Moisture-driven ceramic bilayer actuators from a bio-templating approach

Significance Statement

Stimuli driven actuators are important in technological applications and in nature. They are used to open seed capsules and are implemented in technology to serve as gauges. Particularly, electricity-actuated piezo crystals are useful in sensing and high precision positioning. In nature, actuators are found in pine cones.

However, no ceramic moisture-driven bilayer actuators exist. Such devices would be helpful in controlling chemically reactive environments. Generally, bilayer actuators are prone to chemical attack, radiation and oxidation. This is stemming from their high metallic or polymeric loading. Therefore, ceramic actuators would be resistant to all these conditions.

Motivated by the need to fabricate ceramic bilayer actuators, researchers led by Professor  Cordt Zollfrank from the Chair of Biogenic Polymers of the Technical University of Munich, managed to synthesize ceramic moisture-driven actuators through bio-templating pine cones. The authors applied their findings to existing models and the outcomes corresponded to the concept of silica based actuators, where water absorption is the predominant driving force. Their work is published in a peer-reviewed journal, Advanced Materials.

The actuation process witnessed in the pine cones was due to  the swelling of the sclereid tissues. The authors found that, although the observed movements in ceramic replica and native cones were different in magnitude, the basic moisture-driven mechanism and its actuation direction was maintained. The authors found that this was the first example of angular actuation observed in porous ceramic bilayer actuators triggered by the uptake of water.

The authors observed a bilayer structuring in both the ceramic actuators and their biological pine cone templates. In the ceramic bilayers, the structuring was not as uniform as in the scales of the pine cones.  The studied preparation method could be applied to other natural, or generally to polymeric, bilayer actuators, where one can choose the actuation mechanism as well as geometry of a selected product.

There has been several further exciting research recently in the field of moisture-induced actuation. For example, a published article by Boudot et al used artificially structured silica films on a polymer substrate to attain humidity-derived actuation. Due to the flexible nature of their substrate, they achieved curvatures up to 0.6 cm-1, while using an inorganic -silica- active layer. This translates to angular changes in an exemplary 3 cm long strip of approximately 100°. In contrast, Van Opdenbosch et al obtained smaller angular actuation due to the entire inorganic architecture of their replicated conifer cone materials, which, on the other hand, are resistant to temperatures of at least 500 °C, and also to corrosive environments.

Another work by Ganser et al reported the bending behavior of purely inorganic, artificially-structured silica films on silicon substrates, which led to moisture-induced bending. The 130 μm long structures attained tip deflections of up to 160 nm, which translates to a maximum bending angle of 0.07°. Considering the inorganic nature, the size of the actuator and possible applications as micro- switches or sensors, even these numerically small deflections and bending angles provide a useful technological tool.

Poppinga et al presented in January 2017 their work in Scientific Reports on the actuation of naturally fossilized conifer cones. This provided a highly interesting comparison. Notably, the naturally fossilized cones contain large portions of the original biomass, conserved by the mineralization processes. Therefore, these naturally fossilized cones show maximum actuation angles of 20°, which is more than half of those of the corresponding recent native conifer cones.

Moisture-driven ceramic bilayer actuators from a bio-templating approach - advances in engineering

About the author

Cordt Zollfrank studied Chemistry at the Technische University Munich (TUM), and received his PhD in Forest Science with special emphasis on chemical aspects at TUM in 2000. He worked as a postdoctoral research fellow and later on as a group leader at the Friedrich-Alexander-University Erlangen-Nuremberg in the Department of Materials Science and Engineering – Glass and Ceramics. Since 2011 he is Professor for Biogenic Polymers at the TUM and the Straubing Center of Science for Renewable Resources.

His research work is focused on bioinspired synthetic methods for innovative structural and functional materials. A key area of his work is the formation of biogenic structures and their conversion to composite materials for engineering and biomedical applications. The fundamental chemical and physical transformation processes involved in these conversions are investigated at each level of structural hierarchy.

