Enzyme-catalyzed Living Polymerization And Its Application In The Preparation Of Novel Biodegradable Polymeric Gene Carriers

Biomedical polymers are the latest research disciplines in polymer science and biology,and widely used in many fields such as biological tissue engineering materials,drug delivery and gene therapy systems.Now it has become a hot spot for research and development of scientific researchers.Enzymatic polymerization shows a wide range of application prospects in the preparation of functional polymeric materials due to its mild conditions,high selectivity,and low toxicity and trace residuals of metal catalysts.However,enzymatic polymerization still has many problems to be solved,such as:1)insufficient activity and stability of enzyme molecules in the catalytic process;2)limited structure and application range of enzymatic synthesis products;3)high cost of application and low catalysts recycling.Therefore,the establishment of a new type of highly efficient biocatalytic system to realize the green and controllable synthesis of biomedical polymer materials is a crucial issue in the development of biomedical polymeric materials and also possesses great significance for the clinical applications in future.Based on the above limitations of the enzymatic polymerization,a new type of enzyme and biomimetic enzyme-catalyzed living polymerization were systematically studied in this dissertation and used for the preparation of biomedical polymer materials.This article mainly includes four parts:?1?Firstly,artificial enzyme mimic Deuterohemin-b-Ala-His-Thr-Val-Glu-Lys?DhHP-6?with peroxidase activity was employed,and the DhHP-6@MOF complex was constructed through a biomimetic mineralization strategy.The complex was further used to catalyzed atom transfer radical polymerization reaction?ATRP?of water-phase monomer PEGMA₅₀₀.The structure of the assemble was systematically characterized by SEM,TEM,FTIR,UV-Vis,CLSM and TGA,which proved the efficient assembly of DhHP-6 in the porous metal organic framework?MOF?.The results of ¹H NMR and GPC showed that theassemble can efficiently catalyze the ATRP reactions with monomer conversion and product M_n of 76.1%and 45,900g/mol,respectively.Meanwhile,the molecular weight distribution was very narrow.The above research work significantly improves the efficiency of artificial enzyme catalyst,moreover,it can effectively avoid the residues of metal catalysts in the products,and possessed well biocompatibility,catalyst recyclability and high potential application value.?2?Secondly,Heme conjugated to the surface of the MOFs through covalent bond,and the obtained enzyme mimic was further utilized to catalyze the ATRP.The structure,catalytic activity and Michaelis-Menten of enzyme mimic were systemically characterized by SEM,TEM,FTIR,UV-Vis and TGA.The enzyme mimic Heme-ZrMOF with peroxidase activity was successfully constructed.Then we further explored the application of Heme-ZrMOF in ATRP reactions,demonstrating that the ATRP polymerization catalyzed by this complex is not limited to aqueous systems.More than that,the efficiency and catalytic mechanism of ATRP mediated by this catalyst were studied by ¹H NMR and GPC,which provided a catalyst with excellent performance for the synthesis of novel,efficient and safe biomedical polymeric materials.?3?Thirdly,to address the simple structure and properties of monomers and polymerization methods in the enzymatic polymerization,the combination of enzymatic ring-opening polymerization and ring-opening metathesis polymerization was achieved in a one-pot manner by ester precursor technology for preparing block polymers.The structure and thermodynamic properties of the obtained block polymers were systematically characterized by NMR,GPC,DSC and microTOF-QII MS.The results showed that this new type of tandem reaction strategy is simple and feasible to synthesis block copolymer with clear performance.Compared with the traditional methods,this polymerization method has serveral advantages such as mild reaction conditions and no complicated intermediate purification steps.At the same time,further mechanism study showed that the"one-pot"polymerization of eROP/ROMP is finished in a unique two-stage reaction.This study has greatly broadened the application scope of chemoenzymatic polymerization technology and provided a new strategy for the preparation of green polymers with special strucures or properties.?4?Lastly,enzymatic ring-opening,polycondensation,chemical grafting,and atom transfer radical polymerization were combined to prepare two types of hydrophobic cationic polymer gene carriers.The NMR,FT-IR and GPC analysis indicated that the copolymers have been successfully constructed by this tandem polymerization.The gene vectors are named as cholesterol-g-poly?amine-co-ester?and poly?amine-co-ester?-co-PGEA materials,respectively.Then miR-23b and p53were successfully delivered into tumor cells by these two polymers.The polymers-mediated gene dlivery exhibited high delivery efficiency which could further inhibit the proliferation,migration and invasion of tumors,providing us new ideas for the design and development of anti-tumor nano-gene delivery vectors.In summary,this thesis is based on the interdisciplinary studies of polymer chemistry,enzymology and biology.Moreover,it provided a new basis for enzyme-catalyzed green synthesis of polymers and the industrial development of valuable biomaterials.