The dream of staying clean: Lotus and biomimetic surfaces

The Lotus has been the symbol of purity for thousands of years; contaminations and pathogens are washed off the surfaces of Lotus and some other plants with rain or even dew. After the introduction of scanning electron microscopy, we were able to resolve the mechanism behind this phenomenon. It took some further decades before in-depth studies on self-cleaning with plants were conducted and the effect could be understood in detail. We identified extreme water-repellency ('superhydrophobicity'), characterized by very high contact angles and low sliding angles, as the prerequisite for self-cleaning properties. We could show that the combination of two factors is necessary for obtaining a high degree of water-repellency: (1) low energy surfaces being hydrophobic and (2) surface structures that significantly increase hydrophobicity. It is suggested that this mechanism plays an important role in the protection of plants against pathogens. Our technological application of this effect has resulted in the development of successful, eco-friendly and sustainable industrial products. Another interesting property was found with superhydrophobic surfaces of certain aquatic and semi-aquatic plants and animals: here a layer of air under water is retained. We present a new approach of using this feature for creating structured, air-retaining surfaces for technical underwater applications. It is proposed that such surfaces can reduce significantly the drag of large ships. We conclude that basic biological research is of particular importance for true innovation. Our research on superhydrophobic self-cleaning biological surfaces and the development of similar engineered materials suggests that biomimicry is a matter of multi-stage processes rather than a simple copying of biological developments.

[1]  R. Ohsugi,et al.  δ13C Values and the Occurrence of Suberized Lamellae in Some Panicum Species. , 1988 .

[2]  R. Blossey.  Self-cleaning surfaces — virtual realities , 2003, Nature materials.

[3]  D. F. Cutler,et al.  Regular ArticleClassification and terminology of plant epicuticular waxes , 1998 .

[4]  Hendrik Bargel,et al.  Structure-function relationships of the plant cuticle and cuticular waxes - a smart material? , 2006, Functional plant biology : FPB.

[5]  J. M. Bush,et al.  The hydrodynamics of water strider locomotion , 2003, Nature.

[6]  Wilhelm Barthlott,et al.  Chemistry and Crystal Growth of Plant Wax Tubules of Lotus (Nelumbo nucifera) and Nasturtium (Tropaeolum majus) Leaves on Technical Substrates , 2006 .

[7]  Jonathan P. Rothstein,et al.  Turbulent Drag Reduction Using Superhydrophobic Surfaces , 2008 .

[8]  P. Gennes,et al.  Capillarity and Wetting Phenomena , 2004 .

[9]  J. Vincent,et al.  Biomimetics: its practice and theory , 2006, Journal of The Royal Society Interface.

[10]  Wolfgang E. Krumbein,et al.  Mikrobielle Werkstoffzerstörung – Simulation, Schadensfälle und Gegenmaßnahmen für anorganische nichtmetallische Werkstoffe: Biodeteriorationsprozesse an anorganischen Werkstoffen und mögliche Gegenmaßnahmen , 1994 .

[11]  W. Flückiger,et al.  The effect of dust on photosynthesis and its significance for roadside plants , 1984 .

[12]  Neelesh A Patankar,et al.  Transition between superhydrophobic states on rough surfaces. , 2004, Langmuir : the ACS journal of surfaces and colloids.

[13]  E. A. Baker,et al.  ULTRASTRUCTURE AND RECRYSTALLIZATION OF PLANT EPICUTICULAR WAXES , 1975 .

[14]  Wilhelm Barthlott,et al.  Epidermal and seed surface characters of plants: systematic applicability and some evolutionary aspects , 1981 .

[15]  Markus Oles,et al.  Lotus‐Effect® – surfaces , 2002 .

[16]  Abraham Marmur,et al.  Wetting on Hydrophobic Rough Surfaces: To Be Heterogeneous or Not To Be? , 2003 .

[17]  Tomohiro Onda,et al.  Super-Water-Repellent Fractal Surfaces , 1995 .

[18]  Abraham Marmur,et al.  Underwater superhydrophobicity: theoretical feasibility. , 2006, Langmuir : the ACS journal of surfaces and colloids.

