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Spider dragline silk is a remarkable fiber made by spiders from an aqueous solution of spidroins, and this feat is largely attributed to the tripartite domain architecture of the silk proteins leading to the hierarchical assembly at the nano- and microscales. Although individual amino- and carboxy-terminal domains have been proposed to relate to silk protein assembly, their tentative synergizing roles in recombinant spidroin storage and spinning into synthetic fibers remain elusive. Here, we show biosynthesis and self-assembly of a mimic spidroin composed of amino- and carboxy-terminal domains bracketing 16 consensus repeats of the core region from spider Trichonephila clavipes. The presence of both termini was found essential for self-assembly of the mimic spidroin termed N16C into fibril-like (rather than canonical micellar) nanostructures in concentrated aqueous dope and ordered alignment of these nanofibrils upon extrusion into an acidic coagulation bath. This ultimately led to continuous, macroscopic fibers with a tensile fracture toughness of 100.9 ± 13.2 MJ m-3, which is comparable to that of their natural counterparts. We also found that the recombinant proteins lacking one or both termini were unable to similarly preassemble into fibrillar nanostructures in dopes and thus yielded inferior fiber properties. This work thereby highlights the synergizing role of terminal domains in the storage and processing of recombinant analogues into tough synthetic fibers.

Bioelectronics based on biomaterial substrates are advancing toward biomedical applications. As excellent conductors, poly(3,4-ethylenedioxythiophene) (PEDOT) and its derivatives have been widely developed in this field. However, it is still a big challenge to obtain a functional layer with a good electroconductive property, transparency, and strong adhesion on the biosubstrate. In this work, poly(hydroxymethyl-3,4-ethylenedioxythiophene) (PEDOT-OH) was chemically polymerized and deposited on the surface of a regenerated silk fibroin (RSF) film in an aqueous system. Sodium dodecyl sulfate (SDS) was used as the surfactant to form micelles which are beneficial to the polymer structure. To overcome the trade-off between transparency and the electroconductive property of the PEDOT-OH coating, a composite oxidant recipe of FeCl3 and ammonium persulfate (APS) was developed. Through electrostatic interaction of oppositely charged doping ions, a well-organized conductive nanoscale coating formed and a transparent conductive RSF/PEDOT-OH film was produced, which can hardly be achieved in a traditional single oxidant system. The produced film had a sheet resistance (Rs) of 5.12 × 104 Ω/square corresponding to a conductivity of 8.9 × 10-2 S/cm and a maximum transmittance above 73% in the visible range. In addition, strong adhesion between PEDOT-OH and RSF and favorable electrochemical stability of the film were demonstrated. Desirable transparency of the film allowed real-time observation of live cells. Furthermore, the PEDOT-OH layer provided an improved environment for adhesion and differentiation of PC12 cells compared to the RSF surface alone. Finally, the feasibility of using the RSF/PEDOT-OH film to electrically stimulate PC12 cells was demonstrated.

Antibacterial scaffolds are highly desirable for the repair and reconstruction of injured soft tissues. However, the direct fabrication of scaffolds with excellent biocompatibility, flexibility, and antibacterial capacity remains a challenge, especially those based on biomaterials. In this study, we report the biomaterial-based antibacterial scaffolds based on regenerated silk fibroin, 2-hydroxypropyltrimethyl ammonium chloride chitosan, and bladder acellular matrix graft by blend and coaxial electrospinning. This approach eliminated the use of organic solvents and inorganic nanoparticles, ensuring greater clinical safety, mimicking physiological extracellular matrix structures, and the required softness for a suture material. Thus, the scaffold obtained in this study exhibited excellent biocompatibility, the required mechanical characteristics, and excellent antibacterial capacity. The rate of bacterial elimination of Staphylococcus aureus and Escherichia coli reached up to 99.5 and 98.3%, respectively. The scaffold design favored cell growth and proliferation and resulted in the significant promotion of repair and reconstruction of the urethra, indicating that it can be an ideal antibacterial suture material for soft tissue restoration.

To investigate the synergistic effect of brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF) on cavernous nerve regeneration, two different aligned scaffolds consisting of coaxial electrospun silk fibers were prepared by switching the position of the two factors in either core or shell domain. The order and release rate of the dual factors delivery were relatively different because of the distinct location of two factors in coaxial fibers. An in vitro assay showed that the inner-VEGF/outer-BDNF scaffolds could more obviously accelerate Schwann cells growth, proliferation and spreading owing to the rapid release of BDNF. However, in vivo scaffold implantation demonstrated that the inner-BDNF/outer-VEGF scaffolds significantly facilitated more angiogenesis, and promoted more nerve regeneration based on great benefit of angiogenesis. Results showed that the reasonable dual-delivery order of VEGF and BDNF from scaffolds could enhance synergistic effect of the factors and promote cavernous nerve regeneration.