Controlled preparation of droplets for cell encapsulation by air-focused microfluidic bioprinting

Microfluidics is a facile platform that manipulates fluids for the production of droplets, particles, and microcapsules. However, the application of microfluidics is limited to the manipulation of the droplet position and the presence of a continuous oil phase, which needs to be removed for biomedical applications. Here, we used air as the continuous phase and developed a facile method for droplet generation and patterning by air-focused microfluidic three-dimensional (3D) droplet printing (AFMDP). By tuning the viscous drag of a focused air flow, monodisperse droplets with tunable size were generated in a microfluidic device, and droplet patterns were designed by combining the control system of the 3D printer. When using droplets as templates, hydrogel particles were prepared by AFMDP and crosslinked in a CaCl2 bath. These hydrogel particles were proven to be good carriers for the cell culture, controlled release, and immune therapy using chimeric antigen receptor (CAR) T cells. Cell viability and activity results confirmed that encapsulation of CAR-T cells in hydrogel particles did not compromise their cell activity and functionality but facilitated their manipulation and cell culture. Therefore, the AFMDP system provided a versatile platform for the design of droplets, particles, and microcapsules for biomedical applications.