Measurement with an elastimeter of the stiffness of epithelial vesicles from pupal moth eye.

We have measured the stiffness of the monolayered epithelium which underlies the integument of an insect. Hollow vesicles of this epithelium, the hypodermis, formed during culture in a medium containing ecdysone, from squares of eye crescent integument excised from the moth Manduca sexta. Spherical vesicles were deformed by suction using an elastimeter; a plot of pressure vs. deformation has a slope which indicates the stiffness. This method allows a direct determination of the stiffness in a small patch of hypodermis at various places along the organism's surface. Vesicles produced from a sequence of sites along an adhesion gradient might show a corresponding sequence of stiffnesses. However, any difference in stiffness between vesicles from dorsal vs. ventral eye crescent was obscured by a large scatter in values for stiffness. Variation in the wall thickness of vesicles, and use of a scaling method involving elastic spheres, may underlie this scatter. The mean (±SD) corrected stiffness for all trials was 5.59±2.79 dynes/cm2/μm deformation.