In 2007, the Swiss acrobat Silke Pan was involved in a devastating trapeze accident. Paralysed from the waist down, she was confined to a wheelchair and forced to abandon her acrobatics career. While her athleticism went undiminished – she went on to become one of the world’s leading paracyclists – there was little suggestion that she would ever walk again.

It was nothing short of astonishing, then, when in 2016 she strapped on a robotic exoskeleton and did just that. The device, developed by scientists at the Ecole polytechnique fédérale de Lausanne (EPFL)’s Robotic Systems Laboratory (LSRO), was named TWIICE – so called because the human and the robot walk in tandem.

The initial idea, explains LSRO robotics engineer Mohamed Bouri, had been to develop an exoskeleton for disabled children and teenagers.

“At that time, there were no devices targeting teenagers, so we wanted to create a lightweight, compact device for people under 1.6 metres tall and 50kg,” he says. “We had less than a year to achieve it, because we wanted to participate in the 2016 Cybathalon, so we needed a device that was driven by simplicity.”

Silke Pan – while not a teenager – was small and slim, and, crucially, a professional athlete. She was called in to beta test the device, and within three months was competing at the 2016 Cybathalon in Zurich (the world’s first cyborg Olympics). The TWIICE system came fouurth, narrowly missing a medal. A year later, it took home gold at the 2017 Cybathalon in Dusseldorf.

During the testing process, Pan worked with the engineers to refine the exoskeleton.

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“Silke’s opinions have been really important, in order to improve the mechanical interface between the subject and the device,” says Bouri. “She has given feedback about how we control it and where we place the sensors and the attachments.”

Taking this feedback on board, the team went on to create a new version of the exoskeleton, TWIICE One. Introduced in November 2018, the device is twice as efficient as its predecessor and gives its users even greater independence.

TWIICE as nice: providing users with battery powered independence

One special property of the new device is that users can put it on and take it off by themselves. Moving from their wheelchair to the ‘legs’, they can stand up and walk unaided.

The device, made from carbon fibre and aluminum, has two electric motors on each leg enabling the user to move her hip and knee joints. After slipping into the legs, she fastens them in place via Velcro fasteners, and places the battery pack on her back. She then pulls herself to her feet using crutches, which provide stability and house the controls.

“After installation into the exoskeleton, the user can operate the device without the need of any external assistance,” says Bouri. “They use a dedicated input device fixed at the front end of the right crutch. Each press on the button executes a pre-computed step forward movement. Right and left leg movements are triggered simultaneously, side by side.”

He adds that remote control by a supervisor is also possible, which comes in handy during the early training sessions. There is also a smartphone app, displaying information such as the current operation mode and battery life. Users can choose from three walking speeds and can even walk up and down stairs.

The TWIICE One system has another advantage over its predecessor, in that it delivers twice as much torque. Working in partnership with Sonceboz, a Swiss motor manufacturer, the LSRO scientists were able to make the device far more powerful. This means, although it weighs roughly the same as TWIICE (around 16kg), it is suitable for users up to 90kg.

“This project with LSRO and the TWIICE research team challenged us to develop powerful yet ultra-compact actuators for moving the exoskeleton,” says Olivier Pajot of Sonceboz. “The solution we came up with is integrated into this new version, which Silke tested and which has already delivered promising results in the initial trials.”

Bouri adds that, since the system is modular, it can be customised for any given user.

“We have shown that we can custom-manufacture the device for each user within a week,” he says.

Improving accessibility for a wider range of disabilities

Right from the outset, the team wanted the device to be suitable for patients with different pathologies. They are currently working on developing different exoskeletons for people with other disabilities, such as lower limb amputations.

They also want to improve its scope for ‘sensory substitution’ – i.e., ensuring users can receive sensory input from the legs. This will give them a better sense of where their steps are landing, and help detect obstacles in their path.

“Since paraplegic subjects don’t feel their lower limbs, we want to activate on the upper limbs the feeling of what happens on the lower limb while moving,” says Bouri. “This is something we’re trying to address – improving the sensory substitution and the feeling of walking.”

The next step is to trial the technology on more people. While the exoskeletons are still being made on a customised basis, the researchers are developing a startup, also called TWICE, that will begin to produce the device commercially.

They have also signed up for the 2020 Cybathlon, with the hopes of bringing home another medal. In the interim, they aim to make the device more user-friendly than ever before.

While Bouri is excited about these developments, he is more interested in the bigger picture. For the time being, exoskeletons of this nature are still extremely expensive and out of reach to most of the people who need them. As the costs of the technology come down, and other institutions start to develop similar devices, he hopes that many people like Silke Pan will benefit.

“We want to make the technology as simple and accessible as possible in order to have it implemented by other research teams,” he says. “This means more startups around the world will develop exoskeletons, and more patients will be able to access the technology.”

For the time being, TWIICE One is a step in the right direction.