Tunable, bioactive protein conjugated hyaluronic acid hydrogel for neural engineering applications

Millions of Americans suffer from nervous system injuries. Hydrogels have been investigated to (1) bridge nerve gaps; (2) act as scaffolds for bioactive molecule delivery or cell transplantation; and/or (3) promote axonal outgrowth. In this study, we use a rapid, one-step Michael addition click chemistry reaction to fabricate a hyaluronic acid (HA) scaffold for neural repair. Briefly, some of the primary hydroxyl groups on the HA backbone were modified with vinyl sulfone functional groups for (1) conjugation of thiol based bioactive molecules and (2) hydrogel crosslinking, which was confirmed by proton nuclear magnetic resonance (¹H-NMR) and Fourier transform infrared spectroscopy (FTIR). The degree of crosslinking creates a mechanically tunable hydrogel. Rheology confirmed that the storage modulus was within the order of magnitude to that of nervous tissue. Primary human dermal fibroblasts and primary mouse neural stem cells (NSCs) seeded in the HA hydrogel were viable and proliferative, thus demonstrating that the HA hydrogel is suitable as a scaffold for cell transplantation. The range of pore size demonstrated that the scaffold supports cell migration and neurite extension. Neurite outgrowth of cultured whole embryonic day 9 chick dorsal root ganglions signifies that the hydrogel supports axonal outgrowth. Reduction in immune and inflammatory cell viability was observed in the anti-Fas conjugated HA hydrogel, whereas the NSCs maintained viability in the anti-Fas HA hydrogel. Therefore, this one-step, rapid, controllable reaction is an efficient method for fabrication of tunable, biomolecule conjugated hydrogels for neural engineering applications.