Preparation And Properties Of Poly(L-Lysine) And Its Cationic Hydrogel

As a cationic polymer rich in positive charge,poly-lysine has the advantages of excellent biodegradability,low biological toxicity,antibacterial activity and easy versatility.It has potential application prospects in the field of biomedicine,especially antibacterial.However,in the process of synthesis,the strict requirements of synthetic environment and long time-consuming limit its application.In this thesis,a preparation route of poly amino acids with low environmental requirements and short preparation time was designed,and poly（L-Lysine）（PLys）with different molecular weights were obtained.Two kinds of hydrogels were prepared by physical mixing and chemical modification of poly（L-Lysine）,and the properties of the hydrogel were tested..This hydrogel has potential applications in inhibiting bacterial growth and promoting wound healing.The main research work of this thesis was as follows:（1）A variety ofα-amino acid N-carboxyanhydrides（NCA）monomers were successfully synthesized,including:γ-Tertbutoxycarbonyl-L-Lysine-N-carboxyanhydrides（Boc-L-Lys NCA）,L-glutamic acid-γ-Benzyl ester-N-carboxyanhydrides（Cbz-L-Glu NCA）and L-tyrosine-N-carboxyanhydrides（L-Tyr NCA）.Poly（γ-Tertbutoxycarbonyl-L-Lysine）（P（Boc-L-Lys））with controllable molecular weight was prepared by ring opening polymerization of Boc-L-Lys NCA monomer which lithiu m-hexamethyl-disilazide（Li HMDS）was used as initiator.Poly（L-Lysine）(PLys₂₀₀)with repeating units of200 was obtained by deprotection with trifluoroacetic acid.The preparation cycle of polyaminoic acid is shortened and the complex operation in the preparation process is simplified by this synthetic route of poly（amino acids）.（2）A series of poly（L-Lysine）-（polyvinyl alcohol）hydrogel(PL_n-PVA₁₀)with good antibacterial and mechanical properties were designed and prepared by mixing PLys₂₀₀ with polyvinyl alcohol in aqueous solution.The results show that the PL_n-PVA₁₀ hydrogel has excellent antibacterial properties,and its elongation at break can reach 200%under the tensile strength of KPa,and has excellent structural stability in water and PBS.（3）Two poly（L-Lysine）derivatives（PLys₈-LA₁-B₁ and PLGT₈-LA₁-B₁）were prepared from PLys₂₀₀ by modifying with lauric acid,phenylboric acid and quaternary ammonium salt groups on the side chain of amino group.A series of poly（L-Lysine）derivative hydrogels（（P₈L₁B₁-PVA）_n and（PLGT₈L₁B₁-PVA）_n）with biological tissue adhesive,self healing and antibacterial properties were prepared by mixing the two kinds of polymer aqueous solutions with different concentrations of PVA aqueous solution.The results of bacterial experiment show that the antibacterial rate of PLys₈-LA₁-B₁ and PLGT₈-LA₁-B₁ aqueous solutions with a concentration of 1.875 mg/m L against Escherichia coli was more than 95%.And the sterilization rate of poly（L-Lysine）derivative hydrogels contacting with Escherichia coli for 0.5 h was more than 90%.Compared with PLys₈-LA₁-B₁ with-NH₂ as cationic group,PLGT₈-LA₁-B₁ with quaternary ammonium salt as cationic group has better antibacterial performance.