Since these alloys also absorb and release heat when deformed, they are fundamental to another of the team's key developments: elastocaloric cooling and heating, a climate-friendly and energy-efficient alternative to conventional systems.
The second type of smart material that Motzki and his team are exploring is a thin, highly flexible silicone film with extraordinary capabilities. By adjusting the applied electrical voltage, these polymer films can perform a wide range of movements—vibrating, tapping, pushing, or pulling—making them ideal for creating lightweight, low-power mini-motors. Paul Motzki's team uses these polymer actuators to develop innovative pumps and valves. They also apply them to textiles to create wearable, responsive interfaces that act as a haptic bridge between the body and digital systems. The films can also be used in smartphone screens to create dynamic buttons and haptic feedback.
Paul Motzki is a pioneer in this field and is now, in a world first, combining these two technologies—shape-memory alloys and dielectric elastomer actuators—to take a significant step forward in the emerging field of elastocaloric cooling. The European Research Council, Europe’s largest funder of cutting-edge research, is supporting this pioneering work with an initial ERC grant of approximately €1.5 million over five years.
Both technologies offer key advantages: they are lightweight and energy-efficient, and as environmentally friendly as the electricity that powers them. Because of their ability to exert considerable force in a small space, they are often called "artificial muscles." Motzki's goal is to combine these artificial muscles and mini-motors made from smart materials to create extremely flat, compact, and lightweight refrigeration units that are therefore easy to integrate into other systems.
Motzki is also working to bring elastocaloric technology to market through another EU-funded project. In 2024, Paul Motzki and his team were part of a European consortium that won the prestigious EIC Pathfinder Challenge from the European Innovation Council, receiving €4 million in funding. He and his consortium partners are currently developing a prototype residential air conditioning system based on elastocaloric principles. The EIC Pathfinder award is given in recognition of “new, visionary, and radical technologies that have the potential to facilitate necessary societal transitions, address global challenges, and establish new markets.” Motzki, who in addition to holding a professorship at Saarland University is also the scientific director and managing director of the Center for Mechatronics and Automation Technology in Saarbrücken, explains the difference between the two awards: "The EIC Pathfinder focuses on rapidly translating research into practical applications, while the ERC Starting Grant supports fundamental research aimed at expanding the scientific base of elastocaloric technology."
It is a rare achievement for a researcher to be awarded both the EIC Pathfinder and the ERC Starting Grant by the EU. The additional EU funding for Motzki's research on the use of shape-memory alloys in smart medical implants is provided through the €21 million Horizon Europe project "SmiLE – Smart implants for life enrichment," which involves 25 leading institutions from 12 European countries.
Background:
Elastocaloric
Cooling. Elastocaloric cooling is a novel, climate-friendly, and energy-efficient technology that operates without harmful refrigerants or fossil fuels. For years, Motzki and his doctoral advisor, Stefan Seelecke, have been developing this technology at Saarland University and the Center for Mechatronics and Automation Technology in Saarbrücken through several multi-million-euro research initiatives. The European Commission has identified elastocaloric cooling as the most promising alternative to conventional methods, and the World Economic Forum included it among the “Top Ten Emerging Technologies” for 2024. The Saarbrücken team has already built a prototype mini-fridge and is currently developing systems for vehicle cooling.
Elastocaloric cooling works by repeatedly stretching nickel-titanium wires or sheets and then allowing them to relax again, enabling heat to be absorbed in one area and dissipated in another. Whether used for cooling or heating, the system can achieve temperature differences of around 20°C. "This applies to a single-stage component," explains Motzki. "If we build multi-stage systems, we can achieve much larger temperature differences."
The basis of all the elastocaloric prototypes being developed in Saarbrücken is an unusual property of the nickel-titanium alloy: shape memory. We all know that water can exist in three physical states or “phases”: solid (ice), liquid (water), and gaseous (water vapor). The nickel-titanium alloy has two phases. Although both phases are solid, their crystal lattices have slightly different physical dimensions. The term “shape memory” simply reflects the ability of nickel-titanium to return to a previous state (crystal lattice structure) through a reversible phase transformation. When one phase transforms into the other, wires or sheets made from the nickel-titanium shape memory alloy (SMA) absorb heat; when that phase transforms again, the material dissipates the heat into its surroundings. Thus, the air or liquid flowing over the nickel-titanium alloy during the phase change cools or heats up, and this effect can be harnessed, for example, in heating or cooling systems. "Depending on the specific application, we use SMA wires or thin sheets, or we create 3D-printed components with complex geometries," explains Motzki.
Researchers in Saarbrücken are developing practical cooling and heating systems by designing prototypes with intelligent mechanics that cyclically load and unload shape-memory components. The foundation for this development work was laid in numerous research projects that examined how compact drive systems can be used to keep SMA sheets or wires in constant motion.
The new prototypes currently under development will incorporate dielectric elastomer films as ultracompact motors. “We are using these dielectric elastomers to develop novel drive systems that don’t need to be equipped with additional sensors,” explains Paul Motzki. The films are coated on both sides with a highly flexible, electrically conductive layer, allowing them to respond to voltage changes and perform precise, energy-efficient movements. When researchers apply an electrical voltage to the polymer film, these electrically conductive layers attract each other, compressing the polymer and causing it to expand laterally, increasing its surface area. “By varying the applied electric field, we can control the film’s movement very precisely and make it perform continuously variable bending motions or vibrate at a desired frequency or amplitude. Essentially, we are creating an ultralight, yet efficient, energy-saving motor,” says Motzki.
Both dielectric films and shape-memory cables are inherently capable of providing information through changes in their capacitance or electrical resistance, completely eliminating the need for external sensors. “We can use these measured values to determine how the film or cables are deforming. Our technology is essentially self-sensing, as it has its own built-in position sensors,” he adds. “We use artificial intelligence to map these electrical measurements to specific motion sequences, allowing us to precisely control the movement of our actuators, drives, or motors.”
Horizon Europe
is the EU's ninth research framework program and the world's largest single funding initiative for research and innovation. Its aim is to foster a knowledge-based and innovation-driven society and build a competitive economy, while promoting sustainable development.
ERC Starter Grants are awarded by the European Research Council (ERC) to support early-career researchers pursuing promising approaches in basic research areas.
Professor Paul Motzki
is Professor of Smart Materials Systems at Saarland University and Scientific Director of the Saarbrücken Center for Mechatronics and Automation Technology (ZeMA), where he heads the Smart Materials Systems research division.
He studied mechatronics at Saarland University, where he earned his PhD in 2018 for his research on thermal shape memory alloys. In 2016, he took over as head of the Sensors and Actuators research group at ZeMA. After completing his PhD in 2018, he was able to further expand his research group at ZeMA, leading to the creation of the Smart Materials Systems research division. In 2022, Paul Motzki was appointed Associate Professor at Saarland University (Department of Systems Engineering) and at ZeMA Smart Material Systems for Innovative Production (SMiP). Since 2023, Motzki has been chair of the VDI/VDE Technical Committee GMA 2.16: Intelligent Materials and Systems. He is also a board member of the smart3 network, a director of the SMST board at ASM International, a member of the ASME SMASIS Senate, and a co-founder of the International Elastocalorics Society (IES).
