Biomimetic Underwater Adhesives Based On Co-assembly Of Short Peptides And Polyoxometalates

Short peptides have a significant advantage in the development of biomedical gels,including biocompatibility,biodegradability,molecular diversity and modulating biological activity.Peptide assembly has made substantial progress in the creation of multi-level nanostructures,biosensors and functional materials.One of the ultimate goals of short peptide assembly is to rationally design and mimic the activity and function of natural proteins.The adhesive proteins secreted by marine organisms are impressive because they adhere to different substrates immersed in seawater.The wet adhesion of this protein has spurred the development of biomimetic adhesives.Most biomimetic adhesives are centered on covalent polymers,the adhesives based on short peptides have not been fully considered in most design work.The advantage of the short peptide biomimetic adhesive is that it is close to the natural system and has a simple structure,which is beneficial to study the influence of the residue on the bonding property,reveal the adhesive mechanism of the natural protein,and provide a new idea for the artificial system.However,compared with the existed systems,the main problem of short peptide biomimetic adhesives is that the exploration of the design rules of short peptides remains on the surface,which limits the design of short peptides,and they almost revealed poor mechanical strength.At present,we have a new understanding and progress in this area,and this further research provides an ideal model system.In this paper,we focuse on two aspects of the short peptide and polyoxometalate supermolecular composite assembly system: 1.the law peptide design: includingamino acid sequence,how the residue type affects the phase behavior of the assembly;2.simulating the underwater interface spreading and cross-linking curing of natural systems: based on the understanding of the first chapter,the design of the adhesive coacervate and uses its advantages to achieve interface adhesive,and the phase transformation is used to achieve cross-linking curing.The main research contents of this paper are as follows:First,according to the study of marine organism adhesion protein species,amino acid arrangement,and the previous work with short peptide adhesives in our group,we designed a series of short peptides,assembled with polyoxometalates in aqueous solution,to investigate effect of electrostatic force sites and residue types on short peptide adhesives.Basic conditions for the design of short peptides: a positively charged amino acid residue is introduced to make the peptide chain have a certain charge density;introducing of p H sensitive groups,such as glutamic acid residues with-COOH,to explore the role of polar molecules and the supramolecular assembly of multi-valent synergistic was used to explore the design rules of peptide adhesives.FT-IR and ESI-MS spectra demonstrated the structural integrity of polyoxometalates and short peptides.The tensile shear test demonstrated the effect of different electrostatic force sites on the assembly behavior of the peptide.The hydrophobic amino acid residues and p H-sensitive amino acid residues were replaced with alanine residues,respectively,and the effects of hydrophobic interaction and-COOH on peptide assembly were investigated by comparative experiments.Second,according to the design rules of the peptide sequence,we designed a three-peptide consisting of glycine,histidine and lysine,the peptide self-assembly with polyoxometallate in aqueous solution forms a novel peptide-based coacervates.Shear-dependent viscosity curve revealed a non-Newtonian fluid nature of coacervates based on the typical shear-thinning behavior.At the same time,the flow properties of the coacervates are also observed under an optical microscope,which makes it easy to make interface spreading without high pressure.We combined infrared spectroscopy,elemental analysis,thermogravimetric analysis,ESI-MS spectroscopy and X-ray photoelectron spectroscopy to explore the formation mechanism of agglomerates.The XPS spectrum demonstrates theelectrostatic interaction between the protonated amino group and the polyoxometalate during the formation of the coacervates.The histidine residue is highly sensitive to p H and metal ions,so that the assembly can be transformed from coacervates to the gel state.Scanning electron microscopy showed that the microstructure of the p H-adjusted adhesive consisted of interconnected three-dimensional porous networks.Rheology studies have shown that the adhesive has viscoelastic properties and exhibits a certain mechanical strength and good self-healing ability.The adhesive can bond multiple substrates underwater(such as wood,shells,stones,Stainless steel,glass,polypropylene,titanium,etc).The underwater strength of the short peptide-based adhesive was quantified by lap shear tensile test quantitative analysis.The XPS spectrum describes after the introduction of metal ions,the imidazole ring and carboxylate which are not protonated can coordinate with metal ions.UV-vis spectra shows the absorbance intensity of Co2+ in aqueous solution decreased with the increase of the amount of coacervates.Interestingly,the adhesive gels can tolerate the salt variety.In summary,the design of short peptide underwater adhesive was studied by the assembly behavior of peptides and polyoxometalate in this paper,the effect of sequence or position of the cross-linking site,and the residue types of assembly behavior were studied separately.Based on the understanding of the assembly rules,a simpler short peptide was designed.A kind of stable viscosity coacervate was successfully prepared near neutral p H.And we improved the cohesion and mechanical property of the peptide-based adhesive coacervates by adjusting the p H value or metal ion species.The biomimetic adhesives of underwater injectable and controlled cross-linking curing were constructed by the coordination of short peptide residues and metal ions.This provides an idea for the design of intelligently responsive underwater adhesives.