Gel Mechanism Of Silk Fibroin Based On Molecular Dynamics

Silk is an easily obtained material produced by Bombyx mori,which has excellent biocompatibility,mechanical properties and controllable biodegradability.Silk is composed of silk fibroin and sericin coated on the outer layer.Silk fibroin is the source of physical and chemical properties of silk.Silk fibroin hydrogel was obtained by sol-gel transformation of silk fibroin aqueous solution.Silk fibroin hydrogel has environmental response ability,which can be introduced into textile surface or compounded with textile by graft copolymerization or coating and has great potential in the field of smart wearable clothing.However,the disadvantage of long gel time limits its application.Because molecular dynamics can analyze the interaction of protein molecules at atomic level,based on the construction of silk fibroin hydrogel model,this paper studies the molecular conformation and interaction of silk fibroin hydrogel by molecular dynamics method,makes up for the deficiency of experimental measurement,explores the gel mechanism of silk fibroin hydrogel,and provides theoretical support for improving the application value of silk fibroin hydrogel in degradable smart wearable products.In this paper,based on the molecular conformation of silk fibroin downloaded from the protein database,the molecular structure is complemented by homology modeling,the appropriate gel model is selected from the models of different molecular numbers,and the gel models with different molecular relative positions and center distances are established.Based on the existing experimental results,the silk fibroin hydrogel model was simulated at room temperature and soft freezing temperature.The balance of the system was analyzed by energy and RMSD,and the gel model was verified by the hydrogen bonds between silk fibroin molecules.Through verification and analysis,the rationality of the built model is proved.In this paper,the structure and interaction were characterized by secondary structure,radial distribution function and hydrogen bond.The results showed that the non-bond interaction between silk fibroin molecules and solvents affected the formation of hydrogel.Hydrogen bonds are mainly formed in random coils between the ends and heads of different silk fibroin molecules.In the initial stage of simulation,silk fibroin molecules form hydrogen bonds with water,which leads to aggregation of silk fibroin molecules and gradually forming intermolecular hydrogen bonds.In the gelation process,the electrostatic interaction and polar solvation interaction between random coils have great influence on crosslinking and diffusion.The formation of silk fibroin hydrogel is related to the relative position of silk fibroin molecules.The intermolecular hydrogen bond between the butt joint between the head and tail of two silk fibroin molecules and the convex opposite part is the most stable,while the intermolecular hydrogen bond between the concave opposite part is the least stable,but some hydrogen bonds are still formed.The more stable the hydrogen bond between silk fibroin molecules,the less the contact number between silk fibroin and water molecules,and the greater the diffusion coefficient.Compared with normal temperature,the number of intermolecular hydrogen bonds in silk fibroin hydrogel does not increase significantly at soft freezing temperature.Two silk fibroin molecules do not form intermolecular hydrogen bonds at the butt joint between the head end and the tail end,but the number of intermolecular hydrogen bonds at the opposite part of the convex surface increases.The number of hydrogen bonds in the opposite part of concave surface decreases,the distance between acceptor and donor increases,but the occupancy rate increases obviously,and the stability of hydrogen bonds increases,which indicates that the position relationship between molecules has little effect on hydrogen bonds at soft freezing temperature.At soft freezing temperature,the interaction between silk fibroin molecules and water molecules is enhanced,which promotes the gelation of silk fibroin.This article studies the effect of soft freezing temperature and molecular relative position on silk fibroin gelation from the atomic level,further explains the gel mechanism of silk fibroin,and provides theoretical support for shortening the silk fibroin gel cycle.