Biomimetics

Frontmatter

Chapter 1. Introduction

Abstract

Biomimetics is derived from the Greek word biomimesis. It means mimicking biology or living nature, or living organisms, and is also called biomimicry. The word biomimetics was coined by polymath Otto Schmitt in 1957, who, in his doctoral research, developed a physical device that mimicked the electrical action of a nerve. Another word often used in Europe and Asia is bionics, coined by Jack Steele of Wright-Patterson Air Force Base in Dayton, Ohio in 1960. Bionics combines two words, biology and technology/electronics. It translates to the creation of products, devices, and processes by using materials and processes found in living nature. Bionics today is referred to as robotics and replacement or enhancement of living matter, tissue, body parts, and organs. An example of bionics would be the “bionic man.” Finally, another word used is biognosis, which is defined as the scientific investigation of life.

Bharat Bhushan

Chapter 2. Roughness-Induced Superliquiphilic/Phobic Surfaces: Wetting States and Lessons from Living Nature

Abstract

A solid surface, or more exactly a solid-gas or solid-liquid interface, has a complex structure and properties dependent upon nature of solids, the method of preparation, and the interaction between the surface and the environment. Physical and chemical properties of surfaces affect their interaction with other surfaces.

Bharat Bhushan

Chapter 3. Modeling of Contact Angle for a Liquid in Contact with a Rough Surface for Various Wetting Regimes

Abstract

The roughness distribution affects contact angle and surface wetting. Three surface wetting regimes are discussed, which include Wenzel, Cassie-Baxter, and Cassie regimes. In the Wenzel regime, a liquid droplet completely wets the rough surface with a homogeneous interface. In the Cassie-Baxter regime, a heterogeneous or composite interface with air pockets trapped between the asperities is formed. In a Cassie regime, a liquid film impregnates some of the cavities in an area surrounding the droplet as well.

Bharat Bhushan

Chapter 4. Plant Leaf Surfaces in Living Nature

Abstract

Nature has evolved species with multifunctional properties by using diversity of the structure and morphology in surfaces. Hierarchical structured surfaces are common in nature (Koch et al. 2008, 2009a; Bhushan 2009). The complexity of hierarchical structures and their functionality in biological organisms surpass all abiotic natural surfaces.

Bharat Bhushan

Chapter 5. Nanofabrication Techniques Used for Superhydrophobic Surfaces

Abstract

Nanofabrication of Lotus-like superhydrophobic surfaces has been an area of active research since the mid-1990s. Various nanofabrication techniques are used for micro- and nanostructure fabrication which include lithography, etching, deformation, and deposition.

Bharat Bhushan

Chapter 6. Strategies for Micropatterned, Nanopatterned, and Hierarchically Structured Lotus-like Surfaces

Abstract

It has been demonstrated experimentally that roughness changes contact angle (CA) in accordance with the Wenzel model or the Cassie-Baxter model, depending upon whether the surface is hydrophilic or hydrophobic (Bhushan and Jung 2011). Yost et al. (1995) found that roughness enhances wetting of a copper surface with Sn–Pb eutectic solder, which has a contact angle of 15°–20° for a smooth surface.

Bharat Bhushan

Chapter 7. Fabrication and Characterization of Mechanically Durable Superhydrophobic Surfaces

Abstract

Superhydrophobic surfaces with low contact angle hysteresis can be used for water-repellency, self-cleaning/low adhesion, drag reduction in fluid flow, energy conservation, and energy conversion.

Bharat Bhushan

Chapter 8. Fabrication and Characterization of Micropatterned Structures Inspired by Salvinia molesta

Abstract

The floating water ferns of genus Salvinia are of interest because of their ability to trap and hold an air film under water for up to several months. Within the floating water ferns of the genus Salvinia, morphologically different kinds of water repellent (superhydrophobic) hairs exist. Dependent on the species, the hair size varies in the order of several hundreds of micrometers, and hairs are visible in the order of several hundreds of micrometers, and hairs are visible with the naked eye, Fig. 8.1a. These multi-cellular hairs on the upper (adaxial) side of the leaves form complex hierarchical surface structures that are able to retain an air layer at the surface, even when leaves were fixed under water for several days. The hairs are eggbeater-shaped with tiny crowns Fig. 8.1b, c. The ability to retain air prevents wetting and submersion.

