Organ-on-chip (OOC) devices are micro-engineered three-dimensional (3D) biomimetic systems that can be used to create in vitro models of human tissue. They provide an alternative for conventional cell culture tools in pharmaceutical R&D. Moreover, these devices can contribute in research focused on understanding complex disease processes. OOC often includes porous membranes made of polydimethylsiloxane. The conventional method to create these membranes has drawbacks such as a limited achievable porosity. A novel approach to create porous PDMS membranes is to use micro-electro-mechanical systems (MEMS)-based fabrication technologies such as etching. With this method, the porosity of the membranes can be finely tuned. Quirós-solano et al.1 used this method and created a thin (>10 m) highly porous membrane and 3D scaffolds. Furthermore, their membrane could be easily transferred from its substrate to an OOC. In order to achieve this transfer, they incorporated a sacrificial layer of poly acrylic acid (PAA). The high porosity of the scaffold was created by introducing lateral gaps between the vertical pores of the scaffold. The dimensions of the gaps can be tuned by changing the etching time. However, this resulted in complete etching of the underlying layer. In order to reduce the etching time, this project is focused on the mechanism that created the lateral gaps. The contribution of bias power, chamber pressure and chuck temperature to that mechanism are investigated. With the knowledge gained from these experiments, the dimensions of the gaps were tuned by changing the aforementioned parameters.Furthermore, in this work the fabrication process of Quirós-Solano et al. is adapted to create thick (>20 m) PDMS membranes. These membranes were successfully fabricated and employed by researchers at the University of Technology in Eindhoven.

The process of generating new therapeutics is a complex, highly demanding, and economically challenging procedure. From every 10.000 drug candidates that are introduced to the preclinical phase, only 5 are chosen to be tested for clinical trials. In order to overcome the challenges with current drug screening and toxicity tests, Organ-On-Chip (OOC) systems have been developed. OOCs mainly include a biocompatible membrane or a substrate on which cells or tissue slices are cultured. To perform drug screening tests, the OOC devices need to have a microchannel for drug delivery.
As an example of this class of devices, Brain-On-Chip is presented in this thesis which is developed by TU Delft in collaboration with Leiden University Medical Centre (LUMC). The chip houses a brain slice and electrical activity of the brain tissue is studied before and after cortical spreading depression (CSD) induction. The device consists of a polydimethylsiloxane (PDMS) membrane embedding a microchannel. The PDMS membrane houses the brain tissue and the microchannel delivers chemical needed for CSD induction to a specific region of the tissue.
The main goal of this project is fabrication of the microchannel. To do so, an ultra-thick photoresist (PR) has been characterized which is used for the microchannel fabrication. Unlike most of current OOC fabrications, the Brian-on-chip device presented in this study is fabricated by a clean-room compatible procedure. This may result in a mass-production fabrication and a rapid commercialization. This study aims to validate the Brain-On-Chip by mice brain tissue provided by LUMC. To the best of authors’ knowledge, this is the first attempt to fabricate a clean-room compatible device for CSD induction.

Organ-on-Chips (OOCs) are micro-fabricated devices that combine micro-engineering with in-vitro cell culturing. This combination results in an in-vitro model that mimics the minimal functional unit of a human organ. OOC devices are expected to provide accurate and predictive screening tools that will eventually reduce false negatives and false positives during drug research and development. By exploiting the accuracy of micro-fabrication techniques, multiple features such as micro-channels, micro-fluidics, micro-topologies, micro-pumps, etc., can be embedded in the device to replicate the biological conditions experienced by the cells in an in vivo human tissue. Moreover, it is possible to monitor the behavior and viability of the cells in the model through sensors embedded in the device.
The Cytostretch device, an OOC developed by TU Delft and Philips, consists of a stretchable membrane fabricated on a silicon chip and equipped with microelectrode arrays (MEA) and micro-grooves. This device provides a customizable platform for multiple organ models. The Cytostretch Silicon-based fabrication should guarantee a large-scale fabrication and a rapid commercialization. However, the design choices compromise the electrochemical performance of the Titanium Nitride MEA on the device. In order to solve this problem, this project focused on coating the Cytostretch MEA with PEDOT (Poly (3,4 – Ethylenedioxythiophene)). PEDOT is a conductive polymer, known to exhibit a superior electrochemical performance due to its high porosity. To the best of authors knowledge, this is the first time a PEDOT MEA is embedded in an Organ-on-Chip. Moreover this is the first work reported aiming to produce a stretchable PEDOT MEA at large-scale by following the “polymer-last approach”.
In this project three main issues were addressed and successfully solved. Firstly, the adhesion between the polymer layers composing the Cytostretch device was improved. Secondly, the process and the masks of the Cytostretch were optimized in order to coat the Titanium Nitride MEA with a noble metal (Platinum) in order to facilitate PEDOT deposition. Thirdly, the deposition of PEDOT on top of the Cytostretch electrodes was successfully performed by cyclic voltammetry deposition from an aqueous solution with NaPSS (Sodium-Poly (Styrene Sulfonate)) as the dopant material.
The performance of the novel stretchable PEDOT MEA was assessed with multiple characterization methods such as Electrochemical Impedance Spectroscopy, and Cyclic Voltammetry. Compared to the Titanium Nitride MEA, PEDOT electrodes exhibit an enhanced performance providing an outstanding 94% reduction of the electrochemical impedance at 1 kHz. The new electrodes showed an ohmic behavior over a wider range of frequency. Last but not the least, a significant increase of the total charge delivery capacity (CDC) was obtained during cyclic voltammetry tests. The results reported in this work demonstrate that the electrochemical performance of the Cytostretch can be drastically improved with PEDOT coating. The combination of robust microfabrication and the electrochemical deposition techniques presented in this work is an important step forwards toward the use of the Cytostretch device in pharmacological applications.