Impact of environmental factors on spider silk properties

Negative stain TEM imaging of native spider silk protein superstructures

Native Latrodectus hesperus (black widow) major ampullate spider silk proteins were imaged using negative stain transmission electron microscopy (NS-TEM) by isolating the silk protein hydrogel directly from the organism and solubilizing in urea. Heterogeneous micelle-like structures averaging 300 nm, similar to those imaged previously with CryoEM, were observed when stained with ammonium molybdate. A second smaller population averaging 50 nm was observed as well as large fibrils, highlighting the heterogeneous nature of the silk gland. The population of smaller silk protein micelles was enhanced at higher urea concentrations (5-8 M). This was further supported by dynamic light scattering (DLS), where two populations were observed at low urea concentrations while one small population dominated at high urea concentrations. The approach presented here provides a cost-effective route to imaging silk protein superstructures with conventional NS-TEM methods and may be applicable to other soft nanoparticle systems.

Spider silk tensile performance does not correlate with web use

Spider silk is amongst the toughest materials produced by living systems, but its tensile performance varies considerably between species. Despite the extensive sampling of the material properties and composition of dragline silk, the understanding of why some silks performs better than others is still limited. Here, I adopted a phylogenetic comparative approach to reanalyze structural and mechanical data from the Silkome database and the literature across 164 species to (a) provide an extended model of silk property evolution, (b) test for correlations between structural and mechanical properties, and (c) to test if silk tensile performance differs between web-building and nonweb-building species. Unlike the common notion that orb-weavers have evolved the best-performing silks, outstanding tensile properties were found both in and outside the araneoid clade. Phylogenetic linear models indicated that the mechanical and structural properties of spider draglines poorly correlate, but silk strength and toughness correlated better with birefringence (an indicator of the material anisotropy) than crystallinity. Furthermore, in contrast to previous ideas, silk tensile performance did not differ between ecological guilds. These findings indicate multiple unknown pathways toward the evolution of spider silk tensile super-performance, calling for better integration of nonorb-weaving spiders in spider silk studies.

Modifying Naturally Occurring, Nonmammalian-Sourced Biopolymers for Biomedical Applications

Natural biopolymers have a rich history, with many uses across the fields of healthcare and medicine, including formulations for wound dressings, surgical implants, tissue culture substrates, and drug delivery vehicles. Yet, synthetic-based materials have been more successful in translation due to precise control and regulation achievable during manufacturing. However, there is a renewed interest in natural biopolymers, which offer a diverse landscape of architecture, sustainable sourcing, functional groups, and properties that synthetic counterparts cannot fully replicate as processing and sourcing of these materials has improved. Proteins and polysaccharides derived from various sources (crustaceans, plants, insects, etc.) are highlighted in this review. We discuss the common types of polysaccharide and protein biopolymers used in healthcare and medicine, highlighting methods and strategies to alter structures and intra- and interchain interactions to engineer specific functions, products, or materials. We focus on biopolymers obtained from natural, nonmammalian sources, including silk fibroins, alginates, chitosans, chitins, mucins, keratins, and resilins, while discussing strategies to improve upon their innate properties and sourcing standardization to expand their clinical uses and relevance. Emphasis will be placed on methods that preserve the structural integrity and native biological functions of the biopolymers and their makers. We will conclude by discussing the untapped potential of new technologies to manipulate native biopolymers while controlling their secondary and tertiary structures, offering a perspective on advancing biopolymer utility in novel applications within biomedical engineering, advanced manufacturing, and tissue engineering.

Biomechanics: Rain yields tougher spider silks

Broad ecological sampling of spider silks from multiple species shows that the biomechanical properties of spider silk reflect the habitat in which their orb webs are built. Silk toughness is highest in habitats with dense rain.