[19]  Luquan Ren,et al.  Effects of Methanol on Wettability of the Non-Smooth Surface on Butterfly Wing , 2008 .

[20]  Petros Koumoutsakos,et al.  A theoretical prediction of friction drag reduction in turbulent flow by superhydrophobic surfaces , 2006 .

[21]  W. Barthlott.  Structural botany. III, Cuticular surfaces in plants , 1989 .

[22]  Akira Fujishima,et al.  Transparent Superhydrophobic Thin Films with Self-Cleaning Properties , 2000 .

[23]  Ren Luquan,et al.  Super-hydrophobic characteristics of butterfly wing surface , 1900 .

[24]  Stephan Herminghaus,et al.  How plants keep dry: a physicist's point of view. , 2004, Langmuir : the ACS journal of surfaces and colloids.

[25]  Howard S. Neufeld,et al.  Direct foliar effects of simulated acid rain. II: Leaf surface characteristics , 1985 .

[26]  B. Juniper,et al.  The Leaf from the Inside and the Outside: A Microbe’s Perspective , 1991 .

[27]  Stephan Herminghaus,et al.  Roughness-induced non-wetting , 2000 .

[28]  William E. Ward,et al.  The Lotus Symbol: Its Meaning in Buddhist Art and Philosophy , 1952 .

[29]  William K. Smith,et al.  ADAPTIVE RELATIONSHIP BETWEEN LEAF WATER REPELLENCY, STOMATAL DISTRIBUTION, AND GAS EXCHANGE , 1989 .

[30]  Terence Desmond Blake,et al.  Contact-Angle Hysteresis , 1973 .

[31]  Ce Jeffree,et al.  The cuticle, epicuticular waxes and trichomes of plants, with reference to their structure, functions and evolution , 1986 .

[32]  David Quéré,et al.  Superhydrophobic states , 2003, Nature materials.

[33]  Daniel Schondelmaier,et al.  Orientation and Self-Assembly of Hydrophobic Fluoroalkylsilanes , 2002 .

[34]  Hermann Ziegenspeck.  Zur physikalischen Chemie unbenetzbarer besonders bewachster Blätter , 1942 .

[35]  W. Barthlott,et al.  Purity of the sacred lotus, or escape from contamination in biological surfaces , 1997, Planta.

[36]  Wilhelm Barthlott,et al.  Characterization and Distribution of Water-repellent, Self-cleaning Plant Surfaces , 1997 .

[37]  Wolfgang Sand,et al.  The microbiology of masonry biodeterioration , 1993 .

[38]  Xurong Xu,et al.  Stable superhydrophobic organic-inorganic hybrid films by electrostatic self-assembly. , 2005, The journal of physical chemistry. B.

[39]  Othon K. Rediniotis,et al.  Microstructured Hydrophobic Skin for Hydrodynamic Drag Reduction , 2004 .

[40]  B. Widom.  Capillarity and Wetting Phenomena: Drops, Bubbles, Pearls, Waves , 2003 .

[41]  Carol A. Brewer,et al.  Influence of Simulated Dewfall on Photosynthesis and Yield in Soybean Isolines (Glycine max [L.] Merr. cv Williams) with Different Trichome Densities , 1994, International Journal of Plant Sciences.

[42]  Martin Wulf,et al.  Coatings with self‐cleaning properties , 2002 .

[43]  M. Knoche,et al.  Concentration effects and regeneration of epicuticular waxes after treatment with Triton X-100 surfactant , 1988 .

[44]  Philip W. Rundel,et al.  Surface Dust Impacts on Gas Exchange in Mojave Desert Shrubs , 1997 .

[45]  Ichiro Terashima,et al.  Effects of continuous leaf wetness on photosynthesis: adverse aspects of rainfall , 1995 .

[46]  Wilhelm Barthlott,et al.  Classification and terminology of plant epicuticular waxes , 1998 .

[47]  Abraham Marmur,et al.  Super-hydrophobicity fundamentals: implications to biofouling prevention , 2006, Biofouling.

[48]  T. Hirano,et al.  Physical effects of dust on leaf physiology of cucumber and kidney bean plants. , 1995, Environmental pollution.

