Dharamdeep Jain

Ubiquitous distribution of salts and proteins in spider glue enhances spider silk adhesion

Modern orb-weaving spiders use micron-sized glue droplets on their viscid silk to retain prey in webs. A combination of low molecular weight salts and proteins makes the glue viscoelastic and humidity responsive in a way not easily achieved by synthetic adhesives. Optically, the glue droplet shows a heterogeneous structure, but the spatial arrangement of its chemical components is poorly understood. Here, we use optical and confocal Raman microscopy to show that salts and proteins are present ubiquitously throughout the droplet. The distribution of adhesive proteins in the peripheral region explains the superior prey capture performance of orb webs as it enables the entire surface area of the glue droplet to act as a site for prey capture. The presence of salts throughout the droplet explains the recent Solid-State NMR results that show salts directly facilitate protein mobility. Understanding the function of individual glue components and the role of the droplets macro-structure can help in designing better synthetic adhesives for humid environments.

Composition and Function of Spider Glues Maintained During the Evolution of Cobwebs.

Capture silks are an interesting class of biological glues that help spiders subdue their prey. Viscid capture silk produced by the orb web spiders is a combination of hygroscopic salts that aid in water uptake and interact with adhesive glycoproteins to make them soft and sticky. The orb was a stepping stone to the evolution of new web types, but little is known about the adhesives in these webs. For instance, cobweb spiders evolved from orb-weaving ancestors and utilize glue in specialized sticky gumfoot threads rather than an elastic spiral. Early investigation suggests that gumfoot adhesives are quite different viscid glues because they lack a visible glycoprotein core, act as viscoelastic fluids rather than solids, and are largely invariant to humidity. Here, we use spectroscopic and staining methods to show that the gumfoot silk produced by Latrodectus hesperus (western black widow) is composed of hygroscopic organic salts and water insoluble glycoproteins, similar to viscid silk, in addition to a low concentration of spider coating peptides reported before. Our adhesion studies reveal that the organic salts play an important role in adhesion, similar to that seen in orb web spiders, but modulating function at much lower humidity. Our work shows more similarities in the viscid silk produced by orb web and cobweb spiders than previously anticipated and provide guidelines for developing synthetic adhesives that can work in dry to humid environments.

Superhydrophobicity of the gecko toe pad: biological optimization versus laboratory maximization

While many gecko-inspired hierarchically structured surfaces perform as well as or better than the natural adhesive system, these designs often fail to function across a variety of contexts. For example, the gecko can adhere to rough, wet and dirty surfaces; however, most synthetic mimics cannot maintain function when faced with a similar situation. The solution to this problem lies in a more thorough investigation of the natural system. Here, we review the adhesive system of the gecko toe pad, as well as the far less-well-studied anti-adhesive system that results from the chemistry and structure of the toe pad (superhydrophobicity). This paradoxical relationship serves as motivation to study functional optimization at the system level. As an example, we experimentally investigate the role of surface lipids in adhesion and anti-adhesion, and find a clear performance trade-off related to shear adhesion in air on a hydrophilic surface. This represents the first direct investigation of the role of surface lipids in gecko adhesion and anti-adhesion, and supports the argument that a system-level approach is necessary to elucidate optimization in biological systems. Without such an approach, bioinspired designs will be limited in functionality and context, especially compared to the natural systems they mimic. This article is part of the themed issue ‘Bioinspired hierarchically structured surfaces for green science’.

Application of NMR in polymer characterization

This chapter addresses how developments of solid-state (ss) NMR have contributed to the understanding of the structure and dynamics of various polymers covering synthetic to supramolecular and natural systems as reported in the past decade. Aspects include the packing, conformation, chain trajectory, chemical reactions, and molecular dynamics of synthetic polymers, energy storage materials, supramolecular polymers, and natural polymers. The complete coverage of all polymer systems is beyond our scope, however, the specific systems described are treated as outstanding examples to demonstrate the recent progress in the field.

Unraveling the Design Principles of Black Widow’s Gumfoot Glue

Prey capture adhesives produced by web-building spiders have intrigued humans for many years and provide important insights to develop adhesives that work in humid environments. These humidity-responsive glues are laid down by spiders in various types of webs, primarily orb webs and cobwebs. The formation and function of viscid glue in the capture spirals of orb webs is well-studied compared to the vertically aligned gumfoot glue strands in cobwebs. While the glue droplets in cobwebs contain some peptides, they act as viscoelastic liquids, rather than viscoelastic solids, and the cause of glue stickiness is poorly understood. However, the recent discovery of glycoproteins and hygroscopic salts in the gumfoot adhesives brings a new perspective to explain the mechanism of adhesion of these microscopic droplets. In this chapter, we summarize the current state of our understanding of the chemical composition, morphology, and mechanism of adhesion of gumfoot glue threads. Additionally, we present molecular evidence that both salts and glycoproteins are important for strong adhesion in a humid environment and show how understanding the mechanism of cobweb spider adhesives will help in designing materials that are active and functional in high humidity.