Abstract

Ultrathin porous membranes are currently used for various biomedical applications, ranging from co-culture systems to tissue barrier models. In the blood-brain barrier model, the intimate proximity between endothelial and glial cells plays a significant role in cell-cell communication and transmigration across the barrier, which cannot be physiologically modeled with conventional co-culture systems typically separating cell types by more than 10 μm. A thickness gradient membrane can enable studies where the goal is to understand the physical characteristics of co-culture arrangement in the barrier model. Here, a robust method to generate ultrathin porous Parylene C (UPP) membranes is developed not just with precise thicknesses down to 300 nm but with variable gradients in thicknesses while at the same time having porosities up to 25%. Surface etching leads to improved cell attachment is also shown. Next, the mechanical properties of UPP membranes with varying porosity and thickness are examined, and the data are fitted to previously published models, which can help determine the practical upper limits of porosity and lower limits of thickness. Lastly, a straightforward approach allowing the successful integration of the UPP membranes into a prototyped 3D-printed scaffold is validated, demonstrating mechanical robustness and allowing cell adhesion under varying flow conditions. Given the observed time-persistent effects of plasma treatment and the fact that membrane interaction with cells and tissues directly affects the performance and credibility of barrier models, we vigorously investigate the cell-substrate interactions between endothelial cells and two biocompatible variants of Parylene, Parylene C and Parylene N. We use a simple approach for benchtop oxygen plasma treatment and investigate the changes in cell spreading and ECM deposition as well as the changes in surface properties. Our results support the previous findings on the persistent effects of plasma treatment on Parylene biocompatibility while showing a more pronounced improvement for Parylene C. Overall, the results of this study provide a clear picture of potential mechanisms of plasma-induced changes in synthetic polymers, which have implications for their use in in vitro models. To investigate the effect of membrane thickness on endothelial barrier properties, we use thickness gradient Parylene C membranes with microfabrication techniques with thicknesses ranging from 500-1500 nm within the same device. The membranes are embedded in 3D printed scaffolds designed and are used to co-culture human cerebral microvascular endothelial cells (hCMEC/D3) and astrocytes (CTX-TNA2). Permeation of fluorescein isothiocyanate-dextran, efflux activity, and expression levels of tight junction proteins are used to quantify the effects of cell-cell distance on the barrier integrity. It is observed that increasing the membrane thickness decreases the barrier tightness while increasing the membrane thickness beyond 1 μm exhibits a sharper drop in barrier properties. In addition to the implication of this work on distance-dependent cell-cell interactions, thickness gradient membranes developed here are potentially applicable to in vitro studies where an adjustable well-defined cell-cell distance is required.

Publication Date

6-2022

Document Type

Dissertation

Student Type

Graduate

Degree Name

Microsystems Engineering (Ph.D.)

Department, Program, or Center

Microelectronic Engineering (KGCOE)

Advisor

Thomas R. Gaborski

Advisor/Committee Member

Robert N. Carter

Advisor/Committee Member

Michael Schertzer

Comments

This dissertation has been embargoed. The full-text will be available on or around 6/28/2023.

Campus

RIT – Main Campus

Available for download on Wednesday, June 28, 2023

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