Design And Applications Of Peptide Self-assembling Supramolecular Biofunctional Materials

Self-assembled supramolecular biomaterials have many advantages over traditional polymer materials,including tunable structures,responsiveness,reversibility,and good biocompatibility.Protein,as the executor of all life activities,employs peptides to build self-assembled supramolecular biological materials,which maximize the protein's bioactivities to meet its functions in life.The way that proteins work in life has inspired us an increasing interest to develop novel biological materials through self-assembly of small peptides into supramolecular biofunctional systems.However,despite great advances,it still lacks of a full understanding on how to design self-assembled peptide supramolecular systems and the relationship between their structures and functions.To this end,this thesis mainly focuses on the design and applications of peptide selfassembling supramolecular biofunctional materials,with the expectation to provide a solution for developing safe,effective,and responsive biomaterials.The main research works and as-acquired results are as follows.First,a self-assembling antimicrobial peptide that targets the lipid membrane of bacterial was designed.Antimicrobial peptides,as natural antimicrobial molecules,act on the lipid membranes of microorganisms and have attracted much attention because of their resistance to drug resistance.Polycationic peptides are a kind of antimicrobial peptide that can interact with the negatively charged microbial membranes of pathogenic bacteria,resulting in bacterial death.However,synthesis of the polycationic peptides is economically high cost while their antibacterial efficiency is not strong enough.In this thesis,we developed an antimicrobial peptide that enhances antimicrobial activity of a cationic peptide based on a self-assembling supramolecular strategy.A novel antimicrobial peptide,KRRFFRRK(FF8),was designed by inserting the core self-assembly motif of diphenylalanine(FF)to the hexavalent cationic peptide KRRRRK.The FF8 was found to self-assemble into nanofibers when induced by a negatively charged lipid membrane or pH is above 9.4.The fibers on the membrane broke the lipid membrane,forming pores and significantly reducing its fluidity.FF8 also exhibited enhanced antibacterial activity by significantly increasing the permeability of the inner and outer membranes of Escherichia coli(E.coli)and maintaining the pores of the inner membrane of cells,which caused continuous membrane leakage.By comparing FF8 with another peptide,KRRGGRRK(GG8),it is found that the introduction of a FF self-assembling motif in the peptide sequence result in an increasing of 32 times on the antibacterial performance.Because of its high antibacterial activity,cytocompatibility,and cost-effectiveness,FF8 is a promising antibacterial material.Second,a self-assembled supramolecular system-a reactive oxygen species(ROS)scavenging and biodegradable peptide hydrogel was developed,which can be used as 3D culture scaffold for cardiomyocytes.Myocardial ischemia-reperfusion produces a large amount of ROS,resulting in damage of myocardial tissue.Therefore,local scavenging of excess ROS from myocardial tissue will reduce its damage and avoid metabolic disorders caused by systemic ROS scavenging.The traditional free radical scavenging hydrogels composed of polymers have unclear toxicities and are nonbiodegradable.In this thesis,a free radical scavenging and biodegradable supramolecular peptide(ECAFF,ECF-5)hydrogel was designed as a culture scaffold for cardiomyocytes.The peptide hydrogel significantly preserved the migration and proliferation of cardiomyocytes and reduced their damage from oxidative stress.In addition,the hydrogel degraded during cell growth,which implies that it may avoid thrombosis of the capillaries in practical use,and provide the opportunity for the cells to attach to each other and form a functional tissue.The hydrogel can be used as a 3-D culture scaffold for cardiomyocyte culture and allow cardiomyocytes to grow into tissue-like cell spheres.The excellent nature of the ECF-5 hydrogel enables it to have broad applications in the biomedical field in the future.Third,a microfluidic chip that specifically captures exosomes has been fabricated based on peptide self-assembling supramolecular fibers.Exosomes are complete phospholipid-encased vesicles that are secreted into the extracellular environment by cells,which carry bioactive molecules such as proteins and nucleic acids that contain a lot of information about the mother cell.Currently,there are only limited methods to separate exosomes,and the obtained heterogeneous exosomes lack of stability of analysis results,which limits their application in liquid biopsy.Here,a peptide,D17,that specifically affine to the exosome marker protein CD63 was screened and isolated with a phage display technique.Another peptide,Fmoc-FH13,was designed by fusing the sequences of peptide D17 and a self-assembling peptide motif.It was found that Fmoc-FH13 self-assembled into peptide nanofibers with the CD63 specific binding epitope(D17)on the surface of the fiber.The self-assembled supramolecular platform increased the CD63 affinity epitope,and improved binding efficiency of the exosomes.The obtained peptide fibers can capture and release CD63 positive exosomes in response to pH.Then,the Fmoc-FH13 peptide fibers were decorated in a microfluidic chip,which was used to isolate CD63 positive exosomes.The content of PD-L1 in the isolated exosomes could be detected.