Magnetic iron oxide (Magnetite, Fe₃O₄) nanoparticles are widely utilized in magnetic resonance imaging (MRI) and drug delivery applications due to their superparamagnetism. Surface coatings are often employed to change the properties of the magnetite nanoparticles or to modulate their biological responses. In this study, magnetite nanoparticles were fabricated through hydrothermal synthesis. Hydrophobicity is often increased by surface modification with oleic acid. In this study, however, hydrophobicity was introduced through surface modification with n-octyltriethoxysilane. Both the uncoated (hydrophilic) and coated (hydrophobic) individual nanoparticle sizes measured below 20 nm in diameter, a size range in which magnetite nanoparticles exhibit superparamagnetism. Both types of nanoparticles formed aggregates which were characterized by SEM, TEM, and dynamic light scattering (DLS). The coating process significantly increased both individual particle diameter and aggregate sizes. We tested the neurotoxicity of newly synthesized nanoparticles with two mammalian cell lines, PC12 (rat pheochromocytoma) and ReNcell VM (human neural stem cells). Significant differences were observed in cytotoxicity profiles, which suggests that the cell type (rodent versus human) or the presence of serum matters for nanoparticle toxicology studies. Differences in nanoparticle associations/uptake between the two cell types were observed with Prussian Blue staining. Finally, safe concentrations which did not significantly affect neuronal differentiation profiles were identified for further development of the nanoparticles.

Hyaluronic acid (HA) is a polysaccharide polymer frequently used as a starting material to fabricate hydrogels, especially for recapitulating the brain’s extracellular matrix (ECM) for in vitro neural stem cell (NSC) cultures. Here, we report the successful synthesis of a methacrylated HA (MeHA) polymer from an inexpensive cosmetic-grade hyaluronan starting material. The MeHA polymers synthesized from cosmetic-grade HA yielded similar chemical purity to those from pharmaceutical/research-grade HA reported in the literature. Crosslinked MeHA (x-MeHA) hydrogels were formed using radical polymerization which resulted in mechanical properties matching previously reported mechanical property ranges for enhanced neuronal differentiation of NSCs. We assessed cellular adhesion, spreading, proliferation, and stiffness-dependent neuronal differentiation properties of ReNcell VM human neural stem cells (hNSCs) and compared our results to studies reported in the literature (that utilized non-human and human pluripotent cell-derived NSCs).

Retinoic acid (RA) is a bioactive lipid that has been shown to promote neural stem cell differentiation. However, the highly hydrophobic molecule needs to first solubilize and translocate across the cell membrane in order to exert a biological response. The cell entry of RA can be aided by cell penetrating peptides (CPPs), which are short amino acid sequences that are able to carry bioactive cargo past the cell membrane. In this work, a novel cell penetrating peptide was developed to deliver RA to human neural stem cells and, subsequently, promote neuronal differentiation. The novel CPP consists of a repeating sequence, whose number of repeats is proportional to the efficiency of cell penetration. Using fluorescence microscopy, the mode of translocation was determined to be related to an endocytic pathway. The levels of β-III tubulin (Tubb3) and microtubule associated protein 2 (MAP2) expression in neural stem cells treated with RA conjugated to the CPP were assessed by quantitative immunocytochemistry. 

Protocols for culturing neural stem cells (NSCs) are increasingly finding utilization for studying and growing of tissues that can appropriately model the neural regeneration processes. Two-dimensional (2D) plastic or glass surface-enabled mammalian cell cultures have been the platforms for performing in vitro cell cultures. Isolated mammalian cells, however, come from three-dimensional (3D) spaces, thus recapitulating such 3D microenvironments is among the challenges for many tissue engineering applications. Herein, we present the protocols for culturing NSCs in 3D polysaccharide-based hydrogel microenvironments that mimic, for instance, the native extracellular matrix (ECM) space (of the brain). The protocols include three key steps: (1) generation of 3D hydrogels with living cells, (2) culturing NSCs in 3D environments, and (3) characterization via immunostaining and genetic expression assay (RT-qPCR).

Cell penetrating peptides (CPPs) have shown promise in delivery of therapeutics into cells. CPPs can be described as short amino acid sequences, typically <40-mer, that is able to readily translocate across the cell membranes. The properties and uptake mechanism depend largely on the amino acid sequence, which dictates the CPP secondary structure and overall interactions with the phospholipid bilayer. This book chapter aims to give a general overview on the various classes of CPPs, the cell-entry mechanisms, and published pre-clinical and clinical trials using CPPs.