introduction to tribology (bhushan/introduction) || green tribology and biomimetics

13Green Tribology and Biomimetics

13.1 Introduction

The ecological or green tribology is a relatively new field. Green tribology is defined asthe science and technology of the tribological aspects which provide ecological balance andminimize environmental and biological impacts (Bartz, 2006; Nosonovsky andBhushan, 2010,2012). Reduction in consumption of energy resources is also an important aspect of greentribology. Energy or environmental sustainability and whatever has an impact upon today’senvironment should be emphasized. Green tribology requires the use of environmentallyfriendly materials, lubricants, and processes. The first scientific volume on green tribologywas published in 2010 in Philosophical Transaction of the Royal Society A (Nosonovsky andBhushan, 2010) and later a book came out in 2012 (Nosonovsky and Bhushan, 2012).Tribological aspects are important in various applications. Since the early 2000s, there has

been significant interest in renewable energy production, such as wind turbines, tidal turbines,or solar panels. Many of these energy production technologies present their unique tribologicalchallenges. Environmentally friendly tribological components, materials and surfaces can befabricated bymimicking nature, a field referred to as biomimetics. In this chapter, we introducegreen tribology and biomimetics and its applications in tribology.

13.2 Green Tribology

Green tribology can be viewed in the broader context of two “green” areas: green engi-neering and green chemistry (Nosonovsky and Bhushan, 2010). The US Environmental Pro-tection Agency (EPA) defined green engineering as “the design, commercialization and useof processes and products that are technically and economically feasible while minimizing(i) generation of pollution at the source (ii) risk to human health and the environment” (Anony-mous, 2010).Green chemistry, also known as sustainable chemistry, is defined as “the design of chemical

products and processes that reduce or eliminate the use or generation of hazardous substances”(Anonymous, 2010). Based on Nosonovsky and Bhushan (2010), the focus of green chemistryis onminimizing the hazards andmaximizing the efficiency of any chemical choice. It is distinct

Introduction to Tribology, Second Edition. Bharat Bhushan.© 2013 John Wiley & Sons, Ltd. Published 2013 by John Wiley & Sons, Ltd.

684 Introduction to Tribology

from environmental chemistry which focuses on chemical phenomena in the environment.While environmental chemistry studies the natural environment as well as pollutant chemicalsin nature, green chemistry seeks to reduce and prevent pollution at its source. Green chemistrytechnologies provide a number of benefits, including reduced waste, eliminating costly end-of-the-pipe treatments, safer products, reduced use of energy and resources, and improvedcompetitiveness of chemical manufacturers and their customers. Green chemistry consists ofchemicals and chemical processes designed to reduce or eliminate negative environmentalimpacts. The use and production of these chemicals may involve reduced waste products,non-toxic components, and improved efficiency.The principles of green chemistry are applicable to green tribology as well. However, since

tribology involves not only the chemistry of surfaces but also other aspects related to themechanics and physics of surfaces, there is a need to modify these principles.

13.2.1 Twelve Principles of Green Tribology

Twelve principles of green tribology have been proposed by Nosonovsky and Bhushan (2010).Some principles are related to the design andmanufacturing of tribological applications (iii–x),while others belong to their operation (i–ii and xi–xii).

(i) Minimization of heat and energy dissipation. Friction is the primary source of energydissipation. According to some estimates, about one-third of the energy consumptionin the United States is spent overcoming friction. Most energy dissipated by friction isconverted into heat and leads to heat pollution of the atmosphere and the environment.The control of friction and friction minimization, which leads to both energy conser-vation and the prevention of damage to the environment due to the heat pollution, area primary task of tribology. It is recognized that for certain tribological applications(e.g., car brakes and clutches) high friction is required; however, ways of effective useof energy for these applications should be sought as well.

