Bioprinting of Cell-scaffold Constructs for Liver Tissue Regeneration

Liver diseases, including hepatitis B and C, cirrhosis, hepatocellular carcinoma, non-alcoholic fatty liver disease and drug-induced liver damage, affect over 1.5 billion people globally and pose a heavy burden to national healthcare systems. Currently, liver transplantation is the only definitive treatment for terminal-stage liver diseases but its clinical practices are severely constrained by a very limited supply of donor organs, necessity for post-transplantation immunosuppressive medication, and considerable financial commitment. Liver tissue engineering (LTE) provides a promising alternative to liver transplantation, aiming to create functional, implantable liver tissues or bioartificial liver devices that can restore liver functions in patients. 3D bioprinting is a powerful biomanufacturing platform that can fabricate complex cell-laden living structures for functional liver tissue regeneration, and developing new bioinks underpins advances of bioprinting for LTE. In this study, new hydrogels were formulated for LTE bioprinting. These hydrogel printing inks comprised glycidyl methacrylate-modified hyaluronic acid (HA-GMA), gelatin methacryloyl (GelMA) and gelatin and leveraged the synergy of the three polymer components. By systematically varying concentrations of HA-GMA, GelMA and gelatin in hydrogel printing inks, the rheological behaviour, printability and crosslinking of polymer chains in hydrogels were optimized and consequently, high scaffold fidelity with reference to scaffold design was attained. Additionally, mechanical properties and biodegradation behaviour of 3D printed scaffolds could be tuned. Using tri-component hydrogel based-bioinks containing NCTC1469 mouse hepatocytes, 3D cell-scaffold constructs of the designed grid structure with square pores could be successfully fabricated via extrusion-based 3D bioprinting. The 3D bioprinted constructs maintained structural integrity over extended culture times and supported high cell viability and proliferation. Importantly, the constructs promoted the expression of mature hepatic markers and sustained key liver-specific functions in vitro. This study demonstrated clearly the suitability of new hydrogels for LTE bioprinting and a versatile and scalable bioprinting platform for engineering functional liver tissue.