High-Quality Three-Dimensionally Cultured Cells Using Interfaces of Diblock Copolymers Containing Different Ratios of Zwitterionic <i>N</i>-Oxides

To control three-dimensional (3D) cell spheroid formation, it is well-known the surface physicochemical and mechanical properties of cell culture materials are important; however, the formation and function of 3D cells are still unclear. This study demonstrated the precise control of the formation of 3D cells and 3D cell functions using diblock copolymers containing different ratios of a zwitterionic trimethylamine <i>N</i>-oxide group. The diblock copolymers were composed of poly(<i>n</i>-butyl methacrylate) (PBMA) as the hydrophobic unit for surface coating on a cell culture dish and stabilization in water, and poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) as the precursor of <i>N</i>-oxide. The zwitterionic <i>N</i>-oxide converted from 0 to 100% using PDMAEMA. The wettability and surface zeta potential varied with different ratios of <i>N</i>-oxide diblock copolymer-coated surfaces, and the amount of protein adsorbed in the cell culture medium decreased monotonically with increasing <i>N</i>-oxide ratio. 3D cell spheroid formations were observed by seeding human umbilical cord mesenchymal stem cells (hUC-MSCs) in diblock copolymer-coated flat-bottom well plates, and the <i>N</i>-oxide ratio was over 40%. The cells proliferated in two-dimensions (2D) and did not form spheroids when the <i>N</i>-oxide ratio was less than 20%. Interestingly, the expression of undifferentiated markers of hUC-MSCs was higher on surfaces that adsorbed proteins to some extent and formed 50-150 μm spheroids in the range of 40-70% of <i>N</i>-oxide ratio. We revealed that a moderately protein-adsorbed surface allows precise control of spheroid formation and undifferentiated 3D cells and has potential applications for high-quality spheroids in regenerative medicine and drug screening.