(ii) Minimization of wear is the secondmost important task of tribology which has relevanceto green tribology. In most industrial applications wear is undesirable. It limits thelifetime of components and therefore creates the problem of their recycling. Wear canalso lead to catastrophic failure. In addition, wear creates debris and particles whichcontaminate the environment and can be hazardous for humans in certain situations. Forexample, wear debris generated after human joint replacement surgery is the primarysource of long-term complications in patients.

(iii) Reduction or complete elimination of lubrication and self-lubrication. Lubrication isa focus of tribology since it leads to the reduction of friction and wear. However,lubrication can also lead to environmental hazards. It is desirable to reduce lubricationor achieve the self-lubricating regime, when no external supply of lubrication is required.Tribological systems in living nature often operate in the self-lubricating regime. Forexample, joints form essentially a closed self-sustainable system.

(iv) Natural lubrication (e.g., vegetable oil-based) should be used in cases when possible,since it is usually environmentally friendly.

(v) Biodegradable lubrication should also be used when possible to avoid environmentalcontamination. In particular, water lubrication is an area which has attracted the attention

Green Tribology and Biomimetics 685

of researchers in recent years. Natural oil (such as canola) lubrication is another option,especially discussed in the developing countries.

(vi) Sustainable chemistry and green engineering principles should be used in the manufac-turing of new components for tribological applications, coatings, and lubricants.

(vii) Biomimetic approach should be used whenever possible. This includes biomimeticsurfaces, materials, and other biomimetic and bio-inspired approaches, since they tendto be more ecologically friendly.

(viii) Surface texturing should be applied to control surface properties. Conventional engi-neered surfaces have random roughness, and the randomness is the factor which makesit extremely difficult to overcome friction and wear. On the other hand, many biologicalfunctional surfaces have complex structures with hierarchical roughness, which definestheir properties. Surface texturing provides a way to control many surface propertiesrelevant to making tribo-systems more ecologically friendly.

(ix) Environmental implications of coatings and other methods of surface modification (tex-turing, depositions, etc.) should be investigated and taken into consideration.

(x) Design for degradation of surfaces, coatings, and tribological components. Similar togreen chemistry applications, the ultimate degradation/utilization should be taken intoconsideration during design.

(xi) Real-time monitoring, analysis, and control of tribological systems during their opera-tion should be implemented to prevent the formation of hazardous substances.

(xii) Sustainable energy applications should become the priority of tribological design aswell as engineering design in general.

13.2.2 Areas of Green Tribology

Important areas for green tribology include biodegradable and environmentally-friendly lu-bricants and materials and tribology of renewable and/or sustainable sources of energy(Nosonovsky and Bhushan, 2010, 2012). Bio-inspired materials and surfaces can developedfor green tribology applications and will be discussed in a following section.

13.2.2.1 Biodegradable Lubricants and Materials

Natural (e.g., vegetable-oil based or animal-fat based) biodegradable lubricants, are the oils thatcan be used for engines, hydraulic applications, and metal cutting applications (Nosonovskyand Bhushan, 2010, 2012). In particular, corn, soybean, coconut oils have been used so far(the latter is of particular interest in tropical countries such as India). These lubricants arepotentially biodegradable, although in some cases chemical modification or additives for bestperformance are required. Vegetable oils can have good lubricity, comparable to that of mineraloil. In addition, they have a very high viscosity index and high flash/fire points. However,natural oils often lack sufficient oxidative stability, which means that the oil will oxidizerather quickly during use, becoming thick, and will polymerize to a plastic-like consistency.Chemical modification of vegetable oils and/or the use of antioxidants can address this problem(Mannekote and Kailas, 2009).Ionic liquids (ILs) have been explored as lubricants for various device applications due to

their good electrical conductivity and thermal conductivity, where the latter allows frictional


heating dissipation (Palacio and Bhushan, 2010). Since they do not emit volatile organiccompounds, they are regarded as “green” lubricants. It has been shown that some ILs canmatch or even exceed the tribological behavior of high performance lubricants.Powder lubricants and, in particular, boric acid lubricants tend to be more ecologically

