Mechanical property characterization of the zebrafish embryo chorion.

A microrobotic force sensing system is used to characterize the mechanical properties of the chorion of zebrafish embryos and quantitate the mechanical property differences of the chorion at different developmental stages. Quantitative relationships between applied forces and chorion structural deformations are established for various developmental stages. The measured penetration forces for puncturing chorion at the blastula stage are 1.3 times as large as those at the pre-hatching stage. Through the use of an analytical biomembrane elastic model, chorion elastic modulus values are determined. The modulus at the blastula stage is 1.66 times as large as that at the pre-hatching stage. The experimental results quantitatively describe "chorion softening," which is mostly due to the proteolytic activity at the pre-hatching stage. This study also reveals the effect of pronase treatment on zebrafish chorion, which produces an "artificial chorion softening" effect. This draws an analogy between pronase treatment and proteolytic activities at the pre-hatching stage.