Study On The Controllability Of Gelation Process Of Regenerated Silk Fibroin Hydrogel Bio-ink

Recent years,based on the principle of additive manufacturing,interest in the field of three-dimensional(3D)bioprinting has increased enormously.3D bioprinting combines the fields of biology,stem cells,and computer and materials science to create new research ideas and solutions for various application in tissue and organic regeneration,clinical rehabilitation therapy and organ transplantation.At present,bio-ink is the most important factor restricting the rapid development of biological bioprinting,the pace of research needs to be accelerated.Bombyx mori(silkworm)silk,as an important natural polymer biomaterial,has been a research hotspot in the field of biomedicine,due to its good biocompatibility,controllable biodegradability,robust biomechanical features and sufficient supply.Hydrogel,an important form of silk fibroin(SF),is widely concerned as a natural bio-ink because of its shear thinning performance 、 high viscosity and the gelatinization properties.However,the natural SF hydrogel is slow to form,has poor mechanical properties and its structure is vulnerable to damage.How to improve the printability of SF hydrogel material is an important development trend of bioprinting technology.In this dissertation,the effects of anionic surfactant sodium dodecyl sulfate(SDS)and metal cation on the gelation process of SF were studied based on the gelation process of regenerated fibroin protein.With the aid of the synergistic effect of SDS and metal cation,gelation time,microstructure and mechanical properties of SF hydrogel were controlled by regulating the concentration of SDS,kinds and concentrations of metal ions.And the formation mechanism of SF hydrogel with SDS and metal ions was explored.It provides the technical support and theoretical guidance for SF materials application in bioprinting technology.The main results of this dissertation are outlined as following:(1)Through regulating the anionic surfactant sodium dodecyl sulfate(SDS),the SF gelation process was controlled,and the SF/SDS hydrogel was finally obtained.The effects of SF concentration and SDS concentration on the gelation process of fibroin protein were investigated.The results show that the addition of SDS could significantly accelerate the formation of hydrogels of fibroin,when the concentration of fibroin was 5 w/w%,and the concentration of SDS was 50 g/L(5 w/v%),the gelation time of SF was the shortest.Compared with traditional ethanol-induced SF hydrogel and natural SF hydrogel,SF/SDS hydrogel showed porous structure and the pore diameter was uniform,which formed the network porous structure,and its mechanical properties were significantly enhanced.(2)Adding a certain concentration of potassium ion could shorten the SF gelation time,while sodium ion has a weak effect on the gelation time,calcium ion and magnesium ion could even inhibit the gelation process of silk fibroin.The experiment results indicate that the synergistic effect of SDS and metal ions could control the SF gelation time to a certain extent.In addition,the metal ions could obviously increase the pore diameter of scaffold and reduce the mechanical properties at different levels.(3)The formation mechanism of SF hydrogel with SDS and metal ions was discussed.The results show that the rapid gelation of SF is mainly due to the combined action of hydrophobic、electrostatic interactions and surface tension,it enhances the hydrophobic association between SF molecular chains and the conformation is transformed from the random coil to the β-folding structure to promote rapid formation of gel network between SF molecules.