friendly than the traditional liquid lubricants. Boric acid and MoS2 powder can also be usedas an additive to the natural oil. Friction and wear experiments show that the nanoparticles ofboric acid additive exhibited superior friction and wear performance with respect to variouslubricants (Lovell et al., 2010).It has been suggested that environmental aspects should become an integral part of brake

design (Yun et al., 2010). Preliminary data obtained with animal experiments revealed thatinhaled metallic particles remain deposited in the lungs of rats six months after exposure. Thepresence of inhaled particles had a negative impact on health and led to emphysema (destroyedalveoli), inflammatory response, and morphological changes of the lung tissue.

13.2.2.2 Renewable Energy

The tribology of renewable sources of energy is a relatively new field of tribology (Nosonovskyand Bhushan, 2010, 2012). Based on the US President’s proposed clean energy standard,about 80% of electricity will come from clean energy sources by 2035. There are a numberof renewable energy production sources whose usage continues to grow. Important renewableenergy systems include conversion of wind or tidal streams to rotational motion for generatingelectricity and the use of solar panels to harness solar energy. Wind and tidal turbines includebearings and gears with unique challenges because of the high loads and their size and theneed for field service.Figure 13.2.1 shows a photograph of wind turbine blades. Wind turbines consist of a rotor

with wing-shaped blades that are attached to a hub. The hub is attached to the nacelle which

Figure 13.2.1 Photograph of a wind turbine.


Table 13.2.1 Typical specifications of a commercial three-bladed, upwind, horizontal-axis windturbine for power generation of 1.5 MW (GE Energy 2.5 MW Series TC3).

Parameter Machine data

Number of Blades 3Rotor diameter 103 m

(swept area = 8328 m2)Tower Height: 85–100 m, weight: ∼60,000 kgRotational speed 25–60 RPM

Components Machine data

Nacelle (which houses gear box) Size of a school bus and weight ∼ 50,000 kgGear box Three-stage planetary/helical gears with a gear ratio of 1:78.

Weight: ∼ 20,000 kgBlade-pitch bearings Dual, four-point ball bearingsMain shaft bearings Double-row spherical roller bearingsLubrication system Forced lubrication

houses the gear box, the drive train, the support bearings, and the generator. Table 13.2.1shows the typical specifications of a commercial 2.5 MW wind turbine. Figure 13.2.2 showsa turbine Nacelle layout. Figure 13.2.3 shows a configuration of a three-stage gear box for a2–3 MWwind turbine. Since the turbine power is proportional to the area swept by the blades(the square of the rotor diameter), the size of the rotor blades has increased dramatically

Figure 13.2.2 Wind turbine Nacelle layout which houses gear box, drive train, support bearings andelectric generator (GE Energy 2.5 MW).


Figure 13.2.3 Configuration of three-stage gear box for 2-3 MW wind turbine. Reproduced withpermission from Hau, E. (2006), Wind Turbines, Springer-Verlag, Berlin, Germany. Copyright 2006.Springer.

(Hau, 2006). Furthermore, to take advantage of less turbulent but faster wind, up to 100 mabove ground, blades are mounted on high towers. The weight of the rotating blades dominatesover inertial loads which puts enormous demand on the bearings. To minimize the weight ofthe rotor blades, they are made of fiber composites. The gear box is designed to functionas a speed increaser and transmit power from the 25–60 RPM turbine rotor to the 1000–1800 RPM electric generator. The gear box ratio requirements are rather large. Since thetribological components need to be serviced on-site (on-shore or off-shore) with componentslocated at high elevations, reliability of rather large components becomes a major tribologicalchallenge. Tribological issues in wind turbines include failure of the mainshaft and gearboxbearings and gears, water contamination, electric arcing on generator bearings, and the erosionof blades (due to solid particles, cavitation, rain, hail stones) (Kotzalas and Doll, 2010; Woodet al., 2010; Terrell et al., 2012).Tidal power turbines are another important method of producing renewable energy. Tidal

