Will the knife of the future be able to adapt itself to different tasks? How programmable materials may one day become an everyday reality – and how far we still have to go.

By Mehmet Toprak.

Sometimes, big changes announce their arrival through something small. Chris Eberl is holding an inconspicuous plastic bar in his hand. He presses one end with his finger. Suddenly the bar springs to life, sending a wave from one end of the 20-cm surface to other before becoming rigid again. The process is reversible, too. When Eberl releases his finger, the material returns to its original state as if powered by an internal switch. In fact, the structure of the material contains many tiny integrated switches.

What at first glance looks like a neat trick may in fact be the precursor to a technological revolution. Chris Eberl, professor and deputy director of the Fraunhofer Institute for Mechanics of Materials IWM, prefers the term “paradigm shift”. Eberl is convinced that in the future, the very technology that enables a piece of plastic to generate waves in the Fraunhofer lab in Freiburg will pave the way for the development of entirely new products.

Step by step: Bringing the idea to life

The technology that underpins Eberl’s plastic bar has been the focus of discussion since as early as the 1970s and 1980s. What was once only a distant theory is now, step by step, becoming reality in the form of programmable materials. At their genetic core, programmable materials have the unique ability to process information like a computer and to respond like a machine. However, this information is not processed as an electrical signal; instead it takes the form of physical changes in the shape of the material. This makes it possible to design the internal structure of the material in such a way that, when compressed, a wave emerges at a predefined location and moves along the surface as the material continues to be compressed. And this is because the structure and composition of the material determine its properties, enabling an object to be soft in one area, for example, while being rigid in another. Materials such as these could be used to develop products such as car seats that either embrace the passenger firmly or allow greater freedom of movement, depending on how fast the vehicle is travelling. The material properties which can be manipulated in this way include permeability, hardness, thickness, and thermal and electrical conductivity.

But this is merely the beginning. Eberl explains: “The second step in this process is about creating adaptive materials capable of modifying their properties autonomously as conditions change, i.e. pressure, temperature or humidity.”

The scope of application is broad. Researchers at the Fraunhofer Institute for Applied Polymer Research IAP are also looking into the possibility of developing filters for liquids which close when the liquid heats up and open when it cools. Battery housings for electric vehicles are another potential application for programmable materials. Lithium ion batteries, in particular, are susceptible to heat-related problems. Battery housings made from programmable materials would be capable of modulating their thermal conductivity at pre-defined temperatures in order to discharge heat. And in response to cold temperatures, by contrast, the same housing would assume the properties of a protective insulator. 

Professor Peter Gumbsch, Director of the IWM, underscores the advantages of this technology: “Integrating two or more functions into a single material, without the need for external components such as joints, wires, switches and sensors, saves on both materials and resources.” Ideally, what the end consumer gets is a product which is both easy to use and efficient.  Programmable materials also make disposal and recycling easier, as the products contain fewer different types of materials.

The point isn’t so much to find the best materials for a given function, but to find the right way to integrate the desired functionality into the materials.

Prof. Peter Gumbsch, director of Fraunhofer Institute for Mechanics of Materials IWM

Turning concepts such as these into reality also requires a revolution in the way we think about development and industrial manufacturing. “The point isn’t so much to find the best materials for a given function, but to find the right way to integrate the desired functionality into the materials,” explains Gumbsch.

Pooling expertise: The Fraunhofer Cluster of Excellence Programmable Materials

In response to the enormous challenges faced by researchers in the area of programmable materials, in 2018 the Fraunhofer Institute established a “Cluster of Excellence” research group. The group is comprised of institutes from across Germany, including the Fraunhofer Institutes for Applied Polymer Research IAP, Structural Physics IBP, Chemical Technology ICT, Mechanics of Materials IWM and Machine Tools and Forming Technology IWU, bringing together chemists, mathematicians, physicists, process engineers and product developers.

One of the objectives of the research team is to develop components which are capable not only of switching between two states, but which can also be programmed to carry out “if/then” functions, defined as a switch from property A to property B if environmental condition A is present and environmental condition B has reached a specified value X. Products and components such as these would be capable of performing highly complex functions while comprising few materials. “As we get better at controlling the materials, we’ll be able to integrate more and more complex functions” explains Gumbsch. “The details are in the internal structure,” adds Eberl.

The Fraunhofer experts are convinced: “The technology works, and the concepts are practicable.”

One of the greatest challenges posed by programmable materials is the difficulty in scaling production in order to manufacture not only tiny components, but also complete products.  Building the internal structure of the demonstration units requires high tech tools, such as laser lithography systems and 3D printers, that are capable of working the material at the nano and micro levels and constructing it layer by layer. This difficulty is compounded by the fact that there are currently very few products which can actually be manufactured in this manner.

The Fraunhofer experts Gumsch and Eberl are convinced they can make the manufacture of programmable materials economically viable: » We are already developing demonstration units and prototypes. The technology works, and the concepts are practicable.«

Products are expected to begin entering the market in just a few years, including filtration systems for cleaning water and other liquids, shape-shifting aerodynamic components and grippers and arms for soft robots capable of handling heavy loads. 

Source: weiter vorn 03/2019, Fraunhofer Magazine. Published with kind permission of the Fraunhofer Society.

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