Multi-physical field control piezoelectric inkjet bioprinting for 3D tissue-like structure manufacturing

Abstract

 With high precision, drop-on-demand, and noncontact material delivery advantages, inkjet bioprinting technology has been widely used in tissue manufacturing. However, the main challenge of inkjet bioprinting is that the bioink must be liquid-like in the printhead to avoid clogging the nozzle, then form microdroplets, and finally undergo crosslinking to quickly form a gel and make an object with strength and precision. The primary solution relies on the fast crosslinking of sodium alginate by calcium chloride. Nevertheless, it is difficult to guarantee the precision of inkjet bioprinting with this method, and cumulative errors lead to the inability to print high aspect ratio three-dimensional (3D) structures. Additionally, sodium alginate lacks cell adhesion sites, and calcium chloride at high concentrations is toxic to cells. To solve the above problems, we present a new printing method called multi-physical field control piezoelectric inkjet bioprinting (MFCPIB) for making 3D tissue-like structures using 5% gelatin methacryloyl (GelMA). For extrusion and photocuring 3D bioprinting tasks, 5% GelMA is widely used due to its favorable biocompatibility. In this study, we accomplished a 5% GelMA inkjet bioprinting for the first time by leveraging the MFCPIB method. Our experimental results demonstrated the feasibility of this approach for printing GelMA of different concentrations. The temperature-sensitive GelMA was utilized during the printing process in which GelMA is liquid-like in the high-temperature printhead, cools in the form of microdroplets in cold air after injection, and finally photocrosslinks to form a permanent gel. We analyzed the inverse piezoelectric effect and fluid dynamics to control the pressure field, which in turn controls the velocity and diameter of the microdroplets. After conducting a simulation analysis of the temperature field and performing calculations using the lumped parameter method, we implemented a dual closed-loop control strategy to ensure precise temperature control of the microdroplets. Furthermore, based on the analysis of energy conversion, we obtained the pressure and temperature field control laws corresponding to the ideal printable temperature of the microdroplet. Using the MFCPIB method, different 3D structures were successfully printed with GelMA. For example, a cell-laden vessel-like structure with an aspect ratio of 4.0 was achieved. The proposed MFCPIB method did not influence the viability of smooth muscle cells after printing, demonstrating the potential for fabricating tissues with high bioactivity.