How smart can materials become?

Smart materials have long been designed to respond to external stimuli. But increasingly, researchers are asking a more ambitious question: how much control can we have over that response?

Recent research in Materials Horizons explores new ways to programme, sense and adapt material behaviour - sometimes bringing several of these capabilities together in a single system.

How far can we push programmability?

Shape-memory materials can be programmed to remember a particular shape. But researchers are now exploring ways to make that behaviour reprogrammable, giving greater control over when and how a material changes shape.

One approach uses physical entanglement of ultrahigh molecular weight polymers to create reprogrammable shape-memory ion gels, enabling new ways to control their shape-memory behaviour.

Programmability can also be built into the way materials are manufactured. Multi-responsive nanocomposites demonstrate how 4D printing can create structures that transform remotely and adaptively in response to different stimuli.

The shift is from materials that simply respond to stimuli towards materials whose responses can be deliberately designed and reprogrammed.

Can actuation and sensing become one?

For soft robotics, wearable technologies and haptics, the ability to move is only part of the challenge. Researchers are increasingly looking at how materials can sense their own deformation and movement while they actuate.

A conductive hydrogel combines near-infrared photothermal actuation with multimodal self-sensing, enabling remote movement while detecting strain, movement direction and velocity.

Another approach combines programmable soft magnetic composites and phase-change materials to create a self-sensing haptic interface, capable of producing different types of tactile stimulation while monitoring its own displacement.

Researchers are also exploring new approaches to soft actuation, including a solvent-free, high-dielectric-permittivity polysiloxane ink for electrically responsive multilayer soft actuators.

Actuation and sensing are increasingly being integrated within the same material systems.

Can material properties become dynamically controllable?

Smart behaviour doesn't always mean a material visibly changing shape. Researchers are also finding ways to make functional properties continuously tunable.

Mechanical metamaterials, for example, can be engineered so their bending behaviour can be adjusted in situ, changing how a structure responds without changing its overall shape.

Smart functionality can also involve combining multiple functions within a single material system.

Elsewhere, a dual-layer composite combines broadband microwave absorption, dynamic tunability and self-healing. Its electromagnetic response can be modulated, while its matrix enables the material to repair itself.

The next generation of smart materials may not have a single defined response. Their properties can be designed to change according to what is required.

Where do smart materials go next?

Taken together, these studies point towards a broader shift in smart-materials research.

Rather than designing materials around a single stimulus or function, researchers are increasingly combining programmability, actuation, sensing, adaptability and self-healing.

The result is a new generation of material systems that can do more than respond. They can sense, change and adapt.

This convergence could open up new possibilities across soft robotics, wearable technologies, haptics, advanced manufacturing, adaptive structures and electromagnetic technologies.

And as researchers gain greater control over how materials behave, the boundary between material and machine becomes increasingly blurred.

As researchers learn to programme not just what materials are, but how they behave, the possibilities for smart materials are becoming increasingly open-ended.