Characterization of neuronal viability and network activity under microfluidic flow

• Published in: Journal of neuroscience methods 2021-07, Vol.358, p.109200-109200, Article 109200
• Main Authors: Herzog, Nitzan, Johnstone, Alexander, Bellamy, Tomas, Russell, Noah
• Format: Article
• Language: English
• Subjects: Drug delivery; Flow; Microculture; Microfluidics; Neuronal culture; Rapid flow; Volume transmission
• ISSN: 0165-0270; 1872-678X
• DOI: 10.1016/j.jneumeth.2021.109200

•Tape-based microfluidics for easy fabrication and re-use of microelectrode chips.•Layered devices allow for isolation of cells from direct flow.•Removal of soluble factors by flow, not physical shear, causes neuronal dysfunction.•Mature neuronal cultures with conditioned media exhibit stable network activity.•Rapid bulk solution exchange over neurons can mimic volume transmission conditions. Microfluidics technology has the potential to allow precise control of the temporal and spatial aspects of solute concentration, making it highly relevant for the study of volume transmission mechanisms in neural tissue. However, full utilization of this technology depends on understanding how microfluidic flow at the rates needed for rapid solution exchange affects neuronal viability and network activity. We designed a tape-based pressurized microfluidic flow system that is simple to fabricate and can be attached to commercial microelectrode arrays. The device is multi-layered, allowing the inclusion of a porous polycarbonate membrane to isolate neuronal cultures from shear forces while maintaining diffusive exchange of solutes. We used this system to investigate how flow affected survival and spiking patterns of cultured hippocampal neurons. Viability and network activity of the cultures were reduced in proportion to flow rate. However, shear reduction measures did not improve survival or spiking activity; media conditioning in conjunction with culture age proved to be the critical factors for network stability. Diffusion simulations indicate that dilution of a small molecule accounts for the deleterious effects of flow on neuronal cultures. This work establishes the experimental conditions for real time measurement of network activity during rapid solution exchange, using multi-layered chambers with reversible bonding that allow for reuse of microelectrode arrays. With correct media conditioning, the microfluidic flow system allows drug delivery on a subsecond timescale without disruption of network activity or viability, enabling in vitro reproduction of volume transmission mechanisms.