| Hydrogels are a new type of soft matter constructed by threedimensional cross-linked networks with high water content,and have extraordinary advantages in biomedical and environmental applications.Polysaccharide-based composite hydrogels greatly exhibit the characteristics of biocompatibility and degradability of natural polysaccharides,and also retain the characteristics of hydrophilic,hydroscopic and stable network structure of hydrogels.Conventional construction of natural polysaccharide-based hydrogels mostly employs chemical modification of active sites on the polysaccharides,which might damage the structure of polysaccharides and affect the integrity of polysaccharide functions.Meanwhile,the polymerization process inevitably uses chemical initiators or UV initiation,cross-linking agents and other components that are potentially toxic to living organisms.Therefore,the exploitation of novel methods of polymerization or a green synthesis process is essential to expand the application of natural polysaccharide hydrogels in biomedicine.In the second chapter of this thesis,a novel polymerization method of Reversible Addition-Fragmentation Chain Transfer Polymerization(RAFT)was used,by modifying RAFT groups to dextran molecular chains.Green light was used to initiate polymerization.2-hydroxypropyl methacrylate(HPMA)acts as the monomer.Since HPMA underwent a transition from hydrophilic to hydrophobic during polymerization process due to the increase of Degree of Polymerization,so that occur polymerizationinduced self-assembly(PISA)behavior.By controlling the molecular weight of Dextran chains,the number of RAFT group,the solid content of polymerization solution and the degree of polymerization,the PISA behavior was regulated,and different morphologies such as spherical,short rod-like and worm-like micelles were obtained.And the effects of different morphologies on the gelation of polymerization solution were investigated to obtain a method for constructing polysaccharide-based hydrogels by RAFT-PISA.The reaction conditions and microscopic conditions for the construction of complex hydrogels by means of RAFT-PISA confirmed that the gelation was generated by the entangled cross-linking of wormlike micelle structures due to sphere-sphere fusion,which provided a new idea and construction strategy for the construction of natural polysaccharide-based hydrogels.In the third chapter of this thesis,double bond modified hyaluronic acid and P(AA-co-AM)crosslinking were used as chemically crosslinked hydrogel networks;the addition of Borax to form borate ester bonds,as well as hydrogen bonds to form physically crosslinked hydrogel networks.Tannic acid/silver were used as a redox double catalyst to initiate the freeradicals generation by ammonium persulfate(APS),avoiding the introduction of toxic additives.The hyaluronic acid composite hydrogel had good tensile properties(450 k Pa tensile strength and 482 % elongation at break),good adhesion properties with various substrates,and the prepared hydrogel sensor had good electrochemical stability and highly sensing properties.The composite hydrogel also had good biocompatibility,excellent in-vivo and in-vitro antimicrobial properties and the ability to promote wound healing.In summary,in this thesis,polysaccharide-based composite hydrogels were constructed by using novel polymerization method and green synthesis approach.Visible light-PISA provided a new idea for the construction of polysaccharide hydrogel,and also established a basis for further realization of rapidly in-situ construction of hydrogels under visible light.The polysaccharide composite hydrogels were constructed using a novel dual-catalytic strategy,which enriched the polysaccharide hydrogel construction method,and TA/Ag were used to achieve adhesion properties and mechanical properties while rapidly preparing antibacterial and conductive hydrogels and efficiently to promote the application of hydrogels in wearable skin strain sensors and antibacterial hydrogel dressings on infected wounds. |
