An octopus can adeptly bend one part of an arm around an obstacle while another reaches into a small crevice to grab an object. Reproducing that local control in a soft robot requires multiple actuators — components that turn energy into movement — together with their mounting hardware and connections.
Researchers at the College of Design and Engineering , National University of Singapore (NUS CDE), have taken a cue from the nerve connections that activate small regions along an octopus's arms. Their method allows one continuous artificial muscle to contract from base to tip or only in selected regions, producing several controlled bends without the need for a separate actuator at each location.
This approach could help compact robots reach inside machinery for inspection or assembly, or collect samples in places people cannot easily or safely access. In their work, the team demonstrated a drone-carried arm whose muscles powered both its movement and its gripping and liquid-sampling tools.
The research was led by Professor Cecilia Laschi from the Department of Mechanical Engineering at NUS CDE, Director of the NUS Advanced Robotics Centre and the Soft Robotics Lab based in CDE. The findings were published in Science Advances on 23 September 2026.
"Many robots are built around many individual joints, so they face some of the same movement constraints as animals with skeletons," said Dr Xin Wenci, the paper's first author, a former PhD student at the Soft Robotics Lab and a Postdoctoral Associate at the Singapore-MIT Alliance for Research and Technology (SMART) Centre. "That motivated us to look at the octopus and how it controls movement along a continuous arm."
Precise control along a continuous muscle
The team's artificial muscle is a spring made from shape-memory alloy, a metal that contracts when an electric current heats it and is stretched back to length by the robot's flexible frame as it cools.
The researchers attached electrical contact points, called wire-bonding junctions, at intervals along the spring. When the control system sends current between two selected points, only the section between them heats and contracts. Changing which points are used lets the continuous muscle act as one long section or several shorter controllable sections.
Each continuous muscle, therefore, replaces a row of separate actuators along the arm. Several such muscles can still work together to pull the arm in different directions: two supported side-to-side bending, while four arranged around the body allowed three-dimensional movement.
In one prototype, four continuous muscles controlled six sections of the arm. For comparison, Dr Xin estimates that a conventional motor-driven design would need 24 individual motors to provide comparable control. Using fewer actuators could make dexterous arms lighter and more compact, easing deployment in confined spaces or on drones with limited carrying capacity.
More movement from the same length
In tests on two arms measuring 10 centimetres, the continuous design bent through 91 degrees, compared with 46 degrees for the conventional stacked design under the same driving conditions. Reducing the space taken up by separate mounts and gaps left more of the arm's length available for movement. In addition, computer modelling estimated that the tip could reach a volume of space nearly three times that of the conventional arm.
Further, the new approach allowed the team to adjust how many regions of a longer arm it controlled separately. In a bending test, controlling its full length as one section used about 40% less energy than controlling four sections independently. Controlling more regions separately allowed the arm to form additional bends around obstacles, giving the team a way to match its movement to the task without changing its physical structure.
The researchers also set the arm a recognisable task: reproduce drawings of the letters 'N', 'U' and 'S'. A camera tracked its shape so the control system could adjust the bends to follow each drawing. Using two continuous artificial muscles to control seven regions along the arm, the team demonstrated how several bends could be coordinated to create a chosen shape without a separate muscle for every region.
An octopus-inspired arm takes shape
For aerial deployment, an arm must be light enough for a drone to carry and compact enough to minimise changes to the aircraft's balance in motion. The team's design places lightweight artificial muscles along the arm itself, reducing the need for separate drive motors at its base.
To demonstrate the approach in a deployment setting, the team built an arm-and-gripper system measuring 0.6 metres. Different sections of the same artificial muscles bent the arm, operated the gripper and moved a syringe plunger to draw in or release liquid.
The arm could be rolled up for transport beneath a drone, then extended at the target location. Including its supporting equipment, the robotic attachment weighed about 450 grams. The drone carried the system past obstacles to a simulated hard-to-access location. In separate demonstrations, the arm collected liquid and solid samples through an opening only two centimetres high and retrieved objects at different heights while suspended beneath the drone.
The researchers see potential for similar arms to operate in confined spaces. An example in industry is vehicle or aircraft assembly. By bending different sections in different directions, the arm could guide a tool around surrounding components to reach parts that would otherwise be difficult to access.
"The next challenge is to find out how this approach scales to different sizes, shapes and types of artificial muscle," added Prof Laschi. "A smaller version could be explored for endoscopy, using slender instruments to look inside the body, while a larger, stronger arm could inspect beneath debris during search and rescue operations."
To improve its performance in the air, the team plans to explore new spring geometries and other heat-responsive materials that could generate greater force to work against gravity. They also plan to investigate built-in air cooling to shorten the cooling time between contractions, allowing the arm to reposition more quickly.
"Underwater applications are also particularly interesting because water itself provides a natural cooling environment. This could potentially improve the cooling rate of the actuators and therefore their response speed," Dr Xin added. "But first, we will need to redesign or protect the electronic systems and investigate the use of thermal insulation materials to better manage heat transfer."
