Sequential-crosslinking facilitated droplet-droplet collision inkjet 3D printing of soft biomaterials

Abstract

Droplet-droplet collision (DDC) inkjet three-dimensional (3D) printing presents a novel approach to additive manufacturing (AM) of soft biomaterials for tissue engineering, bioelectronics, and food science, etc. However, limited ink materials and elusive dynamics of the printing process pose significant challenges. This work introduces a sequential-crosslinking facilitated printing strategy that leverages rapid ionic crosslinking triggered by in-air droplet collision to retain structure during printing and entrap the target biomaterial, which is further crosslinked after printing. This versatile approach enables the effective printing of both photocrosslinkable and non-photocrosslinkable soft biomaterials that are challenging to be printed with normal DDC inkjet 3D printing. The dynamics of DDC process with crosslinking is revealed and two distinct DDC modes are identified, namely, coalescence and stretching separation; dimensionless phase diagrams and semi-empirical transition boundaries of DDC modes are developed to improve the stability of printing process and guide the optimization of printing parameters. On this basis, lines exhibiting a minimum width of 122 μm and delicate motifs containing intricate microfeatures are printed. Moreover, the printing process has proved its biocompatibility by imposing negligible effect on the viability and proliferation of printed living cells. This study is believed to expedite the voxelated AM of broader soft biomaterials for healthcare and industry.