Abstract

Can innovation be managed? Very well explained by Albert Einstein Look deep into nature and you will understand everything

History indicates that humans depend on vision and make efforts to understand rational incidence around them. Think the unthinkable and then bring it to reality. One such application is Biomimetics. These are biologically inspired textiles with concepts derived from nature and reviewed to create wonders in fabrics and apparel.

Smart and intelligent textiles are important developing areas in science due to their major commercial viability and public interests. These materials and/or structures can sense and/or respond to the environmental conditions or stimuli. Nature designed biomaterials have structure–functional capabilities that are beyond the reach of man-made materials like silk, leather and wool. Success in harnessing bio-inspired approaches might create intelligent apparel which can perform sensing and actuation, currently considered as science fiction.

1. Introduction

Biomimetics  – synonymous with ‘biomimesis’, ‘biomimicry’, ‘bionics’, ‘biognosis’, ‘biologically inspired design’  words and phrases that imply adaptation from biology – is a relatively young study embracing the practical use of mechanisms and functions of biological science in engineering, design, chemistry, electronics and so on.

In the early 1940s George de Mestral, a Swiss agricultural engineer, went for a walk in the forest with his dog. Upon his return he noticed that dog’s fur and his trousers were covered in cockleburs (Xanthium). His inventor’s curiosity led him to study them under microscope. He discovered the hooked ends of the bristles that stick out from the seeds. This became the base for ZIP and later developed into a two-sided fastener. One side had stiff hooks like the burs; the other had loops like the fabric of his trousers. Result being Velcro, named from the French word ‘velour’ (velvet) and ‘crochet’ (hook). Next challenge was to make machinery to produce textured fabrics that would work reliably. After considerable experimentation, de Mestral developed special looms and hook- cutting machinery.

  1. Biomimetics and its applications in Textiles

This novel concept implementation ranges from fiber forming to the finishing stages for development of products with specific applications.

Fig: 1 An overview of various objects from nature and their selected function

2.1 Lotus Effect – Design of anti-dust, water repellent fabrics:

Fig 2 Lotus Effect

Ever clean, anti-dust and water repellent properties of glassy lotus (Nelumbo nucifera) leaf arise from its surface micro-topography. The plant’s cuticle is made up of soluble lipids, embedded in a polyester matrix – wax. This Micro topography exhibits extensive folding (i.e. papillose epidermal cells) and epi-cuticular wax crystals jutting out from the plant’s surface results in a rough micro- texture.  As a result, the adhesive force on trapped water droplets in the interstitial spaces of the roughened surface is reduced. Such micro architecture results in a reduced liquid-to-solid contact area, exhibiting super hydrophobicity to water and dust particles (Fig.3). Due to this reduced surface area between water and leaf’s microtopography, the water drops roll off taking the attached dirt particles with them, and cleaning the leaf surface forever.

Modern nano-science and micro fabrication technologies are equipped to design such features artificially and incorporate them into fabrics to give water and dust repellent apparel. Super hydrophobic poly-lactic acid (PLA) fabric is created via UV-photo grafting of silica particles functionalized with vinyl surface group over silica microstructure. The result being a robust method to design water and dust repellent fabrics.

Fig: 3 Nature inspired lotus design into fabrics to mimic water and dust repellent apparel. Micro-topography with specialized wax coated epidermal cells (left) and, conventional design mimicking the anti-lotus effect into smart fabric design.

2.2 Shark skin inspired low hydrodynamic surface drag

Fig: 4 Shark skin feature inspired low hydrodynamic surface drag: high efficiency swimsuits design with antibacterial effect

Shark species (super order Selachimorpha) maintain buoyancy due to special ingenious anti-drag design of their skin that reduces drag by 5–10%. Scanning electron microscope studies have revealed  tooth-like V shaped scales of shark skin – dermal denticles (little skin teeth or riblets) that are ribbed with longitudinal grooves (aligned parallel to the direction of local flow of water).  It produces vertical vortices or spirals of water, keeping the water closer to the shark’s body. This results in low surface drag (Fig. 4). This micro scale longitudinal ridges influence the fluid flow in the transverse direction by limiting the degree of momentum transfer. The ratio of scale height to tip-to-tip spacing plays a critical role in reducing the longitudinal and transverse drags. Another remarkable feature of this micro-topography is antibacterial fouling surfaces.

Scientists are inspired to improve swimming suits design based on this hydrodynamics and antimicrobial principles of shark’s skin. In Olympic swimming competitions, where 1/100th of a second can make the difference between winning and losing the event.

These tight fitting suits mimic the properties of a shark’s skin due to superimposed vertical resin stripes -known as Riblet effect (Fig. 4). Swimsuits made with the new fibers and weaving techniques mimicking shark scales cling tightly to the swimmer’s body. It may give the wearer a 6-m equivalent head start in swimming competition by dampening turbulence in the immediate layer of water, next to the skin.

2.3 Spider silk inspired anti-tear fabric design

Fig: 5 Schematic showing spider silk inspired anti-tear fabric design.

