Sensitive detection of cell-derived force and collagen matrix tension in microtissues undergoing large-scale densification

Polydopamine Interfacial Coating for Stable Tumor-on-a-Chip Models: Application for Pancreatic Ductal Adenocarcinoma

Addressing current challenges in solid tumor research requires advanced in vitro three-dimensional (3D) cellular models that replicate the inherently 3D architecture and microenvironment of tumor tissue, including the extracellular matrix (ECM). However, tumor cells exert mechanical forces that can disrupt the physical integrity of the matrix in long-term 3D culture. Therefore, it is necessary to find the optimal balance between cellular forces and the preservation of matrix integrity. This work proposes using polydopamine (PDA) coating for 3D microfluidic cultures of pancreatic cancer cells to overcome matrix adhesion challenges to sustain representative tumor 3D cultures. Using PDA's distinctive adhesion and biocompatibility, our model uses type I collagen hydrogels seeded with different pancreatic cancer cell lines, prompting distinct levels of matrix deformation and contraction. Optimizing the PDA coating enhances the adhesion and stability of collagen hydrogels within microfluidic devices, achieving a balance between the disruptive forces of tumor cells on matrix integrity and the maintenance of long-term 3D cultures. The findings reveal how this tension appears to be a critical determinant in spheroid morphology and growth dynamics. Stable and prolonged 3D culture platforms are crucial for understanding solid tumor cell behavior, dynamics, and responses within a controlled microenvironment. This advancement ultimately offers a powerful tool for drug screening, personalized medicine, and wider cancer therapeutics strategies.

Embedded 3D Bioprinting of Collagen Inks into Microgel Baths to Control Hydrogel Microstructure and Cell Spreading

Microextrusion-based 3D bioprinting into support baths has emerged as a promising technique to pattern soft biomaterials into complex, macroscopic structures. It is hypothesized that interactions between inks and support baths, which are often composed of granular microgels, can be modulated to control the microscopic structure within these macroscopic-printed constructs. Using printed collagen bioinks crosslinked either through physical self-assembly or bioorthogonal covalent chemistry, it is demonstrated that microscopic porosity is introduced into collagen inks printed into microgel support baths but not bulk gel support baths. The overall porosity is governed by the ratio between the ink's shear viscosity and the microgel support bath's zero-shear viscosity. By adjusting the flow rate during extrusion, the ink's shear viscosity is modulated, thus controlling the extent of microscopic porosity independent of the ink composition. For covalently crosslinked collagen, printing into support baths comprised of gelatin microgels (15-50 µm) results in large pores (≈40 µm) that allow human corneal mesenchymal stromal cells (MSCs) to readily spread, while control samples of cast collagen or collagen printed in non-granular support baths do not allow cell spreading. Taken together, these data demonstrate a new method to impart controlled microscale porosity into 3D printed hydrogels using granular microgel support baths.

Inhibitory Effects of Epithelial Cells on Fibrosis Mechanics of Microtissue and Their Spatiotemporal Dependence on the Epithelial-Fibroblast Interaction

Cell-generated contraction force is the primary physical drive for fibrotic densification of biological tissues. Previous studies using two-dimensional culture models have shown that epithelial cells inhibit the myofibroblast-derived contraction force via the regulation of the fibroblast/myofibroblast transition (FMT). However, it remains unclear how epithelial cells interact with fibroblasts and myofibroblasts to determine the mechanical consequences and spatiotemporal regulation of fibrosis development. In this study, we established a three-dimensional microtissue model using an NIH/3T3 fibroblast-laden collagen hydrogel, incorporated with a microstring-based force sensor, to assess fibrosis mechanics. When Madin-Darby canine kidney epithelial cells were cocultured on the microtissue's surface, the densification, stiffness, and contraction force of the microtissue greatly decreased compared to the monocultured microtissue without epithelial cells. The key fibrotic features, such as enhanced protein expression of α-smooth muscle actin, fibronectin, and collagen indicating FMT and matrix deposition, respectively, were also significantly reduced. The antifibrotic effects of epithelial cells on the microtissue were dependent on the intercellular signaling molecule prostaglandin E2 (PGE2) with an effective concentration of 10 μM and their proximity to the fibroblasts, indicating paracrine cellular signaling between the two types of cells during tissue fibrosis. The effect of PGE2 on microtissue contraction was also dependent on the time point when PGE2 was delivered or blocked, suggesting that the presence of epithelial cells at an early stage is critical for preventing or treating advanced fibrosis. Taken together, this study provides insights into the spatiotemporal regulation of mechanical properties of fibrosis by epithelial cells, and the cocultured microtissue model incorporated with a real-time and sensitive force sensor will be a suitable system for evaluating fibrosis and drug screening.