Fabrication Of A Novel Supramolecular Hydrogel From Glycopeptides With Antibacterial Activities

Antibacterial materials are considered to be important biofunctional materials because they are effective in inhibiting bacterial infections.The preparation of antibacterial materials with low immunogenicity,high antibacterial efficiency,low cytotoxicity and biodegradability is the focus of nanotechnology and antibacterial technology research.Therefore,various antibacterial materials comprising antibiotics,quaternary ammonium compounds,metal ions or particles,cationic polymers and antimicrobial peptides have been designed and synthesized in order to combat bacterial infections by binding multiple molecular targets and disrupting multiple cellular functions of pathogens.However,these antibacterial materials can also induce membrane rupture and cell death of mammalian cells,exhibiting high cytotoxicity and limiting their potentials for biomedical materials.In recent years,hydrogels have gradually emerged as an important platform to engineer antibacterial materials for prevention or treatment of infections associated with medical devices and wound healing,because of their high water content,molecular structure and functionality that can be tailored with predictable mechanical properties.The fabrication of hydrogels exhibiting antibacterial activity can be achieved either by encapsulation of antimicrobial agents into a formed gel for controlled release,through covalent attachment of antibiotics,immobilization of metal nanoparticles within the gel matrix or incorporation of cationic polymers with inherent antimicrobial capability.At present,scientists also use positively charged small molecule or polymer to prepare antibacterial hydrogels to inhibit bacterial proliferation.As with cationic polymer hydrogels,antimicrobial peptide hydrogels also tend to be positively charged,acting principally through electrostatic interactions,and ultimately disrupt cell membranes.Because of the non-specificity of such actions,these kinds of hydrogels can also exhibit a high risk of inducing mammalian cell death.Thus,it is desirable to construct safe and effective hydrogels that rely on specific molecular recognition to bind and disrupt the cell membranes of bacteria,thereby reducing cytotoxic effects associated with non-specific electrostatic interactions with mammalian cells.Inspired by the important roles of specific interactions between carbohydrates on the surface of host cells and lectin proteins on cell membranes of bacteria for bacterial adhesion and infection,researchers have developed a series of glycosylated polymers or glycosyl-coated nanoparticles as probes and biosensors,and they can act as competitive inhibitors targeting bacteria,inducing bacterial agglutination or inhibiting pathogenic cell motility,but with no inhibition on bacterial growth.Therefore,the main content of this thesis is to construct a small-molecule scaffold from a glycopeptide(NMYp),which contained a mannose ligand and was able to perform supramolecular self-assembly to present multiple mannose ligands on its self-assembled structure.The mannose moieties exposed on the surface of the NMY hydrogel worked as bioactive cues to target mannose-binding proteins via multivalent mannose-lectin interactions,inducing protein agglutination(Con A),bacterial adhesion and membrane disruption.In the first part of this paper,NMYp was prepared by using solid-phase peptide synthesis with the applications of Fmoc-Tyr(H2PO3)-OH,Fmoc-Ser[Man(OAc)4]-OH,Fmoc-Phe-OH and 2-(naphthalen-6-yl)acetic acid,together with a deprotection reaction to remove the acetyl groups from the mannose residues and Fmoc-Ser[Man(OAc)4]-OH was synthesized from Fmoc-Ser-OH and ?-D-mannose penta-acetate by following a liquid phase synthesis.Firstly,the self-assembling ability and biostability of the NMYp were studied in vitro.Then,the micromorphology,mechanical properties,and secondary structure of the NMY were studied.The second part of this thesis was about the research on the antibacterial effect of NMY hydrogel against E.coli.After supramolecular gelation,the mannose moieties exposed on the surface of the NMY hydrogel worked as bioactive cues to target mannose-binding proteins via multivalent mannose-lectin interactions,inducing protein agglutination(Con A),bacterial adhesion and membrane disruption.More importantly,because of its inherent antibacterial properties,excellent biocompatibility with mammalian cells and good mechanical properties,this self-assembled hydrogel were successfully applied to prevent E.coli infection in vivo and promote wound healing in a full-thickness skin defect model in mice.