Spider (family Theridiidae) creats web by extruding proteinaceous spider silk from its spinnerets to trap the insects. This natural silk exhibits unique properties of stiffness, strength, extensibility and toughness (Fig. 5). It is due to nano-scale crystalline reinforcement where stiff nanometer-size crystallites are embedded uniquely to adhere strongly in soft, stretchy protein matrices.

Scientists are now able to model materials which have strength and stretch ability similar to spider silk. This synthetic nano-reinforced structure provides an opportunity to synthesize and conjugate polymer in future fabrics which will potentially rival the most advanced materials in nature. Using a new solvent-exchange approach, the hard micro domains of polyurethane elastomer (a polymer that consists of long chains composed of small repeating molecular units) is incorporated with tiny clay discs (about 1 nm, or a billionth of a meter thick and 25 nm in diameter). This interesting aspect can be easily tuned to make fibers similar to stretchy compounds such as nylon or Lycra for traditional textile industry.

2.4 Firefly glow designed e-circuited fabrics

Fig: 6 Learning from firefly glow: designing e-circuited luminescence in fabrics.

Glow Light in fireflies arises on account of an enzyme catalyzed (luciferase) bio-chemical reaction called bio-luminescence. This process occurs in specialized light-emitting organs, usually on a firefly’s lower abdomen (Fig. 6). The enzyme luciferase acts on luciferin, in the presence of magnesium ions (Mg2+), adenosene triphosphate (ATP) and oxygen to produce light. This chemical process provides inciting motivation to design glowing clothes in dark that would add valuable assets to fabrics and textile industry.

It is now possible to produce such light-emitting devices with fabric printed circuit boards (PCBs) at large scale and successfully connect them with wearable display format using socket buttons. Thus enabling the firefly glow in fancy dresses by utilizing electronic textile engineering (e-fabric) design.

2.5 Touch sensitive apparel design

Fig: 7 A scheme showing touch sensitive apparel design inspired by touch-me-not (Mimosa spp) pulvinus features.

Touch sensitive plant Mimosa pudica has leaf-moving muscle – pulvinus similar to actin–myosin of human muscles. Pulvini are swollen part at the base of Mimosa leaf stalks or petioles which act as an autonomous organ, housing mechano- and photoreceptors that enables leaf to move in response to external stimuli resulting in touch sensitive hydraulic actuation. Anatomically, all pulvini comprise thick walled, water-conducting vascular tissue, surrounded by thin walled motor cells. These specialized cells undergo visible swelling and shrinking, actuated by changes in turgor pressure and rapid growth expansion across leaf epidermis involving ion transport (Fig. 7). This exhibits one of the remarkable weathering phenomena in plant tissue when touched and exemplifies the fastest plant movements.

Mimosa pulvinus mediated touch sensitive actuation put forth an enormous opportunity to design fabrics which shrink and de-shrink in response to external stimuli such as touch, sound and/or light. In fashion industry, this would represent a dream opportunity to come true when models walking on ramp will show folding–unfolding modes of smart fabrics with novel sensing capacity. Adopting functional mimesis to the Mimosa leaf pulvinus, researchers have designed haptic fabrics by knitted smart materials with touch therapy features. Such wearable fabrics equipped with actuators and sensors perform artificial massaging and aromatizing functions while walking. Most important, such fabrics could provide a sympathetic side of apparel design by attending, understanding and responding to another person’s emotional expressions, a fundamental requisite of elderly person, spending lone time in hospitals.

2.6 Pine cone inspired hygroscopic movements to design smart breathing fabrics.

Fig. 8 Schematic illustration of pine cone inspired hygroscopic movements to design smart breathing fabrics.

The scales of seed-bearing pine (Pinus radiate) cones move in response to changes in relative humidity. This hygroscopic movement is motivated by a structural–functional mechanism at the base of each seed petal or scale of the pine cone. When dry, it automatically opens up by moving away the scales gap, facilitating release of the cone’s seed. In moist (damp) environment, scales close up (Fig. 8.)

Microscopic anatomy reveals two types of scales growing from the main body of the cone: ovuliferous scale and bract scale. The larger ovuliferous scales bear microscopic sclerenchymatous (cellulose) fibers on upper and lower surface. It responds to changes in relative humidity by opening–closing cone aperture. In addition, orientation of cellulose microfibrils between two layers of scales and their expansion in response to relative humidity further controls the vital bending of the scales, facilitating opening–closing of the cone aperture for seed dispersal.

This natural phenomenon inspired to design humid sensitive adaptive cloth, delivering relief from the discomfort caused by moisture in clothing microclimate as experienced in urban environments. The fabric design utilizes two layers: one of thin spikes of wool, water absorbent material which opens up when gets wet by the wearer’s sweat. When the layer dries out, the spikes automatically close up again. An underneath second layer protects the wearer from the rain and this smart fabric works like breathing cloth, taking dry air in while closing the fabric pores and moist air out while opening. Such fabric could adapt to changing temperatures just like a pinecone’s bract.

2.7 Camouflage

Fig: 9 Animated sketch of Chameleon skin derived material design approach for camouflage apparel (military defense).

