Studies On Secondary Structures And Mechanism Of Modified Silkworm Fibroin

Recently silkworm silk, as one of the most important natural biomaterials combined withadjustable hierarchical structures, outstanding mechanical properties and good biologicalcompatibility, has wide potential applications in tissue engineering, drug delivery and otheremerging fields. Fibroin modified by additives currently attracts growing research interests. In thispaper, fibroin fibers obtained by feeding silkworms on fluorescent sodium, rhodamine B (RhB),rhodamine101(Rh101), rhodamin110(Rh110) and acridine orange have been researched. Ageneral principle of selecting or designing proper additives and effects of additives on fibroinsecondary structures were proposed. Besides that, fibroin-graphene oxide blending films,including secondary structures, thermodynamics and conformation transition dynamics aftertemperature-controlled water vapor annealing (TCWVA), have also been studied. The mechanismand effects of alkaline graphene oxide on fibroin secondary structures were preliminary revealed.Conclusions as follows:(1) A general principle of selecting or designing proper feeding additives: Based on classicalfibroin micelle model in vivo, additives should have certain solubility or dispersion in water, lowtoxicity, preferably small size and amphiphile structure. Moreover, the most important, theyshould have low isoelectric points so that fibroin micelles could recognize additives.(2) Effects of feeding additives on fibroin secondary structures: All the four additives madesilk I in fibroin increase and silk II decrease; the content of silk I (silk II), which was dependent onthe content of feeding additives (RhB) in feeds, increased (decreased) with the increase of thecontent of feeding additives.(3) Effects of alkaline graphene oxide on fibroin secondary structures: When combined withfibroin by hydrogen bonding, alkaline graphene oxide could promote the fibroin intramolecularhydrogen bonding that made fibroin transit into the stable-helix conformation.-helix and alkaline graphene oxide with giant steric hindrance would increase the fibroin’s glass transitiontemperature. If the content of alkaline graphene oxide was too high to interact with fibroin, thefibroin’s glass transition temperature, which was also higher than that in pure fibroin films, woulddecrease.(4) Effects of alkaline graphene oxide on fibroin’s conformation transition dynamics aftertemperature-controlled water vapor annealing: There were three periods in fibroin’s conformationdynamics process. Alkaline graphene oxide played a role of stabilizing-helix and suppressingtransition into-sheet.(5) Effects of fibroin on thermostability of alkaline graphene oxide: Fibroin indeed improvedthermostability of alkaline graphene oxide. T=192.2-k v, the parameter k,42.9, reflected thedegree of fibroin affecting thermostability of alkaline graphene oxide; T was the correspondingtemperature of the exothermic peak caused by decomposition; v is the mass ratio of alkalinegraphene in fibroin-graphene oxide films.(6) Responsiveness of pure fibroin to heating rates: non-“water-fibroin” caused Tg(1) andTg(2) had a good liner responsiveness to heating rates, k-31=0.8610-3, Tg(1); k2=3.810, Tg(2).Because of k2/k14.5, the glass transition in Tg(1) was caused by the secondary transition ofsmaller units than segments or the glass transition of preordered alignment before the glasstransition in Tg(2).