| The awareness of upcoming petroleum crisis and increasing price of crude oil have forced more and more attentions to be paid on renewable and environmental friendly biomacromolecular materials, such as cellulose, silk and soy protein, etc. Silk fibroin (SF), the major component of silkworm silk, is one of the structural proteins without biological activity. Due to the unique advantages including low-cost, biocompatibility, biodegradability and impressive mechanical properties, SF has drawn considerable interests from material researchers.It has been confirmed that the "figure of eight" spinning pattern of silkworm creates defects in cocoon fiber, and makes it weaker than its optimal properties (that of the force-drawn fiber). Therefore, researchers have been making efforts to spin artificial silk fibers from regenerated SF solution, with the aim to improve mechanical property. Moreover, after gained considerable knowledge about the primary amino acid sequence, the secondary structure and the condensed state of the silk fiber, people have attempted to prepare SF-based materials with various morphologies and sharps, and explore their application in the areas such as biomineralization, tissue scaffolds, drug delivery, etc. To achieve fore-mentioned objects, one Inevitable approach is to dissolve cocoon silk into solution. During this approach, the solvent with strong hydrogen-bond breaking ability is necessary.Asides from the traditional solvents, such as inorganic salt solution, fluorinated organic solvents and concentrated acids, ionic liquids (ILs) have attracted research attention for its unique characteristics, i.e. low melting point, thermal stability, wide liquid range, high ionic conductivity and easy renewability. Researchers have been exploring the application of ILs in the fields of synthesis, electrochemistry etc. Recently, after it was noticed that ILs has the ability to dissolve biomacromolecules directly, interest is growing on the research of SF/IL and its applications.In previous study, it has been noticed that degumming and dissolving methods make a significant difference in the mechanical performance of regenerated SF-based materials. It’s well known that the mechanical properties highly depend on both of the various structures and the molecular weight of macromolecule. Therefore, understanding the conformation information of SF molecules in solution and the influence of solution-preparing methods to the molecular weight (Mw) of SF are crucial to direct the successful processing of high performance regenerated SF-based material.In this thesis, we prepared a novel SF solution, SF/AmimCl. Then we investigated the conformation and Mw of the SF molecules by the study on rheological properties of the regenerated SF solutions,. Furthermore, to investigate the potential application of them as the biomedical materials, we prepared regenerated SF-based materials, i.e. fiber and porous membrane, by the solution of SF/AmimCl. The detailed results are listed below.In the first part of this work, we developed a novel SF solution, that is, SF/AmimCl solution, which has longer sample storage time (more than one and half years) than regenerated SF aqueous solution without denature. The shearing behavior was studied for both of the regenerated SF solutions. The regenerated SF aqueous solution showed obvious yielding behavior in the lower shear rate without shear thinning in the high shear rate. Combined with the observation of AFM, we suggested that, due to the hydrophobic interaction and hydrogen bond, SF molecules aggregated to "clusters" in water. For the regenerated SF/AmimCl solution, however, the Huggins coefficient between SF and AmimCl was estimated to be far less than0.5, indicating that AmimCl is a good solvent for silk fibroin to swell freely. The shear thinning under high shear rates, reflected by the alignment and orientation of SF molecular chains in AmimCl solvent were similar to that in native silk solutions. This work make it possible to prepare high-performance SF-based materials from SF/AmimCl solution.The oscillatory rheological study showed that the dynamic viscoelastic properties of SF/AmimCl solution in the semidilute region behavior like Rouse model. This enable us to use Rouse model to describe its relationship between Mw and modulus. After incorporating with Gaussian distribution, Rouse model could well fit the experimental dynamic data in the whole frequency. Therefore, the Mw and Mw distribution in SF/AmimCl were estimated. Moreover, several kinds of SF regenerated by traditional methods as well as native SF from silk gland, were dissolved in AmimCl to get the Mw and Mw distribution information using the same approach. This is the first study to quantitatively evaluated the influence of the preparation processes on the molecular weight of regenerated SF, which serves as a guideline for selecting the method of regeneration to prepare SF-based materials with suitable properties in the future.Furthermore, we used a homemade wet-spinning apparatus to produce regenerated silk fiber from the SF/AmimCl solution, with (NH4)2SO4aqueous solution as coagulant. Interestingly, while as-spun fiber from SF aqueous solution was quite brittle, the as-spun fiber from SF/AmimCl showed the significant toughness (breaking strain as high as50%). Combined with the rheological properties, it was speculated that, the free swelling chains of SF in AmimCl rather than the aggregations, contributed to the less entangled chains but more disordered chains in fiber to lead the toughness. The strength and toughness of fiber could also be adjusted by controlling the drawing rate, which can induce the orientation of SF chains. SEM observation showed that the regenerated fiber consisted of microfibers. The interfacial energy of microfibers and the friction between microfibers might also contributed to the toughness by preventing the cracks from further development.By spin-coating the SF/AmimCl solution on the surface of Si wafer, and immersing in various coagulation, we obtained SF films with different morphologies and acceptable mechanical properties in both dry and wet state. Using (NH4)2SO4aqueous solution as coagulations, the regenerated SF films with micro-porous was prepared as well. It has the potential to be used in biomedical fields, such as wound dressing, because of the advantage on the transportation of "nutrient". |
PDF Full Text Request