A fiber optic system for measuring dynamic mechanical properties of embryonic tissues

Dynamic mechanical properties of embryonic tissues, including viscoelasticity and active motility, play a major role in morphogenesis. Mechanical abnormalities resulting from altered cytoskeletal chemistry presumably contribute to spina bifida and other birth defects, but research in this area has been limited by inadequate mechanical measurement techniques. This paper discusses aspects of embryo tissues that make them difficult to measure and describes a versatile new system developed and used to study the biomechanics of morphogenesis in amphibian embryos. It incorporates a flexible optical-fiber probe driven by piezoceramic elements to impose and measure feedback-controlled, two-dimensional, time-varying patterns of stress or strain in the tissue. Compression, tension, and shear geometries are possible. Capacitive displacement sensors provide the precision and low drift rates required for these measurements. Software control permits the system to perform both standard and customized rheological tests, including interactive ones in which test parameters change in response to measured tissue behavior. Sample size range is 50 microns to 5 mm. Displacement range is 60 microns with a resolution of 0.1 microns. Force range is 10 microN with a resolution of 0.02 microN. Frequency range is DC to 20 Hz.