Geometrical constraints dictate assembly and phenotype of human iPSC-derived motoneuronal spheroids.

Background: Neuronal spheroids represent an easy and versatile solution to model neuronal tissue in vitro. Conventional approaches to generate spheroids lack accurate size control, scalability, and customizability. This is even more exacerbated in case of pluripotent stem cell (PSC) derived spheroids, which remain challenging to standardize. Microwell devices address these limitations, providing an optimal balance between accessibility and scalability. With the aim of optimizing culture conditions, we parametrically investigated the role of microwell geometry on the formation and maturation of iPSC-derived motor neuron precursor (MNP) spheroids.

Methods: We developed a customizable mold device using Digital Light Processing (DLP) 3D printing to fabricate agarose microwell arrays with distinct aspect ratios for culturing hiPSC-derived MNP spheroids with high reproducibility. We generated nine different pyramidal microwell array geometries for culturing size-controlled spheroids in the 40-140 μm diameter range. We then evaluated the differential expression of genes related to cell proliferation and motor-neuron differentiation as function of microwell geometry and spheroid size.

Results: Our results indicate that spheroid size is significantly influenced by the microwell geometry, reliably due to cell partitioning at the seeding stage. Expression of proliferation and differentiation markers, such as motor neuron and pancreas homeobox 1 (MNX1) and Islet-1 (ISL1) transcription factors, is also dependent on microwell geometry and spheroid morphological descriptors.

Conclusion: Our approach enables the scalable production of size-controlled MNP spheroids and underscores the effect of geometrical confinement on regulating motor neuron differentiation.