Microfluidic platforms that physically guide axons enable controlled studies of neuronal connectivity, injury, and regeneration in vitro. This thesis investigates two fabrication routes for Polydimethylsiloxane (PDMS)-based axon-guidance structures: direct ink writing of printable PDMS inks and cleanroom microfabrication using photolithography and DRIE, with the goal of achieving high-aspect-ratio and high-density features suitable for neuronal applications. Printable PDMS inks were formulated by blending shear-thinning SE1700 with Sylgard 184 at varying ratios and characterized by shear viscosity and oscillatory rheology at 25 °C. SE1700-containing blends exhibited pronounced shear thinning and gel-like behavior (G′ > G″) in the linear viscoelastic regime. DIW printability was assessed via dual-layer tests and filament-width analysis under different nozzle sizes, speeds, and displacements. The 8:2 ink provided the best balance between extrusion and shape retention; however, multilayer pores still showed sagging or merging depending on overhang span and dose, and dimensional errors on printed microchannels ranged from 32 to 157 µm depending on geometry. Additionally, microfabrication produced high-aspect-ratio features on silicon using positive and negative routes. PDMS–PDMS double casting from positive molds revealed failure modes—lateral collapse and longitudinal tearing, in dense, narrow structures during demolding. Direct PDMS casting from negative silicon molds improved geometric fidelity and avoided tearing; measured aspect ratio is close to the wafer values and spontaneous collapse was not observed after demolding. Overall, DIW enables fast, mold-free prototyping but is limited in resolution and multilayer fidelity; microfabrication delivers micron-precision HAR arrays but entails higher process complexity and demolding risks for dense features. The results outline practical design and process for building PDMS platforms that can be further integrated with MEAs for functional neural studies.  

Neurons are fundamental to cognitive and motor functions, relying on intricate electrical and chemical signaling. However, neurological diseases such as Parkinson’s, Alzheimer’s, and Amyotrophic Lateral Sclerosis impair neural function, posing a growing challenge due to aging populations and limited regenerative capacity of the nervous system. Advances in induced pluripotent stem cells (iPSCs) have enabled human-derived neuronal models for disease study, while neural interfaces, particularly microelectrode arrays (MEAs), facilitate electrophysiological investigation both in vivo and in vitro.

This thesis explores the use of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), a conductive polymer with mixed ionic-electronic conductivity, as a superior neural interface for in vitro neuronal cultures. The study addresses three key objectives: (1) elucidating the electrochemical mechanisms underlying PEDOT:PSS’s performance, (2) validating its biocompatibility and functionality in recording neuronal activity, and (3) establishing protocols for neuronal differentiation and maturation on PEDOT:PSS substrates.

First, a scientific literature search was performed to understand the current standing of PEDOT:PSS as a neuronal interface, exploring the different applications and approaches scientific peers have established, and understanding the working mechanisms of the conduction behind their work. This was complemented with the practical experience with PEDOT:PSS, showcasing its biocompatibility and methods to improve conductivity.

Secondly, neuronal recordings in vitro were made to assess the performance of a custom-built PEDOT:PSS-based MEA and the meaning behind the electrophysiological recordings. Data acquisition, pre-processing, and analysis are discussed to understand the results obtained. Key findings include the performance success of the MEA, while also explaining the shortcomings of the implemented processing algorithms.

Lastly, a motor neuron differentiation protocol from iPSCs was established to further investigate the role of PEDOT:PSS in such context for later studies. The success of the protocol was assessed by morphological, functional, and immunostaining assays.

Future directions include optimizing conductivity through acid treatments, integrating PEDOT:PSS into motor neuron maturation protocols, and exploring electrical stimulation and 3D culture systems. This work contributes to the development of advanced bioelectronic tools for neuronal models and engineering.

Electric stimulation can be used to get cells to behave in all kinds of ways. Examples include getting them to move, proliferate, excrete chemicals, or stop doing any of these things. However, finding the optimal stimulation parameters is a tedious process of trial and error which is made difficult by the equipment that is currently in use. It is often bulky, expensive and only allows for a limited number of experiments to be done simultaneously. To combat this issue, this work aims to create a circuit that allows the simultaneous stimulation of as many different channels of cells as possible without causing accidental damage to the cells through harmful electrochemical reactions. To this end, a printed circuit board is designed to fit underneath a 48-well plate. It can set the waveform timing to be a square wave with variable frequency, duty cycle and amplitude with different settings for the positive and negative part of stimulation. To create this device, research is done to the state of art of the current devices used to stimulate cells. As well as the viability of stainless-steel as a cheaper alternative reference electrode material with respect to platinum and Ag/AgCl electrodes. While the stimulation part of the design works, the charge balancing circuit does not and requires more work.

