Due to its ability to recapitulate key pathological processes in vitro, midbrain organoid technology has significantly advanced the modeling of Parkinson's disease over the last few years. However, some limitations such as insufficient tissue differentiation and maturation, deficient nutrient supply, and low analytical accessibility persist, altogether restricting the technology from reaching its full potential. To overcome these drawbacks, we have developed a multi-sensor integrated organ-on-a-chip platform capable of monitoring the electrophysiological, respiratory, and dopaminergic activity of human midbrain organoids. Our study showed that microfluidic cultivation resulted in a marked reduction in necrotic core formation, improved tissue differentiation as well as the recapitulation of key pathological hallmarks. Non-invasive monitoring employing an orthogonal sensing strategy revealed a clear time dependency in the onset of Parkinson's disease-related phenotypes, reflecting the complex progression of the neurodegenerative disorder. Furthermore, drug-mediated rescue effects were observed after treatment with the repurposed compound 2-hydroxypropyl β-cyclodextrin, highlighting the platform's potential in the context of drug screening applications as well as personalized medicine.

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Stem cell technology and embryonic stem cell models are of great interest in biomedical research since they provide deeper insights into, e.g., neurogenesis and early mammalian brain development. Despite their great scientific potential, the reliable establishment of three-dimensional embryoid bodies (EBs) remains a major challenge, and the current lack of standardization and comparability is still limiting a broader application and translation of stem cell technology. Among others, a vital aspect for the reliable formation of EBs is optimizing differentiation protocols since organized differentiation is influenced by soluble inducers and EB size. A microfluidic biochip array was employed to automate cell loading and optimize directed neuronal and astrocytic differentiation protocols using murine P19 embryoid bodies to facilitate reliable embryonic stem cell differentiation. Our gravity-driven microfluidic size-controlled embryoid body-on-a-chip system allows (a) the robust operation and cultivation of up to 90 EBs in parallel and (b) the reproducible generation of five increasing sizes ranging from 300 µm to 1000 µm diameters. A comparative study adds two differentiation-inducers such as retinoic acid and EC23 to size-controlled embryoid bodies to identify the optimal differentiation protocol. Our study revealed a 1.4 to 1.9-fold higher neuron and astrocyte expression in larger embryoid bodies (above 750 µm) over smaller-sized EBs (below 450 µm), thus highlighting the importance of EB size in the establishment of robust neurodevelopmental in vitro models.

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