Scientists at the University of Birmingham have developed a new smart material that can repeatedly switch between a solid-like gel and a flowing, liquid-like state using different external triggers. The breakthrough could open new possibilities in drug delivery, sensing, catalysis, and advanced materials.The research, published in the Journal of the American Chemical Society, marks the development of the first multi-responsive gel built from synthetic molecules known as foldamers. These molecules can fold into specific shapes and be assembled, dismantled, and rebuilt when required.
One material, multiple responses
The newly developed material behaves differently depending on the stimulus applied to it. Ultraviolet light changes its molecular structure, causing the gel to lose its solid-like form and become liquid-like. Heat can then restore the gel by allowing its molecular network to form again.Acid provides a separate mechanism for dismantling the material by breaking the connections that hold its molecular structure together.This ability to respond to different triggers is what makes the material particularly significant. Instead of being designed to react to only one environmental change, the gel can be controlled through multiple independent mechanisms.
How the molecular network works
At the heart of the material are helical foldamer molecules connected by palladium ions. The metal ions act as four-way molecular junctions, linking the foldamers into an extended network.The network traps liquid within it, giving the material its characteristic gel-like behaviour.When ultraviolet light is applied, light-sensitive components within the foldamers change shape. Although the transformation begins at the molecular level, its effects spread throughout the larger network. The result is a visible transition from a solid-like gel to a flowing state.Heating reverses this process, enabling the molecular network to assemble again. Acid works differently by disrupting the bonds between the foldamers and palladium ions, effectively dismantling the network.
From organic gel to water-based hydrogel
The researchers also converted the material into a hydrogel containing water without destroying the molecular connections responsible for its structure.That development is particularly relevant to biomedical applications. Hydrogels can retain significant amounts of water while maintaining their structure and are already important in areas such as biotechnology, medicine, and drug delivery.A material that can respond to specific triggers could, in principle, be developed for applications such as controlled release of therapeutic compounds or systems designed to respond to changes in their surrounding environment.
Scientists see potential beyond the laboratory
The researchers say the work remains at a fundamental stage, but its ability to incorporate multiple responses into a single material could prove useful in the development of smart sensors, switchable catalysts, and systems capable of capturing and releasing selected molecules.Potential applications include targeted drug delivery, biomedical materials, chemical manufacturing, and responsive sensing technologies.The research also demonstrates how changes at the scale of individual molecules can be translated into large, observable changes in the behaviour of a material.
Atomic-level investigation cuts years of research to hours
Understanding exactly how the gel is assembled was another major part of the study. The team used dynamic nuclear polarisation-enhanced solid-state nuclear magnetic resonance spectroscopy, or DNP NMR, to examine the material at the atomic level.The technique dramatically increased the sensitivity of the measurements. An experiment that could have taken roughly seven years using conventional NMR was reduced to about 12 hours.The researchers also used Magic Angle Spinning NMR to determine how palladium atoms connect the foldamer molecules. A small amount of the gel was placed inside a ceramic rotor and spun at extremely high speed within a powerful magnetic field, allowing the team to investigate the material’s molecular architecture.The findings provide a detailed picture of how the individual building blocks come together to create a material capable of changing its physical state on command.The breakthrough highlights a growing direction in materials science: Designing substances whose properties can be controlled through carefully selected molecular interactions. While practical applications may still be some distance away, the ability to make one material respond independently to light, heat, and acid could offer scientists a new platform for building the next generation of intelligent materials.
