Sun's robotic prosthetic knee quickly earned him fame and won him the Red Dot Best of the Best award in 2020.

He said that the biggest challenge in creating the robotic knee was how to coordinate between the body and the prosthetic. "Walking is an unconscious movement. It's difficult to make prosthetics understand how that works."

Most artificial limbs on the market are made to work like bones and ankles. Sun's invention works a bit like adding muscle to the mechanical parts.

"The prosthesis we've created has a kind of mind of its own, and allows people to move by sensing their intentions," he said.

"I myself use a prosthetic limb, and I'm also a researcher. There are about 4 million people in China whose lower limbs have been amputated," he added. "The cost of an ordinary prosthesis is around 60,000 to 100,000 yuan ($9,400 to $15,700), which many people can't afford, so they use crutches, instead."

Sun said the market is a niche, and most prosthetics are produced in Europe. "I didn't start my company for the money, but to make a product that is useful to society. Amputees have a basic need to walk on two legs," he said.

Sun said that the robotic knee his company produces is priced at around 300,000 yuan per pair, while similar products sold elsewhere average around 800,000 yuan.

Admitting that this is not ideal, he said that his robotic knees are still in small-scale production, resulting in high costs. He hopes that by raising more capital, he'll be able to expand production and lower costs to make his devices more widely affordable.

Zhang Chi contributed to this story.