Study On The Preparation And Properties Of Silk Fibroin-Based Hydrogel For Wet Adhesion

Recently,suturing is the main way to realize wound closure.However,during the healing process,suture-treated wounds and organs may produce scars,or cause postoperative complications due to the unsatisfied sealing efficacy.Although medical hydrogel adhesives have been extensively studied owing to the non-invasive closure feature,instant hemostasis,excellent sealing capability and easy operation property.It is still urgent to explore novel wet hydrogel adhesives,and expand the potential applications.In this thesis,a series of hydrogel adhesives with excellent wet adhesion properties were prepared based on silk fibroin composite hydrogels.In addition,the possible adhesion mechanisms and potential applications were also explored.(1)Four silk fibroin-based hydrogel’s(PSA)with different adhesion energies and mechanical properties were prepared by illuminating the mixture of silk fibroin with monomer(acrylic acid),crosslinking agent(PEGDA-700)and L2959(photoinitiator).The composition,adhesion energy,adhesion mechanism and biocompatibility were investigated by infrared,mechanical test,fluorescent tracing method,hemolysis and cytocompatibility,respectively.In vitro experiments(gastric perforation,pneumothorax,etc.)and in vivo experiments(skin healing,hemostasis,gastric perforation and pneumothorax)were conducted to verify the effectiveness of wet adhesion and the possibility in practical applications,respectively.The results showed that silk fibroin could not only improve the tensile strength of PSA,but also enhance the wet surface adhesion energy of PSA.During the adhesion process,PSA quickly excluded most of the interfacial water,followed by absorbing the residues to eliminate the interface water barriers.Thus,fast(<10s)and high wet adhesion energy(～1440 J m-2)was achieved with the combination of interfacial hydrogen bonding,electrostatic forces and chain entanglement.The hemolysis and subcutaneous implantation showed good biocompatibility.In addition,the PSA could not only rapidly close the wound of abdominal aorta,but also promote the healing process of full-thickness skin wound,gastric perforation in rats and long-term implantation for rabbit lung wound(2 months)without severe damages to the surrounding tissues(2)Macromolecular monomers polyethylene glycol diacrylate(PEGDA)and polytetrahydrofuran diacrylate(PTHFDA)were synthesized via esterification reaction of polyethylene glycol(PEG)and polytetrahydrofuran diacrylate(PTHF)with acrylic acid,respectively.Then,the chemical structures were characterized by 1H NMR.Under illumination with pentapentyltetraol tetra-3-mercaptopropanate(PETMP),the macromolecular monomers could crosslink into polymer networks(P(PTHF-co-PEGco-PETMP))which could own four responsive temperatures.To obtain the polymer physical and chemical properties,DSC,FTIR,DMA and mechanics test were carried out to characterize the thermodynamic properties,components,shape memory behaviors,and mechanical properties of the polymer samples,respectively.On this basis,a PSA adhesive layer was integrated with the polymers to attain a temperature responsive adhesive tape(TRAT),followed by exploring its potential applications by in vitro experiments.The results showed that the macromolecular monomers were successfully synthesized and the corresponding P(PTHF-co-PEG-co-PETMP)exhibited excellent mechanical properties and temperature responsive behaviors.After integrating with adhesion layer,TRAT could also preserve good shape memory behavior without sacrificing the strong wet surface adhesion property(～150 kPa).In addition,TRAT could achieve immediate wet adhesion and rapid wound contraction in response to body temperature.Similarly,based on the excellent temperature-responsive and wet-adhesion feature,TRAT could spontaneously expand from the initial folded state and attach firmly to the inner esophageal surface under a temperature stimulus,exhibiting promising prospects in anti-migration trachea stents.(3)After modifying by glycidyl methacrylate(GMA),the obtained double-bond modified silk fibroin(GS A)could be cross-linked to form hydrogel under photoinitiator and UV light conditions.Twelve hydrogels were prepared by varying the GMA feed,photoinitiator ratio,and GSA concentrations.The amino acid compositions,grafting rate,chemical structure,mechanical properties,cell viability and blood safety were characterized by the amino acid analyzer,1H NMR,FTIR,tensile and compression tests,cell co-culture and hemolysis tests,respectively.The results showed that GSA precursor could in situ form a hydrogel layer to a wet surface under low power UV(25 W)in less than 20 s.The tensile and compressive strength of GSA gradually increased with the increasing proportion of GMA feed ratio.Correspondingly,the swelling ratio of the hydrogel decreased to some extent with increasing precursor concentrations.Based on the good mechanical strength,GSA could effectively in situ form adhesions with wet tissue surfaces.In terms of biocompatibility,it owned lower hemolysis rate and less cytotoxicity,which is beneficial to the further in vivo hemolasis and full-thickness-skin healing.Potential applications were also explored by in vitro(coagulation and arterial sealing)and in vivo(full-thickness skin wounds and skull injuries in rats)experiments.The sealed arterial blood vessels could also hold a gradually increasing pressure(260 mL min-1).In addition,GSA was also capable of promoting full-thickness skin healing,liver hemostasis and skull repair.(4)4-(4-hydroxymethyl-2-methoxy-5-nitrophenoxyl)-butyric acid(NB-OH)was derived from vanillin and methyl 4-butyric acid through four-step synthesis routines including etherification,nitration,hydrolysis and reduction.Through the coupling reaction between carboxyl group and amino group,NB-OH was successfully grafted onto the polylysine side chain to obtain PLL-g-NBOH with two grafting ratios.The chemical structures were clarified by 1H NMR and FTIR,while the photosensitivity mechanism was identified by 1H NMR.Then,three kinds of hydrogels with different mechanical strengths were prepared by adding different contents of PLL-g-NBOH-2 to GSA matrix.The mechanical properties,cell viabilities and blood safety were characterized by tensile test,cell co-culture and hemolysis test.The results showed that 4-(4-hydroxymethyl-2-methoxy-5-nitrophenoxyl)-butyric acid could generate aldehyde groups,and thus form covalent bonds with amino groups via Schiff’s base reaction at the interface of hydrogel and tissue under UV illumination.In order to achieve in situ intraocular crosslinking of GSA,a portable UV device was designed,allowing the formation of hydrogel precursors to a wet porcine skin.And the pratical swelling behavior of the hydrogel was also detected by immersing in PBS solution.The results showed that the obtained hydrogel could quickly in situ adhere to the wet tissue surface,and exhibited excellent anti-swelling behavior.The strong wet adhesion,lower hemolysis ratio and less cytotoxicity contributed great to rapid hemstasis and skin wound healing process.By means of the portable UV divice,GSA-NBA-1 could accomplish both in vitro(porcine retinal reattachment)and in vivo experiments(rabbit retinal reattachment),exhibiting good postoperative results.