Surface wettability is a measure of surface energy. Surface energy can be altered or tuned by the addition of hydrophobic or hydrophilic groups. Plasma treatment, for example, is a well-known procedure for increasing the hydrophilicity of many hydrophobic surfaces including PDMS, PET, PLGA, and COC. The hydrophilicity of a material is a strong determinant of protein adsorption and thus cell adhesion . In 2D cell culture, hydrophilic substrates promote cell adhesion and proliferation , with moderate hydrophilicity yielding often the best cell response . Conversely, in 3D cell culture, specifically for spheroid formation, high hydrophobic substrates induce the formation of spheroid-like cell aggregates at a higher degree of sphericity, as shown by Ferrari et al. and Lee et al. among others . Zan et al. investigated the behaviors of three chondrogenic cell lines on PDMS substrates with different grades of hydrophilicity (WCA: 38.5°-120.4) and different stiffness (elastic modulus: 3.6-214.9 MPa). The response of different cell lines to an identical substrate was different, however, among the two factors influencing cell behaviors, the substrate wettability dominated cell proliferation while the substrate stiffness played a major role in the cell migration and spread and the expression of cell adhesive molecule and chondrogenic gene. This result confirms the suggestion of Wala et al. that initial cell adhesion and proliferation are regulated by surface properties such as hydrophilicity and roughness, while material properties such as stiffness influence later stages of cell growth.