Bioprinting of hydrogel beads to engineer pancreatic tumor-stroma microtissues for drug screening

Pancreatic ductal adenocarcinoma (PDAC) having features of dense fibrotic stromal and extracellular matrix (ECM) components has poor clinical outcome. In vitro construction of relevant preclinical PDAC models recapitulating the tumor-stroma characteristics is therefore in great need for the development of pancreatic cancer therapy. In this work, a three-dimensional (3D) heterogeneous PDAC microtissue based on a dot extrusion printing (DEP) system is reported. Gelatin methacryloyl (GelMA) hydrogel beads encapsulating human pancreatic cancer cells and stromal fibroblasts were printed, which demonstrated the capacity of providing ECM-mimetic microenvironments and thus mimicked the native cell-cell junctions and cell-ECM interactions. Besides, the spherical structure of the generated hydrogel beads, which took the advantage of encapsulating cells in a reduced volume, enabled efficient diffusion of oxygen, nutrients and cell waste, thus allowing the embedded cells to proliferate and eventually form a dense pancreatic tumor-stroma microtissue around hundred microns. Furthermore, a tunable stromal microenvironment was easily achieved by adjusting the density of stromal cells in the hydrogel beads. Based on our results, the produced heterogeneous pancreatic microtissue recapitulated the features of cellular interactions and stromal-like microenvironments, and displayed better anti-cancer drug resistance than mono-cultured pancreatic cancer spheroids. Together, the DEP system possesses the ability to simply and flexibly produce GelMA hydrogel beads, providing a robust manufacturing tool for the pancreatic cancer drug screening platform fabrication. In addition, the engineered pancreatic tumor-stroma microtissue based on bioprinted GelMA hydrogel beads, other than being ECM-biomimetic and stroma-tunable, can be used for observation in situ and may serve as a new drug screening platform.