Organic salt composition of pressure sensitive adhesives produced by spiders

Abstract

Natural glues offer great potential as bio-inspired solutions to problems associated with the performance of synthetic adhesives. Spider viscous glues are elastic pressure sensitive adhesives (PSAs) that physically adhere to surfaces on contact across a range of environmental conditions. Extracting useful components from these secretions remains a challenge that can be met by the comparative analyses of functional analogues. Here we used 1H NMR spectroscopy and mass spectrometry to ascertain the organic salt compositions of the PSAs of four different species of Australian spiders belonging to two lineages that independently acquired aqueous gluey secretions: the St Andrew’s cross (Argiope keyserlingi), the redback (Latrodectus hasselti), the false widow (Steatoda grossa), and the daddy long-legs spider (Pholcus phalangiodes). The PSAs from each of these spiders contained similar organic salts, albeit in variable concentrations. The adhesives of the false widow and daddy long-legs spider had mixtures of only a few components, of which betaine predominated, while the PSAs of the other spiders predominantly contained small organic acids such as GABA/GABA-amide, isethionate, and choline salts. Our results suggest that the PSA composition of spiders is likely to be influenced more by environmental factors than evolutionary history and are guided by common principles. Our findings could be valuable for facilitating the design of more sustainable synthetic glues.

Diversification of spider silk properties in an adaptive radiation of Hawaiian orb-weaving spiders

“…While largely speculative, Tetragnatha stelarobusta may present a set of traits for its capture silk that are similar to those of other moth-specialist spiders and not easily recognized by just looking at web architecture. NMR signals being noisy, relative to other studies (e.g., Wolff et al, 2023), limited our ability to identify fine-scale differences and less abundant compounds for Hawaiian Tetragnatha. For starters, the strength of the NMR machine used in this study may have contributed to the low signal-to-noise ratio obtained.…”

“…All experiments were performed on a Varian 300 MHz spectrometer at 298 K. The spectra were recorded with a scan size of ~512, acquisition time of ~3 s, a 900 pulse width of 15-16 µs, and a sweep width of 5 ppm in the 1 H dimension. Although there may be additional peaks beyond the 5-ppm chemical shift (Hu et al, 2007;Wolff et al, 2023), this was beyond the scope of our study due to the limitations of the NMR equipment, leading to lower resolution and sensitivity, and the limited silk material that we could collect from webs. Once the spectra were processed, different peaks were assigned to known LMWCs using data reported in the literature (Anderson and Tillinghast, 1980;Tillinghast and Christenson, 1984;Tillinghast et al, 1987;Townley et al, 1991;Townley and Tillinghast, 2013;Sahni et al, 2014;Jain et al, 2015Jain et al, , 2006Jain et al, , 2012Vollrath et al, 1990) and an unpublished database provided by Townley.…”

From fibres to adhesives: evolution of spider capture threads from web anchors by radical changes in silk gland function

“…At least five single measurements with 10 accumulations each and an acquisition time of 10 s for each accumulation were acquired from different points within the respective materials and averaged. Betaine (trimethylglycine, Sigma) was used as a spectral standard, as it was previously found to be a major compound of the water soluble fraction of pholcid gumfoot glue [ 9 ]. Raman spectra of glues were taken from clear glue regions devoid of embedded fibres.…”

“…The investigation of convergent evolution of viscid silk could shed light on this unresolved problem. While most viscid silk users belong to the large clade of orb-web and cobweb spiders (Araneoidea), it is a poorly known fact that many daddy-longleg spiders (Pholcidae), including the cosmopolitan house spider Pholcus phalangioides , use similar silks [ 9 ]. Prey capture behaviour in P. phalangioides exhibits a number of striking similarities with that of very distantly related cobweb spiders (basal branch of Theridiidae, which includes species such as the black widows, Latrodectus spp.).…”

“…In these families, viscid silk is produced by the aggregate silk glands with spigots on the posterior lateral spinnerets [ 23 ]. The aggregate secretion contains specific silk proteins called aggregate spidroins (AgSp1 and AgSp2) [ 24 , 25 ], carbohydrates [ 26 ] and a high concentration of organic and inorganic salts [ 9 , 27 , 28 ]. This aqueous solution exhibits the characteristics of viscoelastic fluids in the Theridiidae [ 29 ] and of viscoelastic solids in Araneidae [ 30 ], and self-organizes into beads-on-a-string structures after its application onto the silk line.…”