power turbines are especially popular in Europe (particularly, in the UK), which remains theleader in this area, although several potential sites in North America have been suggested.There are several specific tribological issues related to tidal power turbines, such as theirlubrication (seawater, oils, and greases), erosion, corrosion, and biofouling, as well as theinteraction between these modes of damage (Batten et al., 2008; Wood et al., 2010).Besides tidal, the ocean water flow and wave energy and river flow energy (without dams)

can be used with the application of special turbines, such as the Gorlov helical turbine (Gorbanet al., 2001), which provides the same direction of rotation independent of the direction of thecurrent flow. These applications also involve specific tribological issues.


Geothermal energy plants are used in the United States (in particular, on the Pacific coast andAlaska); however, their use is limited to the geographical areas at the edges of tectonic plates(Rybach, 2007). In 2007, they produced 2.7 GW of energy in the US, with the Philippines(2.0 GW) and Indonesia (1.0 GW) in second and third place (Bertani, 2007). There are manyissues related to the tribology of geothermal energy sources.

13.3 Biomimetics

Biomimetics means mimicking biology or living nature. Biomimetics allows biologicallyinspired design, adaptation, or derivation from nature. The word biomimetics was coinedby the polymath Otto Schmitt in 1957, who, in his doctoral research, developed a physicaldevice that mimicked the electrical action of a nerve. Biomimetics is derived from the Greekword biomimesis. Other words used include bionics (coined in 1960 by Jack Steele of Wright-Patterson Air Force Base in Dayton, OH), biomimicry, and biognosis. The word “biomimetics”first appeared in Webster’s Dictionary in 1974 and is defined as: “the study of the formation,structure or function of biologically produced substances and materials (as enzymes or silk)and biological mechanisms and processes (as protein synthesis or photosynthesis) especiallyfor the purpose of synthesizing similar products by artificial mechanisms which mimic naturalones.” The field of biomimetics is highly interdisciplinary. It involves the understanding ofbiological functions, structures, and principles of various objects found in living nature bybiologists, physicists, chemists, and material scientists, and the biologically-inspired designand fabrication of various materials and devices of commercial interest by engineers, materialscientists, chemists, biologists, and others (Bhushan, 2009, 2012).Nature has evolved over the 3.8 billion years since life is estimated to have appeared on

the Earth (Gordon, 1976). Biological materials are highly organized from the molecular to thenano-, micro-, and macroscales, often in a hierarchical manner with an intricate nanoarchitec-ture that ultimately makes up a myriad of different functional elements (Alberts et al., 2008).Nature uses commonly found materials. Properties of materials and surfaces result from acomplex interplay between surface structure and morphology and physical and chemicalproperties. Many materials, surfaces, and objects in general provide multi-functionality.Bio-inspired materials and surfaces are eco-friendly or green which have generated signif-

icant interest and are helping to shape green science and technology. Many of the biologicalobjects exhibit controlled adhesion, low friction, wear resistance, good lubrication and highmechanical properties.The objective of biomimetics research is to develop biologically-inspired materials and

surfaces of commercial interest (Bhushan, 2012). The approach is threefold:

1. Objects are selected from living nature that provide functionality of commercial interest.2. The objects are characterized to understand how a natural object provides functionality.Then it is modeled and structures are generally fabricated in the lab using nature’s route toverify one’s understanding. Modeling is used to develop optimum structures.

3. Nature has a limited toolbox and uses rather basicmaterials and routine fabricationmethods;it capitalizes on hierarchical structures. Once one understands how nature does it, one canthen fabricate optimum structures using smart materials and fabrication techniques toprovide functionality of interest.


