Continuous-mode encapsulation of human stem cell spheroids using droplet-based glass-capillary microfluidic device for 3D bioprinting technology

Droplet-based microfluidics generates droplets with reproducibility, repeatability, and monodispersity, resulting in decreased reaction time with high yield production. Due to its advantages, its technology has been used to encapsulate biologics for cell therapy, biomaterials, and tissue engineering. However, the encapsulation of superior in vitro culture models, such as cellular spheroids is an ongoing challenge. In this work, we present a continuous process for the encapsulation of mesenchymal stem cell spheroids into alginate hydrogel droplets, using a glass-capillary-based microfluidic device. The device geometry comprises co-flow and hydrodynamic focusing techniques, in which two round glass capillaries are aligned inside a square glass capillary. The encapsulated spheroids were composed of human adipose-derived mesenchymal cells (ASCs) with a diameter of 400 µm. The encapsulation of ASC spheroids was performed into single droplets with approximately 600 µm in size, under a total volumetric flow rate of 14 mL h-1. The developed microdevice was able to generate 200 droplets/min. Moreover, they were able to promote the gelation simultaneously with spheroids encapsulation without compromising their morphology. The stability of the droplet was achieved using 10% of surfactant. In addition, encapsulated spheroids were able to be seeded into PLA scaffolds without compromising either the droplet and their morphology. The successful and homogeneous encapsulation of stem cell spheroids has high applicability in forefront regenerative medicine strategies, such as droplet-based bioprinting. Hence, biofabricating physiological relevant tissue-like constructs with cost and time efficiency.