A Bloomington startup called SubioMed wants to put a new spring in your step.

Based on technology invented by a Minnesota podiatrist, SubioMed is developing a line of hinged carbon-fiber devices worn on the bottom of a cast or inside a "boot" brace that use a springlike mechanism to make it easier to walk more naturally after foot or ankle surgery.

Though braces and casts immobilize all 33 joints in the human foot, a SubioMed device prescribed by a doctor would limit some motion while allowing dozens of other joints in the foot and ankle to keep moving, theoretically improving healing while reducing hip and knee pain that can follow long-term use of a traditional brace.

"I think reducing stresses and strains [created by a rigid brace] will help facilitate healing, improve blood flow, and get people back to work sooner. That is the goal," device inventor and Owatonna podiatrist Dr. Barry Butler said. Longer term, sensors worn with the inserts "will help create a data set that will tell us how we need to change biomechanics in young people so that they can avoid going down the path of developing symptomatic conditions. I hope to eventually change the course of pathology from a preventive standpoint."

The company also sees a broader consumer market for noncustomized, off-the-shelf versions of the bendy devices, which feel a bit like walking with tiny trampolines in your shoes.

Consumers could use the devices to prevent lower-extremity problems, after treatments or before. Brian Bowen, executive vice president at SubioMed, said the patented design for the flexible, lightweight "energy-return" shoe inserts has been in the works for years. Butler was inspired to create the system after seeing the practical limitations of traditional braces, which sometimes cause surgical patients to require rehab on their knee or hip after having braces removed.

"He said from the start … this is going to work, I know it's going to work. It needs to be under as many feet on the planet as it can be," Bowen said, describing Butler's aspirations for the device. "So 12 years later, there is a company started around it. And it's been validated in patients he's put it on."

Butler designed the inserts using what SubioMed calls "suspension biomechanics" to transfer energy across the bottom of the foot — technology that could be as useful to runners as knee-surgery patients.

The lightweight carbon fiber material absorbs energy from the heel strike and transfers it to other parts of the foot, flexing like a diving board as it does. A second innovation is what company officials referred to as "segmentation," which means the device can be customized so that it limits motion only in the parts of the foot where movement needs to be limited, making it "dynamic."

"It's a mechanical hinge that catches energy at the heel and stores it and delivers it all the way through when you push off your toes, tremendous dynamic energy return. And that's half the magic. The other half of the magic gets to this concept of the … dynamic orthotic," Bowen said. The device patent "was granted on segmentalizing these sections of the foot. So not only are we going to get the benefit of this mechanical construct that manages energy, we're also able to use little wedges to control the position of each of these segments, instead of one fixed rigid position."

The SubioMed devices will have differing levels of complexity, based on how many layers of carbon fiber they contain. A single-layer medical device worn inside shoes will be called the SoloMed; a three-layer device in the shoes will be the Tri-Med; and a triple-layer device inside a walker boot is called the Tri-Med Walker.

The prescription devices are intended for use at whatever point the doctor allows the patient to bear weight again. "Physicians who have seen SubioMed are optimistic they could prescribe SubioMed devices in regular shoes instead of going straight to rigid walker boots," Bowen said.

There are no published clinical data on the device, which is expected to be available in its earliest form during the second quarter of 2020. The device is being designed jointly by Maple Grove's Nortech Systems, which is providing overall project management, and Coon Rapids' Kablooe Design, which is providing mechanical and industrial design engineering.

SubioMed plans to pair its carbon fiber shoe inserts with the Insole3 device made by German manufacturer Moticon, which looks like a cushioned insole but contains an array of pressure sensors and a 6-axis gyroscope that transmits telemetry about a person's gait.

Market research shows a strong demand for existing foot and ankle stabilization devices, for which sales are growing at 10% a year worldwide, Bowen said.

"Why? Because we are living longer, and that musculoskeletal machine takes a beating for longer, and we are heavier, so it is carrying more load," he said.