Growth Process and Mechanics of Cell Adhesion Investigated by Optical Tweezers

Cell adhesion between extracellular matrix and integrin is one of essential structure for cell growth, differentiation and cell motility. Paxillin and vinculin reinforce strength of cell adhesion and Src controls aggregation of these proteins at initial phase of cell adhesion. Thus the relationship between molecular and physical properties is important to understand the cell adhesion mechanisms. However, we still don't fully understand the property of cell adhesion. To investigate the characteristics, we have developed a measurement system for the stiffness of cell adhesion by using a collagen coated particle (2-micron diameter), which is manipulated by optical tweezers. In this system, cell adhesion is created under the particle by attaching to mouse fibroblast (Balb-3T3) for 1 min and it is called “initial adhesion”. After that the particle is moved back-and-forth in sinusoidal manner and analyzed the position of the particle recorded by a CCD camera. From that data we can know the actual force exerted on the particle. The minimum force sensitivity of the system is 80 fN. By using this system, we are able to measure the force of cell adhesion during growth process. This force rapidly increases for 30min from initial adhesion and gradually increases after 30 min. And we investigate the force change for 30 seconds after creation of initial adhesion. As a result, we observe the growth of cell adhesion with reinforcement and relaxation of adhesion force. And the stabilization of the reinforcement is occurred with fluctuation of the adhesion force. These phenomena are basic properties of cell adhesion and are important to reveal of molecular mechanism of cell adhesion.