Access Type

Open Access Dissertation

Date of Award

January 2022

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Chemical Engineering and Materials Science

First Advisor

Carolyn Harris

Abstract

It has been hypothesized that physiological shear forces acting on medical devices implanted in the brain significantly accelerate the rate to device failure in patients with chronically indwelling neuroprosthetics. In hydrocephalus shunt devices, shear forces arise from cerebrospinal fluid (CSF) flow. The shunt’s unacceptably high failure rate is mostly due to obstruction with adherent inflammatory cells. Astrocytes are the dominant cell type bound directly to obstructing shunts, rapidly manipulating their activation via shear stress-dependent cytokine secretion. Here we developed a total internal reflection fluorescence microscopy (TIR-FM) combined with a microfluidic shear device chip (MSDC) for quantitative analysis and direct spatial-temporal mapping of secreted cytokines at the single-cell level under physiological shear stress to identify the root cause for shunt failure. Real-time secretion imaging enabled successful detection of a significant increase of astrocyte IL-6 cytokine secretion under shear stress greater than 0.5 dyne/cm2, validating our hypothesis and highlighting the importance of reducing shear stress activation of cells.The tissue obstructing neuroprosthetic devices is largely composed of inflammatory cells with a significant astrocyte component. In a first of its kind study, we profile the astrocyte phenotypes present on hydrocephalus shunts. qPCR and RNA in-situ hybridization were used to quantify pro-inflammatory (A1) and anti-inflammatory (A2) reactive astrocytes by analyzing C3 and EMP1 genes, respectively. Additionally, CSF cytokine levels were quantified using ELISA. The results showed a heterogeneous population of A1 and A2 reactive astrocytes on the shunts with obstructed shunts having a significantly higher fraction of A2 astrocytes. The pro-A2 cytokine IL-6 was also found at higher concentrations among CSF from obstructed samples. Furthermore, cytokine neutralizing antibodies produced a significant reduction in both A1 and A2 astrocyte activation and attachment in an in vitro model of astrocyte growth on shunts. Therefore, targeting cytokines involved with astrocyte activation is a promising intervention aimed to prevent shunt obstruction.

Download

Share

COinS