The phenomenon of camouflage in certain fishes and amphibian occurs due to excellent iridescent lateral stripes or spots which change their color from blue–violet under low light intensity to green, orange and/or red under increased light intensities. These colors are produced by the constructive interference of light from the stacks of thin alternating transparent layers with different refractive indexes. The fish and Chameleon skin has a specialized layer of cells under their transparent outer skin which are filled with chromatophores or alternating layers of iridophores, guanine crystals. In Chameleon, a layer of dark melanin housed in melanophores is situated in deeper skin layers and contains reflective iridophores, which exhibits phenomenal camouflage (Fig. 9).

These cells are filled with efficiently distributed pigment granules located in cytoplasm. High illumination causes the photoreceptor chromatophores to open up sodium channels and resulting accumulation of hydrated Na+ ion increases the thickness of the cytoplasmic layers. Reverse phenomenon takes place in low light illumination and variation in the wavelength of the reflected light stimulates the pigment cells to rapidly relocate their pigments and color of the skin. It gives them inherent ability to adjust their body color and remain indiscernible from the surrounding environment.

Natures this cryptic phenomenon has inspired scientists to design choleric liquid crystals (CLCs) that alter the visible color of an object to create the thermal and visual camouflage in fabrics. The color of CLCs can be changed with temperature sensitive thermocouples. The heating–cooling ability of thermocouples can be used to adjust the color of the liquid crystals to match the object’s background color, providing camouflage or adaptive concealment as schematically depicted in Fig. 9 or 10??? Check original script for number. Moreover, nature- inspired camouflage in animals has stimulated optical camouflage research in fabric design to develop and impregnate the phased optical array (OPA) like holographic designs in three dimensional hologram of background scenery, on an object to be concealed.

  1. 8 Self healing fabric

Fig: 10 Self healing fabric design inspired by nature’s self-healing mechanism in mammalian tissue.

Self healing ability has inspired new ideas and mechanism which are of fundamental interests for the engineers in designing self healing fabric. Healing process in mammals is much complex and involves hemostasis (arrest of bleeding), inflammation (recruiting immune cells to clear of any microbial population and cell debris), proliferation (growth of new tissue), and remodeling (retaining tissue shape like before injury) Fig. 11. All these events take place spontaneously and autonomously in ordered phases, triggered by injury processes at wound site albeit healing process is time consuming. Moreover, in mammals, the intrinsic mechanism of healing is evolved around the chemical reactions of a series of active enzyme cascades and their inactive precursors, known as clotting factors.

In mimicking bio-inspired self-healing program, a reasonably rapid response is required to restore the degree of structural integrity or prevent crack propagation. In addition, mimicking such enormously complex and lengthy process has limitations due to the lack of replenishment of the engineering components in the system designed for self-healing fabrics.

Nonetheless, nature’s healing machinery has inspired to restore mechanical performance of materials via fusion of the failed surfaces. Using biological bleeding approach to healing, White et al. has created the microcapsules reinforced with hollow fibers, polymer composites. This lightweight material exhibits high stiffness and superior elastic strength over the conventional materials. Microencapsulation of self-healing components involves a monomer, dicyclopentadiene (DCPD), stored in urea–formaldehyde microcapsules dispersed within a polymer matrix. When microcapsules are ruptured by a progressing crack, monomer is drawn along the fissure where it comes in contact with a dispersed particulate catalyst (ruthenium based ‘Grubbs’ catalyst), initiating polymerization and thus repairing the crack. Release of active components has clearly shown the restoration of the lost mechanical properties arising from the macro scale crack within a polymer matrix. Moreover, results confirmed that the process was not detrimental to stiffness of the parent architecture. A notable advantage is the ease with which it can be incorporated into a bulk polymer material which could be a potential self healing reinforcement agent for the future fabrics. In another landmark approach to design smart fabrics, the self healing rubber like material has been designed which acts as molecular glue and seals the lost end when two broken pieces are brought together. This thermo-sensitive polymer material has been made by simple supra molecular chemistry of fatty acids and urea, providing an exciting opportunity to be incorporated into fabrics.

3 Conclusions

After billions of years of evolution, nature developed inventions has led to the introduction of highly effective and power efficient biological mechanisms. Humans have always made efforts to imitate and have increasingly reached levels of advancement where it becomes significantly easier to mimic biological methods, processes, and systems. Advances in science and technology are leading to knowledge and capabilities that are multiplying every year. These improvements lead to capabilities that help understand better and implement nature’s principles in more complex ways. Effectively, we have now significant appreciation of nature’s capabilities allowing us to employ, extract, copy, and adapt its inventions. Benefits from the study of biomimetics can be seen in many applications, including stronger fiber, multifunctional materials, improved drugs, superior robots, and many others.

The rapid growth of research motivation in bio inspired engineering and biomimetics has stimulated huge interest of scientists and researchers to apply it for technological innovations. There has been a spirited past of the engineers, architect and scientist, mimicking nature based design to develop splendor and memorable discoveries in the history of mankind.

4 References

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