Synthesis And Application Of Tough Hydrogels With Novel Functions

Polymer hydrogels are soft materials constructed with highly hydrated three dimensional networks,which exhibited significant scientific values and promising application potential for artificial load-bearing scaffold,wound dressing,drug-loading matrix and/or soft actuators.However,most conventional hydrogels showed weak and brittle mechanical features as lack of efficient energy dissipation mechanisms.Effective strategies have been highly desired to achieve tough hydrogels with multiple functional moieties.During the last decades,progress has been widely facilitated based on double network,nanocomposite,slide-ring,polyampholyte and/or macro-crosslinked hydrogels with well-defined energy dissipation moieties in their network.In particular,the combination of those strategies with non-covalent bonding interactions,including electrostatic interactions,hydrogen bonding,host-guest recognition and/or supramolecular assembling,has demonstrated effective in creating hydrogels with superior toughness and smart responsive behaviors.According to the fundamentals above mentioned,novel strategies based on poly(3,4-Ethylenedioxythiophene)(PEDOT)belts,ion/alginate chelating,chemically crosslinked graphene oxide network and core-shell structured macro-crosslinkers,have been demonstrated to achieve tough hydrogels with multiple functions.The detailed investigation has been listed as follows.(1)Novel biomimetic hydrogels were fabricated through in situ synthesis and guided assembling of positively charged poly(3,4-Ethylenedioxythiophene)(PEDOT)belts by using a parent poly(2-Acrylamido-2-methylpropanesulfonic acid)/ poly(acrylamide)(PAMPS/PAAm)gel as the template.The electrostatic interaction of PEDOT belts with negatively charged PAMPS host network led to the formation of biomimetic PEDOT-PAMPS/PAAm brushes.The strong adhesion of PAMPS/PAAm chains,even after fracturing,to the PEDOT belt surface is critical for the uptake and pressurization of fluid,which offerd extraordinary resilience and fatigue resistance with the hydrogels.Moreover,such biomimetic hydrogels were able to recover adequately during cyclic loading-unloading tests.(2)Utilization of controlled ion release from ethylenediaminetetraacetic acid(EDTA)cages were demonstrated to synthesize alginate/PAAm hybrid hydrogels with very high stretchability,toughness,and recovery.Due to the high ion-EDTA chelating constant,the ion/EDTA cages were homogeneously distributed in the hydrogel precursor solution.Such ion/EDTA was decomposed upon an exposure to protons generated by the hydrolysis of glucono-?-lactone(GDL).The released ions formed in situ crosslinking with the alginate chains,leading to a homogeneous and rigid network,with the gelation kinetics and mechanical properties controllable by CGDL.Such alginate hydrogel was used to host in situ free radical polymerization of monomers(e.g.,acrylamide),resulting in hybrid hydrogels with very high stretchability,toughness insensitivity to notches,presumably due to the unzipping of the ion/alginate chelation.The internal damages of tested hydrogels could be recovered,presumably due to the re-formation of ion/alginate chelation.This strategy has been demonstrated versatile for hydrogel synthesis based on many other multivalent ions including Co2+,Cu2+,La3+ and Ce4+.(3)Aqueous dispersible 1,2-bis(2-mercaptoethoxy)ethane(EDDET)crosslinked graphene oxide(E-c GO)skeleton was in situ incorporated into poly(vinyl alchohol)(PVA)matrix,resulting in novel inorganic/organic nanocomposite hydrogels with super mechanical and chondrocyte cell-adhesion properties.It has been demonstrated that the di-functional EDDET molecules reacted with and likely bridged the GO nanosheets into E-c GO networks via multiple spectrum.The unique interpenetrating structure and hydrogen bonding were demonstrated to play critical roles in enhancing the compressive property of those hydrogels,in comparison to the GO and thermal reduced graphene oxide(T-r GO)filled hydrogels.It is noted that the fracture toughness values of these E-c GO/PVA hydrogels(1731.3 ± 114.8 J m-2)were higher than that of articular cartilage(~1000 J m-2).Moreover,the E-c GO/PVA hydrogels have been demonstrated biocompatible,which provided the E-c GO/PVA hydrogels as promising candidate biomaterials for load-bearing bio-tissue substitution.(4)Novel hydrogels based on core-shell structured macro-crosslinkers,were demonstrated to exhibit mechanical tough,multiple-responsive and antifouling properties.Assisted with 0.5 M additional Na+,sodium dodecyl sulfate(SDS)sphere micelles were incorporated with AMPS monomer to achieve wormlike SDS-Na Cl-Na AMPS micelles.In comparison to the sphere SDS micelles,wormlike SDS-Na Cl-Na AMPS micelles exhibited a significant size increment,thus providing larger core space to encapsulate more stearyl methacrylate(C18)hydrophobes.This led to core-shell structured crosslinking units consisting of C18 in the cores and AMPS monomer in the coronal.Upon the subsequent free radical polymerization,AMPS monomers were covalently bonded to the C18 hydrophobes,thus achieving “Poly(C18)-PAMPS” macro-crosslinked polyacrylamide(PAAm)hydrogels.The physical “Poly(C18)-PAMPS” macro-crosslinkers exhibited efficient energy dissipation ability under loading,thus providing the hydrogels with highly stretchable,tough,compressive strong as well as excellent fatigue resistant and recoverable properties.The grafted PAMPS polyelectrolyte chains on the macro-crosslinkers led to swelling response of the hydrogels to various p H and salt solutions.In comparison to the silica wafers,the hydration surfaces ascribed to the grafted PAAm chains even contributed to antifouling performance of those hydrogels against colonization of diatoms.