Noncontact estimation of intercellular breaking force using a femtosecond laser impulse quantified by atomic force microscopy

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 108; no. 5; pp. 1777 - 1782
• Main Authors: Hosokawa, Yoichiroh, Hagiyama, Man, Iino, Takanori, Murakami, Yoshinori, Ito, Akihiko, Hochstrasser, Robin M.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 01.02.2011; National Acad Sciences
• Subjects: Aggregation; Animals; Atomic physics; Biological Sciences; Biophysics; Cantilevers; Cell Adhesion; Cell adhesion & migration; Cell adhesion molecules; Cell aggregates; Cell culture; Cultured cells; Epithelial cells; Estimating techniques; Irradiation; Lasers; Leukocytes; Mice; Microscopy; Microscopy, Atomic Force; NIH 3T3 Cells; Physical Sciences
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1006847108

When a femtosecond laser pulse (fsLP) is focused through an objective lens into a culture medium, an impulsive force (fsLP-IF) is generated that propagates from the laser focal point (O f ) in a micron-sized space. This force can detach individual adherent cells without causing considerable cell damage. In this study, an fsLP-IF was reflected in the vibratory movement of an atomic force microscopy (AFM) cantilever. Based on the magnitude of the vibration and the geometrical relationship between O f and the cantilever, the fsLP-IF generated at O f was calculated as a unit of impulse [N-s]. This impulsive force broke adhesion molecule-mediated intercellular interactions in a manner that depended on the adhesion strength that was estimated by the cell aggregation assay. The force also broke the interactions between streptavidin-coated microspheres and a biotin-coated substrate with a measurement error of approximately 7%. These results suggest that fsLP-IF can be used to break intermolecular and intercellular interactions and estimate the adhesion strength. The fsLP-IF was used to break intercellular contacts in two biologically relevant cultures: a coculture of leukocytes seeded over on an endothelial cell monolayer, and a polarized monolayer culture of epithelial cells. The impulses needed to break leukocyte-endothelial and interepithelial interactions, which were calculated based on the geometrical relationship between O f and the adhesive interface, were on the order of 10⁻¹³ and 10⁻¹² N-s, respectively. When the total impulse at O f is welldefined, fsLP-IF can be used to estimate the force required to break intercellular adhesions in a noncontact manner under biologically relevant conditions.