(Reuters Health) - Patients with severed spinal cords once had no hope of regaining limb function. But a method that helps new nerve cells bridge the damage by growing through a scaffolding structure might one day change that, researchers say.

For now though, it’s only been shown to work in rats. In a proof of principle, researchers used neural progenitor cells to grow a kind of splice reconnecting severed nerve fibers coming from the rats’ brains to the lower parts of the rodents’ bodies. Though the rats weren’t able to get up and walk afterward, they were able to move their legs in a purposeful way.

“This is a marriage of bioengineering technology with stem cell technology to generate what we hope will be an effective therapy for acute spinal cord injury,” said study coauthor Dr. Mark Tuszynski, director of the Center for Neural Repair at the University of California, San Diego, and a neurologist at the San Diego VA Center.

Earlier research by Tuszynski and colleagues produced some success using just neural progenitor cells, which give rise to new neurons and also help create an environment that encourages damage repair. The novel part of the new research is the 3D-printed scaffold, which is honeycombed with tiny tubes that function like highway tunnels keeping the new cells growing on a straight path, the researchers report in Nature Medicine.

The new study focused on testing how well the scaffold design encouraged cells to grow across the gap and how well the scaffold material held up to give cells enough time to make the repair.

The scaffold tubes, each with a diameter twice the width of a human hair, serve as a guide for the cells to grow from one side of the torn spinal cord to the other. Without the scaffold, which is made of materials that will eventually be absorbed by the body, many stem cells wouldn’t make it across the divide. Another benefit of the scaffold is that it protects the stem cells from the toxic environment around the injury site that is caused by inflammation, Tuszynski said.

A few months after the scaffolds and neural progenitor cells were implanted, nerve fibers from the rats’ brains had connected to the new cells, which in turn connected with nerve fibers coming up from the rodents’ lower extremities, allowing the rats to move their legs in a deliberate way.

They “were not quite strong enough to stand up but they could move their legs around each joint,” Tuszynski said. It’s possible, if the technique were used in humans, that other modalities, such as rehab or spinal stimulation, could improve the result, he added.

The ability to keep progenitor cells alive at the injury site is a big advantage, said Dr. Stephen Badylak, a professor of surgery and deputy director of the McGowan Institute for Regenerative Medicine at the University of Pittsburgh Medical Center in Pennsylvania. The new research, “is a pretty big step forward,” Badylak said.

And that may give hope to the hundreds of thousands living with spinal cord injuries, said Dr. Marc Moisi, chief of neurosurgery at the Detroit Receiving Hospital at the Detroit Medical Center in Michigan.

“Over the past 50 years, we’ve made very little progress in treatment for spinal cord injuries,” Moisi said. “We have nothing really to offer patients with spinal cord injuries, whether they are in the acute or even the chronic phase that could give strong hope. And that’s especially true for those with complete injury, which leaves them paralyzed at that level on down for the rest of their lives. To have the potential to be able to bypass the injury and give patients the opportunity to grow cells and to regain some movement would be phenomenal.”

The new research is “great” and an “advance,” said Dr. Larry Benowitz, a professor of neurosurgery at Harvard Medical School and Boston Children’s Hospital.

“The current study combines exquisite 3-D printing with neural progenitor cells to create a synthetic segment of spinal cord that enables some severed nerve fibers to regenerate from neural centers upstream from the injury site into parts of the spinal cord that have lost their normal inputs,” Benowitz, who wasn’t involved in the study, said by email. “The next big question is whether these types of relay circuits can improve voluntary movements in humans.”

SOURCE: go.nature.com/2SS96za Nature Medicine, online January 14, 2019.