An experimental microfluidic model of periarterial spaces in the glymphatic system



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In the glymphatic system, cerebrospinal fluid enters through periarterial spaces and removes metabolic waste from the brain’s interstitial spaces. Previous experiments in live mice have found that a peristaltic wave along artery walls produced by the heartbeat in duces flow in the surrounding periarterial space. However, the mechanisms driving the flow are still not well understood. The brain is complex and many mechanisms may be acting simultaneously. We have designed microfluidic devices to serve as two-dimensional models of periarterial spaces. Using particle tracking velocimetry, we analyze flow induced by a peristaltic wave at the frequency range representative of human heartbeats. We find that the induced flow moves in the same direction as the peristaltic wave and oscillates forward and backward with every pulsation of this wave. As the frequency increases, the bulk forward flow decreases, but the magnitude of these oscillations increases slightly. We also find that the pulsations from the peristaltic pump match the large scale oscillations in the induced flow with no phase shift. In between pulsations, there are periods of rest with considerably less motion, and as the frequency increases the periods of rest become shorter. We conclude that the peristaltic wave along artery walls can induce the periarterial flow that is observed in live mouse brains. Furthermore, we have created detailed characteriza tions of the flow at seven frequencies that are in the range of normal human heartbeats. We have also found a promising power law relationship between the Root-Mean-Squared velocity of the induced flow and frequency. These results may be used in further experimental and computational models to enhance our understanding of the glymphatic system.



Microfluidic model, Biophysics, Fluid mechanics