Active Composites Grown by Plants May Inspire Sustainable Materials by Prof Peter Fratzl (Max Planck Institute)

Biological extracellular tissues are based on proteins, polysaccharides and, in certain cases, minerals. Their complex multiscale structure confers them a wide range of properties in accordance with their functions [1]. While active functionality are usually attributed to cells, there are also examples of materials synthesized by living organisms, such as plant seeds, which fulfil an active function without living cells and work as mechanosensors and actuators [2]. Water is an important component of all such extracellular tissues. While it is well known that the level of hydration determines the mechanical properties of many biological materials, it is less appreciated that water also plays an active role in generating forces within the materials. In particular water absorption and desorption provides actuation in a variety of plant seeds, including wild wheat [3], stone plant [4] and banksia seed capsules [5]. The shape change upon water uptake that provides the actuation is controlled by specific cellulose fibre architectures. In this way, well-controlled movements, such as bending, twisting or curling are programmed in these materials by structure of the underlying cellulose microarchitecture [6]. The required deformation energy is provided by the absorption of water from the environment [7]. Such materials highlight potential concepts for sustainable materials with high functionality [8]. The lecture also discusses the need for more holistic approaches involving science, humanities and design disciplines for developing a more sustainable materials economy [9].

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[1] Eder+ 2018, Science 362: 543-547; [2] Fratzl & Barth 2009, Nature, 462: 442-448; [3] Elbaum+ 2007, Science, 316: 884-886; [4] Harrington+ 2011, Nature Comm. 2: 337; [5] Huss + 2018, Adv. Sci, 5: 1700572; [6] Guiducci+ 2015, Adv. Mater. Interf, 2: 1500011; [7] Bertinetti+ 2013, Phys. Rev. Lett. 111: 238001; [8] Eder+ 2020, Advanced Materials 2001412; [9] Fratzl+ 2020, actech discussion https://en.acatech.de/publication/materials-research/