Finding fusion: an engineer and neurosurgeon unite to improve spinal surgery

It is the summer of 2023, and Dr. Stephen Smith sits face-to-face with a model skeleton in the Engineering North building on the University of Notre Dame campus.

Smith is a neurosurgeon at Beacon Health System’s Memorial Hospital in downtown South Bend, Indiana, about a mile southwest of the University’s campus. He is talking with Ryan Roeder, a professor of aerospace and mechanical engineering, about a spinal fusion surgery Smith had just performed using a brand-new type of implant. Although he is looking at bones, it is clear that where others might see death, Smith sees a system teeming with life.

“Bone is an active organ,” Smith says, “and it undergoes continuous remodeling.”

“Remodeling” is not just an apt metaphor; it’s a technical term for the three-part biological process whereby cells digest old bone and deposit fresh, hardened bone in replacement. Remodeling is a key word for this surgery, because for the surgery to be successful, bone has to fuse with an implant—a lifeless material that Smith must insert into the living system of vertebrae and nerves that make up the cervical spine.

Smith explains the spinal fusion surgery: “The entire procedure is done from the front of the neck,” he says as he shows how he makes a small incision and reaches past the trachea, the esophagus, and the jugular vein to access the spine. There, after using a precision drill called a surgical burr to remove bone and disc one millimeter at a time, Smith inserts the new implant in place of the old tissues.

The implant relieves the compression immediately, but the process of healing takes time. “We follow patients for a full year, taking periodic X-rays to ensure the graft is healing,” Smith says. “We are looking for bone growth. Once new bone shows up, you can be confident of a recovery.”

Smith draws a parallel between this process and the process of casting a broken arm. The cast stops the bone from moving as new bone forms, but, Smith says, the cast is just an intermediate step: “The quicker the healing—the quicker there is a living part of you holding you together—the better.”

Quick healing is also crucial because repeat operations face lower chances of success.

“Your best shot is always the first time,” he says. “The second time, not only does that mean additional pain and recovery, but scar tissue has developed, and other complications can occur as well.”

So Smith expresses his delight that the brand-new implant has two important features. First, its porous structure allows bone to grow into it rather than around it. And second, its cell-friendly surface encourages bone to attach to it, creating a more robust, faster-healing graft.

Smith is also delighted that he was the first surgeon in the world to use the new material—one he and Roeder first discussed in a different meeting on Notre Dame’s campus nearly two decades before.

A new way forward in spinal care

Roeder and Smith met in 2005. Smith, who was born and raised near Notre Dame, had just returned to the area after completing a fellowship at the University of Tennessee Health Sciences Department. He started speaking with Notre Dame faculty about innovations in medicine and was invited to give a lecture on campus to explain the new techniques in minimally invasive surgery he learned during his fellowship.

At first, he thought his lecture had been a flop. He recalls that after he spoke at length about the apparatus he used to connect to the body through small ports or slits in the skin, a student asked, “Dr. Smith, that’s very interesting, but how does the patient live with all this equipment attached to their back?”

“I guess,” he said, “I didn’t explain that I remove the structures when the surgery is complete.”

There were other questions, though, including a question from Roeder, then a new faculty member, who asked about the material Smith was using for spinal grafts.

Smith’s answer was “PEEK”: polyether ether ketone. At the time, PEEK was a cutting-edge product. It had been approved by the FDA in 2001 and was prized for its strength and stability inside the body. As it turned out, though, Roeder and one of his graduate students had been working in their lab on a material they thought might be superior to PEEK—one that would combine the benefits of PEEK with an ability to interact with the living tissue of the bone to help the graft heal faster and remain stronger over time.

Roeder and Smith began discussing whether the improvements his lab had made would be of interest to surgeons.

“An engineer can develop new materials in the lab,” Roeder explained, “but you need someone to validate that it can solve a clinical problem. A clinician understands the problems patients face but needs an engineer with the technical expertise to develop a viable solution.”

Based on his experience, Smith affirmed that the material Roeder described could bring real benefits. It could be made sufficiently dense to bear mechanical loads and also sufficiently porous to allow bone to grow into and through it from end to end. The material contained tiny rod-like mineral structures that would not only reinforce the implant, much like rebar in concrete, but would also encourage new bone to attach to it.

Crossing the ‘Valley of Death’ to revolutionize spinal surgery

Getting the new material into the hands of surgeons was just a matter of time—and, of course, money.

“I often say to my graduate students in the lab that most of what we’re working on is at least 10 and maybe 20 years away from becoming a technology that is ready to become a product on the market,” Roeder said. “And that’s how it should be. The ideas we pursue are unproven, and the reward is uncertain. No one trying to make money would invest that early on.”

