Researchers at the University of Birmingham have developed a new material that can change from a gel to a liquid-like state under ultraviolet light and can be rebuilt with heat.
The scientists created a multi-responsive gel built from what they called 'foldamers' — synthetic molecules that fold into defined shapes which can be assembled, disassembled and reassembled on demand.
The discovery, they said, could lead to smart sensors, switchable catalysts and materials that capture and release selected molecules on demand.
The team published their findings in the Journal of the American Chemical Society, detailing how the material changed from a solid-like gel into a flowing, liquid-like state when exposed to ultraviolet light.
Heating restores the gel, while acid provides another way to break down its molecular network—which could be revolutionary for the pharma industry if medicines can release drugs only when exposed to a specific trigger, such as changes in acidity.
Researchers from Birmingham’s School of Chemistry also converted the material into a water-containing hydrogel without disrupting the molecular connections that hold it together.
The work brought together expertise in designing new gels, led by Dr Sarah Pike, supramolecular chemistry, led by Dr Chiara Arno and atomic-level structure characterisation, led by Dr Dominik Kubicki.
Dr Sarah Pike said: “A very small change in molecular shape translates into a visible change in the whole material — demonstrating how carefully designed molecular components can give us control over the behaviour of a bulk gel.
The research is at a fundamental stage, but the ability to programme more than one response into the same material could ultimately inform the design of smart sensors, switchable catalysts, and materials that capture and release selected molecules on demand.
In the new material, palladium ions join helical foldamer molecules, acting as four-way molecular connectors.
The components form a network that traps liquid, giving the material gel-like properties. Ultraviolet light can change the shape of light-sensitive units within the foldamers, causing the gel to lose its solid structure.
Heating allows the network to reform, while acid disrupts the connections between the foldamers and palladium ions.
Dr Chiara Arno said: “Supramolecular materials are assembled using reversible interactions rather than permanent chemical bonds. That gives us an opportunity to create materials that are robust under normal conditions but can be reorganised or dismantled when we apply the right signal."
"We converted the material from an organic solvent-based gel into a hydrogel containing water, without disrupting its underlying structure. Hydrogels are widely used in biotechnology and medicine because they can hold large amounts of water while maintaining structural integrity."
This represents a significant advance in building materials that behave more like biological systems by responding intelligently to their surroundings — for example, releasing drugs only when exposed to a specific trigger, such as changes in acidity within diseased tissue.
The researchers used dynamic nuclear polarisation-enhanced solid-state nuclear magnetic resonance spectroscopy (DNP NMR) to examine the gel at an atomic level.
DNP's sensitivity enhancement reduced an experiment estimated to take around seven years with conventional NMR to just 12 hours.
Dr Dominik Kubicki said: “Seeing a material change is only half the story. If we want to design better responsive gels, we need to know precisely how their molecular building blocks are connected."
DNP NMR gave us that atomic-level picture in a material that is otherwise exceptionally difficult to study – allowing us to solve a major challenge in gel science.
The team said that future applications of the research could include the following:
- targeted drug delivery
- controlled release of therapeutic molecules
- biomedical materials
- smart sensing systems
- catalysis and chemical manufacturing.
This work was supported by various organisations, including UKRI, the Engineering and Physical Sciences Research Council, the Biotechnology and Biological Sciences Research Council, the Royal Society, the Royal Society of Chemistry, the Leverhulme Trust, and European research programmes.
Access to specialised low-temperature DNP NMR infrastructure was provided by the University of Gothenburg.
