A new technique for direct measurement of the shear force necessary to detach a cell from a material.

Affinity for cells is one of the important properties for biomaterials, because they are always used adjacent to living tissue. For the development of new biomaterials with superior biocompatibility, quantitative evaluation of the materials' affinity for cells is necessary. One of the methods to evaluate the materials' affinity for cells quantitatively is to measure the detachment force of an adherent cell on a material. In this study, a new system was developed to measure directly the shear force necessary to detach a cell from a material. Using a microcantilever, the detachment force was measured in the cell culture medium by applying a lateral load to the cell which adhered to the material. During the measurement, the cell was observed using an optical microscope and the image of the cell was recorded on a video tape through a CCD camera. The cell adhesive area before detaching the cell was measured by analyzing the obtained video image of the cell. Reproducibility of the measurement was demonstrated by repeating the measurement of the shear forces to detach murine fibroblasts L929 incubated for 24 h on glass. The average shear strength, which is a detachment force per unit cell adhesive area, is 530-750 Pa, varying with the day of cell preparation. However, the shear strengths of the cells seeded at the same time into separate dishes are corresponding well to each other. This fact suggests that it is possible to compare the materials' affinity for cells using this system if the cells were seeded at the same time onto different materials.