Organic electrochemical transistors (OECTs) are a promising technology in the field of bioelectronics. They bridge electronics and biology through their ability to operate in aqueous environments. Their ability to transduce biological signals into electronic ones makes them a preferred choice for bioelectronic applications, such as biosensing and neural interfaces. While p-type materials like PEDOT:PSS have become the benchmark for the OECT performance, the development of stable, high-mobility n-type channel materials remains a major challenge. These materials are often limited by poor air stability, low electron mobility, and restricted ionic transport. In this work, a newly developed semiconducting n-type polymer with cleavable side chains is investigated. The polymer, YYBC, undergoes a post-deposition thermal treatment, which leads to a porous, more hydrophilic polymer, YYAC. This cleaved version aims to improve the performance of an n-type OECT.
The research followed three main objectives. OECT devices were first fabricated in a cleanroom environment, then a measurement setup for steady-state and transient characterization was developed, and lastly, the new n-type polymer was evaluated. For device fabrication, standard microfabrication methods were employed. For the measurement setup, programmable source-measure units, a function generator, and an oscilloscope were controlled through MATLAB for data acquisition and analysis. Lastly, the performance of the n-type polymer was assessed using electrochemical and electrical characterization. Parameters such as volumetric capacitance, transconductance, and time response were evaluated.
Results of this work show that the post-deposition side-chain removal significantly improves the polymer’s electrochemical behaviour. The findings show improved performance metrics, indicating that the new n-type polymer can be a promising material for future OECT applications.

Neurostimulation has emerged as a transformative approach for the treatment and management of a broad range of neurological disorders, including depression and epilepsy. The increase in usage of neurostimulation also necessitates high spatial resolution and depth of penetration in order to inflict minimal damage to the surrounding tissue. Optical or light-based stimulation offers unique benefits in this regard, enabling highly spatially resolved neural activation and paving the way for innovative modalities in targeted neural modulation.
In this work, an electronic platform for wireless powering and data transmission is presented,
utilising organic P–N junctions as the core technology for mediating photo-electric stimulation. These junctions are selected for their capacity to provide non-genetic neural activation with excellent spatial resolution. Power delivery to the implantable device is achieved acoustically via ultrasound, taking advantage of ultrasound’s superior tissue penetration characteristics.
Comprehensive characterisation of the organic P–N junctions was performed, culminating in
the identification of the PDCBT/ITIC architecture as the most suitable P-N junction, based on its
favourable optical absorption profile and photocurrent generation capability. In parallel, a dedicated power management and stimulation platform was developed as the initial steps in incorporating acoustic energy harvesting and efficient signal demodulation. Validation experiments confirmed reliable device performance and established a functional basis for wireless optoelectronic neurostimulation.
The results of this thesis establish a promising system-level paradigm for minimally invasive,
wirelessly powered neurostimulation using organic photo-sensitive interfaces and acoustic power links. This approach contributes a viable pathway toward the development of next-generation neural therapies with enhanced implantability.

The physical, chemical, and biological versatility and high water content of hydrogels have been taken advantage of to fabricate hydrogels that mimic the extracellular matrix (ECM) structure of native tissues and applied in the field of cell and tissue engineering to provide the cells with a 3D scaffold structure. Especially in tissue engineering, the creation of a suitable hydrogel scaffold with hard and soft interfaces that is capable of both supporting cell growth and stimulation for guided differentiation for tissue interface studies is a primary concern for advancements in tissue engineering. The ideal scaffold with hard and soft interfaces can be achieved by finetuning its biological, biochemical, structural, and mechanical properties for optimal cell proliferation and differentiation.

In this thesis, a magneto-responsive hydrogel scaffold composed of gelatin (Gel, 2.5%), alginate (Alg, 5%), and iron oxide microparticles (10% w/v) was developed and mechanically and rheologically characterized before, during and after the application of a uniaxial static magnetic field. The magneto-responsive hydrogel scaffolds were created through multi-material 3D printing using magnetic and non-magnetic hydrogel inks. The magnetic inks contained magnetic particle (MP) inclusions within its polymer network while the non-magnetic hydrogel ink had no MPs. The 3D printing process allowed for a local control in the magnetic and non-magnetic hydrogel distribution to create hard and soft hydrogel interfaces. The printability and shape fidelity of various ink compositions were evaluated, so that the final composition of Gel:Alg ratio of 1:2 (2.5%:5.0%) with 10% MP was chosen for further mechanical and rheological characterization. The magnetic hydrogel scaffold exhibited magnetorheological properties as it mainly increased the effective Young’s modulus, storage modulus, and damping factor, and decreased viscosity under a uniaxial static magnetic field application.

In tissue engineering, the developed hydrogel scaffold, which is locally responsive to magnetic cues, shows great potential for creating scaffolds capable of continuously stimulating embedded cells in a non-contact manner. As a proof of concept, a bi-layered, multi-material hydrogel scaffold was created with increased surface area attachment points between each hydrogel material to mimic the osteochondral tissue interface. The increased surface area between both layers was achieved through a checkered pattern design with alternating magnetic and non-magnetic hydrogel sections printed alongside each other.