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Researchers from the Royal College of Surgeons in Ireland (RCSI) University of Medicine and Health Sciences and Trinity College Dublin have developed a 3D printed implant that may support the repair of spinal cord injuries by delivering electrical stimulation to damaged nerve tissue.
Led by Dr Ian Woods and Professor Fergal O’Brien at RCSI’s Tissue Engineering Research Group (TERG), in partnership with the AMBER Centre at Trinity College Dublin, the study was published in Advanced Science. It was supported by the Irish Rugby Football Union Charitable Trust (IRFU-CT), and the Irish Research Council.
The implant is made from a soft, gel-like extracellular matrix composed of hyaluronic acid, collagen type-IV, and fibronectin, designed to resemble the natural environment of the spinal cord. Inside this matrix, the team inserted a fine mesh made of plastic fibers (polycaprolactone, or PCL) coated with MXene nanosheets, microscopic flakes of a conductive material that help transmit electrical signals without harming surrounding cells.
“Promoting the regrowth of neurons after spinal cord injury has been historically difficult; however our group is developing electrically conductive biomaterials that could channel electrical stimulation across the injury, helping the body to repair the damaged tissue,” explains Professor O’Brien.
Printed fibers guide electrical healing
Using a technique called melt electrowriting, the researchers 3D printed these fibers with high precision, spacing them at different densities. They created three versions of the implant: low-, medium-, and high-density fiber networks, with spacing ranging from 1000 to 500 µm. Each variation produced different levels of electrical conductivity, ranging from 0.081 to 18.87 siemens per meter (S/m).
When freeze-dried, the scaffold retained porosity greater than 99% and maintained a compressive stiffness between 0.6 and 3.25 kPa, similar to the softness of spinal cord tissue. To test effectiveness, the researchers grew human-derived neurons, astrocytes, and microglia on the implant.
Neurons showed significantly increased growth and metabolic activity on the MXene-coated fibers compared to controls. Astrocytes were less reactive, which is favorable for nerve repair, and microglia showed no signs of inflammation. These results confirmed that the implant was both safe and compatible with central nervous system cell types.
Further tests assessed the implant’s performance under electrical stimulation. In one experiment, neurons were cultured on the implant for seven days. Those on high-density scaffolds and exposed to electrical signals grew axons averaging 108.5 µm, compared to 74.3 µm in unstimulated controls and 67.4 µm on unstimulated MXene scaffolds. Medium-density scaffolds, however, yielded the longest neurites per cell and the highest levels of BII-tubulin, a marker of neuron maturity.
In a more advanced model, the team used neurospheres, i.e., 3D clusters of neural stem cells from the olfactory bulb of mice. These cells can become various brain and nerve cell types. When stimulated electrically on the implant, those on medium- and high-density scaffolds developed longer axons and showed more signs of maturing into neurons. Axon lengths reached 203.6 µm in the high-density group, compared to 94.1 µm on non-conductive controls and 88.6 µm in the low-density group.
The structure and spacing of the conductive fibers significantly influenced the impact of electrical stimulation. While a tighter mesh improved signal delivery, a medium-density design offered the best environment for overall cell growth. MXene content remained below 0.3% of the scaffold volume, yet proved highly effective when strategically arranged.
The project also benefited from insights provided by an advisory group that included clinicians, researchers, and seriously injured rugby players. Supported by (IRFU-CT), the group helped researchers understand the real-world challenges of spinal cord injury and provided guidance on patient priorities. As Dr. Woods puts it, “our regular meetings allowed for a consistent exchange of input, ideas and results.”
While still in early development, the implant offers a new approach to combining electrical stimulation with soft, biocompatible materials in a precisely tunable 3D printed format.
3D printed implants to restore spinal cord function
Like other areas of regenerative medicine, 3D printing offers strong potential to improve outcomes and increase the effectiveness of spinal repair procedures.
Israeli regenerative medicine firm Matricelf tested a bioprinted spinal cord implant developed using technology from Tel Aviv University (TAU) on paralyzed mice with notable results. Researchers began by reprogramming cells from a patient’s belly fat into stem cells, then embedded them in a personalized hydrogel made from the patient’s own extracellular matrix.
These were bioprinted into spinal cord-like neuronal networks designed to avoid immune rejection. After implantation, all mice with acute paralysis regained movement, while 80% of chronically paralyzed mice recovered. The method mimicked embryonic spinal development, and Matricelf sought to begin human trials by late 2024 following further safety studies.
Additionally, researchers from the University of California San Diego’s School of Medicine and Institute of Engineering in Medicine (IEM) developed a 3D printed spinal cord implant that restored motor function in rats with severe injuries. Each 2 mm implant was produced in just 1.6 seconds, featuring 200 µm-wide channels that guided neural stem cell growth and helped reconnect severed axons.
Implanted into injury sites, the scaffold supported natural vascularization and enabled significant hind limb recovery. To demonstrate clinical potential, the team also printed four-centimeter human-scale implants from MRI scans in under 10 minutes, moving closer to future human trials.
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Featured image shows the Effect of MXene-ECM Scaffold Conductivity and 3D printed Micro-Mesh Design on Neuronal Cell Behavior in Response to Continuous Electrical stimulation. Image via RCSI.
