Silk nanofibril self‐assembly versus electrospinning

Abstract

Natural silk fibers represent one of the most advanced blueprints for (bio)polymer scientists, displaying highly optimized mechanical properties due to their hierarchical structures. Biotechnological production of silk proteins and implementation of advanced processing methods enabled harnessing the potential of these biopolymer not just based on the mechanical properties. In addition to fibers, diverse morphologies can be produced, such as nonwoven meshes, films, hydrogels, foams, capsules and particles. Among them, nanoscale fibrils and fibers are particularly interesting concerning medical and technical applications due to their biocompatibility, environmental and mechanical robustness as well as high surface-to-volume ratio. Therefore, we introduce here self-assembly of silk proteins into hierarchically organized structures such as supramolecular nanofibrils and fabricated materials based thereon. As an alternative to self-assembly, we also present electrospinning a technique to produce nanofibers and nanofibrous mats. Accordingly, we introduce a broad range of silk-based dopes, used in self-assembly and electrospinning: natural silk proteins originating from natural spinning glands, natural silk protein solutions reconstituted from fibers, engineered recombinant silk proteins designed from natural blueprints, genetic fusions of recombinant silk proteins with other structural or functional peptides and moieties, as well as hybrids of recombinant silk proteins chemically conjugated with nonproteinaceous biotic or abiotic molecules. We highlight the advantages but also point out drawbacks of each particular production route. The scope includes studies of the natural self-assembly mechanism during natural silk spinning, production of silk fibrils as new nanostructured non-native scaffolds allowing dynamic morphological switches, as well as studying potential applications. This article is categorized under: Biology-Inspired Nanomaterials > Peptide-Based Structures Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Biology-Inspired Nanomaterials > Protein and Virus-Based Structures.

Silk fibroin nanofibers: a promising ink additive for extrusion three-dimensional bioprinting

“…For clinical use, removal of sericin from silk by degumming is essential because sericin has traditionally been linked to the inflammatory response reported for virgin silk [ 20 , 21 ]. SFNFs have often been prepared based on the electrospinning of silk fibroin solutions obtained by dissolution through the decomposition of the β-sheet structure of silk fibroin that contributes to the mechanical robustness of native silk fibers [ [22] , [23] , [24] ]. However, obtaining SFNFs by mechanical disintegration of degummed silk fibers is simpler and less energy- and time-consuming than preparation of SFNFs by electrospinning [ 25 ].…”

Fibrous Scaffolds From Elastin-Based Materials

“…The presence of silk-like domains confers the engineered SELR with the ability to self-assemble into fibrillary structures via H-bonded nanocrystalline β-sheet structures (Sun and Marelli, 2020). As such, fibrillary morphogenesis, which is not a prevailing feature of the ELRs (Misbah et al, 2015) but has been successfully imitated by the use of electrospinning techniques (Humenik et al, 2018), can be genetically encoded into the SELR constructs, thus conferring the inherent ability to form fibers comprising bundles of fibrils (Tarakanova and Buehler, 2012). In addition, molecular modeling has demonstrated that the thermoresponsive behavior of the elastin-like sequences is preserved in the SELR and favors the silk β-sheet assembly process (Tarakanova et al, 2017).…”

Self‐Assembly in Protein‐Based Bionanomaterials

“…Apart from the assemblies discussed above, many natural fibrous proteins with remarkable chemical, optical, mechan-ical, electrical and electromagnetic properties have been studied. Elastins, [98][99][100] collagens, [101][102][103] (Figure 7A, B) silks, [49,[104][105][106] keratins, [107][108][109] resilins, [110] and amyloid peptides and proteins [111][112][113][114] (Figure 7C) are the most common structural proteins having a set of convenient properties considered for protein-based bionanomaterial synthesis not only at 1D, but also in highly ordered scales. [16,[115][116][117] These families of proteins are characterized by long-range ordered molecular secondary structures (e. g., β-pleated sheets, coiled coils, or triple helices) that arise from the highly repetitive primary amino acid sequences within the proteins.…”

“…Apart from the assemblies discussed above, many natural fibrous proteins with remarkable chemical, optical, mechanical, electrical and electromagnetic properties have been studied. Elastins, [98–100] collagens, [101–103] (Figure 7A, B) silks, [49,104–106] keratins, [107–109] resilins, [110] and amyloid peptides and proteins [111–114] (Figure 7C) are the most common structural proteins having a set of convenient properties considered for protein‐based bionanomaterial synthesis not only at 1D, but also in highly ordered scales [16,115–117] …”