Based on the natural sequence of Araneus diadematus Fibroin 4 (ADF4), the recombinant spider silk protein eADF4(C16) has been engineered. This highly repetitive protein has a molecular weight of 48kDa and is soluble in different solvents (hexafluoroisopropanol (HFIP), formic acid and aqueous buffers). eADF4(C16) provides a high potential for various technical applications when processed into morphologies such as films, capsules, particles, hydrogels, coatings, fibers and nonwoven meshes. Due to their chemical stability and controlled morphology, the latter can be used to improve filter materials. In this protocol, we present a procedure to enhance the efficiency of different air filter devices, by deposition of nonwoven meshes of electrospun recombinant spider silk proteins. Electrospinning of eADF4(C16) dissolved in HFIP results in smooth fibers. Variation of the protein concentration (5-25% w/v) results in different fiber diameters (80-1,100 nm) and thus pore sizes of the nonwoven mesh.Post-treatment of eADF4(C16) electrospun from HFIP is necessary since the protein displays a predominantly α-helical secondary structure in freshly spun fibers, and therefore the fibers are water soluble. Subsequent treatment with ethanol vapor induces formation of water resistant, stable β-sheet structures, preserving the morphology of the silk fibers and meshes. Secondary structure analysis was performed using Fourier transform infrared spectroscopy (FTIR) and subsequent Fourier self-deconvolution (FSD).The primary goal was to improve the filter efficiency of existing filter substrates by adding silk nonwoven layers on top. To evaluate the influence of electrospinning duration and thus nonwoven layer thickness on the filter efficiency, we performed air permeability tests in combination with particle deposition measurements. The experiments were carried out according to standard protocols.
Nanomaterials show extraordinary properties and, among them, polymeric nanofibers are of high interest for several applications. Here, the applicability of a high throughput production system is investigated by combining solution-based electrospinning with centrifugal spinning. Ultrathin nanofibers were generated with diameters in the tens of nanometer regime using polyethylene glycol and polylactic acid, and the productivity of the highly interconnected nanofiber nonwoven meshes was orders of magnitude faster compared to that of materials made with traditional electrospinning methods. Such a manufactured layer of nanofibers shows great potential for filter applications, for example.
State‐of‐the‐art air filter devices have been well‐characterized and optimized for particle deposition of a huge range of particle sizes. However, sustainability of the employed filter materials is usually neglected. In this study, several polymers (recombinant spider silk, recombinant lacewing silk, poly(lactic acid), and poly(ethylene oxide)) are electrospun into fine dust filter layers to evaluate relevant filter parameters such as particle deposition, air permeability, and pressure drop for sub‐micrometer fiber materials. Filters comprising silk proteins show a much lower demand on fine‐dust‐layer material (40–210 mg m−2) in comparison to that of conventional filters (50 g m−2). Filters equipped with silk meshes with fiber diameters in the sub‐micrometer regime (<250 nm) show improved filter qualities in comparison to that of commercially available air filter devices (with melt blown fibers in the >20 µm regime). In particular, sub‐micrometer particles (0.2–1 µm) are filtered more efficiently by the silk‐based filters due to interception and impaction effects yielding a low pressure drop, and therefore these filters show an improved air permeability and lowered pressure drop of, for example, a vacuum cleaner bag in which they can be employed.
Abstract:Silks are well known natural fibers used for textile applications and have got for the first time available upon sericulture of silkworms (Bombyx mori) several thousand years ago in China. In contrast to silkworm silk, spider silks offer better mechanical properties such as higher tensile strength and much better toughness, but natural spider silk is less accessible due to the cannibalistic behavior of spiders prohibiting large scale farming, and therefore has not been employed in textile industry yet. In this study, a biotechnologically produced spider silk protein was introduced as a new material for textile applications in form of foam coating material. The spider silk foam coating was developed to increase the abrasion behavior of natural and polymeric furniture textiles. Modern textiles are high-tech materials and optimized concerning yarn design and fabric weave to fit a wide range of applications. Often hydrofluorocarbons based coatings are used to enhance textile performances. Upon coating with sustainable spider silk, yarn fraying was significantly reduced lowering the tendency to form knots and loops. Further, the textile abrasion resistance, analyzed by pilling tests, was improved significantly (17-200 %) for all tested types of fabrics, in particular long term strain pilling was minimized.
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