Study Of Synthesis And Properties Of Composite Hydrogels Based On PMMA

Traditional injectable hydrogels, because of its plasticity, the porous structure and excellent biocompatibility, become the ideal materials of soft tissue repair or regeneration. However, their applications are limited due to the generally weak mechanical properties. p H–responsive microgels, having high solid content, strong flowability and rapid solidified gelation by changing the p H value, become a new hotspot in the research of the injectable gel.In this thesis, using a p H-responsive microgel poly(methyl methacrylate/methacrylate acid), i.e., poly(MMA/MAA) as the precursor, we designed several preparation methods of composite hydrogels and studied the various influence factors on rheological properties of related hydrogels. The main contents list as follows:(1) Series of cationic poly(HEMA-co-DMA+) copolymer(HEMA, Hydroxyethyl Methacrylate, DMA, dimethylaminoethyl methacrylate) with different moleculelarweights and composition have been prepared through atom transfer radical poly-merization and quaternization reaction, respectively. Ionic bonding composite hydrogels were formed by mixing of cationic copolymer with re-prepared p H- responsive poly(MMA/MAA) microgels and then increasing the system p H value. The results show that the rheological properties of the composite hydro-gels are related to polymer composition,molecular weight and also the weight ratio between polymer and microgel, and so on. When the weight ratio of copolymer in organic composition is about 40%(total solid contentis 19 wt.%), the composite hydrogel has the higher critical yield strain(g* is about 10), compared with the same concentration of poly(MMA/MAA) formed physical gel, which g* value is about 1.75, the shearing deformation of the composite hydrogel is greatly increased. The molecular weight and the molar ratio of DMA+ of copolymer are linearly related to the storage modulus G’ ofcomposite hydrogels.(2) With 2-methacryloyloxyethyl-trimethyl ammonium chloride(DMC) and aminoethanethiol hydrochloride(AET) as functional compounds, through the electrostatic attraction, the surfaces of p H-responsive microgels of poly(MMA/MAA) were modified to get two different functional microgels, named DMC-poly(MMA/MAA) and AET- poly(MMA/MAA) respectively. Doubly crosslinked microgels were formed by self-addition or inter-addition of two kinds of surface modified microgels with carbon-carbon double bond addition, disulfide bond crosslinking and thiol-Michael addition methods,respectively. The rheological results show that the storage modulus of doubly crosslinked microgels prepared from carbon-carbon double bond addition is four times of physical gel made from poly(MMA/MAA) with increasing p H. Even the doubly crosslinked microgels prepared from disulfide bond crosslinking, the highest value of storage modulus is up to 28,000 Pa, which is also greatly improved. Under optimized reaction conditions, the doubly crosslinked microgels with thiol-Michael addition between DMC-poly(MMA/MAA) and AET-poly(MMA/MAA) are similar to carbon-carbon double bond addition,their G’ values are almost 4 times of physical gel from poly(MMA/MAA) with with increasing p H.(3) In this part, we preliminarily investigated the p H-responsive organic/inorganic nanocomposite microgel, i.e. poly(MMA/MAA)/Laponite RD, by Pickering emulsion polymerization. It was found, when 2-acrylamide-2-methyl propane sulfonic acid(AMPS) was 7 wt.% of Laponite RD, the Pickering emulsion has good stability with AMPS modified Laponite RD stabilizing monomer droplets in water. After polymerization, the particle size of poly(MMA-MAA)/ Laponite RD nanocomposite microgel with irregular shape were roughly range between 200 nm and 300 nm. The nanocomposite microgels are easily gathered themselves together, and form large aggregates with micron scale. Preliminary results show that poly(MMA-MAA)/Laponite RD has sensitive p H-responsiveness, and the stable physical gel will form when the concentration of particles and p H value are high enough. This part of work will set up a material foundation for synthesis of biocompatible p H-responsive microgel in the future.