www.advmatinterfaces.de FULL PAPER 1801202 (1 of 10) © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Engineering Fully Organic and Biodegradable Superhydrophobic Materials Athanasios Milionis, Chander Shekhar Sharma, Raoul Hopf, Michael Uggowitzer, Ilker S. Bayer, and Dimos Poulikakos* DOI: 10.1002/admi.201801202 superhydrophobic materials have been reported. [12] However, most of these mate- rials make use of petroleum derivatives and fluorinated compounds, [13] as well as textured inorganic materials, [14] which serve as substrates for surface chemical functionalization. These materials are not inherently biodegradable and thus pose a challenge in terms of environmental impact and recyclability. Especially long- chain fluorinated compounds, which are used often to obtain liquid repellency, are difficult to degrade and tend to bioaccumu- late. [15,16] Furthermore, even if these sub- stances degrade after a prolonged period, some of their by-products are known to be toxic, such as perfluorooctanoic acid [17] and perfluorooctanesulfonate. [18] Recent studies have reported the use of more sustainable methods and materials to obtain the self-cleaning effect. These include the use of biodegradable polymers and natural materials, [19] waterborne spray approaches, [20] alcoholic solvent environ- ment, [21] silicone-based biocompatible materials, [22] reactive polymeric mate- rials, [23] fluorine-free substances, [24–26] cellulose-based, [27] and natural wax-based material compositions. [28,29] The use of the latter two materials (cellulose and wax) is inspired from the fact that they are the main constituents of a broad selection of plants, including the well-known Lotus leaf. [30] Cellulose is the material that mainly constitutes the substrate and is responsible for the leaf’s mechanical properties and microroughness (the latter in the form of macropapillae) in a wide range of plants. On the other hand, the wax nanocrystals cover the microtopog- raphy and are responsible for the superhydrophobicity, both The development of fully organic (cellulose/wax based), biodegradable, and hierarchically textured superhydrophobic material, inspired by natural, self- cleaning plants, like the Lotus leaf is reported. The developed material can reproduce in a controllable and artificial manner the chemical composition and material properties of these natural surfaces. At the same time, the fabrication protocol described here enables realization of properties beyond the ones found in the natural leaves, by allowing facile tuning of the topographical and mechanical properties. The surface topography consists of a micropillar structure assembly with, to the best of the authors’ knowledge, the highest to date reported aspect ratio (7.6) for cellulose materials. Additionally, control and tunability of the material’s mechanical properties are also demonstrated, which is rendered softer (down to 227 MPa Young’s modulus from 997 MPa base value) by adding glycerol as a natural plasticizer. Finally, the self-cleaning properties are demonstrated and the biodegradability of the material is evaluated in a period of ≈3 months, which confirms full biodegradation. Additionally, water drop and jet impact, and folding tests demonstrate that the material can reasonably sustain its wettability properties. Such a truly bioinspired and biodegradable material system could find potential use in various bioengineering applications. Dr. A. Milionis, Dr. C. S. Sharma, [+] M. Uggowitzer, Prof. D. Poulikakos Laboratory of Thermodynamics in Emerging Technologies Department of Mechanical and Process Engineering ETH Zürich Sonneggstrasse 3, 8072 Zürich, Switzerland E-mail: dpoulikakos@ethz.ch Self-Cleaning 1. Introduction Superhydrophobicity is recognized as a critical property in a wide range of potential technologies spanning from industrial, healthcare, to military applications such as self-cleaning tex- tiles, [1] water–oil separation, [2] anti-icing, [3] anti-fouling, [4,5] anti-fingerprint, [6] corrosion resistance, [7] sensors, [8] robotics, [9] and hydrophobization of 3D printed components. [10] Inspired by the discovery of the self-cleaning properties of the Lotus leaf (Nelumbo nucifera), [11] a large number of artificial [+] Present address: Department of Mechanical Engineering, Indian Insti- tute of Technology, Ropar, Nangal Road, Rupnagar, 140 001 Punjab, India Dr. R. Hopf Department of Mechanical and Process Engineering Institute of Mechanical Systems ETH Zürich Leonhardstrasse 21, 8092 Zürich, Switzerland Dr. I. S. Bayer Smart Materials Istituto Italiano di Tecnologia Via Morego 30, 16163 Genoa, Italy The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/admi.201801202. Adv. Mater. Interfaces 2018, 1801202