Bharat Bhushan

Chapter 9. Characterization of Rose Petals and Fabrication and Characterization of Superhydrophobic Surfaces with High and Low Adhesion

Abstract

Unlike the lotus leaf, some rose petals (rosea Rehd), scallions, and garlic exhibit superhydrophobicity with high contact angle hysteresis (CAH). While a water droplet can easily roll off the surface of a lotus leaf, it stays pinned to the surface. The different behavior of wetting between the lotus leaf and the rose petal can be explained by different designs in the surface hierarchical micro—and nanostructure. The rose petal’s microstructure, and possibly nanostructure, has a larger pitch value and lower height than the lotus leaf. Therefore, the liquid is allowed to impregnate between the microstructure and partially penetrates into the nanostructure, which increases the wetted surface area. As a result, contact angle hysteresis increases with increasing wetted surface area. In the case of scallion and garlic leaves, contact angle hysteresis is high due to hydrophobic defects responsible for contact line pinning. Such superhydrophobic surfaces with high adhesion have various potential applications, such as the transport of liquid microdroplets over a surface without sliding or rolling, the analysis of very small volumes of liquid samples, and for the inside of an aircraft surface to minimize the falling of condensed water droplets onto passengers. There have been few attempts to fabricate such surfaces in the laboratory.

Bharat Bhushan

Chapter 10. Strategies for Superliquiphobic/Philic Surfaces

Abstract

Liquid repellent surfaces can be used for self-cleaning and antifouling from organic and biological contaminants both in air and underwater applications and can reduce fluid drag (Bhushan 2009). As a model surface in living nature for a liquid repellent surface in air, the upper side of the lotus leaf surface repels water (superhydrophobic) and is useful for self-cleaning and low adhesion applications (Barthlott and Neinhuis 1997; Bhushan and Jung 2011). As discussed in Chap. 4, the superhydrophobic properties of the leaf surfaces are achieved due to the presence of a hierarchical structure created by a microstructure formed by papillose epidermal cells covered with three dimensional (3-D) epicuticular hydrophobic wax nanotubules, shown in Fig. 10.1a. The wax layer makes the surface hydrophobic and the hierarchical structure makes the surface superhydrophobic. This structure causes water droplets to roll off the leaf surface and take contaminants with them to keep the leaf clean. The lower side of the lotus leaf does not contain 3-D wax crystals (Neinhuis and Barthlott 1997), and consists of rather flat, tabular, and slightly convex papillae (Koch et al. 2009). Therefore, the bottom surface is hydrophilic, but superoleophobic in water, with a contact angle of 155° with n-hexane oil, Fig. 10.1b (Cheng et al. 2011). The lotus leaf exhibits a so-called “Janus interface” (named for the two-faced Roman god), with superhydrophobicity on the upper side, and superoleophobicity under water on the lower side (Cheng et al. 2011).

Bharat Bhushan

Chapter 11. Adaptable Fabrication Techniques for Mechanically Durable Superliquiphobic/philic Surfaces

Abstract

Superliquiphobic and superliquiphilic surfaces have attracted interest within the scientific community and industry for various applications such as self-cleaning, anti-icing, anti-fogging, anti-fouling, finger print resistance, and drag reduction. The surfaces should be wear resistant. For some applications, such as oil-water separation, surfaces with a combination of water and oil repellency and affinity are required.

Bharat Bhushan

Chapter 12. Fabrication and Characterization of Mechanically Durable Superliquiphobic Surfaces

Abstract

Superliquiphobic surfaces are of interest for liquid repellent, self-cleaning, anti-icing, anti-smudge, and antifouling applications. The surfaces should be mechanically durable for commercial applications.

