Recapitulation of Physiologic and Pathophysiologic Pulsatile CSF Flow in Purpose-built High-throughput Hydrocephalus Bioreactors
Authors: Faryami Ahmad , Menkara Adam , Ajaz Shaheer , Roberts Christopher , Jaroudi Ryan , Gura Blake , Hussini Tala , Harris Carolyn A. 
Published: July 2024

Abstract

Background The absence of a tested and validated long-term in-vitro model that can incorporate clinically relevant parameters has limited hypothesis-driven studies and, in turn, limited our progress in understanding mechanisms of shunt obstruction in hydrocephalus. Testing clinical parameters of flow, pressure, shear, catheter material, surface modifications, and others while optimizing for minimal protein, cellular, and blood interactions has yet to be done systematically for ventricular catheters. There are several studies that point to the need to not only understand how cells and tissues have occluded these shunt catheters, but how to stop the likely multi-faceted failure. For instance, studies show us that tissue occluding the ventricular catheter is primarily composed of proliferating astrocytes and cells of the macrophage lineage. Cell reactivity has been observed to follow flow gradients, with elevated levels of typically proinflammatory interleukin-6 produced under shear stress conditions greater than 0.5 dyne/\({cm}^{2}\). But also that shear can shift cellular attachment. The Automated, In vitro Model for hydrocephalus research (AIMS), presented here, improves upon our previous long-term in vitro systems with specific goals of recapitulating bulk pulsatile cerebrospinal fluid (CSF) waveforms and steady-state flow directionality relevant to ventricular catheters used in hydrocephalus.Methods The AIMS setup was developed to recapitulate a wide range of physiologic and pathophysiologic CSF flow patterns with varying pulse amplitude, pulsation rate, and bulk flow rate with high throughput capabilities. These variables were specified in a custom-built user interface to match clinical CSF flow measurements. In addition to flow simulation capabilities, AIMS was developed as a modular setup for chamber testing and quality control. In this study, the capacity and consistency of single inlet resin chambers (N = 40), multiport resin chambers (N = 5), silicone chambers (N = 40), and PETG chambers (N = 50) were investigated. The impact of the internal geometry of the chamber types on flow vectors during pulsatile physiologic and pathophysiologic flow was visualized using computational fluid dynamics (CFD). Parametric data were analyzed using one-way analysis of variance (ANOVA) or repeated measures ANOVA tests. For all tests, a confidence interval was set at 0.95 (α = 0.05). In a subset of experiments, AIMS was also tested for its capability to measure the flow of florescent microspheres through the holes of unused and explanted ventricular catheters.Results The analysis of peak amplitude through chambers indicated no statistically significant differences between the chamber batches. These investigations also demonstrated the negative correlation between peak amplitude and compliance in the chambers (\({R}^{2}\)=0.623). This high throughput setup was able to reproduce clinical measurements of bulk CSF flow tested in up to 50 independent pump channels such that there was no exchange of solution or flow interference between adjacent channels. Physiologic and pathophysiologic clinical measurements of CSF flow patterns were recapitulated in all four chamber types of the AIMS setup with and without augmented compliance. The AIMS setup’s automated priming feature facilitated constant fluid contact throughout the study; no leaks or ruptures were observed during short- (up to 24 hours) or long-term (30 days) experiments. Finally, qualitative microscopy long-exposure image capture revealed microsphere movement under steady-state and pulsatile flow of spheres moving into the shunt catheter.Conclusion AIMS successfully simulates clinical measurements of physiologic and pathophysiologic CSF flow patterns, as exemplified using data of CSF exiting an externalized ventricular drain in four distinct chamber types. This provides a promising platform for investigating the direct interaction between CSF, immune cells, and shunt hardware under relevant flow conditions when both the source of bulk flow and pulsatility are coupled. Implementing this system in future work will enhance our understanding of hydrocephalus pathogenesis and treatment strategies.