San Diego - A spinal cord implant that can be made with 3-D printer in matter of minutes has made it possible for rats to regenerate axons after spinal cord injury. According to the report in Nature Medicine (2019; doi:), the rats have partially recovered from the paralysis after few months.
Nerve fibers can regenerate. After an injury, the severed axons grow along the medullary sheaths to their old destination. This is often possible with peripheral nerves. Sensitivity or motor skills recover after few months. In spinal cord injuries, guardrails are also usually damaged (with the subsequent inflammatory response appearing to increase the damage). Injecting stem cells is also not able to form new bridges.
A team led by Mark Tuszynski from the University of California in San Diego is hoping that an implant with numerous tubes will be necessary for regeneration can provide necessary guardrails. The implants could be made to measure for each patient with 3-D bioprinter within few minutes.
The prototypes that the researchers produced for their experiments on rats contain numerous microchannels with diameter of 200 µm over the length of spinal cord segment. Since the fibers in the spinal cord run only in the white matter, the inner gray core, which contains the nerve cells for the spinal cord reflexes, was made entirely of plastic. Some functions are sacrificed at the level of the implant as result of the implantation. But the implant offers the chance for the axons to regenerate.
The researchers tested the implant on rats. A segment of the spinal cord (at level Th 3) was removed from the animals in an operation and replaced with an implant. In control group, this implant consisted of Aragose gel, which does not allow regeneration. In the other animals, the implant contained the tubes provided. In some animals the tubes were colonized with stem cells. Apparently the best results were achieved here.
According to Tuszynski, the axons grew in the direction of the stem cells to which they formed synapses. The stem cells in turn developed into nerve cells, each of which sent an axon to the nearest relay station. According to Tuszynski, blood vessels also grew into the implants so that the nerve fibers were adequately supplied with nutrients and oxygen. The implants slowly regressed. In the long term, they could be made from fully degradable materials.
After 6 months, the motor function of the hind legs, which were initially paralyzed after the operation, had significantly improved, reports Tuszynski. In the next step, the researchers want to carry out experiments on larger animals. The implants should be provided with proteins in order to further improve regeneration. Clinical studies are not yet planned.