Fig. 1. (A) Parallel plate compression device. The apparatus (not drawn to scale) contains inner and outer rectangular Plexiglas chambers. The outer chamber (OC) is connected to a thermostatted circulating water pump and serves to regulate the temperature of the inner chamber (IC). The lower assembly (LA) screws into the base of the inner chamber. The position of its central core (CC), whose tip is the lower compression plate (LCP), can be adjusted vertically by a screw thread to set the distance between the two plates. The upper compression plate (UCP) is a cylinder about 15 mm long suspended from the arm of a Cahn recording electrobalance, labeled as B, by a 0.15 mm diameter nickel-chromium wire (NCW). Its position can be adjusted horizontally to place the UCP directly above the LCP. Both plates are coated with poly-HEMA before each use. During an experiment, a spheroidal cell aggregate, labeled as A, is positioned on the lower plate and raised until it contacts the upper plate. Compression of the aggregate reduces the load measured by the balance by an amount equal to the force acting upon the cell aggregate. (B) Diagram of a liquid droplet compressed between two parallel plates at shape equilibrium. R₁ and R₂ are the two primary radii of curvature, at the droplet's equator and in a plane through its axis of symmetry, respectively. R₃ is the radius of the droplet's circular area of contact with either compression plate. H is the distance between the upper and lower compression plates. Because R₁, R₂ and H can all be directly measured with greater accuracy than R₃, the latter parameter was calculated using Eqn. 2.

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