13.3.1 Lessons from Nature

The understanding of the functions provided by objects and processes found in nature can guideus to design and produce nanomaterials, nanodevices, and processes (Bhushan, 2009, 2012).There are a large number of objects, including bacteria, plants, land and aquatic animals, andseashells, with properties of commercial interest. Figure 13.3.1 provides an overview of variousobjects from nature and their selected functions (Bhushan, 2009, 2012). These include bac-teria (Jones and Aizawa, 1991), plants (Koch et al., 2008, 2009), insects/spiders/lizards/frogs(Autumn et al., 2000; Gorb, 2001; Bhushan, 2007, 2010), aquatic animals (Bechert et al., 1997,2000;Dean andBhushan, 2010), birds (Jakab, 1990;Bechert et al., 2000), seashells/bones/teeth(Lowenstam andWeiner, 1989; Sarikaya andAksay, 1995;Mann, 2001; Alexander andDiskin,2004; Meyers et al., 2008), spiders’ web (Jin and Kaplan, 2003; Bar-Cohen, 2011), moth-eyeeffect (Genzer and Efimenko, 2006;Mueller, 2008) and structure coloration (Parker, 2009), the

Figure 13.3.1 An overview of various objects from nature and their selected function. Reproducedwith permission from Bhushan, B. (2009), “Biomimetics: Lessons from Nature – An Overview,” Phil.Trans. R. Soc. A 367, 1445–1486, by permission of the Royal Society.


fur and skin of polar bears (Stegmaier et al., 2009), and biological systems with self-healingcapacity (Fratzl and Weinkamer, 2007; Nosonovsky and Bhushan, 2009), and sensory-aiddevices (Barth et al., 2003; Bar-Cohen, 2011).Figure 13.3.2 shows amontage of some examples from nature (Bhushan, 2009, 2012). Some

leaves of water-repellent plants, such as Nelumbo nucifera (Lotus), are known to be super-hydrophobic, self-cleaning, and antifouling, due to their hierarchical roughness (microbumpssuperimposed with a nanostructure) and the presence of a hydrophobic wax coating (Neinhuisand Barthlott, 1997; Barthlott and Neinhuis, 1997; Wagner et al., 2003; Burton and Bhushan,2006; Bhushan and Jung, 2006, 2011; Bhushan, 2009, 2011; Koch et al., 2008, 2009). Waterdroplets on these surfaces readily sit on the apex of nanostructures because air bubbles fillin the valleys of the structure under the droplet. Therefore, these leaves exhibit considerablesuperhydrophobicity, Figure 13.3.2(a). Two strategies used for catching insects by plants fordigestion are having sticky surfaces or sliding structures. As an example, for catching insectsusing sticky surfaces, the glands of the carnivorous plants of the genus Pinguicula (butter-worts) and Drosera (sundew), shown in Figure 13.3.2(b), secrete adhesives and enzymes totrap and digest small insects, such as mosquitoes and fruit flies (Koch et al., 2009). Waterstriders (Gerris remigis) have the ability to stand and walk upon a water surface withoutgetting wet, Figure 13.3.2(c). Even the impact of rain droplets with a size greater than thewater strider’s size does not immerse it in the water. Gao and Jiang (2004) showed that thespecial hierarchical structure of the water strider’s legs, which are covered by large numbersof oriented tiny hairs (microsetae) with fine nanogrooves and covered with cuticle wax, makesthe leg surfaces superhydrophobic, is responsible for the water resistance, and enables themto stand and walk quickly on the water surface.A gecko is the largest animal that can produce high (dry) adhesion to support its weight

with a high factor of safety. Gecko skin is comprised of a complex hierarchical structure oflamellae, setae, branches, and spatula (Autumn et al., 2000; Gao et al., 2005; Bhushan, 2007).The attachment pads on two feet of the Tokay gecko have an area of approximately 220 mm2,Figure 13.3.2(d). Approximately 3×106 setae on their toes that branch off into about threebillion spatula on two feet can produce the clinging ability of approximately 20 N (the verticalforce required to pull a lizard down a nearly vertical (85◦) surface) and allow them to climbvertical surfaces at speeds of over 1 m/s, with the capability to attach or detach their toes inmilliseconds (Bhushan, 2007).Shark skin, which is a model from nature for a low drag surface, is covered by very small

