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How soft robots work, and why medicine cares

Clear, jargon-free explanations of soft robotics and how it could help in medicine. No background needed. Every topic has a Simple and a Technical version, so you can go deeper when you are ready.

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What is a soft robot?

A soft robot is a robot made mainly from soft, flexible materials, such as silicone or rubber, rather than rigid materials like metal. Think of an elephant's trunk or an octopus's arm rather than a traditional robot arm.

Because its body can bend, stretch and change shape, a soft robot can adapt to its surroundings, fit into tight spaces and interact more gently with people and objects.

Soft robots are built from materials with low elastic moduli (typically elastomers, with Young's moduli comparable to biological tissue), so that deformation of the body itself produces motion and compliance. They have, in principle, very many degrees of freedom, which makes them a natural fit for continuum-style motion.

The trade-off is that modelling, sensing and control are harder than for rigid-link robots, because deformation is continuous, nonlinear and often hysteretic.

How do they move?

Most soft robots use fluids, such as air or water, to create movement. The fluid is pushed into small spaces, called chambers, inside the robot. As these chambers fill, they expand and make the robot bend, stretch or twist.

By controlling how much fluid enters each chamber, engineers can control the robot's movement. Other ways of creating movement also exist, including electric motors and materials that change shape when heated or exposed to electricity.

Soft fluidic actuators (SFAs) convert fluid pressure into deformation through internal chambers with deliberately asymmetric stiffness or geometry, using reinforcement such as fibres, strain-limiting layers or bellows-like structures. Pneumatic actuation is lightweight and fast but compressible; hydraulic actuation is stiffer and more precise but needs fluid handling. Hybrid approaches combine the two.

How does a soft robot "feel"?

Because soft robots constantly change shape, fitting them with traditional sensors can be difficult. Researchers use different approaches to help them sense their surroundings. For example, changes in the pressure inside a robot can help estimate how hard it is pushing against something.

Sensing approaches include embedded flexible strain sensors, optical fibres and external tracking, as well as model-based estimation that infers contact forces from internal pressure and volume changes. Using the fluid medium itself as the sensing channel avoids adding bulky electronics in the tip, which matters for miniaturised medical devices. Calibration, hysteresis and drift are the main practical challenges.

How do you steer one?

Steering a soft robot is different from steering a traditional robot. A traditional robot often has joints that can be moved to specific angles. A soft robot bends and changes shape along its body, making its movement harder to predict.

Engineers use computer models and sensors to understand how the robot will move. They can then use this information to adjust the air or liquid inside the robot and guide it towards its target.

Approaches range from analytical models such as piecewise constant curvature, through finite element simulation, to learning-based and data-driven controllers. Real-time use typically needs reduced-order models or learned surrogates, and often benefits from closed-loop feedback from pressure, shape or tip-position sensing.

Where could they help patients?

Looking inside the body: Soft, flexible instruments could make it easier and more comfortable to examine parts of the body, such as the gut or the ear.
Surgery: Flexible robotic tools could reach difficult areas inside the body through small openings, potentially reducing damage to surrounding tissue.
Recovery and rehabilitation: Soft wearable devices could support movement and help people regain strength while remaining comfortable against the skin.
Delivering treatment: Small, flexible robots could one day help deliver medicines directly to specific areas of the body.

An important note: Many of these applications are still being developed and tested in research laboratories. Before they can be used in hospitals, they must go through extensive safety testing and regulatory approval.

Endoscopy and navigation: Steerable continuum devices for the GI tract, airways and ear canal, with a focus on reducing contact forces and improving reach.
Minimally invasive and micro-surgery: Miniaturised soft segments, sometimes combined with concentric tube robots, for confined anatomy such as the eye.
Assistive and rehabilitation devices: Soft exosuits and gloves with pneumatic actuation and compliant interfaces.
Translation barriers: Sterilisation or single-use design, biocompatible materials, repeatability, sensing for safety, and regulatory pathways (for example medical device classification) shape what reaches the clinic.

Mini glossary

Actuator: The part of a robot that creates movement, for example by expanding when filled with air or liquid.
Continuum robot: A robot that bends smoothly along its body, like an elephant's trunk, rather than moving through separate joints.
Compliance: How easily something bends or changes shape when a force is applied. Soft materials are generally more compliant than rigid materials.
Finite Element Method (FEM): A computer-based method used to predict how an object will bend, stretch or deform under different forces.
Endoscope: A thin instrument with a camera and light, used by doctors to look inside the body.

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