Inkjet printing of high-concentration Gelatin methacryloyl (GelMA) ink for biofabrication

Abstract

Inkjet printing can precisely arrange biomaterials at high resolution by jetting picoliter-sized droplets and create complicated 3D structures by stacking a thin layer of hydrogel. So inkjet bioprinting has a great potential to fabricate highly-complex tissue constructs for use in drug screening, cancer research, and transplantation. However, the high-concentration inks that provide appropriate mechanical support and slow degradation rates after gelation generally have too high viscoelasticity to be ejected from inkjet nozzle. Gelatin methacryloyl(GelMA), which is an attractive biomaterial due to its printability, biocompatibility, mechanical tunability, and instant crosslinkability, can be utilized in inkjet printing only at low concentrations. Therefore, it is difficult to produce GelMA hydrogels with a wide range of physical properties by inkjet printing. In this study, we apply sonication for the first time to control the viscoelasticity of high-concentration GelMA ink for inkjet bioprinting. It is found that the viscoelasticity of GelMA ink decreases after sonication, so printing becomes possible. To validate the impact of sonication on polymers, the molecular weight and functional groups of GelMA are analyzed after different sonication times. We then compare the physical hydrogel properties of the 3% (w/v) pristine GelMA ink, 10 h sonicated 6% GelMA ink, and 20 h sonicated 10% GelMA ink which are all printable in the inkjet printer. After the cell-laden GelMA ink is inkjet-printed and gelated, we also quantify cell viability to demonstrate the biocompatibility of inkjet printing and sonicated ink in biofabrication. Finally, 3D hydrogel structures which consist of thin multilayer cells are fabricated by inkjet printing with sonicated ink. The significance of our work is to apply highly viscoelastic biomaterials to inkjet printing by using simple sonication to lower molecular weight and characterize the physical properties of inks and hydrogels. Sonication will deliver a new path to inkjet printing to build microarchitectures with various physical properties by expanding the range of applicable bioinks.