On April 6th 2023 Mees de Graaf successfully defended his thesis, entitled: ‘Engineered 3D-Vessels-on-Chip to study effects of dynamic fluid flow on human induced pluripotent stem cell derived endothelial cells’ at Leiden University. His research was performed under the supervision of Christine Mummery and Valeria Orlova.
To improve the predictive capability of pre-clinical models and reduce the use of animal models in drug discovery and disease modelling, advanced in vitro models are being developed. These microphysiological systems (MPS) or “Organs-on-Chip” (OoC) are being developed to include all aspects of the human physiology to improve the in vitro cellular response. OoCs combined with differentiated human induced pluripotent stem cells (hiPSC) allow the use of cells with patient specific genotypes and aid the development of personalized and precision medicine. However, combining complex stem cell biology with advanced microfabrication technology remains challenging. This thesis describes the development of facile 3D Vessel-on-Chips (3D-VoCs) and perfusion platform to impose and analyse the effects of haemodynamics to hiPSC-derived vascular cells.
A microfluidic technique called Viscous Finger Patterning (VFP) was optimized to engineer 3D-VoCs for dynamic studies to ensure equal shear forces within samples. VFP allows to generate 3D-models that include endothelial cells, mural-cells and tissue specific-cells in a natural hydrogel. It is easily scalable and does not rely on special equipment or reagents and is therefore ideal for a biological orientated laboratory. However, 3D-VoCs remain to have an intrinsic diameter variation due cellular activity and model compliance, which limits the throughput of perfusion experiments. To circumvent this diameter variation in perfusion studies, a special platform was developed to minimize haemodynamic variation while samples have diameter variation. The platform was used to demonstrate the effects of haemodynamics on hiPSC-endothelial cells to highlight the importance of biomechanics in the endothelial phenotype. Finally, photopatterning of hydrogels was investigated for the development of reproducible capillary models. This methodology allowed the formation of perfusable tubular structures at the smallest scale of the microvasculature.