Development of an in situ injectable hydrogel containing hyaluronic acid for neural regeneration

In this work, a novel enzymatically crosslinked injectable hydrogel comprising hyaluronic acid (HyA), dopamine (DA), and 3-(4-hydroxyphenyl) propionic acid (HPA) conjugates was successfully developed. To the best of our knowledge, it is the first time that HPA is conjugated to a HyA-based backbone. In situ hydrogelation of HyA-DA-HPA occurred in the presence of hydrogen peroxide (H₂O₂) as an oxidant and horseradish peroxidase (HRP) as a catalyst. Proton nuclear magnetic resonance and Fourier transform infrared spectroscopy were used to characterize the chemical reactions between HyA, DA, and HPA. Gel formation completed between 3 s to 5 min depending on the concentrations of polymer, HRP, and H₂O₂. Crosslinked HyA-DA-HPA gels acquired storage moduli ranging from ∼100 Pa to ∼20 000 Pa (at f = 2000 rad s^-1). Biocompatibility of the hydrogels was examined with human mesenchymal stem cells (hMSCs) and human induced pluripotent stem cell-derived neural stem cells. The hydrogels made of 2.0 w/v% HyA-DA-HPA hydrogels, 0.24 U ml^-1 HRP and ≤ 0.5 µmol ml^-1 H₂O₂ were found biocompatible with hMSCs cultured on and encapsulated within the hydrogels. Since HyA serves as a backbone of the extracellular matrix in the central nervous system (CNS) and DA acquires the ability to restore dopaminergic neurons, use of this injectable HyA-DA-HPA hydrogel for stem cell transplantation is a potential treatment strategy for CNS repair and regeneration.