Early-stage post-surgical infection monitoring is crucial for preserving patients' health and reducing public healthcare costs. Among various parameters and symptoms, local pH shifts can provide valuable insight into the development of infections. An implantable pH sensor can be employed to monitor localised pH changes. The Ion-Sensitive Field-Effect Transistor (ISFET) is a precise pH sensing device that is compact in size and can be integrated with standard CMOS technology. Due to its small size, the ISFET is promising as an implantable sensor for in vivo pH sensing. To avoid a second surgery for sensor removal after its functional lifespan, biodegradable sensors offer an alternative, as they can degrade and be absorbed by the human body after completing their function.

The aim of this project was to design and fabricate the first fully biodegradable ISFET pH sensor, addressing the challenges of accurate real-time monitoring for post-surgical infection, specifically in hip implantation surgery. This project successfully led to the design and fabrication of an 8-mask ISFET/MOSFET device using fully biodegradable materials and incorporating two rounds of ion implantation. Chip thinning via TMAH wet etching was also explored. Several alternatives were studied to overcome challenges with Molybdenum and Mo-Si contact in having suitable interconnections and Ohmic contact between Molybdenum and Silicon.

In recent years, there has been growing interest in the magnetocaloric effect (MCE) which is a magneto-thermodynamic phenomenon observed in certain magnetic materials. MCE materials undergo temperature changes when subjected to magnetic fields. Researchers are now exploring the possibilities of utilizing this material in biomedical application technologies, as they offer the potential for non-invasive control of their properties through external magnetic fields. However, there is a lack of research on suitable magnetic compositions that exhibit desired magnetic properties for medical purposes, while ensuring no adverse effects on the cells.

This master project explores the potential of a magnetocaloric (Mn,Fe)2(P,Si)-based compound as a biodegradable membrane for multi-cell separation in organ-on-chip platforms. Mn0.65Fe1.30Si0.37P0.65 compound was selected due to its sharp phase transition characteristics and tunable Curie temperature (Tc), which enable self-regulation of temperature within the therapeutic range, thus preventing potential damage to living cells. The synthesized Mn0.65Fe1.30Si0.37P0.65 compound exhibited a transition temperature of 316 K (43°C) with particle sizes ranging from 1-5 µm. A magnetocaloric wax-based composite was synthesized by integrating these particles with a wax component. Characterization under alternating magnetic fields (AMF) showed a significant temperature rise with higher magnetic concentrations and field amplitudes. At an applied AMF of 9 mT and a frequency of 244 kHz, a sample containing 15 vol.% magnetic particles stabilized at 44°C, effectively maintaining controlled temperatures within the therapeutic range (42-47°C) and efficiently melting the wax without harming living cells. Water absorption tests and SEM imaging further demonstrated the composite's low water permeability and minimal development of microcracks over time. These findings validate the potential of magnetocaloric materials with adjustable Curie temperatures for precise self-regulation of temperature in biomedical applications. The observed high heating efficiency and prevention of overheating offer promising opportunities for controlled thermal activation processes across various biomedical fields.

Tissue vitality monitoring is a crucial process to preserve patients’ health during post-surgical recovery or to ensure full adaptation and healing of transplanted organs. Among the many local factors for vitality assessment, tissue oxygenation gives an insight into entire tissue recovery and is directly linked to cell metabolism. To be able to assess oxygenation at the cellular level, NADH fluorescence sensing is used due to its contribution to the cellular respiratory cycle and high sensitivity to oxygen concentration. The current devices for NADH fluorescence sensing are limited to external measurements, where they are suitable for hospital use. This raises the need for a device that is implantable and bioresorbable so that it can stay in the body after the surgery and does not require secondary surgery for removal that puts the patient at risk. The goal of this master’s thesis is to introduce the design of a bioresorbable optical filter and photodetector for the measurements of oxygen through the detection of NADH fluorescence. The design consists of an absorption layer, a Fabry-Perot filter, and a wavelength-specific photodetector; where the overall response is designed to have high sensitivity to the emission wavelength of NADH (470nm) and low sensitivity to the excitation of NADH (350nm). ZnO nanoparticles are chosen to be the absorption layer due to their high absorption properties to 350nm and biodegradability, where the optical response is then tested through spectroscopy measurements. For the Fabry-Perot filter, a design with SiO2 and SiNx layers has been created with simulation and tested with optical measurements. The complete design consists of 15 layers and has a total thickness of approximately 1μm. Lastly; for the photodetector, Spectra simulations have been conducted for the determination of the optimal design properties. The choices are then adapted to a mask design for the fabrication, in which the back side etching of the silicon wafer is required for biodegradability and optical performance. The fabrication of the photodetector has not been completed due to the time frame of the project. The measurements on the combination of ZnO and Fabry-Perot filter show that the transmission of 470nm is 2.5-4 times larger than the transmission of 350nm, which is expected to increase to at least an order of magnitude when combined with the photodetector. For future experiments, it is recommended to conduct more tests on the filters and ZnO to ensure repeatability and consistency.

