title: Spiders Tune Glue Viscosity to Maximize Adhesion.
abstract: Adhesion in humid conditions is a fundamental challenge to both natural and synthetic adhesives. Yet, glue from most spider species becomes stickier as humidity increases. We find the adhesion of spider glue, from five diverse spider species, maximizes at very different humidities that matches their foraging habitats. By using high-speed imaging and spreading power law, we find that the glue viscosity varies over 5 orders of magnitude with humidity for each species, yet the viscosity at maximal adhesion for each species is nearly identical, 10(5)-10(6) cP. Many natural systems take advantage of viscosity to improve functional response, but spider glue's humidity responsiveness is a novel adaptation that makes the glue stickiest in each species' preferred habitat. This tuning is achieved by a combination of proteins and hygroscopic organic salts that determines water uptake in the glue. We therefore anticipate that manipulation of polymer-salts interaction to control viscosity can provide a simple mechanism to design humidity responsive smart adhesives.
authors.forename: Gaurav
authors.initials: G
authors.lastname: Amarpuri
authors.forename: Ci
authors.initials: C
authors.lastname: Zhang
authors.forename: Candido
authors.initials: C
authors.lastname: Diaz
authors.affiliation: Department of Biological Sciences, Virginia Tech , Blacksburg, Virginia 24061, United States.
authors.forename: Brent D
authors.initials: BD
authors.lastname: Opell
authors.forename: Todd A
authors.initials: TA
authors.lastname: Blackledge
authors.forename: Ali
authors.initials: A
authors.lastname: Dhinojwala
mesh_terms: D000268:Adhesiveness; D000269:Adhesives / Q000737:chemistry*; D000818:Animals; D017753:Ecosystem; D006813:Humidity; D013045:Species Specificity; D013112:Spiders / Q000737:chemistry*; D014783:Viscosity
chemical_list: D000269:Adhesives
keywords: adhesion; aggregate protein; humidity; orb web; spider silk; viscid glue; viscosity