Melding behavioural ecology and biomaterials research to track the evolution of mechanical super-performance of spider silk composites

Project Information

SuPerSilk

Grant agreement ID: 101040724

DOI

10.3030/101040724

EC signature date 2 February 2022

Start date 1 September 2022

End date 31 August 2027

Funded under

• European Research Council (ERC)

Total cost

€ 1 788 003,00

EU contribution

€ 1 788 003,00

Coordinated by

UNIVERSITAET GREIFSWALD
Germany

Periodic Reporting for period 1 - SuPerSilk (Melding behavioural ecology and biomaterials research to track the evolution of mechanical super-performance of spider silk composites)

Reporting period: 2022-09-01 to 2025-02-28

Summary of the context and overall objectives of the project

Every organism is built of biological materials. While usually based on only a small number of elements, these materials often exhibit a complex fine structure and combinations of properties that are difficult to achieve in human-designed materials. Some biological materials show outstanding properties, enabling their producers to perform special ecological roles and inspiring human technologies that still struggle to design materials with equal performance.
Spiders produce one of the toughest fibre materials known: spider silk. Spider silk overcomes the trade-off between strength and extensibility that is common to homogeneous materials by mixing hard and rubbery structures on the nanoscopic level. In addition, spiders exhibit a variety of silk glands, each of which produce their own silk materials based on specific protein mixes and with unique properties. There are hard and stiff silks, soft and stretchy silks, sticky silks, light-weight single-use silks and durable tough silks. Spiders do not only use these different silks in isolation, but also process them into straight, twisted and looped threads (fibre bundles), fabric- and lattice-like sheets and diverse web architectures. Under tension such processed fibre materials may exhibit unusual behaviours by the mixed effect of base material properties and the specific interaction between fibre elements within the thread or sheet.

In the project SuPerSilk, we study the diversity and function of spider silk fibre materials from both the perspective of evolutionary biology and functional ecology, and material science, to understand why some natural materials exhibit outstanding mechanical properties and to unravel structural principles in super-performing fibre materials that could be used to design robust and lightweight fabrics.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

SuPerSilk is comprised of different work packages that integrate different aspects of the function and diversity of spider silk fibre materials. The different angles are reflected by our interdisciplinary team which is comprised of a comparative zoologist, a behavioural ecologist, a theoretical physicist and a polymer engineer. By jointly applying our diverse expertise and a mix of observational, experimental and theoretical techniques, we are clarifying why some spider silk materials can better resist dynamic or static loads than others – and what we can learn from them.

Because spiders have different types of silk glands, we first aimed to understand in which behavioural contexts each silk is used. As the gland number and ecology differs between different lineages of spiders, we established a comparative assay of silk use throughout different behaviours involved in locomotion, dispersal, web building and feeding. We found that silk use is surprisingly variable and in most situations multiple types of silk glands are active leading to a mixed composite structure of the produced fibre materials. We started to conduct anatomical and behavioural studies to understand how specific silk glands are activated and deactivated during spinning, which we will intensify in the coming year.

The next important goal was to build a catalogue of natural spider silk materials, which will enable us to infer the evolution of silk properties and identify ‘super-materials’ with outstanding mechanical properties. By the time of this interims report, we have conducted several field trips and started to build a large collection of natural spider silk fibre materials (1,800 samples so far). We have already characterised the structure and mechanical properties of fibres and threads from 65 spider species representing different evolutionary lineages across the spider tree of life. This work uncovered a surprisingly high variation of fibre mixture in spider silk lines with corresponding diversity in silk mechanical properties.
During these assays we discovered silk architectures with remarkable properties, and with the help of empirical measurements and theoretical models we inferred structure-function relationships that could be transferred into artificial material designs in the next step. For example, we found a silk material that can be elongated over forty times its original length before breaking, which is grounded in a hierarchical looping (loops-on-loops) structure.
In addition, we have performed a meta-analysis of available literature data, and found that silks with outstanding strength and toughness evolved multiple times independently in spiders – an important prerequisite to infer general structure-function relationships from natural systems. This work has given us a roadmap for bioprospecting and a plan for an enhanced sampling to run more informative models of property evolution and structure-function relationships in spider silk materials – which we will have accomplished within the next years.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

In our ongoing work, we find growing evidence that the behavioural use and evolution of spider silk is more complex than common paradigms in the silk literature suggest. For example, the finding that silk tensile performance, on average, does not differ between web building and non-web building spiders contradicts a common notion in the growing field of silk research and indicates neglected evolutionary pathways towards high performance. Further, our ongoing work revealed that the widely assumed one-gland-one-function principle of spider silk glands does not hold, neither does the common understanding that only orb weavers can control silk flow in their dragline silk gland ducts. These aspects are pivotal for the choice of models and sampling protocols in applied silk research.

We are making exciting discoveries, which were not anticipated during project planning – simply because biodiversity is always good for surprises. Examples are our finding of the most extensible silk material, the fastest silk spring actuation observed in nature, as well as the finding of a ductile silk fibre composite which can be extended at high speed and recover after extreme deformation. Such discoveries arise from our observational work on different spider species and reveal fascinating design principles for fibre composite materials, that will push the limits of properties achievable with artificial fibre composite materials.

Lastly, the experiences we are gathering in the large-scale comparative study for SuPerSilk prompted us to develop software tools to collect, organise and process samples and trait data across specimens of diverse species. We currently explore the wider applicability of this software for both academic and non-academic users, who take measurements on animals and plants.

By integrating the results from our multi-angled studies across diverse spider species and silk products, by the end of the SuPerSilk project we will have generated a deep insight into the causes and consequences of mechanical property variation of biological materials. Were there key events in the evolution of spider silk – the appearance of novel structures, functions or fibre processing behaviours – that pushed the limits of silk mechanical properties? Were such boosts in property evolution correlated with new ecologies, such as the building of aerial webs that gave access to new food sources? Clarifying these questions will help us to better understand the shapes and functions of biodiversity – and inspire new technologies.

Schematic overview about the integrative approach of the SuPerSilk project.