Wireless small soft robots are extremely desirable in applications like non-invasive surgery. But they must be able to do other difficult tasks in addition to just mobility if they are to replace rigid tools. However, such tasks necessitate large force or torque outputs, which are impossible to do with softer materials alone!
To accomplish this, researchers at Stuttgart’s Max Planck Institute for Intelligent Systems developed a small-scale coiled muscle actuator that uses tunable mechanical properties and radiofrequency magnetic heating to perform surgical tasks that require a high force output and work capacity, such as suturing, cutting, drilling, and clamping tissues.
Artificial muscles in soft robotics are designed to mimic natural muscles’ mechanical adaptability by contracting, expanding, rotating, or bending to efficiently generate motion or complete tasks. The team employed a high-strength nylon fibre as the stiff muscle core and a polymer coating to protect it from external mechanical and thermal stimuli in order to create the muscle actuator.
The researchers used a high-toughness resin matrix layer comprising superparamagnetic Fe3O4 nanoparticles and graphene oxide platelets between the core and the outside cover. When subjected to radiofrequencies, these magnetic nanoparticles produce heat, which actuates the muscle core and improves the actuator’s mechanical strength. They then coiled the resulting structure into a coil to create artificial muscle with a diameter of about 1 mm.
The researchers used an external radiofrequency magnetic field to heat the nanoparticles wirelessly. If the fibre ends are free but cannot rotate, the artificial coiled muscle contracts, or twists if one end of the fibre is fixed while the rest can rotate. To achieve an actuation force and work capacity of around 3.1 N and 3.5 J/g, the researchers methodically tuned the concentration of graphene oxide platelets and the thickness of the active layer. These figures are five and four orders of magnitude higher than prior estimates for magnetic soft actuators.
“Thanks to the muscle actuators integrated to wireless soft medical devices, we can now achieve surgical functions that require high force outputs, such as suturing, cutting, clamping and drilling. Such functions have not been possible so far for wireless soft medical devices,” explain senior authors Wenqi Hu and Metin Sitti. “Our new approach extends the capabilities of wireless medical soft robots to surgical applications. As next steps, we will demonstrate such functions in small animal surgeries in in vivo conditions”
The whole study can be found here.