Characterization of cell-biomaterial adhesion forces that influence 3D cell culture

Biomaterials, such as cellulose, offer advantages in 3D cell culture by mimicking natural cell environments. To further optimize 3D cell culture and explore new potential materials, it is essential to gain a deeper, quantitative knowledge on cell-biomaterial and cell-cell interactions. Herein, atomic force microscopy (AFM)-based techniques, especially single cell force spectroscopy (SCFS) and colloidal probe microscopy (CPM), were utilized to measure cell-cell and cell-biomaterial adhesion forces, and the results were correlated with experimental observations in 3D cell cultures. Two types of cell lines −human liver cancer cells HepG2 and human induced pluripotent stem cells iPS(IMR90)-4−, and 2 types of biomaterials −cellulose nanofibrils (CNF) and Matrigel− were studied in this work. The results showed that within 72 hours, both cell types formed rounded spheroids in CNF-embedded cultures. However, when embedded in Matrigel, the cells produced aggregates with a loose, non-spheroidal morphology. Interestingly, the adhesion force and energy between individual HepG2 cells were larger than between HepG2 cells and CNF. In the case of iPS(IMR90)-4 cells, the cell-Matrigel adhesion was found to be stronger than cell-CNF and cell-cell adhesion. These findings suggest that well-defined spheroids are formed when the cell-cell adhesion is stronger than the cell-material adhesion, as is the case for 3D cell cultures in CNF hydrogels. On the contrary, cell aggregates different from spheroids are formed when the cell-material adhesion prevails over the cell-cell adhesion. Understanding these adhesion mechanisms can optimize 3D cell cultures for in vitro drug development and regulatory studies, reducing reliance on animal testing and, consequently, makingdrug screening more ethical, efficient, and relevant to human physiology. This aligns with the recent elimination of the requirement for animal testing by the US Food and Drug Administration (FDA) in drug development.