OoC-integrated impedance spectroscopy for blood-brain barrier integrity analysis

Abstract

The lack of reliable human physiology models in vitro combined with an ever-increasing set of health and safety requirements imposed by pharmaceutical regulatory agencies across the world is causing a concerningly low number of new drugs to reach the market. Organ-on-Chip (OoC) technology aims to aid faster development of new drugs by providing more accurate in vitro models of human tissue, ultimately leading to a higher number of potentially successful drug candidates during preclinical testing. To achieve this, convergence of different engineering disciplines is necessary for fabricating cell culture environments that closely mimic their in vivo counterparts and offer better technological capabilities compared to conventional cell cultures by incorporating cell stimulation and sensor integration. In the case of human blood-brain barrier (BBB), these models offer invaluable insight into how BBB disruption causes neurodegeneration associated with many progressive diseases such as Alzheimer’s or Parkinson’s disease. In this thesis work, a novel OoC device for measuring permeability of the blood-brain barrier using impedance spectroscopy was designed and fabricated. The core of the device is a suspended, 150nm-thin silicon nitride microporous membrane which enables an in-vivo-like separation distance between cells constituting the BBB. A sidewall electrode topology was proposed as it offers a fully unobstructed view of the cell culture environment. A cleanroom-based fabrication flow was devised which enabled device fabrication of a two-channel microfluidic device with integrated impedance spectroscopy electrodes. Through simulation-based modelling, the electrode topology was optimized and was shown to be highly uniform in terms of measurement sensitivity, removing the need for commonly used measurement correction functions. To go beyond the limits of photolithography, a process flow utilizing convective self-assembly-based nanosphere lithography was demonstrated in fabricating sub-500 nm diameter pores, thereby facilitating higher pore density per cultured cell. A preliminary testing setup was designed, but due to machine unavailability in the cleanroom the full fabrication of the device could not be completed and testing of the final device is expected to be done in the future in a biology lab. The proposed electrode geometry design and fabrication flow can be extended to other OoC-integrated barrier tissue models utilizing more conventional polymer-based substrates.