Because of the variety of materials that make up an insect's body, it is able to adapt to a variety of environments. Evolution has provided these creatures with strong exoskeletons and intricately shaped wings. Academic researchers have worked on materials inspired by these natural innovations to create solutions to a range of problems such as antibiotic resistance and unsustainable packaging.
Borrowing from insects belongs to the field of bionics, which offers an alternative approach to material design that targets structures rather than molecules. As we will see, in the animal kingdom, the way materials are arranged on the micron and nanometer scales is often as important as their specific chemical composition for achieving function - an important insight for sustainable design. The cicada is an insect whose body form opens up new prospects for design.
Antibacterial Cicada
In many countries, the pulsating tones of cicadas are reminiscent of warm summer days. However, the species is not as simple as we hear. Cicada wings are naturally antimicrobial due to the topography of their surfaces, which has inspired the design of self-cleaning materials.
Non-chemical methods of eliminating bacteria may be a means of combating antibiotic resistance. The problem of bacterial resistance to antibiotics is background noise for most people in the developed world, who take for granted the powerful role of modern medicines and cleaning agents in keeping us safe. However, WHO has highlighted this issue as one of the biggest problems facing humanity in the next century.
Numerous factors are accelerating the evolution of superbug strains at an unprecedented rate.In 2019, bacteria that evolved to be unresponsive to antibiotics caused 4.95 million deaths.
One of the main reasons we are facing this problem is the way industrial society has dealt with bacterial infections. The use of harsh chemicals has become the default method - a method that eliminates less active strains, leaving only very robust species to spread without challenge.
Cicada wing design provides a model for a long-term solution to bacterial infections: a self-cleaning surface that removes, rather than kills, microorganisms. Insect wings are antimicrobial because they are hydrophobic. Tiny vertical struts on the wings catch falling water droplets, which absorb the bacteria and roll them away from the surface. Alternatively, the shapes on the wings use surface tension to create lift: as many droplets merge on the wing, the water bounces off the wing, carrying away bacteria.
Self-cleaning surfaces are in the earliest stages of commercialization, with cicada-inspired iterations still in the lab. The research is being conducted simultaneously at several university departments around the world, including the Department of Chemical Engineering at Imperial College, the Department of Mechanical Science and Engineering at the University of Illinois, and the School of Engineering at the University of Edinburgh.
Everyday exoskeleton
The structure of an insect's body provides clues for optimizing biomaterial properties.Shrilk's single-use, fully degradable bioplastics are a good example.
Shrilk is very strong but lightweight. It is also rapidly biodegradable under composting conditions because of its composition of natural materials: chitosan, a material found in the shells of crustaceans, and a protein from silk.
The material was developed in the 1910s by researchers at Harvard University's Wyss Institute for Bioengineering, which specializes in "bio-inspired technologies".
Deacetylated chitosan-silk composites are inherently quite fragile. However, when arranged into the microstructure of insect exoskeletons, such as in grasshoppers, this material becomes very strong overall.
This points to the fundamental benefit of bionics. Evolution has been experimenting and testing its materials for millions of years, providing researchers with templates for combining a wide range of properties that human creativity has not yet been able to achieve in a single product.
Nanoscale design
The work of the Wyss researchers doesn't stop there. They hope to summarize their findings by creating a "how-to" for others trying to use chitosan to make any alternative to petroleum-based plastics.
Chitosan is an abundant natural material. However, its properties fall short of the desired range needed for the target application. One way to edit its properties is to add other materials to create composites with new properties. Another way is to change the basic structure of the material The researchers behind Shrilk have taken this route.
Wyss researchers have created a way to turn chitosan polymers into a whole range of slightly different materials through structural adjustments. Changing the micron- and nanoscale arrangements in the polymers produced new features such as color, mechanical properties and wettability.
There are no mutants.
Bionics offers an elegant solution to a common complaint about some 100% bio-based materials in some applications: they still don't perform as well as oil-based plastics and chemicals.
Bionics focuses on altering the structure of biomaterials to fine-tune their properties, as opposed to altering biomolecules to make them chemically similar to the synthetic equivalents they are meant to replace.
This could become a highly functional material. However, molecular changes will undermine its sustainability benefits. Often, when a biobased material resembles a synthetic material at the molecular level, it no longer behaves like a natural material during the processing or reuse phase. Such mutated molecules do not readily biodegrade or require specialized plants to break down their components.
Changing the structure rather than the molecules is important for achieving both functions and sustainable materials. If molecules found in nature can be preserved but their function can be enhanced by structural arrangements, they can be fully absorbed by ecosystems at the end of their lives, thus preventing them from becoming toxic landfill waste.
In developing Shrilk, the researchers at the Wyss Institute were guided by one principle: "Do not change the molecule."
Space will be the ultimate testing ground for this design philosophy. Researchers at the University of Wisconsin believe that their low-energy manufacturing method - bio-inspired structural changes to chitin materials - will become important in the "later stages" of a Mars mission. Humanity will then turn to biotechnology and biomanufacturing to sustain itself in the long term.
However, the production cost of bionanomaterials is still higher than that of ordinary biomaterials. This is because the manufacturing process involves precise alterations of micro- and nanoscale structures. This requires unique technology that is very different from traditional petroleum plastic production lines, where more obtuse pressure and heat instruments are used to obtain perfectly functional materials. Technically, Shrilk can be used in a variety of applications such as high-volume, low-cost, and disposable bags and films, but the practical use of Shrilk is limited to medical applications, contact lenses, bandages, and tissue-engineered scaffolds, where biocompatibility takes precedence over size and cost.
Considering that lithium bromide must be used to extract the silk material, the material has a relatively high environmental impact. Nonetheless, the project demonstrated that structural alteration is a very effective way to change the properties of a material without creating substances that are resistant to degradation, which opens the way for biomaterials that perform well without damaging the environment at the end of the product's life.
Muscle and Brain
Strength combined with lightness are key attributes of insect exoskeletons. Naturally, the U.S. military expressed interest.
The U.S. Air Force funded researchers at the University of California, Irvine, in March 2024 to investigate the shells of the poisonous iron and Japanese rhinoceros beetles. The team was led by David Kisselus, a professor of materials science and engineering who specializes in bionic materials.
This Iron Beetle looks as intimidating as it sounds, a large beetle with a spotted black shell and large, powerful legs. Despite being 2.5 centimeters long, this beetle can even withstand being run over by a car.
The secret of the Demon Iron Beetle is the way its shell plates are put together. The pieces that make up its exoskeleton lock together like a jigsaw puzzle. In close proximity to vital organs, these pieces are sandwiched together with tiny, intricate teeth. This makes the shell hard and resistant to bending. Near its base, the upper and lower parts of the exoskeleton arms are more flexible, allowing the beetle to absorb any impact.
Researchers at the University of California, Irvine are analyzing the shells of these large insects. They hope to learn how the material protects the insects' internal organs from both powerful impacts and the hot and cold effects of the desert environment. Based on this, they will work on high-performance materials that can be used in defense, aerospace and other applications.
The insect is more than just a tough-looking model organism. Its brain structure has sparked excitement in the artificial intelligence research community, and a spinoff of Opteran Technologies is using insect intelligence to inspire alternative ways of building smaller, smarter robots.
Optran's main insight is that bees, which have fewer neurons than mammals, can achieve complex behaviors. The company believes that studying the brains of bees could allow them to build autonomous machines that are more memory efficient and less expensive.
