Researchers from the University of California San Diego (UCSD) School of Medicine and Institute of Engineering in Medicine (IEM) have successfully 3D printed a two-millimeter spinal cord implant to repair spinal cord injuries in rats.
In yesterday’s issue of Nature Medicine, the researchers explained in their study that the 3D printed implant contains 200-micrometer-wide channels (twice the width of a human hair) that guide neural stem cell growth, ultimately restoring connections and lost function.
“This shows the flexibility of our 3D printing technology,” said co-first author Wei Zhu, PhD, a nanoengineering postdoctoral fellow in the Chen group.
“We can quickly print out an implant that’s just right to match the injured site of the host spinal cord regardless of the size and shape.”
3D bioprinting and vascularization
Vascularization is the process in which blood vessels are formed. According to Zhu, it is “one of the main obstacles in engineering tissue implants that can last in the body for a long time.”
“3D printed tissues need vasculature to get enough nutrition and discharge waste. Our group has done work on 3D printed blood vessel networks before, but we didn’t include it in this work. Biology just naturally takes care of it for us due to the excellent biocompatibility of our 3D scaffolds.”
In December, UCSD bioengineers developed a 3D bioprinting method that integrates natural materials which produce lifelike organ tissue models. Prior to this, the researchers gained experience in bioengineering by 3D printing a framework of functional blood vessels using a Digital Light Processing (DLP) method with hydrogel and encapsulated cells.
A 3D printed spinal cord implant
The 3D printing technology used by the researchers produced the two-millimeter-sized implants in 1.6 seconds. In comparison, the study states that traditional nozzle printers take several hours to produce much simpler structures.
Loaded with neural stem cells, the team grafted the implants into sites of severe spinal cord injury in rats. In a few months, new spinal cord tissue had regrown across the injury and connected the severed ends and axons (long, threadlike extensions on nerve cells) of the host spinal cord.
This experiment resulted in the treated rats regaining significant functional motor improvement in their hind legs. Following this, the researchers proved this process was scalable to human spinal cord sizes by 3D printing four-centimeter-sized implants modeled from MRI scans within 10 minutes.
“This marks another key step toward conducting clinical trials to repair spinal cord injuries in people,” said Kobi Koffler, PhD, Assistant Project Scientist at the Center for Neural Repair, UCSD.
Mark Tuszynski, MD, PhD, professor of neuroscience and director of the Translational Neuroscience Institute at UC San Diego School of Medicine, concluded:
“We’ve progressively moved closer to the goal of abundant, long-distance regeneration of injured axons in spinal cord injury, which is fundamental to any true restoration of physical function.”
The research paper “Biomimetic 3D printed scaffolds for spinal cord injury repair,” is co-authored by Xin Qu, Oleksandr Platoshyn, Jennifer Dulin, John Brock, Lori Graham, Paul Lu, Martin Marsala, and Jeff Sakamoto.
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Featured image shows the 3D printed implant used as scaffolding to repair spinal cord injuries in rats. Image via Jacob Koffler/Wei Zhu, UCSD.