Sitting at the kitchen table of his Affton home, Mark Stark pulls out his friend Dave's left hand.
The fingers are clenched. With a quick movement, Stark opens the hand and picks up a wine glass.
Stark, a mechanical designer and basement inventor, stands up, then places his prosthetic hand on the table, and says,
"It's delicate enough to hold a glass. But you can also lift a chair."
Constructed from plastic, each finger and joint on the hand operates individually. The fingertips have attached rubber finger cots, much like postal workers use for rifling paper. The palm of the hand uses the grip from a glove. Other building materials include rivets, fishing line, screws and springs.
Stark calls his invention the "Natural Dexterous Hand," or "Stark Hand."
It's mechanically simple and decidedly low-tech.
But this humble device has already changed the life of Dave Vogt.
Pending negotiations with a manufacturer, it could soon be available to thousands more. At least one expert believes that it has the potential to have a major impact on the market for prosthetics.
Keeping it simple
Vogt, a long-time friend of Stark, was born without his left hand because of a congenital birth defect. He had used a hook prosthesis from birth.
Stark had always mused about improving his friend's quality of life, but the idea for the Stark Hand took years to crystallize.
"There really was no epiphany. My friend had used a hook his whole life and I saw the limitations. I always wanted to help him, but had no specific idea."
After a lengthy period of incubation, the idea for the hand finally emerged in the wake of another invention.
Stark said his idea came to him about 15 years ago after a robotic hand was developed by an American university. The hand used three motors on each finger to provide individually controllable joints. Stark said.
"It was an awesome device. But it was also incredibly complex."
Stark, operating from the "keep it simple" principle of mechanical design, thought he could do better while gearing the device to prosthetics rather than robotics.
In the mold of the true basement inventor, he began scrounging for readily available items to create a prototype. Among the parts used for the first hand prototype were plastic cable housing and a hinge from a screen door. Stark said.
"Things I could buy at a hardware store."
While Stark was fairly certain the prototype would work, given its simple design, building the hand was no quick task. Working as a full-time mechanical designer for Emerson Electric's White-Rodgers division, Stark tinkered in his spare time.
Putting it to the test
When the first prototype was completed in 2004, Stark invited Vogt over to test it out. Vogt unscrewed his hook and screwed the hand into the slot.
Stark tossed him a tennis ball. Vogt caught the ball on the first attempt. Stark said.
"It was absolutely amazing."
Vogt was thrilled and gratified by the gift. Vogt said.
"I didn't know he had been working on it for years. Then he called me and told me he had this thing. I was surprised and excited."
Vogt took awhile to adapt to the hand. He said.
"I was so used to the hook. My body and brain had adapted to it."
Soon the compulsion to use the hook faded. Now, Vogt wears the hand everywhere, with the exception of work, where his job as a machinist requires heavy lifting better suited for the hook.
The hand works in much the same way as a hook. Vogt wears a body harness and a cable and can control the hand with upper body movement, such as a shrug. In essence, the hand is a screw-on attachment that replaces the hook.
Vogt said the Stark Hand offers superior functionality. He said.
"On a personal level it's been a great help."
Though the hand can grasp, it does not have the ability to perform more specialized tasks such as punching keys on a remote control.
Along with function, Vogt said the hand is an aesthetic improvement over the hook. Such considerations were in the forefront of Stark's mind during the design process. Stark said.
"They give bad guys in films hooks to make them look more evil. That's terrible."
A low-cost alternative
The hand may have been designed to help a friend, but it also provides another choice among limited prosthetic options.
Hooks can cost only a few hundred dollars, but are limited functionally. Cosmetic prosthetic hands resemble the real thing, but are about as functional as a mannequin's hand.
Electric models offer the best of both worlds, but are often prohibitively expensive. The hand, plus surgery to attach, can cost up to $60,000.
Stark's hand aims to offer increased functionality at a cost closer to hooks.
He spent seven years and roughly $17,000 developing the device. Most of that money was spent in securing a patent.
When asked why such a relatively simple and useful device had yet to be invented, Stark conceded he wasn't sure. Stark said.
"That's a good question. The basic concept could have been whittled from wood 100 years ago."
Stark said the final production model of the hand will likely feature changes, including improved materials and a more life-like appearance.
Publicity shy by nature, Stark didn't set out to make a pile of money, but the commercial prospects for the Stark hand appear promising. Edison Nation, a company that helps amateur inventors, is working with Stark to market the device to manufacturers. Said Karen Dickson, a spokeswoman for Edison Nation.
"This is a low-cost solution to a pretty widespread problem."
Dickson said the company is negotiating with a major prosthetics manufacturer with the goal of bringing the Stark Hand to market. Kenneth Paulus, Edison Nation's vice president of business development, said the device could prove popular on the international market, given its projected cost of around $1,000. Said Paulus.
"There's an opportunity to transform the lives of people in war-torn countries. People with war injuries, land mines, that kind of environment."
Jack Engsberg, an associate professor of occupational therapy at Washington University, said the invention possesses significant commercial potential. Engsberg said.
"I believe there's a huge market for the device if it is as functional as it's (claimed to be)."
Engsberg, who developed an easier and less expensive way to make sockets for artificial limbs, said the device takes the best elements of the hook system (feel and touch) while adding the extra-capability of five digits.
Stark's invention has drawn national media attention. The Stark Hand earned a spot on the cover of last month's issue of Popular Science magazine, a mention on CNN, and is slated to appear on PBS this fall. Stark said.
"The attention is kind of strange."
Stark, who gives the impression he'd rather be quietly tinkering in the workshop, said he's trying his best to manage expectations. He said.
"It's difficult. I don't know how much money I'll make or even how much I want. Notoriety was not the goal."
The goal was more personal. Stark said.
"I was trying to help a friend. But there's more than one person out there missing a hand."
Tying shoelaces takes a degree of manual skill that is difficult to achieve among some prosthetic limbs, but the Natural Dexterous Hand can easily handle tasks that require smaller, more intricate hand movements.