The purity of sacred lotus: superhydrophobic self-cleaning plant surfaces and the consequences revisited

Superhydrophobicity and self-cleaning (Lotus Effect) came only in focus of research after 1997. Botanic systematic studies led to a paradigm shift in materials science and numerous technical applications. However, physics behind it is still not fully understood. Details on the discovery, consequences, and open questions are presented. Extreme water repellency (superhydrophobicity) is a feature of many biological surfaces from terrestrial cyanobacteria to green plants and animals. The initially controversially discussed publication "Purity of sacred Lotus or escape from contamination on biological surfaces" (Planta 1997) showed that defined hierarchically structured superhydrophobic surfaces reduce the adhesion of pathogens and particles as defense mechanism. The technical applicability was indicated, and the publication initiated about 2000 publications annually and numerous applications in our daily life. Although cuticular plant surfaces are probably the largest homogenous interfaces on our planet, they came very late in the focus of research. Functional principles, occurrence of self-cleaning biological surfaces, the physical background, patenting consequences, and open questions are discussed.