Structural Buckling Leads to Soft Actuator Design

Harvard engineers take inspiration from human muscle to design robotic actuators for smooth motion.

VAMPs shown actuated and cut open in cross section. The cross section shows the inner chambers that collapse when vacuum is applied. (Image courtesy of Wyss Institute at Harvard University.)

VAMPs shown actuated and cut open in cross section. The cross section shows the inner chambers that collapse when vacuum is applied. (Image courtesy of Wyss Institute at Harvard University.)

Robots and humans working side-by-side is no longer just science-fiction. Everything from factories, operating rooms and even everyday household routines are incorporating some form of robotic technology to make our lives easier.

Our relationship with technology presents challenges as we grow closer to it. This includes ensuring that we can safely work with our mechanical friends in a world where we are more and more frequently surrounded by pistons, arms, and presses.

An engineering researcher at Harvard’s Wyss Institute for Biologically Inspired Engineering, George Whitesides, is working with his team to create a potential solution to this problem: a new model of pneumatic actuator that is safer, softer and more durable than other robotic actuators.

The team’s recently unveiled their Vacuum-Actuated Muscle-Inspired Pneumatic Structure (VAMPS). VAMPS is crafted from a durable polymer material called Elastocil, rather than the industrial metals used in traditional “rigid” pneumatics, which already makes it safer to operate. The rubbery polymer of the VAMPS arm is arranged into a “honeycomb”- structure made up of hollow, air-tight tubes.

To activate the VAMPS and accomplish work in the “limb,” air is sucked out of these hollow tubes, collapsing them and causing a shortening of the structure as a whole.


VAMPs are functionally modeled after the human bicep, similar to the biological muscle in terms of response time and efficiency.(Image courtesy of Wyss Institute at Harvard University.)

The end product is an actuator that uses vacuum pressure to generate linear motion which mimics the contraction of human muscle. This is in contrast to traditional air-powered pneumatics, which often use mechanics inspired by the McKibben Actuator, a design initially pioneered in the 50’s that uses the inflation of an elastic “bladder” to accomplish its task. 

A staple in prosthetic limbs for decades, the McKibben actuator’s use of pressurized inflation means that, should it fail, the actuator could potentially explode and harm someone nearby. 

Through the use of a vacuum (rather than inflation) to do work, the VAMPS gets around this issue. Should one of these actuators fail in a way that hinders functioning, it will do so safely; the Elastocil web simply collapsing back to its minimum possible size.

Even so, that’s presuming that you successfully cause the VAMPS actuator to fail in the first place, which according to the researcher’s report, is no easy feat! Even when pierced with a cannula that punctured several of the sealed polymer chambers, the actuator continued to function without a significant amount of impairment.

In addition, the polymer web of the actuator can take a beating, having been tested with over one million repetitions without detectable wear and tear. The VAMPS continue to show that you can’t keep a good robot down, even if they incur an “injury” that results in failure. 

They may also be able to repair themselves. This builds on research by such teams as Vrije Universiteit Brussel in Belgium, who created a soft actuator that can “heal itself from perforations, incisions, and deformations,” re-sealing itself without any sign of previous damage, in roughly a day.

Despite a durable, self-healing robot evoking terrifying flashbacks of the T-1000 from Terminator 2, it’s clear that the VAMPS will be a great boon to a world where the divide between humans and robotics grows smaller by the way. Perhaps most intriguing in a story with plenty of interesting aspects is the fact that it’s through the purposeful buckling of actuators that Whitesides and his research team were able to achieve this feat.

Typically, buckling and failure are something to be avoided through rigorous design and testing, but the Wyss Institute team has flipped conventional wisdom on its head to create something more advanced than what established methods have previously produced.

For more information, visit the Harvard University’s Wyss Institute, or you can read the team’s research paper available here.