Soft actuator

Pick up a ripe tomato with a metal claw and you will either crush it or drop it. The gap between those two failures is measured in millimetres of force that rigid actuators are too coarse to navigate safely. An octopus tentacle has no such problem — it is soft throughout, distributes force across its entire surface, and conforms to whatever it touches. Roboticists looked at the octopus, the earthworm, and the elephant trunk and asked: what if the robot's body itself were the actuator?

Soft actuators are devices that produce movement using inherently flexible, compliant materials. Instead of aluminium joints and steel cables, they use silicone rubber tubes that inflate and curl, fabric pouches that expand, shape-changing gels, or thermally activated polymers. Because the material itself deforms to create motion, the boundary between structure and actuator dissolves.

How they move

The most common soft actuator is a pneumatic artificial muscle (PAM) — a sealed silicone or elastomer chamber with a particular geometry. Inflate it with air and the geometry forces it to bend, curl, or extend in a predictable direction. The Harvard Soft Robotics group's PneuNets (pneumatic networks) are a widely studied example: a silicone finger with a series of internal chambers that, when pressurised, curl the finger closed like a hand grasping.

Other mechanisms include:

• Hydraulically amplified electrostatic actuators (HASEL) — thin pouches of dielectric liquid that deform when high voltage is applied across them, contracting at speeds approaching muscle.
• Dielectric elastomers — stretchable polymer films sandwiched between compliant electrodes; an applied voltage squeezes the film thinner, causing it to spread outward.
• Thermally activated hydrogels — materials that swell or contract with temperature change, used in micro-scale soft robots responding to environmental heat.

Real-world example

Soft Robotics Inc. (now integrated into larger automation supply chains) commercialised silicone soft grippers widely used in food handling — picking strawberries, placing pastries, handling irregularly shaped produce that would be damaged by rigid jaws. The grippers conform to the object on contact, distributing grip force across the whole surface. Ocado, the UK online grocer, has tested soft robotic hands in its highly automated warehouses specifically because the range of product sizes and fragility makes rigid grippers impractical.

Why it matters

Rigid robots dominate structured industrial environments because structure is predictable. The real world — hospitals, kitchens, farms, homes — is full of fragile, irregular, and living objects. Soft actuators are the technology bet that robots can eventually operate safely in those environments. The field is young, manufacturing is still difficult (silicone moulding at scale is not trivial), and durability under millions of cycles remains an open research problem. But the biological world has already proven the concept works — almost every animal that grasps uses soft tissue as its primary actuator.

Some of the most capable soft robots in existence right now are not robots at all — they are the muscles, tentacles, and trunks of animals that evolution spent 500 million years optimising.