Microfluidic-assisted bioprinting of tissues and organoids at high cell concentrations

Despite its simplicity, which makes it the most commonly used bioprinting method today, extrusion-based bioprinting suffers from its inability to reproduce the complex tissue architecture found in organs. Generally, this printing method allows for the dispensing of solutions of a predefined cell concentration through a rudimentary needle. Moreover, to avoid cell lysis in the dispensing needle, which is detrimental to the viability of the printed tissue, as well as cell loss in dead volumes of tubing, thereby increasing the cost of printing tissue, a common strategy has been to print with cell concentrations much lower in comparison to the concentrations found in living tissues. As a result, cell-to-cell distance is increased in the dispensed samples impairing communication through cytokines. Here, we present a microfluidic-based print head capable of modulating the printed cell concentration in real-time. This device allows bioprinting at high cell concentrations by concentrating and dispensing fibroblasts at concentrations up to 10 million cells∙mL^-1. We also demonstrate that this device can be used to print bladder organoids. As the cell seeding concentration is of major importance for organogenesis in 3D culture, organoid printing allows the user to standardize the process of organoid formation and achieve more reliable and reproducible results.