SuitX

Paralyzed below the waist from a car accident four years earlier, Austin Whitney did the unthinkable in 2011. He stood up from his wheelchair and walked 10 feet across the stage to get his diploma during a graduation ceremony at the University of California, Berkeley.

Whitney had strapped on an exoskeleton suit -- essentially, a battery-powered wearable robot with joints at the hips and knees to help power his movements.

As of this past Monday, anyone could order an updated version of that experimental machine, for delivery next month.

Built by SuitX (aka US Bionics Lab) in Berkeley, the 27-pound Phoenix can help paraplegics walk for up to 4 hours of continuous movement, at up to 1.1 miles per hour, the company says. At $40,000, it's less expensive than some competing products, like the ReWalk, which costs about $70,000.

Still, few are calling it cheap. Its cost and limited battery life mean hospitals and rehab clinics will be the most likely customers, said Homayoon Kazerooni, founder of SuitX and director of the Berkeley Robotics and Human Engineering Laboratory at UC Berkeley.

"For anyone who got paralyzed through an accident or through birth, it's a big deal." Jacob Rosen, UCLA robotics professor

Exoskeletons aren't new. The US military's Defense Advanced Research Projects Arm, or DARPA, has been funding their development since the early 2000s. The goal: build lightweight, motorized armor that will enhance soldiers' strength and endurance.

But wearable robots have the potential to do more than create 21st century super soldiers. Robotic arms are helping stroke victims regain control over their bodies and giving amputees the ability to feel again. Robotic suits let factory workers pick up heavy loads, and robotic legs are allowing the disabled to walk. Put another way, they're expanding the limits of being human.

Between 2014 and 2015, such promise spurred a fourfold spike in private investment, to $388 million, according to venture capital research firm CB Insights.

"For anyone who got paralyzed through an accident or through birth, it's a big deal," says UCLA medical robotics professor Jacob Rosen. "They don't need ramps. They can walk up stairs. It sort of brings them back to normal."

RoboCop

Of course, military applications aren't going away.

Consider HULC, or the human universal load carrier. Currently being developed by Lockheed Martin, the hydraulic-powered suit of armor aims to help soldiers carry 200-pound loads over long distances and difficult terrain. You can watch a soldier walking and jumping with one here.

There's also TALOS. That stands for tactical assault light operator suit, but the gadget could just as easily be called RoboCop. Made of a strong yet flexible material called liquid armor, TALOS is designed by Army researchers to offer soldiers lightweight bulletproof protection and "superhuman strength." It's expected to be available by 2018.

Wearable robots could also find a place on the factory floor. Japanese electronics giant Panasonic revealed last year that it was developing an upper-body suit to help workers lift heavy loads and reduce repetitive strain injuries.

And then there's the bionic boot from, well, Bionic Boot. Invented by Keahi Seymour, the spring-loaded boots will let you run up to 25 miles per hour. Videos show Seymour sprinting up mountains without breaking a sweat.

But exoskeletons have their limitations. Ask Kazerooni, who created the Phoenix. Yes, his machine helps the paralyzed get up and walk, but their movements will still be robotic.

"People want more than a robot that you wear," he said. "People want a smoother design and lower cost."

When will that come?

He says he's working on it.

Update, 4:40 p.m. PT: Adds details.

Correction, 4:45 p.m. PT: The original version of this story cited the wrong source for the data on robotics investment. That information was provided by CB Insights.