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Abstract

Abstract Glaucoma is a prevalent eye disease and one of the leading causes of blindness worldwide. Among various risk factors like genetics or age, elevated intraocular pressure (IOP) remains the only modifiable variable to slow down the disease progression. In all types of glaucoma, IOP elevation results from obstructions in aqueous outflow, caused by changes in the extracellular matrix (ECM) of the ocular outflow structures, primarily the trabecular meshwork (TM). One such alteration is the precipitation of calcium phosphate (CaP), in form of hydroxyapatite (HAp), which stiffens the TM and increases outflow resistance. The artificial drainage of excess fluid is the only way to reduce the IOP and preserve eyesight. Glaucoma drainage devices (GDDs) are common treatment options, but until today current implants are neither completely reliable nor long lasting and prone to issues like hypotony, implant occlusion, fibrosis or poor biocompatibility. This thesis investigates the glaucoma disease from two complementary perspectives: treatment development (part I) and the underlying pathological mechanisms (part II). The first part of this thesis focused on the development and evaluation of a new type of GDD designed to address key issues of existing implants for controlling IOP. The core innovation of this device is a hyaluronan (HA) hydrogel, aiming to prevent hypotony, cell occlusion and providing pressure-depending drainage to reduce elevated IOP. The main concept of the new GDD was established by Michael Thaller, PhD student in the team of Joachim Spatz of the Max Planck Institute for Medical Research (MPI-MR), which included the conceptualization and fabrication of large model prototypes with valve functionality. This thesis advances the design through miniaturization to dimensions comparable to those of real glaucoma implants (ID=0.5-1 mm, l=3-6 mm) and the exploration of various hydrogel compositions including a combination with polyethylene glycol (PEG). HA-PEG hydrogels, when immobilized within the implants, demonstrated superior enzymatic stability, making them promising for long-term use. Moreover, a new microfluidic measurement setup was developed to assess the pressure regulation capabilities of model tubes under realistic physiological conditions. The model implants demonstrated consistent pressure regulation under conventional flowrates and daily IOP fluctuations, albeit with the need for further optimizations to align with physiological IOP levels. In a last approach, iterative design and testing of 3D-printed patterns enhanced the reproducibility of model implant fabrication. These advancements, provide a solid foundation for scalable, biocompatible GDDs capable of effective long-term personalized IOP management, though further refinement of hydrogel compositions and in vivo validation remain necessary. In the second part, the picture is extended by another aspect: the occurrence of calcification processes in glaucomatous eyes and the design of a new biomimetic model for biomineralization studies of CaP. A droplet-based system was developed to mimic early stages of mineral formation within matrix vesicles (MVs), including ion accumulation and crystal formation. Mineralized particles formed within droplets revealed needle-like structures indicative of HAp, which differed significantly from those observed in bulk systems. This finding suggests a distinct mineralization pathway in the droplet-based model that could provide new insights into mineralization in MVs. Further exploration addressed the anti-calcification properties of matrix gla protein (MGP), a known inhibitor of tissue calcification. Peptides, derived from MGP, with varying amount and position of gamma-carboxyglutamic acid (gla) residues, were tested for their effects on mineralization. Although, no significant reduction in mineral formation was observed, peptides containing gla residues altered crystal morphology, forming fiber-like bundles and nano-spherical aggregates similar to HAp. These findings highlight the potential of the droplet-based approach for investigating CaP mineralization and crystal morphology. This new droplet-based mineralization model combines simplicity with controllability, by bridging the gap between simple bulk systems and the confined, controllable environment of MVs. This enhances control over mineralization conditions and minimizes side reactions and influences from the external environment by isolating the reaction components within a confined space. In addition, the high-throughput analysis of uniform droplets enables reproducible and efficient analysis of mineralization processes. Future efforts should focus on reducing droplet size, incorporating peptides at a later stage of mineralization and fusion of droplets, to better mimic natural MVs and extracellular processes. Furthermore, a characterization of the mineralized particles via x-ray diffraction (XRD) will be necessary. Together, both experimental parts contribute to the development of improved GDDs and enhance the understanding of glaucomatous calcification processes, offering valuable insights for both glaucoma management and biomimetic material design.