Determination of mechanical properties of the egg by the sessile drop method.

TLDR: It is stated that neglecting the rigidity of the endoplasm may not introduce serious errors in surface force determination in unfertilized sea urchin eggs and in fertilized eggs, however, the errors may be larger because structures having considerable rigidity such as the sperm aster or mitotic apparatus are formed in theendoplasm.

Abstract: Publisher Summary This chapter discusses the mechanical properties of the egg by the sessile drop method. The stiffness expressed by the different parameters depends on various mechanical properties of the cell components, for example, the surface force, rigidity of the cortex, intracellular pressure, or rigidity of endoplasmic structures. The surface force is determined from the degree of deformation of the egg under a gravitational or centrifugal force, the density difference between the egg protoplasm and the surrounding medium, the size of the egg, and the magnitude of the gravitational or centrifugal acceleration, using relationships obtained from the form of a theoretical sessile drop. A simple and accurate method to determine the density of the egg protoplasm is by the “isopycnotic method”. The chapter discusses possible errors and limitations of the sessile drop method in determining the surface force of the sea urchin eggs. It stated that neglecting the rigidity of the endoplasm may not introduce serious errors in surface force determination in unfertilized sea urchin eggs. In fertilized eggs, however, the errors may be larger because structures having considerable rigidity such as the sperm aster or mitotic apparatus are formed in the endoplasm. It is supposed that the density of the protoplasm is practically uniform in echinoderm eggs because eggs do not display any orientations in gravitational fields.