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A three-layer artificial tube containing living Schwann cells helped repair damaged sciatic nerves in rats. Its performance was similar to that of a natural nerve graft, according to a peer-reviewed study published in the International Journal of Extreme Manufacturing. The device combined a strong outer support, a porous middle membrane, and an inner layer of tiny, cell-filled fibers lined up to guide growing nerve fibers across a 10 mm gap. Over 16 weeks, the tubes carried electrical signals, supported the growth of nerve bundles covered with myelin, and reduced muscle loss. These results suggest that this living structure could serve as an engineered bridge to repair nerves outside the brain and spinal cord.
Peripheral nerves carry messages between the brain and the limbs. A serious injury can completely break these connections. Without a structure to guide them, growing nerve fibers may head in the wrong direction. This can leave the muscles beyond the injury without electrical signals and at risk of permanent shrinkage. Surgeons often repair a damaged section by using an autograft. This means taking a healthy sensory nerve from another part of the same patient's body and using it to bridge the gap.
Although this method is well established in medical care, it requires removing another nerve. This can cause numbness where the nerve was taken, long-lasting pain, or a shortage of suitable tissue. Hollow plastic tubes avoid the need to remove another nerve, but they may not work well across larger gaps. The release notes that these tubes may not provide the physical guidance and chemical support that growing nerve fibers need. To address this problem, the research team combined three manufacturing methods on one direct-writing platform: melt writing to make the strong outer layer, electrospinning to create the porous middle membrane, and low-temperature cell patterning to form the living tracks inside.
The team made the entire tube in one continuous process instead of moving delicate parts between separate machines. The outer layer is an open mesh made of polycaprolactone. It acts like a skeleton around the tube and can withstand squeezing and stitching forces of up to 1.64 N. The middle layer is a membrane made of extremely fine fibers, with pores averaging 0.55 micrometers across. These tiny openings allow oxygen and nutrients to pass through while helping prevent scar-forming connective tissue from growing into the tube.
The innermost layer contains tiny fibers filled with Schwann cells, creating a biological pathway to guide nerve regrowth. A major challenge was printing these living cells. Schwann cells normally support peripheral nerve fibers by helping insulate them and guide their growth. Electro-assisted bioprinting uses electricity to pull cell-containing ink through tiny nozzles and form fine fibers. However, printing very small structures can damage the cells.
Thick inks tend to keep their shape after printing, but pushing them through narrow nozzles creates strong forces called shear stress. These forces can tear cell membranes. Thinning the ink reduces this stress, but the printed fibers may then spread out and collapse into puddles. Chemicals used to harden the material can harm the cells, while the relatively high voltages needed to make very fine fibers can also damage living material.
The researchers addressed this problem by controlling temperature. Their bioink contained alginate, polyethylene oxide, and gelatin methacryloyl, a material that responds to temperature, along with living Schwann cells. They kept the nozzle at 25 °C, where the mixture was fluid enough to pass through without creating the high shear stress caused by a thicker ink.
A chilled collection plate kept at 4 °C quickly firmed up each deposited stream before it could spread out. Using a relatively gentle electric field of 1.0 kilovolt, the system produced continuous tiny fibers about 36 micrometers in diameter. Temperature therefore helped control how easily the material flowed during printing and how well it held its shape immediately afterward.
In laboratory tests, nerve cells attached to the printed tracks and formed dense strips that lined up in the same direction instead of spreading randomly. RNA sequencing, a method used to study gene activity, suggested a possible molecular reason for this behavior. Contact with the tiny fibers, along with chemical signals from the Schwann cells, activated genes involved in guiding nerve growth, including Ephb1 and Gnai1.
These signals were linked to cell structures that help steer growing nerve fibers. At the same time, the activity of genes linked to programmed cell death and normal cell multiplication decreased. The cells instead shifted their activity toward growing long structures that carry signals. These findings come from laboratory cell cultures and measurements of gene activity. The release does not report a separate clinical assessment of the molecular processes behind these effects.
The researchers implanted the combined tubes across 10 mm gaps in rat sciatic nerves and studied them for 16 weeks. They compared the results with natural nerve grafts and tubes that contained no living cells. In the tubes with living cells, the regrowing nerve bundles developed myelin, an insulating covering around nerve fibers, with an average thickness of 1.02 micrometers. This was close to the 1.15-micrometer average measured in the natural grafts. Repaired nerves in the group with living tubes carried electrical signals at 5.67 meters per second, compared with 5.88 meters per second in the natural-graft control group.
The signal speed in the living tubes was almost twice that measured in tubes without cells. These results suggest that the two repair methods performed similarly in this rat study, but they do not prove that the methods are equally effective in people. The experiment also showed that tubes with living, carefully arranged tracks produced different results from empty tubes. However, the release does not give a numerical signal speed for the group without cells.
The benefits were not limited to the speed of electrical signals. When nerve connections are cut, the calf muscles beyond the injury can lose their nerve supply and shrink. The tubes containing living cells preserved about 49% of the wet weight of the lower calf muscles. In comparison, empty tubes preserved less than 24%.
Walking tests also showed that rats treated with the living tubes regained normal coordination of their hind paws. Together, the electrical tests and behavior results suggest that the engineered bridge did more than provide a passive path for growing nerves. The arranged Schwann-cell tracks helped nerves grow in an organized way, supporting recovery of movement and reducing muscle loss during the study. The findings therefore include more than electrical measurements: they also include evidence of myelin-covered nerve bundles, muscle preservation, and improved movement.
The study shows that it is possible to manufacture implants with several layers and living cells, but the evidence is still from animal experiments. Before testing the device in people, the researchers will need to study it across gaps several centimeters long in large animal models. They must also develop ways to sterilize the tubes at low temperatures without killing the Schwann cells inside. In addition, they need to adjust how quickly the polycaprolactone outer shell breaks down so that it matches the slower healing process of human nerves.
The reported results support further testing in large animals, not an immediate recommendation for use in patients. If the next stage is successful, this method could provide another option for people who cannot donate a healthy nerve or do not have enough suitable tissue for a conventional graft. The importance of the work is that one device combines several functions: physical support, the controlled movement of substances between the tube and its surroundings, and a living inner surface with aligned tracks to guide nerve fibers.
The device is more than a hollow tube because its inner tracks contain cells that can provide chemical signals, while the printed structure gives growing nerve fibers a physical path to follow. The outer polycaprolactone layer is designed to withstand handling, while the middle membrane helps stop connective tissue from growing inward. This provides an example of how melt writing, electrospinning, and low-temperature bioprinting can be combined without moving delicate structures between separate machines.
The study's main claim is based on tests in rats before human trials: under the conditions tested, a living tube made by bioprinting supported nerve regrowth across a 10 mm gap, with functional results close to those of a natural nerve graft. Its wider use will depend on successful testing across longer gaps, sterilization methods that keep the living cells alive, an outer shell that breaks down at the right rate, and eventual testing in people.
Subject of Research: Bioprinted nerve tubes tested in rats before human use to help repair peripheral nerves
Article Title: Living "railway tracks" bioprinted inside artificial conduits match gold-standard nerve repair
Article References: Living "railway tracks" bioprinted inside artificial conduits match gold-standard nerve repair. Original publication (Bibliographic details unavailable.)
Image Credits: AI-generated
DOI: Not provided
Keywords: peripheral nerve repair, 3D bioprinting, Schwann cells, nerve guidance, tissue engineering, sciatic nerve, rat study, aligned microfilaments, biofabrication, electrospinning, living cells, railway tracks