About the author

Daniel Van Opdenbosch studied materials science and engineering at the Friedrich-Alexander-University Erlangen-Nuremberg and at Alfred University. He received the degree doctor of natural sciences from the Technical University of Munich in 2013. With scholarships from the European Cooperation in Science and Technology and the Max Kade Foundation respectively, he worked at the Romanian National Institute for Laser, Plasma & Radiation Physics and at the University of Utah. Since 2014, he is leading the research group Bio-mediated Material Synthesis at the Chair of Biogenic Polymers of the Technical University of Munich, located at the Straubing Center of Science.

His scientific interests are biologically inspired or -derived hierarchical inorganic or composite materials with novel structure-derived functionalities, and novel approaches to light-based structuring and structural analyses.

About the author

Gerhard Popovski studied chemistry at Karl-Franzens University Graz, obtaining his PhD in 2000. He performed postoctoral research at BASF in Ludwigshafen and at the University of Delaware. Returning to Graz 2003, he obtained his venia legendi in Physical Chemistry in 2009. From there onwards he worked at the University of Leoben. He is currently working at the Material Center Leoben (MCL).

His research interests are the characterization of nanostructures by scattering technique. He focusses on porous materials, as well as self-assembled, and biological structures.

About the author

Oskar Paris studied Physics at the University of Vienna and received his PhD in Metal Physics from the University of Vienna in 1996. He worked at the University of Vienna, at the ETH Zürich, the Montanuniversität Leoben, and the Max-Planck-Institute of Colloids and Interfaces in Potsdam. Since 2009 he is full Professor of Physics and Chair of the Institute of Physics at the University of Leoben.

His scientific interests are on the structure, properties and energy related applications of complex nanomaterials such as carbon nanomaterials, nanoparticles, nanoporous materials, and biological materials. He is an expert in structure characterization based on scattering methods using synchrotron radiation X-ray and neutron facilities.

About the author

Wolfgang Wagermaier is Research Group Leader at the Max Planck Institute of Colloids and Interfaces in Potsdam, Germany. He studied materials science at the University of Leoben, Austria, from where he also received a doctorate in materials science, based on research he did at the Max Planck Institute of Colloids and Interfaces in 2006. From 2007 to 2009, he worked as a postdoctoral researcher at the Helmholtz-Zentrum Geesthacht in Teltow, Germany.

The main aim of Wolfgang Wagermaier’s research is to understand the role of structure in biological and biomimetic materials with respect to mechanical properties and biological functions at different length scales. To examine these materials, high-resolution imaging techniques from materials science are employed to characterize the dynamic evolution of the micro- and nanometer structures.


Daniel Van Opdenbosch1, Gerhard Fritz-Popovski2, Wolfgang Wagermaier3, Oskar Paris2, and Cordt Zollfrank1. Moisture-driven ceramic bilayer actuators from a bio-templating approach. Advanced materials, volume 28 (2016), pages 5235-5240.

Go To Advanced Materials 


Show Affiliations
  1. Professur für Biogene Polymere, Technische Universität München, Straubing Center of Science for Renewable Resources, Schulgasse 16, D-94315, Straubing, Germany.
  2. Institut für Physik, Montanuniversität Leoben, Franz-Josef-Straße 18, A-8700, Leoben, Austria.
  3. Max-Planck-Institut für Kolloid- und Grenzflächenforschung, Abteilung Biomaterialien, Am Mühlenberg 1, D-14476, Potsdam, Germany.

Boudot, M., Elettro, H. & Grosso, D. Converting Water Adsorption and Capillary Condensation in Usable Forces with Simple Porous Inorganic Thin Films. ACS Nano 10, 10031–10040 (2016).

Ganser, C. et al. Cantilever bending based on humidity-actuated mesoporous silica/silicon bilayers. Beilstein J. Nanotechnol. 7, 637–644 (2016).

Poppinga, S. et al. Hygroscopic motions of fossil conifer cones. Sci. Rep. 7, 40302 (2017).

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