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Assessment of the Effects of Surface Potential on the Kinetics of HEK293T Cell Adhesion Behavior Using a Quartz Crystal Microbalance with Dissipation Monitoring

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posted on 15.12.2017, 00:00 by Wei-Lun Kao, Hsun-Yun Chang, Kang-Yi Lin, Yi-Wei Lee, Jing-Jong Shyue
Cell adhesion plays a key role in biomaterial development. Self-assembled monolayers (SAMs) provide a convenient and versatile means of modifying surface properties to study how environmental cues affect the cell adhesion process. Serial ζ-potential surfaces can be realized by introducing various ratios of oppositely charged functional groups on a gold surface. A quartz crystal microbalance with dissipation monitoring (QCM-D) has advantages for examining real-time viscoelastic changes on surfaces. This surface-sensitive technique can be applied in cell adhesion studies to investigate the cell–surface interactions. In this work, HEK293T epithelial cells were used to examine the adhesion kinetics of semiadherent cells on NH2–COOH binary SAM-modified surfaces with serial surface potential. Immunofluorescence staining was used to examine focal adhesion sites after a 4-h cell adhesion process. Combined with optical microscopy, QCM-D was used to record in situ and real-time viscoelastic and morphological changes. It was found that HEK293T cells were prone to spread and form more focal adhesion sites on surfaces with more positive charge (more NH2 groups) but aggregated and remained highly mobile on surfaces with more negative charge (more COOH groups). On NH2-rich surfaces, cells underwent three-phase kinetics during the adhesion process. Initially, cells adhered and spread quickly on the NH2-rich surfaces with little or no extracellular matrix (ECM) by the attractive interaction between the positively charged amine groups and negatively charged cell membrane. The epithelial cells then shrank their filopodia in the second phase to normalize their size. In the final phase, cells underwent ECM remodeling and formed matured ECM. On COOH-rich surfaces, four phases were identified during the cell adhesion process. Initially, due to electrostatic repulsion between the negatively charged cell membrane and surfaces, direct cell adhesion and spreading were restricted. However, ECM was quickly deposited. In the second phase, cells adhered on and interacted with the surface through the ECM layer. In the third phase, cells underwent ECM remodeling, and additional ECM was deposited on the surfaces. Finally, instead of cell–surface interactions, the cells aggregated to form cell–cell junctions. In summary, the cell adhesion process shifted from direct cell–surface interaction to cell–ECM–surface interaction and cell–cell junctions when the surface potential shifted from positive to negative.