Abstract
Spiders achieve superior silk fibres by controlling the molecular assembly of silk proteins and the hierarchical structure of fibres. However, current wet-spinning process for recombinant spidroins oversimplifies the natural spinning process. Here, water-soluble recombinant spider dragline silk protein (with a low molecular weight of 47 kDa) was adopted to prepare aqueous spinning dope. Artificial spider silks were spun via microfluidic wet-spinning, using a continuous post-spin drawing process (WS-PSD). By mimicking the natural spinning apparatus, shearing and elongational sections were integrated in the microfluidic spinning chip to induce assembly, orientation of spidroins, and fibril structure formation. The additional post-spin drawing process following the wet-spinning section partially mimics the spinning process of natural spider silk and substantially contributes to the compact aggregation of microfibrils. Subsequent post-stretching further improves the hierarchical structure of the fibres, including the crystalline structure, orientation, and fibril melting. The tensile strength and elongation of post-treated fibres reached up to 510 MPa and 15%, respectively.
Highlights
In hexafluoroisopropanol and coagulated in either methanol or isopropanol
During the wet-spinning process, recombinant spidroin dope was subjected to shearing forces along the microfluidic channel, before it was extruded into the ethanol coagulation (Fig. 1b)
The drawing process in air has normally been applied in the forced reeling of natural spider dragline silk[8,9], natural silkworm silk[28,29], and in the production of RSF silk[30,31]
Summary
In hexafluoroisopropanol and coagulated in either methanol or isopropanol. These denaturing solvents may result in an incorrectly folded secondary structure and disappointing mechanical properties[21]. Despite fundamental differences in composition and structure of spider MA and silkworm fibroin proteins, the silk glands of both organisms have been shown to function . In both glands, highly concentrated spinning dope flows through the contracted geometry of the silk gland and is exposed to ionic gradients that regulate its state of crystallization by forming liquid crystalline and inducing protein conformational changes and aggregations[7,10,27]. The additional step in air, which is necessary for the spinning process of the spider, induces the re-assembly of protein in air If done this way, fibre yielded is much more compact and homogeneous compared to microfluidic wet-spinning
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