Bharat Bhushan

Chapter 13. Shark Skin Surface for Fluid-Drag Reduction in Turbulent Flow

Abstract

Nature has created ways of reducing drag in fluid flow, evident in the efficient movement of fish, dolphins, and sharks. The mucus secreted by fish reduces drag as they move through water, protects the fish from abrasion by making the fish slide across objects rather than scrape, and prevents disease by making the surface of the fish difficult for microscopic organisms to adhere to, minimizing biofouling (Shephard in Rev Fish Biol Fish 4:401–429, 1994). Applications of drag reducing polymers has been long known.

Bharat Bhushan

Chapter 14. Skimmer Bird Beak (Rynchops) Surface for Fluid Drag Reduction in Turbulent Flow

Abstract

Nature has evolved many aquatic species with low drag surfaces, which include fish, dolphins, and sharks. Low drag surfaces are of interest in both internal and external fluid flow applications. The skin of fast-swimming sharks is a design inspiration for low-drag surfaces (Bhushan 2009; Dean and Bhushan 2010; Bixler and Bhushan 2013a, b). Sharks are able to move quickly through turbulent water flow due to the surface features on their scales. These scales called dermal denticles have riblets, which are microscopic grooves aligned parallel to fluid flow. Adequately-sized riblets lift streamwise vortices that are responsible for large shear stresses and drag. Streamwise vortices are approximately cylindrical vortices rotating along an axis in the streamwise direction. By lifting these vortices from a surface, shear stresses are decreased, resulting in low drag (Martin and Bhushan 2014, 2016a, b).

Bharat Bhushan

Chapter 15. Rice Leaf and Butterfly Wing Effect

Abstract

Fluid drag reduction and antifouling are of commercial interest (Bhushan and Jung 2011; Bixler and Bhushan 2012a, 2015). Many flora and fauna flourish in living nature due to their low drag and antifouling properties, with commonly studied examples including shark skin and lotus leaves. Inspired by shark skin and lotus leaves, Bixler and Bhushan (2012b) found that rice leaves and butterfly wings combine the shark skin and lotus effects. Sinusoidal grooves in rice leaves and aligned shingle-like scales in butterfly wings provide the anisotropic flow. Hierarchical structures consisting of micropapillae superimposed by waxy nanobumps in rice leaves and microgrooves on top of shingle like scales in butterfly wings provide superhydrophobicity and low adhesion. Various studies suggest that this combination of anisotropic flow, superhydrophobicity, and low adhesion leads to improved drag reduction, self-cleaning, and antifouling (Bixler and Bhushan 2012b, 2013a, d, 2014; Bixler et al. 2014). Bixler and Bhushan (2015) provide a review and details follow.

Bharat Bhushan

Chapter 16. Bio- and Inorganic Fouling

Abstract

Fouling is generally undesirable for most applications (Bhushan 2016, 2017). Fouling includes biological fouling (commonly referred to as biofouling) and inorganic fouling. Biofouling is the accumulation of unwanted biological matter on surfaces, with biofilms created by microorganisms, and macroscale biofouling (simply called macrofouling) created by macroorganisms.

Bharat Bhushan

Chapter 17. Bioinspired Strategies for Water Collection and Water Purification

Abstract

Fresh water sustains human life and is vital for human health. There is enough fresh water for everyone on Earth. However, due to bad economics or poor infrastructure, water scarcity affects more than 40% of the global population and is projected to rise. It is estimated that more than 800 million people do not have access to clean water and over 1.7 billion people are currently living in river basins where water use exceeds recharge.

Bharat Bhushan

Chapter 18. Role of Liquid Repellency on Fluid Slip, Fluid Drag, and Formation of Nanobubbles

Abstract

The reduction of fluid drag is of scientific interest in many fluid flow applications, including micro/nanofluidic systems used in biological, chemical, and medical fields (Bhushan 2016, 2017a, b). Fluid flow is known to have zero slip on liquiphilic surfaces. In the no-slip boundary condition, the relative velocity between a solid wall and liquid flow is zero at the solid-liquid interface (Batchelor 1970).

