The nervous system is highly complex which is responsible for the sophisticated coordination of actions and sensory information by transmitting signals to and from different parts of its body. Establishment of 3D neuronal networks is a promising field in regenerative medicine and promise to bring functional restoration of injured nervous systems such as in peripheral neuropathy. Recent research reports highlighted the importance of facilitated tissue regeneration via innervation and provision of in vitro models to encode neuronal signal integration, network function, and cell–matrix interactions. Ideally, synaptic communication between neurons leads to the establishment of functional neural circuits or networks to mediate sensory and motor processing by transmitting signals to and from different parts of the body. Researchers have devoted much time and resources to interrogate the unique contribution of biochemical signals such as neurotrophin and growth factors to neural circuit formation. Beyond the demonstration of controllable formation into connected networks, however, these in vitro efforts are based on 2D patterning, which cannot achieve 3D spatial extensions of axons and dendrites, and consequently, fail to reconstruct 3D neural networks with similarity to in vivo complexity and interactions. Furthermore, the it has been established that the use of rigid substrates for micropatterning with a high fidelity also limits their suitability for in vivo utility. Obviously, designing 3D tissue-engineering scaffolds with a desirable geometric resolution to regulate neural network development has profound implications for future translation.
Scaffold-guided formation of neuronal-like networks, especially under electrical stimulation, can be an appealing avenue toward functional restoration of injured nervous systems. Recognition of the importance of transmitting electrical impulses across nervous systems has inspired efforts to develop conductive substrates in an attempt to anticipate neurogenesis. As such, efforts are also made to explore other conductive materials. Graphene, due to its superior mechanical properties and outstanding electrical conductivity, has been explored for biomedical applications. Still, much research is required. In this regard, Stevens Institute of Technology researchers: Dr. Juan Wang, Dr. Haoyu Wang and Professor Hongjun Wang, in collaboration with Professor Xiumei Mo at the Donghua University developed a new fabrication avenue for 3D conductive scaffolds based on printed microfiber constructs using near-field electrostatic printing (NFEP) and graphene oxide (GO) coating. Their work is currently published in the research journal, Advanced Materials.
With the assistance of branched polyethyleneimine (BPEI), graphene oxide was coated layer-by-layer (L-b-L) onto poly(L-lactic acid-co-caprolactone) (PLCL) microfibers via electrostatic interactions and then converted in situ to conductive reduced graphene oxide. Technically, by taking advantage of the stable jet from the Taylor cone of electrospinning, NFEP used a short collection distance for direct deposition of the stretched polymer solution on a grounded surface to form microfibers upon solvent evaporation. Overall, the researchers demonstrated a number of prototypes that combined the unique attributes of NFEP and graphene-based materials with simple-to-complex structural organizations along with optimization of key fabrication parameters favorable for neuronal network formation.
The research team reported that depending on the coating layer thickness, reduced GO coating endowed PLCL microfibers with stable yet significantly improved electrical conductivity while increasing surface roughness. Respective culture of primary mouse hippocampal neurons and rat pheochromocytoma, closely resembling neuron-like cells, on reduced GO-encapsulated PLCL microfibers showed preferable outgrowth of neurites along with microfibers under an optimal electrical stimulation.
In summary, the new study showed that coating GO/reduced GO onto the surface of 3D PLCL microfiber templates to yield conductive scaffolds is an effective strategy to achieve both structural complexity and high electrical conductivity. Typically, with the assistance of NFEP, the size of microfibers and their 3D spatial organization could be customized to provide unique topographical cues for guided development of 3D neural networks. In a statement to Advances in Engineering, Professor Hongjun Wang said their work presented an innovative attempt to develop a hierarchical neuronal-like network with guidance from conductive substrates; nonetheless, further efforts were necessary to extensively investigate the responses of primary neuronal cells or induced pluripotent stem cell-derived neuronal cells on such scaffolds.
Juan Wang, Haoyu Wang, Xiumei Mo, and Hongjun Wang. Reduced Graphene Oxide-Encapsulated Microfiber Patterns Enable Controllable Formation of Neuronal-Like Networks. Advanced Materials 2020: volume 32, 2004555.