New insights into the developmental biomechanics of the atrioventricular valves.

In this issue, Butcher et al, 1 provide elegant data on the mechanical performance and material properties of stage 17, 21, and 25 chick embryonic atrioventricular (AV) cushions during normal development and following the selective digestion of AV cushion constituents. These data are then interpreted using a strain-energy based pseudoelasticity theory to determine maturational changes in AV cushion material coefficients and effective modulus. The experimental approach developed by Butcher and colleagues and their observation that developmental changes in AV cushion function are because of changes in cushion constituents and material properties represent an important advance in our understanding of the role of tissue composition on valve morphogenesis. Further, this study represents the first direct correlation of in vivo AV cushion kinematics and blood velocity with biomechanical properties during AV valve morphogenesis that includes experimental validation via the selective enzymatic digestion of either glycosaminoglycans or collagens to alter cushion properties.