individual tooth-like scales called dermal denticles (little skin teeth), ribbed with longitudinalgrooves (aligned parallel to the local flow direction of the water). These grooved scales liftvortices to the tips of the scales, resulting in water moving efficiently over their surface(Bechert et al., 2000; Dean and Bhushan, 2010). The spacing between these dermal denticlesis such that microscopic aquatic organisms have difficulty adhering to the surface, making theskin surface antifouling (Carman et al., 2006; Genzer and Efimenko, 2006; Kesel and Liedert,2007; Ralston and Swain, 2009; Bixler and Bhushan, 2012). An example of scale structure onthe right front of a Galapagos shark (Carcharhinus galapagensis) is shown in Figure 13.3.2(e)(Jung and Bhushan, 2010).Birds consist of several consecutive rows of covering feathers on their wings, which are

flexible, Figure 13.3.2(f). These movable flaps develop the lift. When a bird lands, a fewfeathers are deployed in front of the leading edges of the wings, which help to reduce the dragon the wings.


Figure 13.3.2 Montage of some examples from nature: (a) Lotus effect (Source: Bhushan, B., Jung,Y.C., and Koch, K. (2009), “Micro-, Nano- and Hierarchical Structures for Superhydrophobicity, Self-Cleaning andLowAdhesion,”Phil. Trans. R. Soc. A 367, 1631–1672, by permission of theRoyal Society),(b) glands of carnivorous plant secrete adhesive to trap insects (Reproduced with permission from Koch,K., Bhushan, B., and Barthlott, W. (2009), “Multifunctional Surface Structures of Plants: An Inspirationfor Biomimetics,” Prog. Mater. Sci. 54, 137–178. Copyright 2009. Elsevier), (c) water strider walking onwater (Reproduced with permission from Gao, X. F. and Jiang, L. (2004), “Biophysics: Water-repellentLegs of Water Striders,” Nature 432, 36. Copyright 2004. Nature Publishing Group), (d) gecko footexhibiting reversible adhesion (Reproduced with permission from Gao, H., Wang, X., Yao, H., Gorb, S.,and Arzt, E. (2005), “Mechanics of Hierarchical Adhesion Structures of Geckos,”Mech. Mater. 37, 275–285. Copyright 2005. Elsevier), (e) scale structure of shark reducing drag (Reproduced with permissionfrom Jung, Y. C. and Bhushan, B. (2010), “Biomimetic Structures for Fluid Drag Reduction in Laminarand Turbulent Flows,” J. Phys.: Condens. Matter 22, 035104. Copyright 2010. IOP Science), (f) wingsof a bird in landing approach, (g) spiderweb made of silk material (Reproduced with permission fromBar-Cohen, Y. (2011), Biomimetics: Nature-Based Innovation, CRC Press, Boca Raton, FL. Copyright2011. Taylor and Francis), and (h) antireflective moth’s eye (Reproduced with permission from Genzer,J. and Efimenko, K. (2006), “Recent Developments in Superhydrophobic Surfaces and Their Relevanceto Marine Fouling: A Review,” Biofouling 22, 339–360. Copyright 2006. Taylor and Francis).


The spider generates silk fiber and has a sufficient supply of raw material for its silk tospan great distances (Jin and Kaplan, 2003; Bar-Cohen, 2011). Spiderweb is a structure builtof a one-dimensional fiber, Figure 13.3.2(g). The fiber is very strong and continuous and isinsoluble in water. The web can hold a significant amount of water droplets, and it is resistantto rain, wind, and sunlight (Sarikaya and Aksay, 1995; Bar-Cohen, 2011).The eyes of moths are antireflective to visible light and consist of hundreds of hexagonally

organized nanoscopic pillars, each approximately 200 nm in diameter and height, whichresult in a very low reflectance for visible light, Figure 13.3.2(h) (Genzer and Efimenko,2006; Mueller, 2008). These nanostructures’ optical surfaces make the eye surface nearlyantireflective in any direction.