The money needed to further develop this material was hard to find. Roeder ran into one dead end after another. Federal funding agencies told him to seek corporate funding. When he approached corporations, he found himself turned back again.

“The consistent response when we pitched it to federal funding agencies was, ‘Somebody in industry should be doing that.’ When we pitched it to industry, we heard, ‘We’re not interested unless we can make money on the idea in the next three years. Someone else should fund that,’” Roeder said.

Roeder and Smith had entered a territory well-known to researchers and entrepreneurs—so well-known, in fact, that it has a name: the valley of death. It’s the gap between public investments that fund discoveries and private investments that turn those discoveries into new products. Many great ideas, technologies, and breakthroughs simply stall in the valley of death and never reach the people whose lives they could improve.

One last path presented itself: Roeder and Smith could cross the valley of death by becoming entrepreneurs themselves.

“We were what you might call reluctant entrepreneurs,” Roeder said.

“But we were just more reluctant to let the dream die because we so thoroughly saw how it would be better than what was available at the time,” Smith added.

For most entrepreneurs, getting through the valley usually includes perfecting the product, securing patents, and finding a way to convert lab-based processes to a commercial scale so the product can be produced in a cost-effective way. When the product is related to human health, entrepreneurs face even more challenges. Medical innovations are highly regulated, and the process of gaining clearance from relevant regulatory bodies, such as the US Food and Drug Administration, can be long and difficult.

For Roeder and Smith, the process of commercializing the new implant also involved waiting for the right time to enter the market.

“New ideas have to be ahead of their time; if they are not, they’re not new ideas,” Smith said.

In the case of Roeder’s new material, the problem stemmed from the growing popularity of PEEK throughout the first decade of the 2000s.

“PEEK was new, and it was performing well in the market,” Roeder said. “The last thing companies wanted to do was change it.”

In the 2010s, however, the market began to shift due to the arrival of 3D printing technologies.

“Suddenly, the hot new product was 3D-printed titanium,” said Roeder.

This innovation highlighted the superiority of a porous structure and the deficiencies of PEEK.

“The market was beginning to realize what we saw long before—that PEEK wasn’t perfect,” Roeder said.

But for Roeder and Smith, moving to titanium implants was a step backward.

“Titanium had been the standard before PEEK,” Smith said, “and many of the characteristics of titanium that had previously made PEEK a more attractive option were still true.”

For one thing, titanium was too rigid, “which is not the benefit that you might think,” Smith said. “It can present a problem because it can shield the bone from experiencing physical stress from the body’s movement. The physical stresses of tension, compression, bending, shear, and torsion actually stimulate bone growth.”

Titanium also presents a problem for the periodic X-rays surgeons use to determine if the graft has successfully fused.

“Titanium implants are radiopaque, meaning they block X-rays and show up bright on a radiograph. This can make it difficult for surgeons to assess whether the bone is growing through the implant; the titanium masks that,” Smith said. “But our material is radiolucent, meaning that you can see the healing happening in and through it on an X-ray.”

A “HAPPE” ending for spinal surgery patients

In 2018, Roeder officially launched his company, HAPPE Spine, in partnership with Genesis Innovation Group, a technology incubator in Grand Rapids, Michigan, that accelerated the process to commercialize the material and implant with funding to get the product across the finish line. Smith continued to provide feedback for the final implant design. Roeder would come to serve as HAPPE Spine’s chief technology officer.

During this leg of the journey, the team was awarded several patents, and Roeder received the 1st Source Bank Commercialization Award, which recognizes faculty from Notre Dame or Indiana University School of Medicine–South Bend for translating an exceptional research discovery into a marketable product or service.

In May 2023, HAPPE Spine’s implant received clearance from the FDA, allowing it to be placed on the market for the first time.

Once he completed the first surgery with the new implant in the summer of 2023, Smith could see the difference the new material made.

“It went to work right away,” he said. “The porous surface drew in blood and growth factors. On X-rays, it immediately looked like living bone, and on the three-month follow-up, new bone was already present.”

The product was named a Best New Spine Technology of 2023 by Orthopedics This Week. By the spring of 2025, it had improved outcomes for more than 600 patients with 1,200 implants, and the company attracted a new round of investors—including Notre Dame’s own Pit Road Fund, an investment fund launched by the IDEA Center to accelerate faculty, student, alumni, and community startups.

When asked what it has been like to take an innovative idea and see it through the long process of commercialization, Smith joked, “Mostly painful.” (“No pain, no gain!” Roeder retorted.)

Smith said the most satisfying part about finally crossing the valley of death is not just that it happened, but where it happened.

“It means a lot being from this city that this innovation happened here,” he said. “Others might view South Bend as a small town, but there is nothing about our skills, talent, or service that is small. I want to show my patients that they are getting better care here than they would get anywhere else, and I’m glad this has been part of that mission.”