Using 3D printing, scientists from the University of California, San Diego, have developed a technique to build the scaffolding around which stem cells can be implanted. The printing technology used was capable of creating each implant in less than two seconds per device – whereas traditional printers would have taken several hours.
After a long time and numerous failed experiments (some of the first designs broke or totally disintegrated in a matter of weeks; others were rejected by the rats’ immune systems), they finally figure out the right material to use. The successful implants were made of a material called polyethylene glycol–gelatin methacrylate, which is a flexible hydrogel designed specifically to be biocompatible.
The implants contain dozens of tiny channels that are just 200-micrometres wide, the same size as the thickest of human hairs. These channels guide neural stem cells and axon growth along the spinal cord injuries. According to the researchers, axons are “the long, threadlike extensions on nerve cells that reach out to connect to other cells.” The scaffolding’s biocompatible design allows for the body’s blood vessel system to naturally grow so that the nerve fibers are kept alive and fed with nutrients as well as discharge waste.
They have already been successful in helping previously-paralyzed rats regain significant motor control in their hind legs, about six months after surgery. How? The scaffolds helped the animals regrow tissue and the stem cells nerve fibers inside of the scaffolding expanded out into the host spinal cord. Details on how the team printed a spinal cord which was loaded with neural stem cells and the study has been published in the journal Nature.
In a nutshell, the stem cells embedded into the new experimental implant’s channels grew down the length of the animal’s spine. At the same time, existing nerve cells in the rats’ spines recognized the scaffolding and extended their axons (the long tail-like structures through which nerve cells transmit signals) down along the new bridge, as well as blood vessels.
Professor Mark Tuszybski, a trained doctor and scientist who directs the Translational Neuroscience Institute at UC San Diego School of Medicine and senior co-author of the paper, said:
In recent years and papers, 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.
Dr Kobi Koffler, a co-author of the paper and an assistant project scientist in Professor Tuszynski’s lab added:
The new work puts us even closer to real thing because the 3D scaffolding recapitulates the slender, bundled arrays of axons in the spinal cord.
Professor Shaochen Chen, another of the paper’s co-authors and a professor of nanoengineering and a faculty member in the Institute of Engineering in Medicine at UC San Diego, explained the printing technology as being:
Like a bridge, it aligns regenerating axons from one end of the spinal cord injury to the other. It helps organise regenerating axons to replicate the anatomy of the pre-injured spinal cord. Axons by themselves can diffuse and regrow in any direction, but the scaffold keeps axons in order, guiding them to grow in the right direction to complete the spinal cord connection.
This research offers hope to humans with severe spinal cord injuries. If they have been able to successfully treated rats with the same condition, there is a chance they’ll find a way to do it for people too.
