In-vitro 3D organoid cultures constitute an essential component of modern-day biological research, with key application areas in drug and therapy testing, and Organ-on-a-Chip models. The increasing demand for reliable models comes with the challenge of boosting the throughput of production of these cultures. The currently researched 3D culture methods pose the challenge of not being contact-free, of limited versatility and throughput in organoid culturing, and often lack a stimulus to promote cell agglomeration. This work presents acoustofluidics as a stimulus-driven solution to promote the clustering of cells in a levitated, suspended environment. In order to establish this objective experimentally, an SBAW resonator was designed, fabricated, and tested as a PoC (Proof-of-Concept). The experiments were carried out with the fabricated PoC which was characterized to assess the trapping performance and determine the controllable experimental variables to tune the acoustofluidic effects aptly, leading to the formation of stable clusters in SBAW nodal planes. On successful fabrication, the device showed repeatable trapping over a wide bandwidth of 300 kHz, and trap stiffnesses of up to 1.7 fN/μm determined experimentally based on the processing of particle agglomerate imaging. It was observed that the trap stiffness was adequate for levitation over several hours, and yet allowed for the formation of a 3D agglomerate of particles. It was also shown that a frequency-sweep actuation was successful in overcoming fabrication limitations and suppressing streaming, and a suitable working range of experimental parameters could be determined to achieve initial clustering in under 3 minutes. A futuristic outlook on the in-plane particle confinement methods to further improve the target performance, and considerations for biological experiments as the immediate next step have been presented as a concluding note in this thesis. This work thus paves the way for the integration of this technique into laboratory organoid culture formats. This positively complements the objective of cutting down the agglomeration time for initial organoid clustering, for an anticipated positive impact on the production throughput and developmental aspects of organoid cultures, with the in-house fabricated and characterized PoC presented in this work as an enabler.

This thesis aims to characterize the photopolymer resins designed for the 3D printing of Gradient Refractive Index (GRIN) lenses. This thesis focuses explicitly on preparing UV-curable inks doped with nanoparticles that are custom-synthesized for sophisticated optical applications. Four different ink formulations have been studied, including epoxy-based and PMMA-based, together with two commercial UV-curable resins, which are a combination of acrylates and epoxies. Spectroscopy testing of these inks is conducted to study their optical performance for properties like the transmittance and absorbance over the UV, visible light, and NIR regions. The results show that it is possible to obtain significantly different behavior in the optical properties of materials compared to the inks without nanoparticles, offering a promising pathway for developing GRIN lenses with superior characteristics. This research also reports on some modifications performed on an Elegoo Mars 4 DLP printer to control a projector and the DMD device for arbitrary exposure times, further contributing to the development of high-performance optical devices through additive manufacturing.

Background: Bilateral tubal ligation (BTL) is the most common method of contraception worldwide because it is safe and effective. However, its accessibility remains unequal among women in rural India, in part due to a lack of laparoscopic equipment. Rural hospitals therefore resort to gas insufflation-less laparoscopic surgery (GILLS) because it requires less complex equipment. The pneumoperitoneum is replaced by an abdominal wall lift (AWL) device, but these devices suffer from limitations concerning visibility and working space.
Methods: Initiated by the identified medical needs in rural India, a novel AWL device with an integrated imaging system is designed based on methods from literature and input from local end-users. It is a stainless steel hollow circular hook housing an LED lighting system and a 5 MP camera module. It can be connected to any laptop with a USB-A port. The device substitutes for both the traditional AWL device and currently used laparoscopes. The design is exemplified by a fully functional aluminium prototype used for verification and validation.
Results: The selected camera module is the key technology of this design because it provides state-of-the-art imaging at an unmatched price point. The lighting system used for the prototype does not provide enough light, has an asymmetric illumination distribution, and generates too much heat. A structural strength test showed that the strength of the prototype exceeds the material-adjusted design load by 30%. Furthermore, the prototype is cost-effective, lightweight, compatible with current AWL systems, and has limited waterproofness. User tests with an expert rural surgeon confirmed that this design has the potential to improve surgical outcomes of BTL and other procedures, and can increase access to specialized medical care in rural India.
Conclusions: It is strongly recommended to continue the development of this AWL device. The focus points should be the shape and size of the loop (and related cost-effective production techniques), a new lighting system, and the waterproofness of the device. Collaboration with rural surgeons and local biomedical engineers is crucial for context-driven development and implementation.

Cerebral oxygen saturation is an important indicator that reflects the oxygen metabolism of the brain tissues in such patients. The utilization of near-infrared spectroscopy (NIRS) enables the identification of the oxygen saturation levels in nearby tissues by analyzing the distinct oxygenation states of hemoglobin-oxyhemoglobin (HbO2) and the distinctive molecular spectrum of deoxygenated hemoglobin (Hb). It is helpful to realize the objective of noninvasive continuous detection on cerebral oxygen saturation because near-infrared radiation can directly penetrate the skull to obtain the characteristics of the average oxygen saturation of the brain tissues. This also allows a noninvasive way to monitor blood flow in the brain. A frequency comb is a pulsed laser in the time domain and a sequence of discrete, uniformly spaced frequency lines in the frequency domain. Applying the frequency comb to NIRS has the potential to develop a high-speed and fs-level time-of-flight resolution blood flow measurement system. The objective of this thesis is to utilize a chip-based optical frequency comb as an illuminating source in order to conduct time-of-flight measurements of a single target, employing a Michelson interference experiment. The establishment of the time of flight in the single-layer case and the investigation of the non-ambiguity range form the fundamental basis for future experiments multi-layer.

