Dipeptide Nanotubes Reinforced Hydrogels for Neural Injuries

The study of self-assembled, nanomaterial scaffolding has become a rapidly-growing area of biomedical research, particularly in the realm of regenerative medicine and tissue engineering applications for neurological injuries and diseases. Currently, there are limited self-repair strategies and treatments for central nervous system deficits, as the process of neurite growth is often slow, complex, and occurring in inhibitory environments, ultimately leading to permanent nerve damage. Preliminary findings from our team support the efficacy of PECVD deposited, vertically-aligned, dipeptide-based nanotube substrates for stimulating neural cell proliferation and differentiation. Peptide-based building blocks are utilized as they have the capacity to self-assemble into highly organized nanoscale structures that possess key functional properties such as biocompatibility, biodegradability, molecular recognition, high aspect ratios, semi- conductivity, and stiffness. The lingering issue is the need to successfully develop a vehicle to introduce these nanostructures into targeted regions of the body for in-vivo testing while retaining their structure, orientation, and organization. One potential solution involves combining these nanotubes with hydrogels for noninvasive, ease of implantation.<br/><br/>Within this study we aim 1) to fabricate a dipeptide nanotube reinforced-hydrogel with optimized structural properties for cell adhesion, proliferation, and differentiation, 2) to investigate the <i>in vitro </i>effects of human neural stem cells cultured within the scaffold, and 3) to explore the logistics of incorporating a 3D printable, bioresorbable, electrical stimulation circuit. We hypothesize that incorporation of semiconductive, dipeptide-based nanotubes into a hydrogel scaffold can positively impact the regeneration capacity of nerve and support cells via mechanical cues as well as via electrical stimulation. In essence, these functionalized scaffolds will create tissue mimics that can encourage repair along short sections of injured neurons. Peptides containing tryptophan-tyrosine residues are of particular interest due to their well-characterized redox potential and their multiple roles in neurotransmitter synthesis. Gelatin and sodium alginate will be the natural polymer bases for the hydrogel component of the biomaterial, as they have been linked to numerous salutary advantages for central nervous system repair, including tunable degradation rates, slow release of bioactive factors, and low immunogenicity. Nanotubes synthesized through solution phase self-assembly mechanisms are incorporated in concentrations ranging from 0-1 mg/mL to circumvent issues with cell viability and accelerated degradation reported at higher concentrations. Examination of physiochemical characteristics, biological interactions, cellular proliferation, gene expression, and cytotoxicity at the cell-scaffold interface via various imaging techniques and cell culture analyses will reveal whether this option is a worthy investment for neurological research.<br/><br/>The nanocomposite will be further 3D bioprinted to create scaffolds that can be predesigned to custom fit to an individual’s unique site of nerve injury, thus, constraining exogenous/endogenous neurite growth and recreating developmental neurogenesis. Furthermore, the scaffolds inherent electrical properties can be harnessed for neurological activation and repair, introducing potential gradients through periodic voltage treatments that induce membrane depolarization and impact the functionality of enzyme-activated and ion-transport membrane proteins. Thus far, the idealized parameters for bioprinting while maintaining maximum cell viability has been achieved and initial morphological and in-vitro analyses of these samples have commenced.