Construction Of Chitin-Based Hydrogel By Polyphenol Mediating Self-Assembly Strategy For Biomedical Applications

With the introduction of concept of sustainable development,carbon emission reduction and green chemistry,the efficient development and high-value conversion of renewable biomass resources has gained attractive attention in the world today.Chitin biomass,as the second most abundant natural polymer after cellulose,has drawn extensive attentions,due to its good biocompatibility,renewability,biodegradation and non-toxicity.The extensive non-covalent bonds(hydrogen bonding and hydrophobic interaction)and high crystallinity exist among the chitin chains,which limit the development of chitin biomass.Therefore,it is still a challenging problem to achieve high value conversion of chitin biomass by adjusting the chitin chains assembly and then achieving structural design.In this thesis,we focused on a key scientific question of how the polyphenol induced the chitin chains assembly.First,we studied the effect of polyphenol-mediated chitins self-assembly on the aggregation structure and property of the resulted hydrogel.Then,we found that the relatively weak chitin-polyphenol dynamic noncovalent crosslinking network could improve the molecular mobility,which could allow the chitin chains alignment under the mechanical deformation.Besides,TA also could enhance the interfacial interaction between chitin and 2D materials,which benefited the 2D materials orientation under the chitin chains driving.Finally,a facile and lowcost polyphenol-mediated non-covalent driven assembly strategy was developed for fabricating homogeneous chitin-polyphenol-metal hydrogels,achieving a series of hydrogels with photothermal effect,which promoted wound healing in infected rats.The major investigations and conclusions of this thesis included the following three parts.(1)This study was focused on the effect of polyphenol-mediated chitins selfassembly on the aggregation structure and property of the resulted hydrogel.Herein,a polyphenol mediating self-assembly strategy was designed to simultaneously improve the chitin hydrogel toughness and strength,which was distinctive from the rigid-soft double network energy dissipation approaches.The introduced polyphenol competed with the chitin chains self-assembly for simultaneously forming the weak chitinpolyphenol soft networks and strong chitin-chitin rigid networks.High-density crosslinking networks involving hydrogen hydrophobic interaction,bonding,ionic interaction endowed the resulted chitin-polyphenol hydrogels with prominent mechanical properties.The relatively weaker chitin-polyphenol crosslinking domains acted as the sacrificial bonds to effectively dissipate the energy,resulting in the high fracture energy.The mechanical properties of the chitin-tannic acid hydrogels regulated by the tannic acid concentration and ethanol aqueous coagulation,which mainly attributed to the hydrophilic and hydrophobic domains formation.The full natural chitin-tannic acid hydrogels presented excellent degradability(simulated gastric fluid degradation,soil degradation and in vitro degradation),good biocompatibility and considerable antibacterial properties,enabling the potential in food,sustainable and biomedical applications.(2)Based on the results of the first study,the chitin-polyphenol dynamic noncovalent crosslinking network dramatically improved the mobility of the rigid chitin chain,which could achieve the anisotropic structural hydrogel by mechanical deformation.Anisotropic structure plays an important role in biomimetic functions of anisotropic hydrogels.However,the anisotropic hydrogels research should not be limited to its architecture design but ought to include the understanding and improvement of the internal interaction among their components.Herein,we developed a tannic acid mediated assembly strategy to not only improve the rigid chitin chains mobility and but enhance the interfacial interaction between chitin chains and twodimension materials(2D materials,molybdenum disulfide nano-sheets and brushite macro-sheets as example),for obtaining the high aligned arrangement chitin/2D materials hydrogels via the mechanical deformation.The tannic acid was used to(i)introduce the dynamic noncovalent crosslinking structure among the chitin chains for endowing chitin chains with the considerable molecular mobility to allow the chitin chains orientation movement under the drafting force;(ii)improve the chitin-2D interfacial interaction for benefiting the 2D sheets alignment under the chitin chains driving.Our design concept achieves the multiple noncovalent assembly networks(rigid chitin-chitin,soft chitin-TA and chitin-TA-2D)and biomimetic aligned nanofibrous structure,resulting in the superior mechanical properties.As a demonstration,the anisotropic chitin-tannic acid/brushite macro-sheet hydrogel effectively enhanced the bone regeneration by improving the bone marrow mesenchymal stem cells directional migration and osteogenic differentiation.We anticipated our polyphenol mediated assembly concept could be used to fabricate other natural polymer based composite anisotropic hydrogel for diverse applications.(3)Based on the results of the first study,a facile and low-cost polyphenolmediating non-covalent driven assembly strategy was constructed for fabricating homogeneous chitin-polyphenol-metal nanomaterials hydrogels.On the one hand,polyphenols crosslinked chitin chains by noncovalent bindings.On the other hand,metal nanomaterials oxidized from metal substrates under alkaline solution were captured by polyphenols and anchored in chitin-polyphenol hydrogel networks.A range of metal(iron,copper,titanium,zinc)based nanomaterials and polyphenol(gallic acid,tannic acid,pyrogallic acid,quercetin)species could be incorporated into the chitin-polyphenol-metal nanomaterials hydrogel framework.The chitin-polyphenolmetal nanomaterials hydrogel exhibited superior photothermal effect and antibacterial activity.As a demonstration,the chitin-polyphenol-Cu nanomaterials hydrogel showed an effectively antibacterial properties under near-infrared irradiation.Moreover,due to the appropriate content of Cu and photothermal effect,this hydrogel significantly accelerated infected wound healing via promoting the cell proliferation and angiogenesis,showing the potential in wound dressing.The low cost,versatility and flexibility of the polyphenol-mediating non-covalent driven assembly process can be used to fabricate diverse polymer-polyphenol-metal nanomaterials hydrogel,thereby enabling their use in various applications.