Soft robots are able to do a number of different things but they move slowly. Actuators, the artificial muscles for soft robots, usually use pneumatics or hydraulics. These are hard to store and don’t respond quickly. There is, however, a solution for this in the form of dielectric elastomers.

Dielectric elastomers have some of the important qualities necessary for this use including good insulation and soft materials but they are lacking the ability to provide high voltage and rigid components so that their form can be maintained. These elastomers use inefficient and complex circuitry to provide high voltage and, without rigid components, they are unable to keep their form.

A new dielectric elastomer has been developed by researchers at the John A. Paulson School of Engineering and Applied Sciences at Harvard that can work with low-voltage, offers a better range of motion and doesn’t require rigid components.

A graduate student from the school and the first author of the study paper named Mishu Duduta says that this soft robotic could potentially be the Holy Grail for soft robotics. The research that has been carried out offers solutions for the issues with soft actuation. Actuation voltage is reduced while the energy density is increased and the rigid components are eliminated. She goes on to say that up until this point soft robot actuators required electrical fields that were too high.

An artificial muscle built from a sandwich of soft, flexible elastomers and electrodes made of carbon nanotubes. (Image Credits: Peter Allen/Harvard SEAS)

The team of researchers used two different materials to build the dielectric elastomer including a carbon nanotubes electrode that had been developed already in the Clarke Lab. The second was an elastomer based on one that had previously been created at UCLA and this one did not require rigid components for its use. When these two materials were used together they complemented each other perfectly and as a result the new device was able to outperform other dielectric elastomer actuators.

Most elastomers have to be pre-stretched before they can be attached to a rigid frame and thus offer only a limited motion range. The UCLA-developed elastomer began as a liquid which was put under a UV light to cure and no pre-stretching was required. This produced sheets with 2 sticky sides that were paper thin so they could adhere well to the electrodes and to each other.

Thin nanotubes made of carbon replaced the commonly used carbon grease as the electrode. When these nanotubes are used the energy density does not decrease and the elastomer stiffness does not increase. This means that significant force is still produced since the elastomer is still able to stretch.

This soft muscle can move with very low volume of electricity. Actuator could be used in everything from wearable devices to laparoscopic surgical tools, fully soft robots or artificial muscles in more complex robotics. (Image Credit: Mishu Duduta/Harvard SEAS)

The research team put together a multilayer of elastomers and electrodes so that one electrode could power both the elastomer above it and below it.

According to Duduta, it’s important to make a dielectric elastomer very thin since the thicker the material the more voltage is required. If the elastomer is too thin, however, it won’t be able to produce enough force and will be flimsy. With a multilayer approach significant force is available and the device is robust. She goes on to say that this research was especially significant due to the combining of the materials and their processing to overcome the current limitations of pre-stretching and high-voltage use.

Soft Robotics
An artificial muscle built from a sandwich of soft, flexible elastomers and electrodes made of carbon nanotubes. (Image Credits: Peter Allen/Harvard SEAS)

The potential for this actuator is quite limitless since it could be used for a variety of devices including complex robotic artificial muscles, soft robots, laparoscopic tools or soft grippers.

The work has been published recently in Advanced Materials.