Paraplegics want a device that lets them be vertical and walk a bit, preferably as often as possible. That would help them deal with a host of medical problems that able-bodied folks don't experience, like cardiovascular issues, pressure sores, incontinence, loss of muscle tone and depression, to name a few.

Being able to stand and walk without the discomfort of crutches would not only provide a huge psychological boost but also help reduce or eliminate many of those symptoms. "Our friends in wheelchairs told us, 'OK, if there was a device that would enable us to be able to walk again, there is no price that I wouldn't pay,'" said Masselin.

Without crutches, assistive exoskeletons (or "exos," as the team prefers to call them) are orders of magnitude more complex. Wandercraft's latest device, the fourth-generation model, weighs nearly 130 pounds (60kg) and must have perfect, humanlike balance so it won't fall over and injure the patient. "We discovered that stability and the human gait are some of the hardest problems we've ever encountered in robotics," Masselin said.

Unlike most current exos, which are more like motorized braces, the Wandercraft is a rigid, robotic structure. It has multiple powerful, compact electric motors at the hips, knees and ankle joints. A large battery is fitted at the back, along with an Intel Core i7-equipped microcomputer that does the complex math needed to ensure the machine can balance and walk.

Building a robot is hard enough, but attaching a human to it multiplies the degree of difficulty. "If the exo bends the knee, it has to stop before the knee of the person breaks, obviously," Masselin noted.

To make such a complex device work, the company recruits top roboticists, mechanical engineers and coders -- all fields in high demand. It must also enlist folks from biomedical, medical, biomechanical and other diverse areas and train them to work with the development team. To top it off, the exoskeleton and the code have to conform to medical protocols, and Wandercraft must run an elaborate regulatory gauntlet before patients can ever use it.

After five years of dealing with those nearly overwhelming challenges, the company finally tested its Atalante exo with patients. They're not ready to show video to the public yet -- for reasons I'll explain shortly -- but I was able to see it in action during a private showing.

Patients are first attached to the device by straps that are specially designed to distribute pressure evenly, at the waist, hips, knees and ankles. Those can fully support users' weight while their feet are placed on metal walking pads with rubber grips.

You start by sitting in the device and then make a gesture to stand up by bending at the waist. That activates motors that automatically drive the exoskeleton to a standing position. Walking can then be cued either by patient gestures or automatic programs started by the therapist.

The gait movement is obviously slow, but patients can take multiple steps without any crutches or external assistance. They assume a slightly bent posture, but it looks far more comfortable than the demonstration I saw of Ekso Bionics' system back in 2013. I'd describe the motion as controlled lurching, but keep in mind that such tech has never been tried and many of the test subjects hadn't risen from their wheelchairs in years. With time, patients would develop more skill, and the exoskeleton is bound to get smoother.