3D-multi-electrode arrays (3D-MEAs) are needed to overcome the limitations of 2D-multi-electrode arrays (2D-MEAs) and enable the electrical characterization of 3D neuronal cultures in in vitro brain models, advancing the understanding of neurological disorders and paving the way to personalized medicine. The aim of this thesis was to overcome some of the limitations of current 3D-MEA devices and develop structures approaching the stiffness of the brain microenvironment, by using materials softer than conventional Silicon.A polymeric 3D-MEA was designed and developed by means of an innovative combination of two-photon polymerization (2PP), a 3D printing technology with sub-micrometer resolution, and standard wafer-level microfabrication methods from the semiconductor industry. Two novel fabrication protocols were developed, the first being a combination of 2PP with high-aspect ratio photolithography, which, though feasible, proved to require an inconveniently laborious process flow. The second fabrication process employed instead 2PP to fabricate the polymeric structures, pattern the microelectrodes, and provide electrical insulation. The 2PP-based process flow was ultimately preferred due to its potential for fabrication of structures of higher aspect ratio and geometrical complexity for 3D-MEA, extending their measurement resolution. Furthermore, a wafer-level alignment routine was developed with an alignment repeatability of 2PP structures of ±5 µm, which enabled the multi-step 2PP fabrication process. A novel maskless photolithography via 2PP process was also developed to pattern thin films over slanted surfaces, utilizing photoresist and glycerol-based immersion optics. The resulting 3D-MEA consisted of 15 printed polymeric pyramids featuring a total of 60 gold microelectrodes. The electrical insulation of the traces was partially successful, and will require further process development.The results demonstrate the feasibility of merging, for the first time, the 2PP process with standard wafer-level microfabrication techniques, specifically for the fabrication of a 3D-MEA for in vitro studies of human induced pluripotent stem cell (hiPSC) neuronal cultures. The 2PP-based solutions provided in this thesis show a promising pathway for the development of more complex and biomimetic 3D-MEAs. More generally, the developed wafer-level alignment routine and maskless photolithography via 2PP process for high-aspect ratio structures contribute to advance the field of microfabrication, and may enable the development of other types of innovative microdevices.

Proteins play a key role in many biological processes and are thus useful indicators of health and disease states. Since the size of proteins is few hundred nanometers, it is necessary to explore new techniques to manipulate and 'read' them. This thesis aims to identify and build a platform that enables sub-micron bead manipulation, which will be used to actively deliver the biomolecules attached to the beads to the single-molecule sensor. During this process, accurate positioning, speed control, and multiplexing of the beads need to be solved to give high-resolution and high-throughput sequencing capabilities. We identify surface acoustics wave (SAW) devices as powerful tools to achieve both beads transport and massively parallel manipulation. Our hypothesis is that we can increase the efficiency and precision of bead capture and manipulation by using SAW devices combined with a microcavity layer. In this master thesis, we fabricate the SAW device with an average 2 $\mu m$ thick film, and there are cavity arrays on the film. In addition, we investigate the performance of trapping sub-micron objects during the actuation. Further more, we discuss few challenges found through the experiments and provide possible solutions for them. At last, this thesis is concluded by discussing the work been done and providing suggestions for future experiments.

The performance of hydrostatic bearings is in part decided by their lubrication-film height shape. Imaging the shape can be done by dissolving fluorescent dyes in the layer. However, current imaging techniques are rooted in heuristics, and as such, their physics, design parameters, and error sources are not quantitively understood. To fully grasp and consequently design the ultimate measurement system, the governing equation—the fluorescent radiative transfer equation—is solved analytically for a plane-parallel system. The new solution method assumes that fluorescent radiative transfer is well-described by the first two photon generations. Verification is done experimentally and by a concurrent Monte Carlo method. The model also successfully predicted the response of a real measurement setup. Further model analysis led to the understanding of factors such as: camera positioning; light source design; and the effect of the reflective background on which the lubrication layer lays. The insights suggest a practical implementation for a dynamic imaging setup.

This work investigates low-cost three-dimensional (3D) ultrasound reconstruction from a two-dimensional (2D) hand-held probe with motion tracking. The best available motion tracking is an optical tracking system, which is expensive and requires external tracking hardware. Here, a low-cost manoeuvrable motion tracker, an inertial measurement unit (IMU) sensor, has been tested by comparing it with an optical tracking system. The motion of the probe has been divided into a rotation and translation movement. Comparing the IMU sensor rotation tracking with the optical tracking, while rotating 40 degrees, resulted in an average Pearson’s correlation of 0.99 ± 0.0056. The average Pearson’s correlation between the translation tracking of the IMU sensor and the optical tracking system, in a translation of 15 centimetres, was 0.13 ± 0.78. The rotation and translation tracking is used to reconstruct the ultrasound volume of a phantom. In a rocking motion reconstructed volume the horizontal distance between phantom features had a mean error of 45%, a vertical distance was reconstructed with a mean error of 0.25%. In a translation motion reconstructed volume these errors were 29% and 1.4% for respectively horizontal feature distance and vertical feature distance. This study demonstrates that an IMU sensor can be used to track the motion of the probe. The rotation tracking of the IMU sensor is comparable with the rotation tracking of an optical tracking system. The translation tracking of the IMU sensor is on average not comparable with an optical tracking system, however some translations have been tracked with a high correlation. A reason to explain the low average correlation of the translation tracking of the IMU sensor is the method of gravity vector correction in the accelerometer data. Future research should focus on the clinical evaluation of the rotation tracking and the development of an accurate translation tracking method by studying the initial gravity vector or looking at different translation tracking methods.