The interaction mechanism between biphasic systems in suspension printing and its application in constructing organ models

Abstract

In recent decades, 3D bioprinting technology based on a 'bottom-up' assembly strategy allows for the creation of replacements that mimic the complex structure and physiological function of human tissues and organs. Suspension bioprinting is an emerging and highly promising 3D bioprinting technology. This technology embeds bioinks in a supporting system for printing, and previous studies have shown its wide application in creating complex structures of artificial tissues and organ models. However, most suspension printing research is limited to shape replication, lacking studies on the relationships between ink and supporting systems. This thesis aims to verify and evaluate the mechanisms and laws of the interaction between ink and supporting systems (including infiltration-induced regulation and initiation effects) in suspension printing. Firstly, the mechanism by which the suspension system modulated the scaffold formed by the ink through infiltration was elucidated. A novel hyaluronic acid-based suspension system with high light transmission, shear thinning, and self-healing properties was established for the study. The embedded ink was subjected to controlled dehydration or swelling by the osmotic pressure difference between the suspension system and the ink, which subsequently affected properties such as printing resolution, Young's modulus, surface micromorphology and water absorption. Based on this mechanism, a new printing technology, Infiltration-Induced Suspension Bioprinting （IISBP）was proposed that was compatible with different bioink systems and could print scaffolds with a gradient structure. On the basis of the above, the IISBP technology was applied to the bioprinting of loading cells to evaluate its potential for the preparation of 3D culture models. The IISBP technology enabled the printing of scaffolds loaded with human umbilical vein endothelial cells with tunable printing resolution and high cell viability within the supporting gels. The endothelial cells in each group of scaffolds showed various adhesion, proliferation, and functional expression behaviors. Additionally, an 3D culture model loaded with mesenchymal stem cells was constructed and used to perform a tentative study on osteogenesis. The results showed that this scaffold developed into a mineralized structure similar to natural bone tissues in vitro. Finally, the pattern of influence of the ink on the suspension system was investigated. The initiator system within the ink triggered the reverse phase polymerization of hydrogel monomers at the interface, which subsequently diffused into the interior of the suspension system to form a tubular hydrogel layer. Exposure time, monomer content, hyaluronic acid content, extrusion pressure and initiator concentration could all effectively regulate the polymerization reaction. Based on this, an Inverted Phase Suspension Printing technology was proposed for the personalization of tubular scaffolds, with unique advantages for the printing of scaffolds with branched connecting tubular structures, which was expected to be used for the preparation of artificial vascular grafts. In conclusion, this thesis verified and discussed the interactions mechanism between the ink and the suspension system in the suspension printing. These mechanisms will provide theoretical guidance for the development of various novel printing methods, which will assist to establish complex organ cultivation models and research methods for subsequent biomedical research on organ substitutes.