The physical properties of the stick insect pad secretion are independent of body size.

Many insects use adhesive organs to climb. The ability to cling to surfaces is advantageous but is increasingly challenged as animals grow, due to the associated reduction in surface-to-volume ratio. Previous work has demonstrated that some climbing animals overcome this scaling problem by systematically altering the maximum force per area that their adhesive pads can sustain; their adhesive organs become more efficient as they grow, an observation which is also of substantial relevance for the design of bioinspired adhesives. What is the origin of this change in efficiency? In insects, adhesive contact is mediated by a thin film of a liquid, thought to increase adhesive performance via capillary and viscous forces. Here, we use interference reflection microscopy and dewetting experiments to measure the contact angle and dewetting speed of the secretion of pre-tarsal adhesive pads of Indian stick insects, varying in mass by over two orders of magnitude. Neither contact angle nor dewetting speed change significantly with body mass, suggesting that the key physical properties of the pad secretion-its surface tension and viscosity-are size-invariant. Thus, the observed change in pad efficiency is unlikely to arise from systematic changes of the physical properties of the pad secretion; the functional role of the secretion remains unclear.

Fabrication of Amyloid Curli Fibers-Alginate Nanocomposite Hydrogels with Enhanced Stiffness.

Alginate hydrogels are biocompatible, biodegradable, low-cost, and widely used as bioinks, cell encapsulates, three-dimensional culture matrices, drug delivery systems, and scaffolds for tissue engineering. Nevertheless, their limited stiffness hinders their use for certain biomedical applications. Many research groups have tried to address this problem by reinforcing alginate hydrogels with graphene, carbon nanotubes, or silver nanoparticles. However, these materials present nanotoxicity issues, limiting their use for biomedical applications. Other studies show that electrospinning or wet spinning can be used to fabricate biocompatible, micro- and nanofibers to reinforce hydrogels. As a relatively simple and cheap alternative, in this study we used bioengineered bacteria to fabricate amyloid curli fibers to enhance the stiffness of alginate hydrogels. We have fabricated for the first time bioengineered amyloid curli fibers-hydrogel composites and characterized them by a combination of (i) atomic force microscopy (AFM) to measure the Young's modulus of the bioengineered amyloid curli fibers and study their topography, (ii) nanoindentation to measure the Young's modulus of the amyloid curli fibers-alginate nanocomposite hydrogels, and (iii) Fourier-transform infrared spectroscopy (FTIR) to analyze their composition. The fabricated nanocomposites resulted in a highly improved Young's modulus (up to 4-fold) and showed very similar physical and chemical properties, opening the window for their use in applications where the properties alginate hydrogels are convenient but do not match the stiffness needed.

On the use of nanomechanical atomic force microscopy to characterise oil-exposed surfaces.

Oil-exposed surfaces are susceptible to carbonaceous deposits (CDs). In turn, deposits are responsible for fouling, compromising performance and reducing profitability across the hydrocarbon value chain. An understanding of the deposition behaviour of these organic molecules is therefore imperative. In this paper we address the question of understanding the deposition in upstream operation, where the CDs are known to be asphaltenes, the heaviest fraction of oil. Systematic characterisation of fouled oil-exposed surfaces constitutes an initial step towards that direction and it is a challenging task in itself. We demonstrate the use of Atomic Force Microscopy (AFM) to map surface mechanical properties and how they can be used to determine differences between deposit types. We also demonstrate that the use of an adhesion inhibitor (AI) has a dramatic effect not only on the morphology but also on the mechanical properties of asphaltene deposits.