Bharat Bhushan

Chapter 19. Gecko Adhesion

Abstract

The leg attachment pads of several animals are capable of attaching to and detaching from a variety of surfaces and are used for locomotion, even on vertical walls or across the ceiling (Gorb 2001; Bhushan 2007). These include many insects, spiders, and lizards. Biological evolution has led to the optimization of their leg attachment systems. This dynamic attachment ability is referred to as reversible adhesion or smart adhesion (Bhushan et al. 2006). Many insects (e.g., beetles and flies) and spiders have been the subject of investigative interest. However, the attachment pads of geckos have been the most widely studied because they have the highest body mass and exhibit the most versatile and effective adhesive known in nature. Therefore, this chapter will be concerned primarily with gecko adhesion.

Bharat Bhushan

Chapter 20. Insects Locomotion, Piercing, Sucking and Stinging Mechanisms

Abstract

Some 10 million different species of animals and plants are known to exist on earth. Of which, arthropods make up the largest category with roughly 5 million species. The word, arthropods, is derived from two Greek words: arthron (joint) + podos (foot), meaning jointed-feet. These are spineless animals with segmented bodies, paired and jointed legs, exoskeletons, and bilateral symmetry. Arthropods, being one of the major class of animals, create medical problems. They attack other organisms, cause allergic reactions, release toxins and venoms, and may even cause death.

Bharat Bhushan

Chapter 21. Structure and Mechanical Properties of Nacre

Abstract

Many biological organisms exhibit unique chemical and physical properties (Lowenstam and Werner 1989). They often use components that contain both inorganic and organic compounds with complex structures, and are often hierarchically organized, ranging from nano- to meso-levels. The hierarchical structure provides a high tolerance against defects at all length scales. Most biological materials are multifunctional and often tend to have self-healing abilities (Vincent 1991; Ratner and Bryant 2004). In two-component biological materials, such as bones, teeth, and abalone shells, the mineral component provides high mechanical strength and the organic component hinders crack propagation, which increases fracture toughness responsible for high durability (Meyers et al. 2006). A biomineral system, which has been much investigated, is the inner layer of abalone, called nacre.

Bharat Bhushan

Chapter 22. Structural Coloration

Abstract

In living nature, flora and fauna produce color through pigments, bioluminescence, or structural coloration. Biological pigments, or simply pigments, are substances produced by living organisms, which produce color resulting from selective light adsorption and reflection of a specific light wavelength. These include plant and flower pigments, such as green pigment chlorophyll used by plants for photosynthesis. Many biological structures contain pigments such as melanin in skin, eyes, fur, and hair. Bioluminescence is the production and emission of visible light by a living organism. It occurs widely in marine organisms, as well as in some fungi, bacteria, and terrestrial invertebrates, such as fireflies. Structural coloration is the production of color by selective light reflection by nanostructured surfaces with features of the same scale as incident visible light wavelengths. While pigments degrade and their colors fade over time, structural coloration can persist for long periods, even after the death of the organism.

Bharat Bhushan

Chapter 23. Self-healing Materials and Defense Mechanisms

Abstract

In living nature, an organism uses healing and defense mechanisms to survive. Healing can occur through repair or regeneration of damaged tissue, noting that to regenerate is to repair 100% of the damage. The ability to heal is intrinsic to all multicellular organisms (Holliman 1995; Firestein et al. 2012; Cremaldi and Bhushan 2018). Living nature may use defense mechanisms for avoidance of predators. As an example, organisms change to blend in with their immediate surrounding.

Bharat Bhushan

Chapter 24. Outlook

Abstract

Biomimetics, or more accurately, biological inspiration or bioinspiration, allows engineers and scientists to develop materials and devices of commercial interest by taking inspiration from nature. Functionality of biological materials and surfaces result from a complex interplay between surface morphology and physical and chemical properties. In nature, hierarchical structures with dimensions of features ranging from the macroscale to the nanoscale are extremely common and provide properties of interest.

Bharat Bhushan

Backmatter