Mesenchymal stem cells (MSCs) are multipotent stem cells that can support various tissues including bone marrow, adipose tissue, and synovial fluids, from which they can be readily isolated. The objective of this study is to harness the advantages of microfluidic systems for controlling and enhancing the maintenance and viability, and regenerative properties of MSCs by providing a 3D culture microenvironment with gelatin methacrylate (GelMA) hydrogel and exposing the cells to a slow fluid flow and low shear stress conditions. GelMA has methacryloyl groups and can be crosslinked by a photocuring process using biocompatible photoinitiators. The most common used photoinitiator for cellular encapsulation within hydrogels is the ultraviolet (UV) initiator 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone (Irgacure 2959 or I2959), but due to its low water solubility and the necessity of using a shorter wavelength light (365 nm), it can lead to cellular phototoxic and genotoxic effects. To overcome these limitations, lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP) have recently been used with GelMA as an alternative photoinitiator. Because LAP is highly water soluble and has a 10 times faster polymerization rate, and it requires a visible light (λ = 405 nm) which makes it much safer for the cells, we use 10% GelMA together with 0.05% LAP photoinitiator for bioprinting human adipose tissue derived MSCs (hAT-MSCs) onto a membrane that has a 40 µm mesh size. To demonstrate a microfluidic culture advancement for improving the biological activities and regenerative capacity of the cells including cell adhesion, growth, viability and proliferation capacity as ultimate goals of this study, the membrane carrying the bioprinted construct was placed in a PDMS microchannel and exposed to the fluid to obtain dynamic microenvironments found in the human body. As a result, the cells were successfully maintained in the microfluidic 3D cell culture for two days, with a high cell viability of 99%.

Key words: MSCs, GelMA, 3D cell culture, cell adhesion, Organ on a chip