[49]  Carol A. Brewer,et al.  What's So Bad about Being Wet All Over: Investigating Leaf Surface Wetness. , 1996 .

[50]  Itaru Honma,et al.  Superhydrophobic perpendicular nanopin film by the bottom-up process. , 2005, Journal of the American Chemical Society.

[51]  Wilhelm Barthlott,et al.  Self‐Assembly of Epicuticular Waxes on Living Plant Surfaces by Atomic Force Microscopy , 2003 .

[52]  B. Juniper,et al.  The cuticles of plants , 1971 .

[53]  W. Barthlott,et al.  Seasonal changes of leaf surface contamination in beech, oak, and ginkgo in relation to leaf micromorphology and wettability , 1998 .

[54]  Wilhelm Barthlott,et al.  Wettability and Contaminability of Insect Wings as a Function of Their Surface Sculptures , 1996 .

[55]  Peter Walzel,et al.  Wetting and self-cleaning properties of artificial superhydrophobic surfaces. , 2005, Langmuir : the ACS journal of surfaces and colloids.

[56]  A. Cassie,et al.  Wettability of porous surfaces , 1944 .

[57]  K. Autumn,et al.  Evidence for self-cleaning in gecko setae. , 2005, Proceedings of the National Academy of Sciences of the United States of America.

[58]  K. Wandelt,et al.  Structural analysis of wheat wax (Triticum aestivum, c.v. ‘Naturastar’ L.): from the molecular level to three dimensional crystals , 2005, Planta.

[59]  C. G. L. Furmidge.  The Cuticles of Plants , 1970 .

[60]  Neelesh A Patankar,et al.  Mimicking the lotus effect: influence of double roughness structures and slender pillars. , 2004, Langmuir : the ACS journal of surfaces and colloids.

[61]  Jr H B Tukey,et al.  The Leaching of Substances from Plants , 1970 .

[62]  Wilhelm Barthlott,et al.  Cuticular Surfaces in Plants , 1989 .

[63]  David Quéré,et al.  Surface chemistry: Fakir droplets. , 2002, Nature materials.

[64]  R. Scholes,et al.  Ecosystems and human well-being: current state and trends , 2005 .

[65]  R. H. Dettre,et al.  Contact Angle Hysteresis: II. Contact Angle Measurements on Rough Surfaces , 1964 .

[66]  Kenneth S. Breuer,et al.  Turbulent Drag Reduction Using Superhydrophobic Surfaces , 2006 .

[67]  Didem Öner,et al.  Ultrahydrophobic Surfaces. Effects of Topography Length Scales on Wettability , 2000 .

[68]  H. Lugt,et al.  Laminar flow behavior under slip−boundary conditions , 1975 .

[69]  Wolfram Köller,et al.  The Plant Cuticle , 1991 .

[70]  Yasukiyo Ueda,et al.  The Lowest Surface Free Energy Based on −CF3 Alignment , 1999 .

[71]  W. Barthlott,et al.  Movement and regeneration of epicuticular waxes through plant cuticles , 2001, Planta.

[72]  J. Braams,et al.  Biodeterioration of stone: a review , 2000 .

[73]  D W Eveling,et al.  Scanning Electron Microscopy of Damage by Dust Deposits to Leaves and Petals , 1986, Botanical Gazette.

[74]  Hendrik Bargel,et al.  Plant cuticles: Multifunctional interfaces between plant and environment , 2004 .

[75]  Yang-Tse Cheng,et al.  Effects of micro- and nano-structures on the self-cleaning behaviour of lotus leaves , 2006 .

[76]  Chang-Jin Kim,et al.  Nanostructured surfaces for dramatic reduction of flow resistance in droplet-based microfluidics , 2002, Technical Digest. MEMS 2002 IEEE International Conference. Fifteenth IEEE International Conference on Micro Electro Mechanical Systems (Cat. No.02CH37266).

[77]  Zhiguang Guo,et al.  Biomimic from the superhydrophobic plant leaves in nature: Binary structure and unitary structure , 2007 .

[78]  Wei Chen,et al.  Ultrahydrophobic and Ultralyophobic Surfaces: Some Comments and Examples , 1999 .

[79]  Е.В. Князев,et al.  A method for producing , 1995 .