Measuring mechanical properties of embryos and embryonic tissues.

Cell- and tissue-scale mechanics integrates numerous processes within the developing embryo to bring about both local cell movements and global tissue sculpting during morphogenesis. Rapid advances in molecular genetic approaches have outpaced quantitative approaches to study mechanics in early embryos. In this chapter, we present a device that is capable of carrying out a stress-relaxation test to measure the time-dependent elastic modulus of embryonic tissue explants a few hundreds of micrometers on a side. The device can detect forces from 25 nN to several micronewtons and allows the determination of extremely low modulii, as low as 5 Pa, found in frog embryonic tissues during gastrulation. We describe this device along with the methodology of its use and discuss the general challenges of working with embryonic tissues.