and tissue engineering fields.