Organ-on-Chip (OoC) is a technology that aims to increase the efficiency of drug development processes and organ models by engineering well-defined cell culture environments. Physiological relevant mechanical, chemical, or electrical cues provide in vivo-like microenvironments for realistic cell maturation. Biodegradable technologies have gained attention for the development of novel OoCs by integrating transient features to the culture platforms imitating the ever-changing environment inside the human body. Current efforts to replicate durable brain tissue models from organoids are limited by the lack of sufficient vascularisation introducing cell necrosis inside the 3D cell culture.
This report presents the design and fabrication of a 3D-printed OoC-platform that combines two independent cell protocols for a Vessel-on-Chip and a cortical brain organoid. The microfluidic chip is embedded with a biodegradable membrane, that separates the two cell cultures for a strictly defined time period. The membrane, composed of bayberry wax, lanolin, and carbonyl iron particles, enables the controlled opening via alternating magnetic field exposure. The thermal behaviour of the membrane is analysed with DSC and the magnetic particles with a SQUID magnetometer. Inductive heating experiments determine the optimal composite composition and exposure profile to facilitate membrane opening and subsequent communication between neural and vascular cells. The integrated membrane proved to be successful during the injection and evacuation phase. This positive result paves the way for co-culturing two inherently different cell protocols on a single chip. This master project lays the foundation for collaborative efforts towards vascularised brain organoids-on-chip and showcases the potential of additive manufacturing and biodegradable materials in OoC technology.

Resolving the underlying mechanisms of complex brain functions and associated disorders remains a major challenge in neuroscience, largely due to the difficulty in mapping large-scale neural network dynamics with high temporal and spatial resolution. Multimodal neural platforms that integrate optical and electrical modalities offer a promising solution, with microelectrode arrays (MEAs) being particularly effective for capturing electrophysiological activity across multiple neurons at the cellular level. Graphene has emerged as a highly attractive material for such neural interfaces due to its unique combination of biophysical, electrical, mechanical, biological, and optical properties. However, current graphene-based electrodes face challenges, including the need for transferring pre-grown graphene layers, which causes reliability issues.

In this work, microelectrode arrays based on transfer-free multilayer graphene and PEDOT:PSS are developed, and their feasibility for in vitro neural activity detection is evaluated through a brain slice culture. Firstly, the design and fabrication of graphene-based MEAs (grMEA) on transparent substrates is presented, establishing optimized microfabrication procedures for the integration of transfer-free multilayer graphene technology on in vitro MEAs. Several electrode diameters, ranging from 10 μm to 500 μm, are included to accommodate different experimental requirements and test the limits of the technology. Second, the combination of graphene and PEDOT:PSS conductive polymer is explored to overcome the fundamental limitations associated with graphene electrodes, such as high impedance at small electrode sizes, without compromising the optical transparency. A technique to integrate patterned PEDOT:PSS polymer coating on the electrodes to form graphene/PEDOT:PSS microelectrodes
(grppMEA) is developed.

The electrochemical performance, including charge storage capacity (CSC) and impedance properties, of the grMEA and grppMEA devices are evaluated. Obtained results, comparable with state-of-the-art neural interfaces, show that the PEDOT:PSS coating increases CSC values more than the double and substantially reduces the impedance by 10-20 times (e.g., from 247 kΩ to 13 kΩ for 50 μm diameter electrodes). This demonstrates the potential of the devices for efficient electrical coupling with neural tissue. Additionally, the volumetric capacitance of grppMEA electrodes was found to be 55.7 F/cm3, highlighting the volumetric ionic-electronic interaction coming from the PEDOT:PSS film, a feature absent in metal electrodes.

A custom-made interface that effectively connects the MEA devices to specific recording systems is developed to enable the acquisition of neural signals. The electrophysiological recording capabilities of the grMEA and grppMEA devices were subsequently evaluated through in vitro cerebellar brain slice cultures. Acute recordings of spontaneous activity and spike pattern characteristics of Purkinje cells and other neurons have been successfully obtained. The obtained signal-to-noise ratio values, ∼ 30 dB, demonstrate the great recording potential of the proposed MEAs. Overall, the results presented in this work demonstrate that transfer-free multilayer graphene MEA technology, especially when combined with PEDOT:PSS, overcomes the current limitations and offers the possibility for high-density recordings with single-cell resolution.

The current drug development process is a costly effort both in terms of budget and time. Organ-on-Chip (OoC) technologies are rapidly developing and are used for various applications and studies that aim to reduce the costs of this process. They represent the convergence between tissue engineering and microfluidic technology to provide researchers with an in vitro tool that can better recreate the environmental conditions in which cells would normally develop in vivo. One of the applications of this tool is the implementation of such platforms to study heart and muscle tissue. Electrical stimulation of this tissue is of great importance for these studies. There exist different ways in which these cells can be electrically stimulated such as microelectrode arrays (MEAs) or external electrodes. These methods pose several challenges that need to be addressed.

The scope of this project is to implement 3D microelectrodes into an already existing device from the company Bi/ond to electrically stimulate the cells developing inside. This approach aims to solve the existing challenges in current methods for the electrical stimulation of tissue. This project succeeded in developing such 3D microelectrodes although the functionality of the device could not be proven. However, several approaches were also studied and propositions were made on how to continue with this project.