title: Granular gel support-enabled extrusion of three-dimensional alginate and cellular structures.
abstract: Freeform fabrication of soft structures has been of great interest in recent years. In particular, it is viewed as a critical step toward the grand vision of organ printing--the on-demand design and fabrication of three-dimensional (3D) human organ constructs for implantation and regenerative medicine. The objective of this study is to develop a novel granular gel support material-enabled, two-step gelation-based 'printing-then-gelation' approach to fabricate 3D alginate structures using filament extrusion. Specifically, a granular Carbopol microgel bath holds the ungelled alginate structure being extruded, avoiding the instantaneous gelation of each printed layer as well as resultant surface tension-induced nozzle clogging. Since Carbopol microgels react with multivalent cations, which are needed for alginate crosslinking, gelatin is introduced as a sacrificial material to make an alginate and gelatin bioink for extrusion, which gels thermally (step-one gelation) to initially stabilize the printed structure for removal from Carbopol. Then gelatin is melted and diffused away while alginate is ionically crosslinked in a 37 °C calcium chloride bath (step-two gelation), resulting in an alginate structure. The proposed 'printing-then-gelation' approach works for alginate structure fabrication, and it is also applicable for the printing of cellular constructs and other similar homogeneous soft structures using a two-step or even multi-step approach. The main conclusions are: (1) 0.8% (w/v) Carbopol bath with a neutral pH value may be most suitable for soft structure printing; (2) it is most effective to use a 0.9% (w/v) NaCl solution to facilitate the removal of residual Carbopol; and (3) alginate structures fabricated using the proposed approach demonstrate better mechanical properties than those fabricated using the conventional 'gelation-while-printing' approach.
authors.affiliation: Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL 32611, USA.
authors.forename: Yifei
authors.initials: Y
authors.lastname: Jin
authors.forename: Ashley
authors.initials: A
authors.lastname: Compaan
authors.forename: Tapomoy
authors.initials: T
authors.lastname: Bhattacharjee
authors.forename: Yong
authors.initials: Y
authors.lastname: Huang
mesh_terms: D000464:Alginates / Q000737:chemistry*; D000818:Animals; D001696:Biomechanical Phenomena; D062028:Bioprinting / Q000295:instrumentation; D002470:Cell Survival; D002477:Cells / Q000737:chemistry* / Q000166:cytology; D005780:Gelatin / Q000737:chemistry; D005782:Gels / Q000737:chemistry; D020723:Glucuronic Acid / Q000737:chemistry; D006603:Hexuronic Acids / Q000737:chemistry; D006801:Humans; D051379:Mice; D041681:NIH 3T3 Cells; D066330:Printing, Three-Dimensional / Q000295:instrumentation*; D023822:Tissue Engineering / Q000295:instrumentation*; D054457:Tissue Scaffolds / Q000737:chemistry*
chemical_list: D000464:Alginates; D005782:Gels; D006603:Hexuronic Acids; D020723:Glucuronic Acid; D005780:Gelatin