SeSaMe

Colouration – the natural way Colour affects our perception, our idea of quality, influences our senses and our mood – it is the visual marker that is weighted with meaning. In Industry, the norm is to chemically synthesise pigmentation in laboratories but there is demand for a more natural method of colouring everything from the food we eat to products we use. That’s why a project headed

by Dr Silvia Vignolini is focusing on innovation in more natural colouration techniques Traditionally, the colouring of commercial products relies on chemical and inorganic materials which have been artificially synthesised. The SeSaMe project is taking a different direction, by exploring the use of natural materials like cellulose and chitin to obtain the desired pigmentation.

There is a growing demand for more environmentally friendly ways to add colour – especially in food products.

Colour dyes used to enhance the look of food and food packaging and dyes in general have long been tainted with controversy, with concerns over toxins and health impacts – to a point where consumers are increasingly scrutinising ingredients or how things are made, for anything that looks unnatural and potentially harmful.

However, colour is important as a visual indicator and something we are used to using as a gauge for quality, attractiveness, freshness or taste.

This is why the pioneering science undertaken by the researchers working on the SeSaMe project could have far reaching appeal as they examine ways to mimic nature’s methods for producing colours.

“We use natural materials to create a novel type of pigment called photonic pigments. These pigments can be used in many everyday life applications (such as for cosmetics or food colourations) – so

Figure 1: Cellulose can self-assemble inside aqueous droplets to form coloured Microparticles, which can be observed with an optical polarising microscope (a), and a scanning electron microscope (b, c). The cross section of the microparticles shown in (d) reveals the cellulose helical architecture responsible of the coloration. they have a strong commercial relevance,” explains Dr Silvia Vignolini of the SeSaMe project.

The nature of colour SeSaMe’s approach is based around how nature creates colour, using a technique called self-assembly.

Nature has been using colour since the beginnings of life itself, as an indicator of sexual health, to warn off predators or to encourage pollination. Creating colour is something nature does very well and so it follows that it should be possible to

let nature teach us how to produce colour without resorting to toxic or synthetic solutions.

“A lot of our research is inspired by nature and how it creates and uses colour. The strategies that have been developed in nature are incredibly optimised. We really study the natural structures produce coloration using material like cellulose and polysaccharides and how the plants can control and assemble these material in order to form such incredible structures.

“The idea is that instead of trying to re-invent this, we are trying to copy what nature does. We observe how this structure, this cellulose for example, is organised in nature, then we try to reproduce it in the lab with the same material, to achieve a similar type of optical response,” said Vignolini.

“We have two aims, one is to try and understand how these natural structures are made and the other is to develop pigments from the optical response. We aim to learn how to make copies in more detail, in order to make a functional material.”

The full spectrum By replicating this natural process and embedding it in materials, a range of desired colours can be achieved. The researchers will produce colours across

Examples of structural coloration with natural materials: (from left to right) Microscope Image of structurally coloured cellulose film: different colour can be obtaining changing the evaporation conditions, microscope Image of the epicure of Pollia Japonica fruits, microscope image of cellulose suspension in cross polarisation between capillaries, revealing the typical textures of liquid crystalline systems.

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the entire spectrum, from ultraviolet to infrared, including white.

“The optical appearance of white does not necessarily mean a lack of pigment.

Often white is obtained with chemical additives that enhance scattering of light,” explains Dr Vignolini.

Researchers are also able to tailor the optical response of the material in multiple ways, not only by changing the colour but by determining the full extent of the optical appearance.

“The full optical appearance of an object is a concept which is more complicated than just the colour itself. Colours can look matt, glossy or very metallic, and we can directly embed this functionality in our material,” said Dr Vignolini.

“There is a growing interest in the use of natural materials in industry,” asserts Dr Vignolini. “We are trying to understand the fundamental aspects of these materials, as such understanding will

Macroscopic images of coloration obtained with cellulose: photograph of a macroscopic cellulose film with Structural coloration.

Below: Self-Assembly process of cellulose Microparticles: Comparison between (a) theoretical and (b) experimental images obtained from the confinement of a cholesterol cellulose suspension within a spherical geometry, when viewed through cross-polarisers (top row) and upon addition of a first-order tint plate (bottom row). Upon loss of water the Maltese cross typical of chiral nematic ordering is retained, until drying.

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Full Project Title Bio-Inspired Photonics (SeSaMe).

Project Objectives SeSaMe is an ERC study where researchers attempt to understand and replicate nature’s methods for producing colours and optical response. The research could lead to the production of low-cost, biodegradable photonic materials and in turn, replace the potentially hazardous, traditional colourants, that have often proven to be controversial in product development.

Project Funding SeSaMe is an ERC funded project.

environment. If we want to have a wider impact in society then we need to make these materials on a large scale. To do that, we need to have scalable technology.”

We use natural materials to create a novel type of pigment called photonic pigments. These pigments can be used in many everyday life applications (such as for cosmetics or food colourations) – so they have a strong commercial relevance open up new technological possibilities, which is why we are collaborating with several companies to explore how to take our technology forward. From my perspective as a scientist, I’m interested in the challenge of how to make this material from a fundamental point of view, but this research could provide a benefit to society too, enabling a new technology that is cleaner and better for the

At a glance

To this end, those close collaborations established with the commercial sector will ensure the best chance for exploiting new and exciting opportunities, born from the project’s research.

Contact Details Project Coordinator, Dr Silvia Vignolini, Ph.D University of Cambridge Department of Chemistry Lensfield Road Cambridge CB2 1EW UK T: +44 1223 761490 E: sv319@cam.ac.uk W: http://www.ch.cam.ac.uk/group/vignolini/

SEM image of a cross section of a cellulose film revealing the helical architecture responsible of the coloration.

Dr Silvia Vignolini, Ph.D

Photograph by Gabriella Bocchetti.

Dr Silvia Vignolini was awarded a PhD in Physics at the European Laboratory for non-Linear Spectroscopy and the Physics Department at the University of Florence.

During her PhD, she studied light-matter interaction in the near-field regime. In 2010, she joined as a Research Associate the Cavendish Laboratory in Cambridge, UK, working on optical properties of soft-materials. She joined the Chemistry Department in Cambridge as an academic in 2014, and in 2015 she has been awarded an ERC Starting Grant.

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