The process of 4D printing is an extension of 3D printing, in which solid objects are created using materials that can change shape when exposed to certain stimuli like heat, water, or light. At the University of Queensland’s Australian Institute for Bioengineering and Nanotechnology (AIBN), researchers have printed 4D structures using liquid metal polymers that can be coaxed into performing a range of mechanical tasks with infrared lasers. AIBN researchers Ruirui Qiao (left) and Liwen Zhang have developed a new method to prepare liquid metal polymers for 4D printing. The solid 4D structures created by their lab can be manipulated into different shapes with an infrared laser. Courtesy of AIBN. Lead researchers Liwen Zhang and Ruirui Qiao said the unique preparation methods developed by their lab allow them to produce 4D designs that are solid and durable while also being able to bend, grasp, lift, and release items five times their weight, or revert to a pre-programmed shape. “4D printing takes traditional 3D printing and adds a new dimension — the dimension of time,” Zhang said. “Our method allows us to produce smart liquid metals that can be customized, shaped, and prompted to change over time without needing wires or circuits. 4D printed objects are usually prepared with a 3D printer using specific ingredients that give the finished product new qualities and abilities. Previous research has demonstrated the utility of nanomaterials in printing polymers, though challenges with establishing the necessary percolated network have led to the flexibility and the level of shape change being compromised. The current work used gallium-based spherical liquid metal nanoparticles to prepare printing resins that respond to near-infrared light. The researchers grafted the liquid metal nanoparticles with reversible addition-fragmentation chain transfer agents to enable polymerization for 3D printing. The grafted nanoparticles, importantly, can be directly prepared in 3D printed resins, allowing a one-step printing approach. The resulting objects can be stimulated with a NIR laser to guide the materials to bend, grab, and release items. The structures printed by the Qiao-Davis lab showed that they could be manipulated into performing basic mechanical tasks, such as grasping and lifting items up to five times their weight. Courtesy of AIBN. While the technology is in its early stages — 60 seconds is required to induce the shape change, and repeatability stands at about 25 shape changes — Qiao said there is great potential to use it in the design of soft robotics, or technologies that mimic natural movements and interactions. This could mean a number of applications across the aeronautical engineering and medical device sectors, including coronary stents, artificial muscles, and other devices that adapt and change shape inside the body. More broadly, Qiao said the ability to customize and shape materials after they had been printed would lead to wider manufacturing breakthroughs and consumer innovations, from climate-reactive clothes and building materials to self-assembling furniture. “4D printing is a rapidly evolving field that is really only limited by imagination,” Qiao said. The research was published in Nature Communications (www.doi.org/10.1038/s41467-023-43667-4).