LOS ALAMITOS, CALIF. —Seven-year-old Faith Lennox never thought about putting a prosthetic limb where her missing left hand had once been — not until she learned she could design her own, easily strap it on and the jump on her bike and ride at speeds previously only imagined.

With family members occasionally shouting “be careful” and “watch out for that car,” Faith firmly placed her new hand’s bright blue and pink fingers on her bike’s left handlebar and took off for a seemingly endless ride around the Build It Workspace on Tuesday morning. Inside, just a short time before, that hand had rolled off a 3D printer that built it overnight.

“I don’t think we’ll ever get her off it,” said her mother, Nicole, smiling as she watched her daughter circle the parking lot in this Orange County suburb.

The prosthetic represents a breakthrough in the field of artificial limbs. It weighs only a pound and costs just $50 to construct out of the same materials used to make drones and automobile parts.

When Faith outgrows it in six months or a year, a replacement can be made just as easily and inexpensively, said Mark Muller, a prosthetics professor at California State University, Dominguez Hills, who helped with the design. He said a heavier adult model with sensors attached to a person’s muscles would run $15,000 to $20,000.

Faith manipulates her hand without sensors. Instead, as she demonstrated after the bike ride, she moves her upper arm back and forth. That in turn opens and closes its blue and pink fingers — “my favourite colours,” she said with a smile — that she uses to grasp objects like the plush toy she brought with her.

The oldest of three children, Faith had compartment syndrome when her position during childbirth cut off the flow of blood to her left forearm, irreparably damaging tissue, muscle and bone. After nine months of trying to save the limb, doctors determined they had to amputate just below the elbow.

She had tried a couple more traditional — and more expensive — prosthetics over the years but found them bulky, heavy and hard to use.

Her parents were working with the non-profit group e-NABLE to get her a 3D-printed hand, but the technology is so new there’s a waiting list, her mother said. Then she learned of what Build It Workspace could do from a friend whose son visited with his scout troop. The small studio teaches people to use high-tech printers, provides access to them for projects and does its own commercial printing.

Although the company, founded less than a year ago by mechanical engineer Mark Lengsfeld, has printed everything from pumps for oil and gas companies to parts for unmanned aerial vehicles, this was the first hand Lengsfeld and his employees built.

So he used e-NABLE’s open-source technology and called the experts at the university for guidance.

When Faith quickly strapped on their new creation and headed out to ride Tuesday morning, as TV cameras captured the moment, Lengsfeld admitted he was nervous. After being up all night finishing the hand, he wanted to test it himself to be sure it worked.

“But she did fine with it,” he said.

After her test run, Faith gave the prosthetic a positive review.

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“I didn’t have to lean so much,” she said of the difficulty she previously had steering a bike with just one hand.

But when asked to demonstrate how the hand can help with other activities such as school work, she got busy. She placed her new hand firmly on a piece of paper, holding it in place as she drew a picture.

What did she draw? Her new hand, of course, with robot fingers in perfect detail.