Spatial Engineering of Human Breast Tissue Cultures by 3D Bioprinting

Abstract

Extracellular matrix (ECM) is an integral part of breast tissue microenvironment, and it plays important roles in mammary gland development and homeostasis as well as in breast cancer progression. However, the in vivo architecture of mammary epithelium and ECM is poorly recapitulated by the current in vitro models. Three-dimensional (3D) bioprinting is an emerging approach to improve tissue-mimicry of 3D cell cultures. The aim of this research project was to develop and optimize a protocol for 3D-bioprinted breast tissue cultures. In the model, mammary epithelial cells (MCF10A) are printed into a branched shape that is surrounded by collagenous matrix to mimic mammary gland microenvironment. Different biomaterials were tested as bioinks, but most biologically relevant bioinks had too low viscosity for 3D bioprinting or too high stiffness for mammary gland tissue culture. While the mixture of collagen I and basement membrane extract (BME) was observed to have appropriate viscosity and stiffness, it could not be printed in layers. Therefore, the mammary epithelial cells were printed directly inside a non-polymerized collagen I-BME matrix, which supported the cells to remain in the printed shape. In the 3D-bioprinted cultures, cells proliferated and formed spheroids that ultimately started to fuse together while remaining in the printed shape. Also, signs of lumen formation and organotypic polarization of cells were detected. In future studies, additional ECM molecules can be printed at specific locations within the cultures to study the effects of different ECM patterns on epithelial growth, which may reveal new regulatory mechanisms that control mammary gland morphogenesis and homeostasis.