title: Novel Processing Technologies for Recombinant Spider Silk Proteins
Creators: name: Jokisch, Stephan
Publisher: name: University of Bayreuth
Year: 2020
Subjects: subject: Air filtration
subject: Sub-micrometer fibers
subject: Foam coating
subject: Textiles
subject: Aqueous solutions
subject: Green Chemistry
subject: Surface Properties
subject: Biodegradable Polymers
subject: Spider Silk
subject: Lacewing Silk
subject: 620
subject: 660

description: Sustainable and environmentally friendly alternatives to crude oil based materials are nowadays extensively investigated. Biopolymers, such as spider silk, have been employed by humans as an alternative ever since, and are additionally known for their good mechanical stability. The greatest drawback of spider silk is the lack of availability. During the last decades the reverse decoding of protein structures into designed gene sequences enabled the development of recombinant production of silk proteins such as Araneus diadematus dragline silk protein (eADF4(C16)) or Chrysoperla carnea egg stalk protein (ChryC1). The focus of this work was the development of two processing methods for spider silk proteins and the evaluation of their upscaling potential. The first application was an environmentally friendly and water-based protective spider silk protein foam coating for furniture textiles to reduce abrasive textile destruction derived from pilling. Parameters were investigated to achieve stable and uniform aqueous foams, and spider silk foaming dopes were analyzed. Subsequently, a novel foam coating was developed. Three different fabrics were foam-coated with recombinant spider silk protein (eADF4(C16)) and analyzed regarding their vulnerability to friction and resulting yarn fraying, as well as pilling. One fabric mainly contained the natural materials cotton and rayon. The two other polymeric fabrics comprised PES and PA. Primarily homogeneous and stable coatings were applied to single yarns, which were then analyzed regarding yarn fraying. Subsequently, complex fabrics were coated and they revealed an increase in durability and a decrease in pilling tendency upon abrasive friction analyzes.[247] A film-like fiber surface coating and smoothing in combination with fibrous contact points reduced the friction and ripping out of single filaments, preventing the consequent pilling and prolonging the life-time of the furniture fabric. In the presence of the silk coating a clear correlation between lowered yarn fraying and pilling tendency was determined. For all three tested fabrics these effects were significantly reduced, and upon silk foam coating the fabric quality was doubled in short as well as long-term abrasion tests. The second part of this work aimed at the production of electro-spun submicron nonwoven fiber mats. Four different submicron fiber mats were tested and compared regarding their applicability as fine dust particle filter meshes, including the synthetic polymers PEO and PLA and two biopolymers, namely recombinant silk protein ChryC1 and eADF4(C16). In a first approach, nonwoven fiber meshes with different fiber diameters were successfully electro-spun on a commercially available PA support-woven. A clear dependency could be determined regarding the filtration efficiency fiber diameter and coating thickness. Centrifuge electrospinning was employed for the production of submicron nonwoven fiber meshes on PA mesh material to test the potential for large-scale production. The most critical step was the proper adjustment of the electrospinning process’s spinning conditions to the novel method, as well as, the adjustment of its spinning parameters. Process-related spinning parameters introduce additional shear forces into the fibers. Those yielded fiber diameters below 100 nm and an increased content of crystalline β-sheet structures as spun. The inherent random coil secondary structure content rendered centrifuge spun spider silk nonwoven fibers water soluble. Hence, additional posttreatment was required. Electro-spun spider silk meshes were the best material tested concerning particle deposition, air permeability and pressure drop. Additionally, the negative surface net charge of eADF4(C16) submicron fibers contributed to the better performance of spider silk nonwoven meshes. A new silk-containing filter set-up was developed as a prototype providing a significantly higher filtration quality factor than a conventional filter bag. As calculated in previous studies, the use of such spider silk-containing dust bags could save 9 kg of CO2-equivalents per domestic home and per year in an industrial country such as Germany.[265] The results of both approaches highlight the promising upscaling potential of spider silk applications.