Light-based multi-material bioprinting of vascularised adipose tissue for breast fatty tissue engineering

Reconstructive surgery following breast cancer ablation is a surgical gold standard and of increasing importance, but current options comprising autogenous fatty tissue transfer and artificial soft tissue implants are inferior. With the advent of powerful biofabrication technologies like bioprinting, researchers for the first time have the tools to engineer life-like tissues with the ultimate goal of clinical application. In this work, we apply multi-material stereolithographic bioprinting together with a novel sacrificial biomaterial system to engineer complex fatty tissue constructs. Biomaterials, cellular composition and cultivation conditions of these constructs were designed to enable in vitro creation of vascularised fatty tissue. Cells within the constructs showed an overall good survival (>93%) indicated by Calcein-AM staining for living cells and cytotoxicity levels below 7 % (PI-positivity), which even decreased during The constructs showed highay significant increase in cellular viability and activity overthe entire cultivation the culture period of 27 days. Bioprinted aAdipose-derived stem cells were successfully differentiated into adipocytes in situ and expressed PPARy as well as FABP4. Additionally, secretion of adipokines leptin and adiponectin into culture supernatants increased significantly. Endothelial cells vascularised the constructs, creating macro- and microvascular structures within the printed channels and extending beyond with culture time. Multi-modal imaging revealed dynamic cell activitymigration of cells within the bioprinted constructs and signs of progressing maturation towards fatty tissue. Moreover, cells invaded into the surrounding hydrogel. The engineered fatty tissue constructs could serve as a base to develop patient-specific tissue building blocks with the final goal to achieve an all-natural reconstruction of the breast.