Construction strategy and application of silk sericin hydrogels
Sericin,a by-product of silk production,has good hydrophilicity,biodegradability and reactivity because of the rich polar amino acids and loose spatial structure.Sericin also has many biological activities such as anti-oxidation,anti-coagulation,hypoglycemic and promoting cell proliferation and differentiation.Sericin hydrogels formed by self-assembly or crosslinking agent have multiple advantages and are widely used in tissue engineering,wound repair,drug release and other fields.The construction strategies of sericin hydrogels include physical methods,chemical crosslinking,ultraviolet photocatalysis and transgenic functional modification.Physical methods are used to construct sericin hydrogels mainly by triggering the polymerization of sericin molecules to generate intermolecular forces to form cross-linked networks.Inducing sericin hydrogels with ultrasound is to use the ultrasonic cavitation phenomenon in solution to act on sericin molecules in aqueous solution,cause a more violent collision between molecules and form a more stable and orderly spatial structure by rearrangement,so as to obtain a stable gel network structure insoluble in water.Vacuum freeze-drying technology facilitates the physical cross-linking to form a stable and firm spatial network structure using the characteristics of molecular response to ambient temperature changes.Sericin hydrogels prepared by high temperature,high pressure and self-assembly method have the advantages of mild reaction conditions and controllable gelation process.Repeated freezing and thawing is a safe and effective method for preparing porous gels.The obtained sericin hydrogels not only have excellent mechanical properties,high pore expansion ratio,good hydrophilicity and thermal stability,but the ability to load and release small molecule drugs and nanoparticles.In addition,adding an appropriate concentration of ethanol(15％)to the sericin solution can accelerate the gelation process of sericin and enhance the mechanical properties of the gel.Chemical crosslinking promotes the formation of stable covalent bonds between sericin molecules,and enables sericin in solution to form a network structure and gelatinize,which can not only improve the mechanical properties of sericin hydrogels,but also make sericin and other component materials mixed into a multi-functional composite network structure of hydrogels.The stable pure sericin hydrogel or sericin complex gel that can be effectively constructed by using single crosslinking agents such as genipin,peroxidase and glutaraldehyde or compound crosslinking agents has been widely used in ischemic myocardial repair therapy,skin tissue regeneration and repair,tissue engineering scaffolds,drug delivery carriers,supporting neuronal network development,and improving the thermal stability and mechanical properties of cotton fabrics.When chemical agents are used to cross-link sericin hydrogels,the crosslinkers with low toxicity,few residues or easy removal should be preferentially selected,and the cytotoxicity of hydrogels should be evaluated to ensure the further application of hydrogels.In addition to physical and chemical crosslinking methods,sericin hydrogels can also constructed by means of ultraviolet photocatalytic crosslinking and transgenic functional modification.UV light can induce free radical polymerization and construct in situ cross-linked transparent porous sericin-based hydrogels.With the use of 3D printing technology,sericin-based hydrogel scaffolds with large pore structure can be customized,which is conducive to maintaining the wet and clean environment required for wound healing,and is an ideal choice for visual wound care.By introducing the coding genes of functional proteins into the genome of silkworms and spinning into the sericin layer of silk,sericin biomaterials with various biological functions can be prepared conveniently and economically,which strategically avoids sourcing and safety risks from exogenously added functional proteins during materials fabrication.Sericin hydrogels have excellent histocompatibility,abundant chemical modification sites,high hydrophilicity and controllable degradability.Sericin gels prepared with different construction strategies have been widely used in skin wound dressing,nerve regeneration,cartilage repair,functional drug delivery and other fields.Sericin gels are mainly developed and applied from the directions of improving the mechanical properties of gels,avoiding the toxic effects of chemical crosslinking agents and exploring new functions of gel materials,so as to obtain greater application value.
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