What if the display of your phone could help you find the right button to press? Or if we could make materials that are able to learn and make decisions? This may sound like science fiction, but we are closer to such applications than most of us realize. At the Institute for Complex Molecular Systems (ICMS), scientists are developing these kinds of materials. And they cover the whole track; from molecules to devices.

‘It is sometimes hard to pin down whether a material is truly adaptive at the molecular level,’ says Ghislaine Vantomme, assistant professor of Supramolecular Chemistry. ‘Is it simply responsive, reacting the same way each time to an external trigger, or does it actually reconfigure itself so that its response evolves in a changing environment, as natural materials do? That is what we aim for.’

‘Balancing responsiveness and stability is hard; you want the material to react quickly without falling apart over time’

Ghislaine Vantomme

So, what constitutes an adaptive material? ‘We usually put this label on materials that can repeatedly change their structure or shape upon exposure to external stimuli like light or an electrical current’, explains associate professor Human Interactive Materials Danqing Liu. Think for example of materials that can shrink and expand, which could make them suitable as a sensor or to move across a surface.

Training

The emergence of adaptive materials brings about a shift in the way material scientists think. Vantomme: ‘We are moving from materials designed to perform a specific task, to materials that can be trained by the end-user.’ But why would we want or need this? What kind of problems can these new materials address? ‘That is hard to imagine’, says Liu. ‘We think that there are so many opportunities, but since this is a whole new way of looking at materials, we cannot yet grasp every possibility.’

That doesn’t limit researchers to come up with ideas. ‘If you rely solely on mechanics to make your materials move, it is very hard to make a robot that will always move towards light’, says Bas Overvelde, associate professor Soft Robotic Matter. ‘But if you integrate materials that respond to light, it can be done.’ Another big idea relates to the concept of personalized health. Vantomme: ‘If you can make a sensor out of a material that for instance can be trained in real time on patient data to predict medical needs before they actually arise, that would be a game changer.’

‘By controlling the directions in which it expands and shrinks, we can make protrusions in the screen’

Danqing Liu

To achieve this, you need to stepwise cover the whole track from molecule to material ánd from material to device. Vantomme’s focus is mainly on the first stage. ‘We try to find molecular systems that have adaptive properties and can form switchable ordered structures, so that molecular changes become visible in the material itself.’

At present, she uses polymeric materials like oligomers, and the resulting material can switch its property under the influence of light. ‘These switches change the conductivity, so it is a way to store data, for example.’ It sounds quite straightforward, but: ‘It is hard to balance responsiveness and stability in adaptive materials. You want the material to react quickly and efficiently, but without falling apart over time.’

The synthesis of these materials is also a delicate matter, says Vantomme. ‘The molecular systems we design are extremely sensitive to changes, so reproducibility becomes a real challenge. The properties depend on the exact formulation, and even tiny impurities can affect the performance.’ That is why Vantomme puts robots to work in the lab. ‘Robots can repeat the process exactly the same way every time, which gives us much more reproducible results.’

Protrusions

The next step is processing these molecules into working materials. This is Danqing Liu’s expertise. ‘I work with liquid crystal polymers that you find in LCD-screens.’ She uses these for their mechanical properties, particularly the so-called N-isotropic deformation. ‘When you heat a liquid crystal, it expands in certain directions while it shrinks in other directions. By controlling the directions in which it expands and shrinks, we can make protrusions in the screen’, explains Liu.

To control this movement, she uses electricity. ‘The electricity is normally used for individual pixels, but we can tune this to make very precise protrusions.’ Even though Liu has been working on this idea for ten years, she does realize that such materials still sound crazy to many people. ‘At first, I almost couldn’t get my work published, and nobody understood the possibilities.’ Laughing: ‘But now that we actually managed to figure it out, everybody lines up to get this technology. Especially since it can be made by adding a layer to existing LCD-screens, so it is very easy.’

‘It would be really interesting if we could embed decision-making processes in the materials’

Bas Overvelde

One obvious application is for people with visual impairments, to help them navigate displays easier and even “see” images. But there are more options. ‘Huawei approached me to put this function into their new foldable laptop. They got complaints because it didn’t have a physical keyboard.’ Liu also had to decline some projects. ‘If you switch the protrusions on and off you can self-clean a surface. NASA has asked me to apply this for their Mars Rover, but I don’t have the capacity.’ Her focus is on the display, which is still on a watch-size scale. ‘We will now develop it further in a start-up. We need more experience in electrical and mechanical engineering to get it to work in a real device.’

Pumping

And that is where Bas Overvelde comes in. ‘I work solely on the mechanical side, to translate these ideas into actual devices and solve mechanical problems.’ He is working with Liu and many other ICMS colleagues. One of his big projects is the so-called hybrid heart. ‘We want to make an artificial heart that is capable of pumping blood through the body and emulates our own heart better than current artificial hearts do.’

This project doesn’t really employ adaptive materials yet, but Overvelde foresees that the knowledge gained from these materials will become useful in the future. ‘The heart needs to withstand different conditions. And once we get a working prototype, I think it would also be interesting to see if we can use adaptive materials to make this heart work even better.’

He hopes to test the hybrid heart in a large animal model, like a sheep, within six years. ‘If it works, it could be a life changer.’ Despite all these ideas, we are still far away from the full potential of adaptive materials, says Overvelde. ‘It would be really interesting if we could embed decision making processes – a sort of brain – in the materials. Like the branches of a tree that know which direction to grow without consciously making that decision.’ This would create devices smart enough to respond to their environment and adapt to their user. What will those materials look like? ‘No idea’, laughs Vantomme. ‘It is hard to predict what will work. But we will get there, and it will make a difference.’