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Plant-inspired materials and surfaces

Periodic Reporting for period 2 - PlaMatSu (Plant-inspired materials and surfaces)

Reporting period: 2018-10-01 to 2020-09-30

The cuticle of plant leaves and petals is a multifunctional, multicomponent and hierarchically structured material with a lot of potential to act as concept generator for novel bio-inspired materials. The overall aims of PlaMatSu were (1) to address the challenge of creating new functional polymeric materials and surfaces by studying structure formation and function-property relationships in plant cuticles and (2) to educate the next generation of scientists who have the necessary interdisciplinary knowledge for turning bio-inspired scientific results into innovation. PlaMatSu therefore trained nine Early Stage Researchers (ESRs) at PhD student level in a network of multi-disciplinary labs composed of biologists, physicists, and chemists.
WP1 Project management: The Coordination Office consisted of a project manager, a project assistant and the coordinator Prof. Nico Bruns. It administrated the project and organized all network-wide activities.

WP2 Recruitment: 9 ESR positions were filled with outstanding young scientists from Germany, France, Greece, Netherlands, South Korea, and India. Two ESRs are female, seven ESRs male. All ESRs successfully completed their MSCA fellowship.

WP3 Research: Research covered diverse topics, from the genetic and developmental foundation of structure formation in plant cuticles, to the synthesis of novel bio-inspired polymeric materials and surfaces, to the physical characterization of wrinkled colloids and polymer dewetting in thin films. A summary of PlaMatSu’s research results can be found in the Impact Section below.

WP4 Training: The ESRs worked under the supervision of distinguished scientists in the field of bio-inspired materials, thereby receiving world-class training-by-research. PlaMatSu organised five training workshops, an away weekend, and a winter school on bio-inspired materials. The training included technology transfer and innovation, ethics, outreach through Wikipedia, introduction to R&D in industry, preparation for job search, outreach via an exhibition, and writing and presentation skills. The ESRs undertook secondments between the research groups and at the industry partners, which exposed them to interdisciplinary research environments, fostered collaborative teamwork across research groups, and gave them first-hand experience of R&D in companies.

WP5 Communication, dissemination, and exploitations: Apart from communication measures such as a creation of a brand logo (Figure 1), webpage, social media presence, press releases, and presentations at conferences, PlaMatSu published a special issue on bio-inspired materials in Advanced Materials (Figure 2). Moreover, 13 original research papers and reviews were published with many more in development. PlaMatSu’s ESRs reached out to the general public by organising the exhibition “Our Future is Nature Inspired” at the Cambridge University Botanic Garden in 2020 (Figure 3). A video on nature-inspired design was produced for the exhibition and is available on PlaMatSu´s webpage (Figure 4). The exhibition received TV and radio coverage and was promoted on social media.
PlaMatSu achieved a fundamental understanding of the genetic and developmental factors that govern structure formation in plant cuticles. These structures lead, e.g. to structural color on petals which is an important feature of flowers like Hibiscus to attract pollinators. PlaMatSu researches also deciphered how microscopic surface roughness develops during the growth of leaves of, e.g. the rubber tree. The cuticle furthermore acts as a barrier for water evaporation, and the mechanism that result in asymmetric water transport properties were revealed.
Another fundamental process during structure formation of natural and synthetic polymer films is dewetting. PlaMatSu investigated these dewetting phenomena using synthetic polymers as model compounds.
The remarkable properties of cuticles and the underlying structure-property relationships inspired the network to develop novel synthetic materials with similar properties. Structurally colored materials were achieved with cellulose nanocrystals (CNCs). Thanks to the research in PlaMatSu, these rainbow-colored materials can now be produced as flexible films on a large scale, and could find application as edible, biodegradable and environmentally friendly glitter in cosmetics, the food industry and in coatings. Other structurally colored materials developed by PlaMatSu are hybrid materials of silk proteins and CNCs, as well as cellulose films that feature disordered diffraction gratings.
PlaMatSu developed several routes to plant-inspired surfaces, including high precision replication of micro-structured plant leaf surfaces. The resulting replicas allow biomechanical experiments, ecological and evolutionary studies, and industrial applications like surfaces with improved haptic properties. Polymerization-induced wrinkling and electrospraying of wrinkled colloids were two other methods to create bio-mimetic low friction surfaces that are slippery for insects and therefore of potential interest for crop protection. Lubrication and low friction surfaces are also of importance in fine mechanics. PlaMatSu developed a novel surface modification based on an amphiphilic protein that hinders lubricants from spreading in an uncontrolled way, thus paving the way to environmentally friendly lubrication.
Many plant leaves are covered by hairs that play a role in moisture management and provide protection from sun light. Inspired by these biological role models, a process was developed to 3D-print hairy surfaces with a specially developed polymer ink.
Leaf-cuticle inspired membranes were prepared that allowed for asymmetric permeability of water and ethanol, thereby opening pathways to membranes that allow to remove and recover ethanol from water-ethanol mixtures.
Silk proteins are ideally suited as biologically-derived building blocks for bio-inspired materials, as the protein displays excellent mechanical and optical properties. Unfortunately, it cannot be readily stacked into lamellar cuticle-inspired structures because the protein tends to detach from synthetic polymers. To address this issue, PlaMatSu developed a novel photo-crosslinker for silk. It stabilizes silk protein films and bonds them covalently to polymer surfaces.
Apart from ground breaking scientific results PlaMatSu also yielded materials and technologies that have the potential for commercialization. The most advanced technology for exploitation are structurally coloured cellulose pigments which are of high appeal for cosmetics and coatings. A team at the University of Cambridge is pursuing this technology for commercialization.
Bio-inspired research is ideally suited to draw the attention of the general public to the importance of STEM subjects. With the help of the Cambridge University Botanical Garden, PlaMatSu organized an exhibition in the garden that explained the fantastic properties of plant cuticles and their potential to inspire the next generation of novel materials (Figure 3). The exhibition was an ideal outreach activity to engage with a broad public on site, but also through PlaMatSu’s social media channels and through conventional media. To quote BBC’s Louise Hulland while reporting about the exhibition: “Plants with superpowers: Move over Spider-Man, move over Wonder Women. Captain Pampas Grass is here!”