For people whose spinal cords are injured in traffic accidents, sports mishaps, or other traumatic events, cell-based treatments have emerged as a potential avenue for encouraging healing. Now, taking advantage of advances in 3D printing technology, researchers have created customized implants that may boost the power of cell-based therapies for repairing injured spinal cords.
Credit: Jacob Koffler and Wei Zhu, University of California, San Diego
Made of soft hydrogels that mimic spinal cord tissue, the implant pictured here measures just 2 millimeters across and is about as thick as a penny. It was specially designed to encourage healing in rats with spinal cord injuries. The tiny, open channels that surround the solid “H”-shaped core are designed to guide the growth of new neural extensions, keeping them aligned properly with the spinal cord.
When left on their own, neural cells have a tendency to grow haphazardly. But the 3D-printed implant is engineered to act as a scaffold, keeping new cells directed toward the goal of patching up the injured part of the spinal cord.
For the new work, an NIH-funded research team, led by Jacob Koffler, Wei Zhu, Shaochen Chen, and Mark Tuszynski of the University of California, San Diego (UCSD), used an innovative 3D printing technology called microscale continuous projection printing. This technology relies on a computer projection system and precisely controlled mirrors, which direct light into a solution containing photo-sensitive polymers and cells to produce the final product. Using this approach, the researchers fabricated finely detailed, rodent-sized implants in less than 2 seconds. That’s about 1,000 times faster than a traditional 3D printer!
In a study published recently in Nature Medicine, the researchers placed their custom-made implants, loaded with rat embryonic neural stem cells, into the injured spinal cords of 11 rats. Other rats with similar injuries received empty implants or stem cells without the implant. Within 5 months, rats with the cell-loaded implants had new neural cells bridging the injured area, along with spontaneous regrowth of blood vessels to feed the new neural tissue. Most importantly, they had regained use of their hind limbs. Animals receiving empty implants or cell-based therapy without an implant didn’t show that kind of recovery.
The new findings offer proof-of-principle that 3D printing technology can be used to create implants tailored to the precise shape and size of an injury. In fact, the researchers have already scaled up the process to produce 4-centimeter-sized implants to match several different, complex spinal cord injuries in humans. These implants were printed in a mere 10 minutes.
The UCSD team continues to work on further improvements, including the addition of growth factors or other ingredients that may further encourage neuron growth and functional recovery. If all goes well, the team hopes to launch human clinical trials of their cell-based treatments for spinal cord injury within a few years. And that should provide hope for the hundreds of thousands of people around the world who suffer serious spinal cord injuries each year.