Cellulose for bio-inspired photonic materials

Biological photonic structures, optimized over millennia by the rigorous process of evolution, can provide broad inspiration for novel artificial and multifunctional photonic materials. The most brilliant and striking colours in nature are in fact obtained without the use of any pigments, but by nano-structuring transparent materials: for example, colour in plants can be obtained using only cellulose. By periodically arranging cellulose nano-fibres in the cell wall, different plant species obtain incredibly vivid colours across the entire visible spectrum, from the deepest violet to the most intense red.

In this project, I propose to use cellulose as a new photonic material in order to produce structures ranging from photonic crystals to completely random structures, providing materials with strong colouration and ultra-white response, respectively. Such materials will find highly sustainable uses in everyday life. As an example, edible cellulose-based nanostructures with structural colour can be use to substitute toxic dyes and colorants in food. Moreover, the fact that the processes involved in cellulose extraction and manipulation are already used in the paper industry facilitates the use of such materials for industrial applications such as security labelling or cosmetics.
Knowledge about disorder in such structures, and the study of completely random systems is also extremely important to our understanding of the biological significance of disorder both in natural structures and for the fabrication of new materials. In particular it will aid our understanding of the extent to which natural photonic crystals and bio-inspired structures are tolerant of structural disorder.
Mimicking natural photonic structures, using the same materials that are involved in Nature, unveils information regarding the mysterious processes of the natural development of plant cells.

In conclusion, by taking inspiration from nature it is possible to obtain smart multifunctional materials that are fabricated by sustainable routes with abundant and cheap materials like cellulose.

Nature's most vivid colours rely on ordered, quasi-ordered or disordered structures with lattice constants or scattering element sizes on the order of the wavelength of visible radiation. Knowledge of the interplay between the morphology, composition and optical appearance of biological photonic systems can provide inspiration for novel artificial photonic materials. Plants develop nanostructured tissues with a strong photonic response. Many flowers develop a striated epidermal layer that produces iridescent colouration, which can be used as a cue by pollinators. Complex multilayers structures made on cellulose are observed in several kinds of cells and in a wide variety of plants. Such structures provide a strong and colour-selective reflection in a narrow wavelength region. The way in which these structures are produced in plant cell walls remains an unresolved problem in developmental biology.
Replicating cellulose-based architectures is extremely interesting as it sheds light on the biological processes at work in growing these structures in the cell walls, and it equips us to fabricate novel photonic structures using low cost materials in ambient conditions.
This project will lead to the fabrication of cellulose-based smart optical materials and metamaterials using a scalable and sustainable approach. The cellulose-based photonic structures fabricated will find applications in everyday life, for example as replacements for toxic colorants in foods and for security labelling in banknotes.
The project will open a completely new field of research that combines different disciplines and techniques in order to understand the biological significance of disorder in Nature. In the case of flowers, the optical response from the fabricated structures will be experimentally and theoretically investigated and the produced samples will be then used for behavioural experiments with bees in order to understand the effect of disorder in plant-pollinator signalling.

IMPACT SUMMARY

The proposed research has interdisciplinary aims. The research will benefit academics in various sectors, from physicists, to material scientists, to biologists both on a national level (the UK is one of the leading countries in the field of bio-inspired photonics) and international level. Within the project I will promote national and international collaboration to create a network of young researchers from different backgrounds.

Within this research I will address fundamental problems of biology including the formation of the plant cell wall and the role of disorder in natural photonic crystals from the evolutionary point of view, but I will also develop new methodologies to fabricate materials that can control the flow of light propagating inside them, work which will be equally extremely interesting for material scientists and the nano-photonics communities.

In this project I aim to improve established techniques, and to explore novel ideas and methods for revolutionary solutions to the many challenges in the fabrication of photonic structures using cellulose. Any breakthrough (but also incremental improvements) on existing techniques will have highly significant impact on the advance of nanosciences overall. The project will also promote the training of indivudal researchers and collaboration within different research institutions within UK and abroad. A PDRA and several Masters students will be trained during the project and they will benefit from the knowledge and facilities of different collaborators involved, thus promoting and improving their research skills. At the same time, my own leadership and management skills will be further improved, as a result of overall management of the project: for instance, I will develop my abilities in supervising students, coordinating with collaborators, and forging strong interactions with many researchers within and outside the Host Institution.

The fact that the project's aims cross different disciplines also makes it engaging for the general public. In order to maximize the impact on society, we will make timely contact with mass media (radio, TV and press) to coincide with important publications; this will raise public awareness and understanding of science, and at the same time, it will promote the role of women in science. For this I will participate in public outreach events and involve schools, proposing activities during open days and developing a website with sections aimed at general audiences. These sections will be rich in pictorial examples and simple explanations of physical processes linked to everyday life (for example, the idea of thin film interference iridescence can be explained by using a soap bubble). I already have significant experience in outreach and public engagement (see CV).

The project will also contribute more directly to the improvement of quality of life, health and well-being, since it aims to use a sustainable polymer (cellulose is also one of the most abundant bio-polymers on earth) as a new photonic material for a wide range of applications. For example, the project aims to fabricate edible coloured structures, cosmetics and security labeling using scalable and cheap processes. This will lead to the exploitation of scientific knowledge, leading to the publication of patents and eventually to the development of commercial products. The host institution is particularly suitable in such aims since it provides the services of Cambridge Enterprise, which will help to target commercial uses of the research findings at industrial partners. I already have experience in collaborating with industry and have published a patent during my PhD (see Pathways to Impact).