Recoil Dynamics after Laser Ablation of Single Cell Edges in Embyronic Epithelia

In order to determine the interfacial tensions along cell-cell boundaries in living fruit fly (\textit{Drosophila}) embryos, we have developed a microsurgical method based on laser ablation and laser-scanning confocal microscopy. Following ablation of one cell edge, we follow the recoil dynamics (strain relaxation) of adjacent GFP-labeled cell edges (with time resolution down to 2 ms). The recoils are consistently fit best by a double exponential decay with one time constant around 80 ms and the other around 1.2 s. The initial recoil velocities are in the range of 10-20 $\mu $m/s. We observe the same biphasic strain relaxation in multiple (N = 60) embryos at different developmental stages. Both recoil time constants are much longer than either the plasma lifetime or the duration of cavitation.