Experimental and numerical approaches for optimizing conjunction area design to enhance switching efficiency in single-nozzle multi-ink bioprinting systems

Three-dimensional (3D) bioprinting has emerged as a promising technology in the field of tissue engineering. Notably, the advancement of multi-ink printing technology is crucial for further progress in 3D bioprinting. In this study, we developed a single-nozzle system with multiple inlets for multi-ink bioprinting that achieves high switching efficiency through a combination of numerical and experimental approaches. This single-nozzle system demonstrates the potential for higher-resolution printing and quicker ink switching compared with multi-nozzle printing systems. In general, inks used in bioprinting have low viscosity (<10 Pa・s); however, their behaviors inside a single nozzle have not been thoroughly investigated. Initially, we conducted numerical simulations to analyze fluid behavior within single nozzles, focusing on the junction of multiple ink inlets, to propose an advanced nozzle design. We proposed a novel index, Se, for evaluating the switching behavior of the bioink inside the single nozzle. Numerical simulation results showed that the nozzle design and combinations of inks affected Se. In addition, subsequent experimental analysis confirmed the consistency of the simulation results. The proposed design, developed using simulations, featured a single nozzle with enhanced switching efficiency, demonstrating a smaller transition length compared with that of conventional single nozzles or T-junction nozzles in printing line structures of different viscous inks. This is the first study to employ numerical simulation in designing a single nozzle with multiple inlets to switch ink in multi-ink bioprinting. This methodology will broaden the potential of single nozzles for high-resolution printing in bioprinting applications.