Biomimics covers a vast area in the modern research and innovation of products in the textile and apparel arena. In the last article the innovation process from biomimicry and the scopes in the textile industry to develop products imitating bio-systems have been illustrated. This is the next episode of the previous article (published at September 2015 issue) where more detailed product innovations from biomimicry are shown along with the introduction of organizations involved with the biomimic research.
There are lots of areas where products can be imitated from nature in textiles and apparels and extensive research is going on to find out the most natural design of textile prodcuts that has the least ill effect to environment. Following are some of the most impactful innovations in textile products from biomimics.
Breathable Fabrics Inspired by Leaves
One of the most important finding that has been applied to the technical textiles using biomimetic principles is the development of novel breathable fabrics via mimicking the breathing mechanism of the stomatal pores in the leaves. A group of researchers working in the British Defense and Clothing Agency has applied the breathing activity of pores in the leaves to the fabrics in order to provide higher performance to the soldiers who works under extreme conditions.
Physiologically, a leaf opens its stomatal pores when the heat increased in its micro-climate and closes if it needs to avoid heat loss.The
AkzoNobel Company has patented this phenomenon by developing a neoprene based Stomatex biomimetic insulation foam material incorporating convex domes for breathable clothing. These biomimetic domes mimic the leaf breathing mechanism by making a controlled vapor release.
Impact Absorption Function of Wood for Bio-mimetic Designs
It is a little known but very important fact that most bullet-proof vests have been designed by mimicking the structure of wood. The structure of wood is formed from tubular fibers providing wood a high toughness. When a wood cell was broken inward, then it absorbs impact energy and separates itself from other cells surrounding it. Even the broken areas create a crack along the fibers, general wood structure remains without damaging and even if the wood is broken, it has strength to bear a certain extent of force. Woods raw material known as cellulose, possesses a complicated chemical structure. If the chemical bonds or atoms comprising cellulose were different, then wood wouldn’t be so strong and flexible. The structure of the bullet-proof vest is modeled on wood for making it flexible but resilient enough to absorb the energy of a bullet. The clothing is made according to the following principles.
1. Carefully placed fibers to imitate the spiral winding of the tube walls in wood.
2. Resin reinforced with glass fibers.
3. Corrugated layer between flat plates.
4. Layers arranged to imitate the tube structure of wood.
Thermal Insulating Materials
The duck feathers present thermal insulation properties, attributed to “cushions” of air formed within the hierarchical nanostructure. Another model that has attracted the attention of researchers is the penguin feathers. Penguins have to withstand low temperature for 120 days (during the incubation period of the egg), with a thermal gradient of about 80°C, to a layer of feathers that has only 2cm. In addition to thermal insulation, penguin feathers are also waterproof. These properties are due to the special construction of the feathers. Their main shaft, called rachis, is flexible yet very strong. From this shaft rows of overlapping barbs emerge. They form the flag, or the flat side of the feather. Barbs are joined together by means of hundreds of tiny barbules which are provided with hooks (barbicels) and can easily attach to each other like a “zipper.” On the underside, along the rachis, there is a groove. This simple element of feather’s structure brings resistance to the shaft, allowing it to bend and twist without breaking. Under the waterproof layer of feathers there is a thick layer composed of soft feathers, called down. The down is formed of about 47 barbs, with an average length of 24mm. Each barb is coated with about 1,250 barbules, who are about 335cm long. These structures contain air spaces of approximately 50mm in diameter, which create a high insulation surface.
Attempts to mimic this feature in order to obtain innovative textile materials led to the development of a textile system characterized by its variable geometry. Other biomimetic innovations designed on the same principles are GoreTex clothing products, with changing thermal insulation termed as Airvantage Adjustable Insulation.They are based on the existence of an inflatable room between two layers of fabric.
Thermal insulation mechanism of polar bears was also a subject of study for a long time. Polar bear fur is a great insulator, allowing them to survive in the cold arctic. Their fur appears completely black illuminated with UV light, and with an infrared camera polar bears are nearly invisible due to minimal heat loss through the fur.
The hair from which the fur is composed has a tubular form, filled with a foamable material. Initially, it was thought that polar bears hair acts as an optical fibre that captures sunlight and then sends it to the black skin underneath. But further study showed that polar bear hair is a weak waveguide absorbing UV light. Inspired by these functions, Stegmaier et al. have developed a solar thermal collector with high transmission capacity composed of a layered textile material, coated on both sides with a translucent film.
Nature presents unique abilities of manipulating light. Most natural surfaces, in addition to being multifunctional, have also magnificent aesthetic characteristics, producing bright, vivid, and iridescent colours. They are the result of complex photonic structures and are called structural colours. Structural colours are not due to the presence of pigments, but only to interference phenomena, diffraction, and selective reflection of incident light on the complex structure of the photonic material if its components have a periodicity equal to the wavelength of visible light.
Colour is one of the essential characteristics of a textile product and studying structural colours of nature could bring new perspectives of designing textile fibres and materials.
Butterflies present perhaps the greatest diversity of optical microstructures, which led to their intensive study. From these studies, it appears that butterfly wings are covered with two layers of tiny scales, overlapped on a membrane. The average size of the scales is about 200 m long and 50 m wide. Scales are completely transparent, while the wing membrane may contain pigments such as melanin or pterin. These pigments are designed to enhance the colours produced by light reflection on the scales microstructure.
Inspired by scales structure of Morpho butterflies, Kuraray Corp. fibre manufacturer designed a polyester material with low reflectivity, but with intense colour. This material, called Diphorl, was made of rectangular cross section fibres. The fibres are spun from two types of polyester with different thermal properties who are heat-treated after weaving and produce some twists in the yarn (about 80?120?twists/inch). It is assumed that this structure produces alternative alignments on horizontal and vertical directions, causing the multiple reflection and absorption of incident light, thus producing bright colours.
Nature is an extremely vast database of structures and mechanisms that proved to be clearly superior to those man-made. This is why perhaps extensive institutional research is going on in biomimicry and a lot of applications are found effective in the textile arena. Biomimicry is one of the many organizations who are dedicatedly concentrating on unveiling natural systems that can be imitated in the material products for benefit.The purpose of the Biomimicry Institute is to naturalize biomimicry in the culture by promoting the transfer of ideas, designs, and strategies from biology to sustainable human systems design. They envision a world in which people view nature not as a warehouse of goods but as a storehouse of knowledge and inspiration for sustainable solutions.
There are other organizations like ASK-Nature, INVENTIA who are also working to discover natural mechanisms and mimic them to design purposeful solutions.
The Designs described in this article are some of the most important inventions in the textiles and apparel world from biomimicry; there are hundreds of other product designs that are made imitating natural systems and there are thousands of further scopes to design sustainable products from the nature.