Insects are adapted to all kinds of environments thanks to the diverse materials which make up their bodies.
Evolution has furnished these creatures with strong exoskeletons and intricately-shaped wings. Researchers are building materials inspired by these natural innovations to solve a wide set of problems like antibiotic resistance and unsustainable packaging.
Borrowing from insects falls under the field of biomimicry, which offers an alternative approach to material design that targets structure rather than molecules.
As we will see, the way materials are arranged on a micro- and nano-scale is often just as important in the animal kingdom as their particular chemical makeup in achieving functionality – an important insight for sustainable design.
One insect species opening new vistas in design with its bodily morphology is the cicada.
Anti-bacterial cicada wings
In many countries, the pulsing pitch of cicada songs evokes balmy summer days. Yet there is more to the species than meets the ear. Cicada wings are naturally antimicrobial thanks to the topography of their surfaces, offering inspiration for the design of self-cleaning materials.
Chemical-free methods of removing bacteria could be a tool in the fight against antibiotic resistance. The problem of bacterial resistance to antibiotics is background noise for most of us in the developed world who take for granted the powerful effect of modern medicines and detergents in keeping us safe. However, the WHO has highlighted the issue as one of the biggest problems facing humanity over the coming century.
Numerous factors are accelerating the evolution of super-strength bacterial strains like never before. Bacteria that had evolved to become unresponsive to antimicrobials contributed to 4.95 million deaths in 2019.
A major reason we face this is the way industrial society has approached the problem of bacterial infections. The use of harsh chemicals has become the default- a method that eliminates less vigorous strains, leaving only very robust species to spread without challenge.
Cicada wing design offers a model for a longer-term solution to bacterial infection: self-cleaning surfaces that remove rather than kill microbes. The insect’s wings are antimicrobial because it is hydrophobic (water-repellent). Microscopic vertical pillars on the wing catch falling water droplets that absorb the bacteria and roll them off the surface. Alternatively, the shapes on the wings create a lifting force using surface tension: when many droplets merge on the wing, the water springs off the wing, taking the bacteria with it.
Self-cleaning surfaces are in the earliest stages of commercialisation and the cicada-inspired iterations are still in the laboratory stage. The research has been going on simultaneously in several university departments around the world including Imperial’s Department of Chemical Engineering, University of Illinois’ department of mechanical science and engineering, and the University of Edinburgh’s School of Engineering.
Everyday exoskeletons
The structure of insect bodies holds clues to optimising biomaterials performance. Shrilk, a fully degradable bioplastic for single-use applications, is a good example of this.
Shrilk is extremely strong yet lightweight. It is also rapidly biodegradable in composting conditions as its constituents are natural materials: chitosan, a material found in crustacean shells, and a protein from silk.
The material was developed in the 2010s by researchers at the Wyss Institute for Biologically Engineering at Harvard University, which specialises in ‘bioinspired technologies’.
On their own, a chitosan-silk composite would be rather weak. However, when arranged into the microarchitecture of insect exoskeletons such as in grasshoppers, the material becomes very robust overall.
This points out the foundational benefit of biomimicry. Evolution has tried and tested its materials over many millions of years, giving researchers templates that combine multiple properties that human ingenuity had not yet managed to bring together in a single product.
Nanoscale design
The Wyss researchers’ work didn’t stop there. They wanted to generalise their findings by creating a sort of ‘how to’ for others trying to create any oil plastic substitutes using chitosan.
Chitosan is an abundant natural material. Yet its properties fall just short of the desirable range needed to be useful in target applications. One way to edit its properties is to add other materials in to create a composite with new properties. Another is to alter the material’s fundamental structure – a route that the researchers behind Shrilk have taken.
Wyss researchers created a methodology for turning chitosan polymers into a whole palette of slightly different materials using structural adjustments. Changing the way the micro and nanoscale arrangements sat in the polymers produced new colours, mechanical properties, and functionalities like wettability.
No mutant molecules
Biomimicry offers elegant solutions to a common complaint about some 100% biobased materials in certain applications: that they still don’t perform on par with oil based plastics and chemicals.
Biomimicry focuses on altering the structure of biological materials to finetune its properties, in contrast to approaches that alter biological molecules to make them chemically resemble the synthetic equivalents that they are meant to replace.
This might make for a highly functional material. Yet the molecular changes will diminish its sustainability gains. Often, when a biobased material resembles a synthetic one at a molecular scale, it stops behaving like a natural material at the stages of disposal or reuse. The mutant molecule will not biodegrade as easily or will need specialised plants to break down into its constituent parts.
Altering structures rather than molecules is important to achieving both functional and sustainable materials. If the molecules found in nature can be preserved but functionality enhanced using structural arrangements, the molecules can be absorbed completely by the ecosystem at the end of its life, preventing it from becoming toxic landfill waste.
In developing Shrilk, the Wyss Institute Researchers respected a single principle: “no modification of the molecule”.
Space would be the ultimate testing ground for this design philosophy. The Wyss researchers argued that their low-energy manufacturing method – bio-inspired structural alterations of chitin materials – will become important in ‘later stages’ of Mars missions where humans turn to biotech and biomanufacturing to sustain themselves long-term.
Niche products
Biomimicry materials, however, remain even costlier to produce than ordinary biomaterials. This is because the manufacturing process involves the precise alteration of structure at the microscopic and nanoscales. This demands unique technology distant from those in legacy production lines for oil plastics, where the blunter instruments of pressure and heat are used to achieve materials with perfect functionality. Shrilk could technically be used in high volume, low cost and every application like disposable bags and films but the real-world uses of Shrilk have been limited to medical applications, contact lenses, bandages, and tissue engineering scaffolds where biocompatibility takes priority over scale and cost.
The environmental impact of the material is relatively high given that lithium bromide has to be used to extract the silk material. Nonetheless, the project demonstrated that structural alterations are a highly effective way of altering material properties without creating substances resistant to degradation, opening the way for biomaterials that both perform well and are not environmentally damaging at the end of its product life.
The brawn and the brain
Strength combined with lightness is a key attribute of insect exoskeletons. Naturally, the US military has expressed an interest.
The US Air Force funded UC Irvine researchers in March 2024 to investigate the outer shell of the diabolical ironclad beetles and the Japanese rhinoceros beetle. The group is led by David Kisailus, professor of materials science and engineering who specialises in biomimetic materials.
The diabolical ironclad beetle looks as intimidating as it sounds, a large beetle with a black outer shell mottled with bumps, and large, powerful legs. Despite being 2.5 cm long, the beetle can even withstand being run over by a car.
The secret of the diabolical ironclad beetle is the way the plates of its shell fit together. The sections that make up its exoskeleton lock together in the same way as jigsaw pieces. Towards its vital organs, these pieces clamp together with small, intricate, teeth. This makes the shell stiff and resistant to bending. Near its bottom, the top and bottom halves of the exoskeleton arm are more flexible, allowing the beetle to absorb any impact.
The UC Irvine researchers are on a mission to analyse the outer shells of these powerhouse insects. They hope to learn how the material simultaneously protects the insects’ innards from high force impact as well as the cold and heat of desert environments. Based on this, they will work out high-performance materials useful in national defence, aerospace, and other applications.
Insects are not just a model organism for its tough exteriors. Its brain structure is sparking excitement in the AI research community, with Opteran Technologies a spinout that is using insect intelligence to inspire alternative ways to build smaller, more intelligent robots.
Opteran’s primary insight is that a honeybee, which has fewer neurons than mammals, can achieve complex behaviours. The company believes that studying bee brains could allow them to build more memory-efficient, lower-cost autonomous machines.