13.3.2 Industrial Significance

Theword biomimetics is relatively new; however, our ancestors looked to nature for inspirationand development of various materials and devices many centuries ago (Ball, 2002; Bar-Cohen,2011; Vincent et al., 2006; Anonymous, 2007; Meyers et al., 2008; Bhushan, 2012). Forexample, the Chinese tried to make artificial silk some 3000 years ago. Leonardo da Vinci,a genius of his time, studied how birds fly and proposed designs of flying machines. Inthe twentieth century, various products, including the design of aircraft, have been inspiredby nature. Since the 1980s, the artificial intelligence and neural networks in informationtechnology have been inspired by the desire tomimic the human brain. The existence of biocellsand deoxyribonucleic acid (DNA) serves as a source of inspiration for nanotechnologists whohope one day to build self-assembled molecular-scale devices. In molecular biomimetics,proteins are being utilized in controlling materials formation in practical engineering towardsself-assembled, hybrid, functional materials structure (Grunwald et al., 2009; Tamerler andSarikaya, 2009). Since the mid-1990s, the so-called Lotus effect has been used to develop avariety of surfaces for superhydrophobicity, self-cleaning, low adhesion, and drag reductionin fluid flow, as well as antifouling (Bhushan et al., 2009; Bhushan, 2011; Bhushan and Jung,2011). Replication of the dynamic climbing and peeling ability of geckos has been carried outto develop treads of wall-climbing robots (Cutkosky and Kim, 2009). Replication of shark skinhas been used to develop moving objects with low drag, for example, wholebody swimsuits(Dean and Bhushan, 2010). Nanoscale architecture used in nature for optical reflection andanti-reflection has been used to develop reflecting and anti-reflecting surfaces. In the field ofbiomimetic materials, there is an area of bio-inspired ceramics based on seashells and otherbiomimetic materials. Inspired by the fur of the polar bear, artificial furs and textiles have beendeveloped. Self-healing of biological systems found in nature is of interest for self-repair.Biomimetics is also guiding in the development of sensory-aid devices.Various features found in nature objects are on the nanoscale. The major emphasis on

nanoscience and nanotechnology since early 1990s has provided a significant impetus inmimicking nature using nanofabrication techniques for commercial applications (Bhushan,2010). Biomimetics has spurred interest across many disciplines.

13.4 Closure

Green tribology is a novel area of science and technology. It is related to other areas oftribology as well as other “green” disciplines, namely, green engineering and green chemistry.


The twelve principles of green tribology are formulated. The field of biomimetics offers manyexamples in nature of materials and surfaces which can be exploited in green tribology.

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Further Reading

Bhushan, B. (2009), “Biomimetics: Lessons from Nature – An Overview,” Phil. Trans. R. Soc. A 367, 1445–1486.Bhushan, B. (ed.) (2009), Special Journal Issue on Biomimetics I: Functional Biosurfaces and II: Fabrication and

Applications., Phil. Trans. R. Soc. A 367, No. 1893 and 1894.Bhushan, B. (2012), Biomimetics: Bioinspired Hierarchical-Structured Surfaces for Green Science and Technology,

Springer-Verlag, Heidelberg, Germany.Nosonovsky, M. and Bhushan, B. (2010), Special Journal Issue on Green Tribology, Phil. Trans. R. Soc A 368,

No. 1929.Nosonovsky, M. and Bhushan, B. (2012), Green Tribology: Biomimetics, Energy Conservation and Sustainability,

Springer-Verlag, Heidelberg, Germany.

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