Enzyme-mediated Deoxidation/initiation Processes For RAFT Polymerization And Rapid Hydrogel Dressing Preparation

Reversible deactivation radical polymerization（RDRP）could solve the problem of lack of control over free radical polymerization,is a revolutionary technology that can precisely regulate the molecular weight,composition,topology,and terminal groups of the synthesized polymers.And it has been used to synthesize a wide variety of vinyl polymers,which are used in many fields,including household products,pharmaceuticals,energy,and electronics.However,its poor tolerance to oxygen（O₂）and the need to use complex physical means for deoxygenation limits its practical production and implementation application in many areas.The use of glucose oxidase（GOx）to consume O₂ has been introduced as a general in situ oxygen removal technique in RDRP such as atom transfer radical polymerization（ATRP）and reversible addition-fragmentation chain transfer polymerization（RAFT）polymerization,while the use of hydrogen peroxide（H₂O₂）generated in the O₂ depletion reaction allows for interesting"O₂-initiated"polymerization.Several methods are available for this purpose,but these methods still encounter many limitations in practice,such as poor robustness to harsh environments that are harmful to most enzymatic systems,while other biologically friendly and simple techniques may have slow reaction kinetics that limits their application in practice.To address the problems encountered by enzyme systems in oxygen-tolerant RAFT polymerization applications,this thesis aims to improve the environmental tolerance of enzyme systems in RAFT polymerization applications through immobilization to expand the scope of Enzymatic deoxidation RAFT polymerization applications and to confer recyclability to the enzyme systems,and bio-inspired enhancement of the redox-initiated RAFT polymerization of GOx deoxygenation has led to the development of a new in situ deoxygenation-rapid initiation system through the activation of the peroxide bond of H₂O₂ by hemin,which substantially increases the polymerization rate of GOx deoxygenation redox-initiated RAFT polymerization and enables the regulation of the polymerization reaction rate.In addition,we applied this rapid initiation system to the rapid in situ free radical polymerization of hydrogel dressings and developed a rapid gel dressing formation technique for the in situ formation of hydrogel dressings of arbitrary shapes with antimicrobial properties,and GOx in the hydrogel gives the dressing the ability to lower local blood sugar.This hydrogel dressing can be used to address the problem of non-healing diabetic wounds.The details of the study are as follows.（1）To solve the problem of poor tolerance to organic systems and high-temperature environments when performing enzyme-deoxygen RAFT polymerization,we prepared an immobilized enzyme cascade system GOx&DhHP-6@ZIF-8 by immobilizing the GOx/HRP mimic（Deuterohemin-β-Ala-His-Thr-Val-Glu-Lys,DhHP-6）system required for enzymatic oxygen-tolerant RAFT polymerization in a ZIF-8 metal-organic framework using biomimetic mineralization.This method is easy to operate and allows for efficient enzyme sequestration while maintaining enzyme activity.This immobilized enzyme successfully implemented the RAFT polymerization of various monomers including methacrylate,acrylate,and acrylamide.The polymerization followed the essential characteristics of RAFT polymerization without additional de-oxygenation,in which the molecular weight increased linearly with the conversion rate during the reaction and maintained a low dispersity（（?））.Since the enzyme is protected by ZIF-8,GOx&DhHP-6@ZIF-8 can be used in solvent systems with high organic solvent content and in high-temperature environments,enabling successful RAFT polymerization using enzymatic deoxygenation for monomers that cannot be polymerized in mild conditions.In addition,GOx&DhHP-6@ZIF-8 can be reused at least five times,reducing the cost of enzyme usage.（2）In order to solve the problem of the slow rate of GOx deoxygenated H₂O₂/ascorbic acid-initiated RAFT polymerization reaction,inspired by the transport of O₂ by hemoglobin,we introduced hemin into the system to activate H₂O₂ and increased the initiation rate of this redox initiation by reducing the activation energy of the reaction between H₂O₂ and Asc acid,completing the bio-enhancement of GOx deoxygenated redox-initiated RAFT polymerization,so that the RAFT polymerization reaction which originally takes several hours to reach 80%conversion can be almost completely converted within a few tens minutes.In the paper,the factors affecting the reaction,including solvent p H,hemin dosage,and Asc acid dosage,were studied in detail to understand the enhanced system further,and the role of hemin as a catalyst and Asc acid as a reactant was confirmed.Accordingly,we propose a possible mechanism for this bio-enhancement and perform preliminary validation.In addition,we were able to regulate the rate of RAFT polymerization by controlling the addition of Asc acid.（3）Hydrogel dressing is an emerging dressing that has been proven to be effective in promoting wound healing.In order to adapt to different wound shapes and different application environments,gels that can be formed in situ are undoubtedly more valuable.To satisfy the need for rapid polymerization of in situ formed hydrogels,we applied the previously described rapid bio-enhanced initiator to the initiation of in situ formed hydrogels’free radical polymerization,using hydroxyethyl acrylate（HEA）as a monomer and adding hyaluronic acid functionalized with methacrylate（HA-g-GMA）as a macromolecular cross-linker,providing a technique that can prepare hydrogels in situ in a short time.The hydrogels can be formed in a minimum of one minute.The resulting gels have excellent elasticity and toughness,are homogeneous and transparent,and can adhere to the skin,making them a superb hydrogel material suitable for dressings.In addition,the prepared hydrogel material has excellent antibacterial activity and low biotoxicity,and the GOx immobilized in situ in the gel matrix can also reduce local blood glucose concentration,further in vivo experiments have demonstrated its effective promotion of infected wound healing in diabetic mice.In summary,this thesis combines the intersection of polymer chemistry,enzymology and life sciences to provide new technologies and ideas for implementing enzymatic oxygen-tolerant RDRP and the application of enzymatic free radical initiation processes to the research and development of biomedical materials.