Europium complex harvests ambient energy to power minirobots

Inchworm robots driven by cunning coordination chemistry are on the march, their flexible bodies powered by nothing more than the warmth of their surroundings (Angew. Chem., Int. Ed. 2025, DOI: 10.1002/anie.202518011).Researchers have previously used soft materials to create a menagerie of robots that can grip, wriggle, and even dance. But most require relatively concentrated energy sources—light, electric fields, or chemical reagents—that can gradually degrade the robots’ soft structures.A team led by Ximin He of the University of California, Los Angeles, and Tao Chen of Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, set out to create soft robots that instead rely on ambient thermal energy, enabling continuous motion for long periods of time.The researchers’ robots are based on a polymer called polydimethylsiloxane (PDMS) that expands when heated. The researchers created PDMS chains that carry metal-binding pyridinediimine ligands, and then they added europium ions into the mix. At room temperature, the ions coordinate the ligands to pull PDMS chains together. But mild heating breaks the coordination bonds and allows the chains to move apart, making the material expand 25 times as much as pure PDMS.When the team coated this europium-enhanced polymer onto paper, the warmth of a hand made it expand so that the structure flexed upward. As it cooled, the europium complexes reformed and made the polymer layer contract until it met the hand again, restarting the cycle.Building on this concept, the researchers crafted a series of inchworm-like robots that crawl around by flexing back and forth,