Spinal cord injury (SCI) is a debilitating condition: currently, 238,000 – 332,000 of persons in the US live with SCI. The SCI prognoses are dire – less than 1% of persons experience complete neurologic recovery: thus, there is a great need for treatments that could lead to functional recovery. In recent years, significant progress has been made in describing the interactions between carbon nanotubes (CNTs) and nerve cells which have implications in the field of neural tissue engineering for promoting nerve repair such as in spinal cord injuries. Specifically, it has been shown that patterned and aligned CNTs can promote directional neural growth. Our work focuses on designing a method for CNT alignment onto hydrogels and further investigating the effect of carbon nanotubes on neurite extensions. For this work we chose polyethylene glycol (PEG) hydrogel because it is bioinert, hydrophilic, and possesses a degree of flexibility very similar to that of brain.
To align CNTs onto the PEG hydrogel, we developed a novel two-step technique. We first grew high density, aligned CNTs onto an annealed quartz wafer. The quality and semiconductive nature of the CNTs was confirmed by Raman spectroscopy analysis, alignment was confirmed by scanning electrone microscopy (SEM) imaging, and phase change of the quartz was confirmed by x-ray diffraction. Next, we stamped the CNT pattern from the quartz on the hydrogel surface. Successful transfer was confirmed by SEM imaging as well as atomic force microscopy (AFM) analysis. The hydrogel itself was prepared by UV polymerization of 10% w/v PEG-diacrylate (PEGDA) and 0.1% w/v Irgacure ® 2959. We then seeded PC12 cells on top of the CNT-stamped hydrogels and cultured them at standard cell culture environment for up to 7 days. Nerve growth factor was used to induce cell differentiation into the neural phenotype. Neurite outgrowth as a function of CNT presence and alignment was studied.
In summary, this project describes a novel method to align CNTs on a hydrogel such as PEG with the goal of eliciting directed neurite outgrowth. With further developments, a material such as the one described here, which can guide axon regeneration holds a great promise for developing SCI cures that can promote axon regeneration and lead to functional recovery.