Special Poster Session Biofabrication
In biofabrication, 3D multicellular spheroids represent attractive building blocks for tissue constructs in regenerative medicine and in the development of disease models. However, the use of spheroids in 3D bioprinting approaches as components of bioinks is associated with major challenges regarding the printing process impacting on spheroid distribution and cell viability. Therefore, in this study, employing 3D spheroids made from human adipose-derived stromal cells (ASC), we established a suitable bioink composition and determined favorable processing parameters enabling 3D bioprinting. Furthermore, adipogenic differentiation and cytokine secretion of ASC within the spheroids were evaluated after printing.
ASC spheroids with different cell numbers were generated using a micro-mold system facilitating large-scale production. Spheroids composed of 2500 cells (diameter 220 µm) were suspended in a hydrogel solution consisting of thiol-functionalized hyaluronic acid and allyl-modified polyglycidol for UV crosslinking. The addition of 1 wt.% unmodified high molecular weight HA (hmHA) increased bioink viscosity enabling bioprinting. Furthermore, supplementation with hmHA decisively decreased spheroid sedimentation during printing and UV crosslinking resulting in a distinctly more homogeneous spheroid distribution in the final constructs. With regard to printing process parameters, stainless steel precision needles with an inner diameter of 330 μm, and a pressure of 1 bar proved to be most suitable for spheroid printing, as shown by viability and metabolic assays. Adipogenic differentiation of ASC was demonstrated over 21 days in cast and printed constructs, with distinctly higher amounts of synthesized triglycerides and strongly increased mRNA expression (qRT-PCR) of marker genes such as PPARG and aP2, as compared to undifferentiated constructs. Regarding cytokine secretion, also clear differences were detected between supernatants of undifferentiated (e.g., higher IL-6 levels) and differentiated ASC (e.g., higher adiponectin levels). Under favorable processing conditions, with regard to cell viability, differentiation capacity, and secretion behavior, no differences between printed and cast constructs were observed. The study facilitates the future use of multicellular spheroids as building blocks in 3D bioprinting, e.g., ASC spheroids may be utilized in disease model development as an important stromal component in 3D models of breast cancer.