Organ-on-a-chip (OoC) technology has revolutionized the biomedical research field by offering dynamic platforms which accurately mimic physiological environments of human tissue. This technology has become a promising option to study human biology in vitro, including disease modeling, drug screening and personalized medicine. Organoids, 3D cell cultures derived from human stem cells, represent a promising tool to investigate 3D tissue growth in vitro. However, integration of vasculature in these organoids remains a significant challenge. Establishment of vasculature is essential to enable significant organoid growth, allowing nutrient and oxygen supply and waste removal.

This report aims to develop a Pluronic F127 based hydrogel as a transient barrier in an OoC-platform that combines cell cultures of Vasculature-on-a-Chip and cortical brain organoids. This transient barrier separates the two cell cultures until sufficient maturation of the cortical organoid. Due to thermoreversible gelation, the Pluronic F127 hydrogel barrier can be removed from the barrier channel by a decrease in temperature. Pluronic F127 and di-acrylated Pluronic F127 hydrogels were synthesizes and characterized using rheometry, differential scanning calorimetry and degradation testing to determine the optimal Pluronic F127 hydrogel. Simultaneously, optimization of the OoC-platform was done by fabrication of the platform using Polydimethylsiloxane (PDMS).

It was shown that the OoC platform for Vascularized Organoids-on-a-Chip could effectively by fabricated using PDMS molding. This was achieved through both PDMS-PDMS and PDMS-glass bonding. Pluronic F127 hydrogels were shown to be a viable option to function as a transient barrier for Vascularized Organoids-on-a-Chip. Pluronic F127 hydrogels effectively blocked fluid flow through the barrier channel for seven days. To increase this time, di-acrylated Pluronic F127 was synthesizes. A degree of acrylation of 57% was achieved. This was shown to be insufficient to significantly increase the longevity of Pluronic F127 hydrogels.

Further research needs to be done to find the optimal synthesis and photo-polymerization conditions of di-acrylated Pluronic F127 hydrogels. Ideally, di-acrylated Pluronic F127 hydrogels exhibit a low degradation rate while maintaining the thermoreversible properties of Pluronic F127 hydrogels.

Conventional techniques for audio monitoring, including Passive Audio Monitoring (PAM), often call for the use of environmentally unsustainable and challenging equipment. This among other limitations can disrupt the very environment that is meant to be studied and may also limit the ability to observe an ecosystem in its natural state.

This thesis explores the possibility of a passive wireless biodegradable microphone for the purpose of audio monitoring in fragile environments. This project introduces the "The BioThing - A biodegradable microphone for monitoring biodiversity".
The BioThing uses a biodegradable material, to address the current challenges of state-of-art monitoring techniques. The design utilises a resonant cavity to function as a listening device through the implementation of the backscatter wave modulation technique and with a primary working resonant frequency of around 1.7 GHz.

This report presents a detailed analysis of the device's design and function to optimize its geometry for various frequencies, operational ranges, and functionalities by investigating the effect of critical parameters such as the variable capacitances namely the distance between the diaphragm and the tuning post, and the distance between the tuning post and the antenna. Additionally, it also analyses the effect of device geometry on resonance properties by investigating the impact of parameters such as tuning post height, membrane thickness, and cavity height. The report also investigates the possibilities for device enlargement for long-distance operation and device miniaturisation to facilitate faster degradation. This optimization process aims to achieve improved performance, ultimately leading to a more effective listening device. A prototype was fabricated using commercially available Zinc and plant-based resin.

This research works towards a new generation of ecologically sustainable audio monitoring equipment that will allow a deeper insight into the soundscapes of fragile environments without disturbing the ecosystems.

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.

