Silvia Vignolini, Reader in Chemistry and Biomaterials at University of Cambridge explores the wonderful world of colour and how it affects our perception and mood
Colour is a powerful communication tool, it deeply affects our perception of the world, stimulating our senses. It is not by chance that since the beginning of our society colouration is used as a visual marker for concepts such as quality and desirability. Industry today employs synthetic pigments to colour the objects around us, however there is a growing demand for natural methods of producing colorants for many applications. This challenge has inspired a new project headed by Dr Silvia Vignolini to develop a sustainable and scalable pathway to innovative natural pigments.
Colourants in industry
Colourants are used universally in industry, from paints and cosmetics to food and textiles, where they play a central role in visually upgrading a product by acting as a gauge for quality, attractiveness, freshness or taste. The pigment industry has long relied on the use of complex synthetic dyes or inorganic particles to produce colours and visual effects (e.g. hues, brightness, shine).
However, there is a growing demand for more natural or environmentally-friendly ways to add colour – especially in food and cosmetic products. Dyes are commonly used to enhance the look of food and food packaging but have long been tainted with controversy, with concerns over toxins and health impacts – to a point where consumers are increasingly scrutinising ingredients for anything that looks unnatural and potentially harmful.
The bio-inspired photonics group, led by Dr Silvia Vignolini, is taking a different direction. By drawing inspiration from nature and exploiting sustainable biomaterials, such as cellulose or chitin, her group focuses on manufacturing colours by carefully controlling the assembly of matter on the nanoscale rather than chemical composition. Such non-fading “structural colouration”, is responsible for many of the most vibrant colours in nature, as found in the wings of butterflies, the feathers of birds and in the epidermis of plants.
The strategies that have been developed in nature to create colour are incredibly optimised. By directing the assembly of discrete biological building blocks, typically biopolymers (e.g. proteins and polysaccharides) or nanoscale mineral deposits, natural architectures produce not only intense coloration but also often display intriguing visual effects, such as iridescence.
Cellulose, for example, is ubiquitous in the cell wall of plants and is responsible for the high rigidity in wood. However, in certain fruits and leaves, the cellulose fibres are assembled at the nano-scale into a helicoidal structure, such that it intensely reflects blue light. By replicating the natural assembly process within the plant cell and embedding it into materials, the researchers are developing a range of cellulose-based “photonic” pigments.
Cellulose nanocrystals, extracted from naturally-abundant cellulose fibres, are a highly promising material due to their inherent biocompatibility, biodegradability and scalable production. When dispersed into water, cellulose nanocrystals have been shown to spontaneously assemble on the nanoscale to mimic the natural helicoidal architecture. Upon drying, this structure is retained, enabling the reflection of visible light. Using this approach, the researchers can produce colours from across the entire spectrum, from ultraviolet to infrared, with an optical appearance tailored from matte to glossy or metallic. The key challenge now is how to develop large-scale fabrication of cellulose-based photonic pigments.
Cellulose nanocrystals are an industrial reality, with the number of patents increased exponentially over the last decade. The development of cellulose-based photonic pigments is therefore extremely timely, with growing industrial interest both from the manufacturers, who are eager to push cellulose in novel application directions and from end-users in seek of natural and sustainable alternatives to conventional pigments.
Cellulose-based pigments are suitable for use in printing ink ($20.4 billion by 2022), colouration of food ($ 3.75 billion by 2022), cosmetics ($429.8 billion in 2022) and sun-creams ($11.1 billion in 2020). The successful scale-up of the fabrication of cellulose-based photonic pigments will allow for the manufacture of a truly sustainable, biocompatible and potentially edible alternative to conventional synthetic dyes for mass-market applications.
The Vignolini group has recently developed a disruptive methodology to control the assembly of cellulose nanocrystals in the confined geometry of a micron-sized water droplet. Upon drying, each droplet produces a single coloured cellulose nanoparticle that can be used as a photonic pigment. The advantage of their patented approach is that it can readily build upon existing industrial emulsion technologies to produce a dry powder that can be directly incorporated into existing formulations, eliminating the need for synthetic dyes.
The researchers are now exploring the scalability of this methodology and how it can be translated out of the laboratory to an industrial-scale process capable of meeting the demands of the pigment industry. To this end, Silvia Vignolini has established close collaborations with leading pigment companies and end-users that will ensure the best chance of exploiting the new and exciting opportunities born from the project’s research.
By understanding the fundamental science behind the assembly of cellulose nanocrystal droplets many new technological possibilities will be opened, which is why the researchers are also actively exploring how cellulose-based pigments can be coated directly onto a surface for use in security printing or as smart/responsive packaging.
A truly renewable and sustainable resource
Cellulose is the most abundant biopolymer on the planet and therefore is a truly renewable and sustainable resource. Its natural degradation pathway avoids concerns over bio-accumulation, an area of intense scrutiny as the environmental implications of synthetic micro-plastics becomes more apparent.
Additionally, by removing the dependence on mica, a glittery mineral used in car paint and makeup and whose extraction raises ethical concerns over child labour in illegal mines, cellulose-based photonics has the potential to have significant societal as well as environmental impact. Therefore, the pioneering science undertaken by the bio-inspired photonics group could have far-reaching appeal as they examine new ways to mimic nature’s methods of producing colour.
Please Note: this is a commercial profile
Dr. Silvia Vignolini
Reader in Chemistry and Biomaterials
University of Cambridge
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