Tuning orb spider glycoprotein glue performance to habitat humidity

Abstract

Orb-weaving spiders use adhesive threads to delay the escape of insects from their webs until the spiders can locate and subdue the insects. These viscous threads are spun as paired flagelliform axial fibers coated by a cylinder of solution derived from the aggregate glands. As low molecular mass compounds (LMMCs) in the aggregate solution attract atmospheric moisture, the enlarging cylinder becomes unstable and divides into droplets. Within each droplet an adhesive glycoprotein core condenses. The plasticity and axial line extensibility of the glycoproteins are maintained by hygroscopic LMMCs. These compounds cause droplet volume to track changes in humidity and glycoprotein viscosity to vary approximately 1000-fold over the course of a day. Natural selection has tuned the performance of glycoprotein cores to the humidity of a species' foraging environment by altering the composition of its LMMCs. Thus, species from low-humidity habits have more hygroscopic threads than those from humid forests. However, at their respective foraging humidities, these species' glycoproteins have remarkably similar viscosities, ensuring optimal droplet adhesion by balancing glycoprotein adhesion and cohesion. Optimal viscosity is also essential for integrating the adhesion force of multiple droplets. As force is transferred to a thread's support line, extending droplets draw it into a parabolic configuration, implementing a suspension bridge mechanism that sums the adhesive force generated over the thread span. Thus, viscous capture threads extend an orb spider's phenotype as a highly integrated complex of large proteins and small molecules that function as a self-assembling, highly tuned, environmentally responsive, adhesive biomaterial. Understanding the synergistic role of chemistry and design in spider adhesives, particularly the ability to stick in wet conditions, provides insight in designing synthetic adhesives for biomedical applications.

1D Stretchable Block Copolymer Yarn‐Based Energy Harvesters via BaTiO3/Polydimethylsiloxane Composite‐Carbon Conductive Ink

“…First, the SIS elastomer is coated on a metal thread as a sacrificial buffer layer for a uniform PDMS coating on the metal thread via the thermal extrusion process, which can roughly allow for the semi‐automatic continuous manufacturing steps (Figure S1, Supporting Information) . Direct PDMS coating of the metal thread causes the formation of nonuniform small droplets over the entire 1D surface, possibly from Plateau–Rayleigh instability (Figure S2a, Supporting Information) . BaTiO 3 NPs are added to the PDMS‐coated SIS layer via dip coating, yielding a layer henceforth referred to as the PDMS/BaTiO 3 NP composite for convenience.…”

“…[28] Direct PDMS coating of the metal thread causes the formation of nonuniform small droplets over the entire 1D surface, possibly from Plateau-Rayleigh instability ( Figure S2a, Supporting Information). [29] BaTiO 3 NPs are added to the PDMS-coated SIS layer via dip coating, yielding a layer henceforth referred to as the PDMS/BaTiO 3 NP composite for convenience. After natural solidification at room temperature, the sacrificial metal thread is easily peeled from the cured PDMS/ BaTiO 3 NP composite because of the inherently poor adhesion between these materials.…”

Linking properties of an orb‐weaving spider's capture thread glycoprotein adhesive and flagelliform fiber components to prey retention time

“…A growing number of studies on the properties and performance of orb‐weaver prey capture thread have revealed details about this natural adhesive system and how it responds to environmental humidity (Figure d), temperature, ultraviolet light, and insect surface texture (Opell Clouse & Andrews, ; Opell, Jain, et al, ; Opell & Schwend, ; Stellwagen, Opell, & Clouse, , ; Stellwagen, Opell, & Short, ). Humidity has a pronounced effect on glue droplet adhesion, and interspecific differences in this response have been attributed to natural selection that optimizes thread performance to the humidity of each species' habitat (Amarpuri, Zhang, et al, ).…”

“…The LMMCs serve several important functions. Along with glycoproteins, they confer hygroscopicity, causing the droplets' size and performance to change over the course of a day as they track environmental humidity (Figure d; Jain et al, ; Opell, Clouse, & Andrews, ; Opell, Jain, et al, ), they maintain glycoprotein structure and solvate glycoprotein, enhancing its surface interaction (Sahni et al, ), and they remove interfacial water from a droplet's contact footprint, enhancing adhesion (Singla, Amarpuri, Dhopatkar, Blackledge, & Dhinojwala, ). Optimal adhesion of an araneoid glue droplet is achieved when the viscosity of the droplet's glycoprotein is low enough to spread on a surface to establish sufficient adhesive contact, but high enough to ensure that the glycoprotein will cohere as it extends, thereby transferring adhesive force to the thread's axial lines (Figure c; Amarpuri, Zhang, Blackledge, & Dhinojwala, ; Amarpuri, Zhang, et al, ).…”

“…Optimal adhesion of an araneoid glue droplet is achieved when the viscosity of the droplet's glycoprotein is low enough to spread on a surface to establish sufficient adhesive contact, but high enough to ensure that the glycoprotein will cohere as it extends, thereby transferring adhesive force to the thread's axial lines (Figure c; Amarpuri, Zhang, Blackledge, & Dhinojwala, ; Amarpuri, Zhang, et al, ). Glycoprotein viscosity is determined primarily by the LMMCs in the droplets aqueous layer (Jain et al, ; Opell, Clouse, & Andrews, ; Opell, Jain, et al, ) and tuned to the humidity of an orb‐weaving species' habitat during a spider's foraging time (Amarpuri, Zhang, et al, ).…”