This thesis analyzes and describes a wearable pressure sensor to detect intraocular pressure and guide clinician diagnosis of glaucoma. Although glaucoma has many
symptoms and risk factors, high intraocular pressure is the most predominant. A method to continuously and accurately record intraocular pressure measurements and fluctuations in a patient could lead to a more reliable glaucoma diagnosis and a better understanding of glaucoma progression. The proposed sensor consists of an ecoflex dielectric layer, between two graphene-silver nanowire spiral antenna electrodes which also act as the membrane structure. The sensor deflection depends on the intraocular pressure fluctuations; higher pressure leads to larger deflection values, therefore, larger capacitance change. The capacitance change leads to a shift of the resonant frequency, which is simulated in this thesis. The sensor must be smaller than 11 mm2
to fit on a commercial lens. Specifically, this thesis analyzes and simulates the effects
of electrode thickness and shape on the overall performance of the sensor. The optimum geometry of the capacitive sensor is analyzed to maximize sensor sensitivity and quality factor, with a correlated frequency appropriate for a wearable lens. Using Computer Simulation Technology, the optimized antenna dimensions are spiral-electrodes with a plate thickness of 350µm, and 3 spiral revolutions; leading to an increase in sensitivity of 1.4 MHz/mmHg.

Hip replacement surgery, also termed total hip arthroplasty, is a surgical intervention intended to substitute a deteriorated or dysfunctional hip joint with an artificial prosthesis. This procedure is commonly indicated for individuals experiencing severe hip discomfort resulting from conditions like osteoarthritis, rheumatoid arthritis, hip fractures, or other hip-related issues that significantly impair mobility.

Globally, more than 1 million total hip replacement surgeries are conducted annually. Given the substantial mechanical loads experienced by hip implants during regular activities, a thorough understanding and early identification of potential issues before implant failure are imperative. Continuous monitoring of strain is crucial to assess how the implant responds to various stresses over time. This monitoring aids in evaluating the implant’s durability and performance under diverse stress conditions, enabling proactive interventions, if necessary, to prevent critical failures.

Strain monitoring acts as a diagnostic tool to assess the implant’s status and the surrounding tissues. Deviations in strain patterns may signify problems such as implant loosening, wear, or bone loss around the implant. Moreover, this monitoring technique helps customize rehabilitation programs and recommend specific activities based on individual strain levels. Consequently, this tailored approach enhances recovery outcomes while mitigating associated risks.

This project involves the development of a passive wireless resonant circuit that will be used in the future in a sensor designed to detect strain on hip implants for early failure detection. The strain is anticipated to cause fluctuations in the frequency. To evaluate the LC (inductor-capacitor) resonator design at a specific frequency, a simulation model was established using the Computer Simulation Technology (CST) Microwave Studio as the simulation platform. The fabrication of this LC resonant circuit employs cleanroom techniques and protocols to ensure precision and reliability in its structure. Subsequent to fabrication, the resonator underwent characterization employing an antenna to ascertain resonance frequency alterations in accordance with theoretical expectations. The results indicated a detectable shift in resonant frequency corresponding to designs representing different strains.

Organ-on-chip (OoC) is invented around 10 years ago which is used to do pre-clinical drug test without live animals. Physiological microenvironment of different cells can be mimicked in OoC. In order to better form of tissue in OoC, mechanical stimulation can offer through different ways including pneumatic, thermal, and electric stimulations. As another way to offer mechanical deformation, magnetic stimulation has high reacting speed and wireless operation.

In vitro models are fundamental in the study of cell behaviour, the physiological function of organs, and their response to drugs and toxins. However, the shortage of accurate and reliable in vitro models calls for the development of in vitro lung models that better recapitulate lung physiology and pathology. Lung-on- a-chip models are promising to this end. To date, most membranes used in these models are made of poly(dimethylsiloxane), which has significant disadvantages. Moreover, there is a need to establish adequate membrane pore sizes throughout the cell culture duration. A design of a novel LOC membrane containing a dynamic membrane pore size to recapitulate the pulmonary alveolar-capillary barrier was designed and its viability evaluated. Poly(octamethylene maleate (anhydride) citrate) (POMaC) is evaluated as a membrane material on its cytotoxicity, biodegradability and imaging properties. For creating a thin and porous membrane, spincoating, moulding and 2-photon polymerization were studied.

The results provide promising support for fabricating a thin membrane. It was concluded that thin, uniform POMaC layers and a conical micropillar mould could be created. Moreover, stiffness of POMaC was in the expected range, and the bioimaging properties were found to be suitable. The degradation results did not support the hypothesis that a structural pore size could increase, which likely impedes the increase of pore diameter necessary for immune cell transmigration. Therefore, a model of the degradation characteristics of POMaC is proposed.