Probing regional mechanical properties of embryonic tissue using microindentation and optical coherence tomography.

Physical forces regulate morphogenetic movements and the mechanical properties of embryonic tissues during development. Such quantities are closely interrelated, as increases in material stiffness can limit force-induced deformations and vice versa. Here we present a minimally invasive method to quantify spatiotemporal changes in mechanical properties during morphogenesis. Regional stiffness is measured using microindentation, while displacement and strain distributions near the indenter are computed from the motion of tissue labels tracked from 3-D optical coherence tomography (OCT) images. Applied forces, displacements, and strain distributions are then used in conjunction with finite-element models to estimate regional material properties. This method is applicable to a wide variety of experimental systems and can be used to better understand the dynamic interrelation between tissue deformations and material properties that occur during time-lapse studies of embryogenesis. Such information is important to improve our understanding of the etiology of congenital disease where dynamic changes in mechanical properties are likely involved, such as situs inversus in the heart, hydrocephalus in the brain, and microphthalmia in the eye.