Comparison of cation and anion-mediated resolution enhancement of bioprinted hydrogels for membranous tissue fabrication

Fabrication of engineered thin membranous tissues (TMTs) presents a significant challenge to researchers, as these structures are small in scale, but present complex anatomies containing multiple stratified cell layers. While numerous methodologies exist to fabricate such tissues, many are limited by poor mechanical properties, need for post-fabrication, or lack of cytocompatibility. Extrusion bioprinting can address these issues, but lacks the resolution necessary to generate biomimetic, microscale TMT structures. Therefore, our goal was to develop a strategy that enhances bioprinting resolution below its traditional limit of 150 μm and delivers a viable cell population. We have generated a system to effectively shrink printed gels via electrostatic interactions between anionic and cationic polymers. Base hydrogels are composed of gelatin methacrylate type A (cationic), or B (anionic) treated with anionic alginate, and cationic poly-L-lysine, respectively. Through a complex coacervation-like mechanism, the charges attract, causing compaction of the base GelMA network, leading to reduced sample dimensions. In this work, we evaluate the role of both base hydrogel and shrinking polymer charge on effective print resolution and cell viability. The alginate anion-mediated system demonstrated the ability to reach bioprinting resolutions of 70 μm, while maintaining a viable cell population. To our knowledge, this is the first study that has produced such significant enhancement in extrusion bioprinting capabilities, while also remaining cytocompatible.