MIT Unveils “Banana Finger” Soft Pneumatic Actuators

May 04, 2022 by Jake Hertz

Massachusetts Institute of Technology (MIT) researchers have created a new manufacturing technique that could allow for more cost-effective soft pneumatic actuators.

One of the most difficult challenges in designing assistive wearables and robotics is mimicking the intricately unique aspects of the human body. Specifically, recreating the human hand's motion, precision, control, and sensing abilities has been a topic of much interest in academia and industry alike.

Here, the economic challenges are as significant as the technical challenges, where a complex system will be costly and difficult to manufacture. 

This week, researchers from MIT have come up with a new way to manufacture soft pneumatic actuators that hope to bring down costs for these kinds of systems. 


MIT's banana-like soft actuators.

MIT's banana-like soft actuators. Image used courtesy of MIT


This article will talk about pneumatic actuators, some of their relevant use cases, and how MIT's new research could impact the technology.


Soft Pneumatic Actuators for Human Touch

There are many significant challenges and tradeoffs in designing systems to mimic or assist the human hand.

The human hand is unique in the way it combines a high level of precision, strength, and control while being gentle and tactically sensitive. Recreating this becomes a challenge of creating a lightweight, customizable, and effective system that also won't break the desired object when grabbed, the same way a hand knows when to stop squeezing.

One highly touted solution to this problem is the soft pneumatic actuator.


Examples of fabric-based soft pneumatic actuators.

Examples of fabric-based soft pneumatic actuators. Image used courtesy of Nguyen and Zhang


Soft pneumatic actuators are devices that combine the low response time and large output power of pneumatic actuators with soft materials that may mimic living tissue. These soft materials are often elastomers like silicone or fabric-based, knitted materials. 

With soft pneumatic actuators, roboticists can achieve an essential mix of power, control, and flexibility while ensuring careful and safe care of a grabbed object, thanks to the soft materials used.


Manufacturing Soft Pneumatic Actuator Challenges

While proven to be a highly effective technology, soft pneumatic actuators historically come with various manufacturing challenges.

According to MIT researchers, past attempts have been made at creating such devices using different techniques, including: 

  • Composing fabrics with different stiffnesses
  • Programming textile stiffness with yarn properties
  • Applying unique knitting shaping techniques
  • Casting extrinsic reinforcement on textiles

However, the challenge with most existing techniques is extremely labor-intensive and meticulous.

On top of this, many of the previously attempted techniques are incapable of integrating sensing capabilities into soft materials during manufacturing. This difficulty represents a further challenge, as sensing materials must either be post-processed into the material or forgotten altogether.

All in all, an "ideal" solution for creating cost-efficient soft pneumatic actuators requires something that engineers can automate, easily integrate into existing workflows, and include sensing capabilities without the need for post-processing.


MIT's PneuAct Method

This week, researchers from MIT announced a new method for manufacturing pneumatic soft actuators that claims to solve many of the challenges with existing workflows.

In their recently published paper, the researchers describe their new method, dubbed PneuAct, which is being called "a scalable pipeline to computationally design and digitally fabricate soft pneumatic actuators." 

The actuator itself simply consists of a standard silicone tube that is covered and confined by a specially-crafted knitted sheath.


The soft pneumatic actuator consists of a silicone tube and a specially woven sheath.

The soft pneumatic actuator consists of a silicone tube and a specially woven sheath. Image used courtesy of Luo et al


The knitted sheath is created using a machine knitting process to create elastic stitches to create non-homogenous structures that influence the actuators' bending when inflated. 

When inflated, the deformation of the actuators is mainly defined by the knitted sheath. On top of this, the researchers were also able to integrate pressure and capacitive sensing structures into the actuator through the use of meticulously woven conductive yarns.

An important aspect of this new technique is using a machine knitting approach, which results in increased speed, digital programmability, and access to more materials than available in other methods. 

As a result, the researchers show that their method allowed them to create an entire knitted structure automatically in a single machine run.

Overall, research such as this, which aims to find new and potentially better manufacturing technology methods, can be a practical next step in pushing technology forward. It will be interesting to see how soft pneumatic actuators and robotic tactile touch continues to develop with this type of research.