Properties of Biomimetic Artificial Spider Silk Fibers Tuned by PostSpin Bath Incubation

Abstract

Efficient production of artificial spider silk fibers with properties that match its natural counterpart has still not been achieved. Recently, a biomimetic process for spinning recombinant spider silk proteins (spidroins) was presented, in which important molecular mechanisms involved in native spider silk spinning were recapitulated. However, drawbacks of these fibers included inferior mechanical properties and problems with low resistance to aqueous environments. In this work, we show that ≥5 h incubation of the fibers, in a collection bath of 500 mM NaAc and 200 mM NaCl, at pH 5 results in fibers that do not dissolve in water or phosphate buffered saline, which implies that the fibers can be used for applications that involve wet/humid conditions. Furthermore, incubation in the collection bath improved the strain at break and was associated with increased β-sheet content, but did not affect the fiber morphology. In summary, we present a simple way to improve artificial spider silk fiber strain at break and resistance to aqueous solvents.

An Image-Analysis-Based Method for the Prediction of Recombinant Protein Fiber Tensile Strength

“…In the engineering stress-strain curve, the ultimate strength is represented by the last point before fracture. From what we observed of the protein fibers in this study, as well as in previous works [52,53,59], NT2RepCT fibers have a non-circular cross-section with a longitudinal groove, as seen in Figure S8a. As depicted in Figure S8b, measuring the diameter in the face of a fiber with such a groove will result in an overestimation of the true area.…”

“…After purification, NT2RepCT was concentrated to 300 mg/mL using an Amicon Ultra-15 centrifugal filter unit (Merck-Millipore, Darmstadt, Germany) equipped with an ultracel-10 membrane (10 kDa cutoff) at 4000× g and 4 • C. The final concentration of the protein solution (dope) was calculated with the protein-specific extinction coefficient of 18,910 M −1 cm −1 after carefully diluting the dope 500 times into 20 mM Tris (pH 8) and measuring the absorbance at 280 nm in triplicates. Then, the dope was transferred into a 1 mL syringe Luer Lock tip (BD, Franklin Lakes, NJ, USA) and connected via a 27 G blunt end steel needle (B. Braun, Melsungen, Germany) with an outer diameter of 0.40 mm to silicon tubing as detailed in Greco et al (2020) [53]. At the end of the silicone tubing a pulled glass capillary with a tapered tip and an opening between 39 and 67 µm was inserted.…”

“…The spinning dope was extruded through the glass capillary at 17 µL/min into an 80 cm long spinning bath containing 4 L of a 750 mM acetate buffer at pH 5. Fibers were collected continuously at the end of the bath with frames placed on a rotating wheel with a circumference of 35 cm as detailed in Greco et al (2020) [53], at 50 rpm to 120 rpm (29 and 69 cm/s, respectively).…”

Artificial and natural silk materials have high mechanical property variability regardless of sample size

“…Second, since silk is a viscoelastic material 33 , forced silking procedures and spinning conditions affect the silk tensional states, the secondary structure content of the fibres, and thus their mechanical properties 34 , 35 . The same is true for artificial silk fibres as well as silk fibroin fibres, where the spinning protocols or the degumming process affect the mechanical properties of the fibres 23 , 36 , 37 . Third, a major cause for the variability may be found in the fact that the calculation of the stress is dependent on a precise measurement of the fibre cross-sectional area.…”

Comparing Modern and Classical Perspectives on Spider Silks and Webs

“…For spider silk, the most common uses to date requires transforming fibers into hydrogels, nanoparticles, films, or foams which are used primarily for tissue engineering or drug delivery (Huemmerich et al 2006;Humenik et al 2011;Schacht et al 2015;Jastrzebska et al 2018;Gustafsson et al 2018;Dellaquila et al 2019;Yang et al 2020). However, progress in this area requires innovation in up-scaling, as these applications require large amounts of spider silk (Rising and Johansson 2015;Greco et al 2020a), and this in particular, much like the calls of M. Bon 300 years ago (Bon 1710), represents one of the main challenges for the field (Koeppel and Holland 2017;Edlund et al 2018).…”