LARGE-DEFORMATION MECHANICAL TESTING OF BIOLOGICAL-MEMBRANES USING SPECKLE INTERFEROMETRY IN TRANSMISSION .1. EXPERIMENTAL APPARATUS

This paper describes an apparatus designed to study large mechanical d eformations in biological membranes. The task of mechanically characte rizing biological membranes is challenging because of the anisotropic and nonlinear nature of their material properties. The apparatus descr ibed here is well suited to the task because it uses speckle interfero metry to measure in-plane displacements in a distributed fashion and h as multiple degrees of freedom in the applied stress mechanism. In thi s way few a priori assumptions or restrictions are imposed on the appl ied stress and strain fields. The interferometer operates in transmiss ion mode to increase the Light efficiency of the system since the samp le biological membranes are translucent and reflect little light. The experimental results confirm that the strain fields in the biological membranes that are generated in the experiments are highly nonuniform and cannot be properly estimated from a small number of point measurem ents. (C) 1997 Optical Society of America.