Materials modelled after nature

Materials modelled after nature

24 Oct 2016

As a result of evolution, nature has created materials with extraordinary qualities. Well-known examples include light-weight, high-tensile materials, such the mother-of-pearl found in seashells, the exoskeletons of insects, or silk.

“Natural materials can have special properties – they can be self-cleansing, self-repairing and luminescent. New, interesting combinations of qualities are still being discovered in a range of natural organisms,” says Olli Ikkala, an Academy Professor.

Ikkala’s field of expertise is biomimetics, which involves mimicking natural materials and their properties in order to create new materials. In addition to his Academy Professorship, Ikkala heads the Academy of Finland’s Centre of Excellence in Molecular Engineering of Biosynthetic Hybrid Materials at Aalto University. He is also a visiting professor at the University of Grenoble in France.

Mother-of-pearl in seashells is of particular interest to scientists owing to its light-weight, high-tensile structure and resilience. These properties are the result of a self-organised, nanocomposite structure in which biological nanometre scales and polymers alternate like Lego bricks.

According to Ikkala, this type of material would be suitable for a motorcycle helmet – it would be light to wear but highly protective against injuries. Tough but light-weight materials would also be ideal for use in vehicles, since they would save energy thanks to their light weight.

Ikkala made progress in his research on biomimetic nanocomposites in a project funded by the Academy of Finland in 2012–2016. Five years ago, Ikkala’s research group was the first in the world to successfully manufacture a strong, self-organising nanocomposite material similar to mother-of-pearl.

“At the time, we were still unable to achieve the desired tensility, but we’ve now also made progress in this respect. We’re currently working on methods of industrially producing the material.”

The meticulous structure of natural, self-organised materials grows over a long period of time, which is why producing them at high speed in an industrial context is difficult. The mother-of-pearl layer on a seashell takes years to build, while cradled in the depths of the sea.

“The manufacturing process of biomimetic materials has to be different to that of natural biological materials. The material should also be inexpensive and fast to make, without compromising its properties.”

However, Ikkala is confident that the industrial production of certain biomimetic materials is not too far off:

“We’re talking about years rather than decades.”

New properties in nano-cellulose

Ikkala has also studied the possibility of integrating new types of functionalities with natural materials. One of the materials he is researching is nano-cellulose.

The fibres of nano-cellulose are light-weight, but almost as resilient as steel. Trees growing in woods are not, however, like rigid steel, as they can grow and bend towards the light. Between the extremely tough fibrils, there is softer biological matter that serves as conduits for water and nutrients, allowing the tree to grow and adapt.

“From the wood, we remove all biological material that is of no use to our application and replace it with a functional material that will be useful in future applications,” Ikkala explains.

Together with Professor Esko Kauppinen’s team of researchers, Ikkala’s research group has managed to attach carbon nanotubes to nano-cellulose.

“We have made transparent nano-cellulose membranes and coated them with pliable, conductive carbon nanotubes. This type of material would be useful in, say, stretchable electronics, which are currently being introduced in consumer markets.”

Nano-cellulose could also be of use in medical applications, as it can support cells.

“We’ve investigated the potential of nano-cellulose in surgical thread used for sutures. Stem cells could be grown inside thread made from nano-cellulose, which would speed up the healing of a surgical wound. This research work has been performed in collaboration with Professor Marjo Yliperttula’s research team at the University of Helsinki.”

Simplified versions of nature’s creations

The perfect mimicking of natural materials is not, however, possible or even sensible, because nature is highly complex.

“Man-made materials are usually simple, with simple properties. In nature, materials are structurally complex – and their structures and functions are intertwined and integrated.”

The functional properties of natural materials – such as the resilience of mother-of-pearl in seashells – are based on the self-organisation of molecules and structures.

“In the case of self-organisation, structural information is, as it were, coded into the mutual interdependencies between self-organised elements. Nature does this quite elegantly, for example through the order of protein chain sequences.”

As Ikkala points out, the possibilities offered by natural methods are so numerous that the link between the code and the actual structure is not entirely clear to scientists. In fact, in biomimetics the aim is to create a simplified application of the methods in question: the only sequences of self-organised molecules and structures that are copied are those whose function can be predicted and understood, and which seem most useful.

“In biomimetics, we aim to cherry-pick,” Ikkala says.

Multidisciplinarity creates challenges

In Ikkala’s opinion, the biggest challenge in biomimetic research is multidisciplinarity. Biomimetics requires in-depth knowledge of at least physics, chemistry, materials science, genetics and biological organisms. Ikkala’s own background lies very much in physics.

“No one person can master every subject. That’s why there’s always an element of uncertainty in this type of research. You need to find collaboration networks and partners with whom you can ponder these issues together.”

Sharing a common language between experts in different fields is not, however, always a given.

“Together with researchers in forest product technology, we launched the nano-cellulose research project as early as 2003, but it took us something like five years to learn to understand each other.”

Of his future plans, Ikkala reveals that he intends to move forward, expanding his range of interests to include living organisms in addition to inorganic materials.

“The functioning of living organisms is based on energy consumption. Next, I’d like to come up with completely new types of biomimetic materials, which would be given new properties by providing them with energy,” Ikkala says.

Text by Tea Kalska
Picture by Pekka Kiirala

Last modified 24 Oct 2016
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