Investigating protein structure change in the zona pellucida with a microrobotic system

In this paper we present a microwbotic system that integrates microscope vision and microforce feedback for characterizing biomembrane mechanical properties. We describe robust visual tracking of deformable biomembrane contours using physics-based models. A multi-axis microelectromechanical systems based force sensor is used to determine applied forces on biomembranes and to develop a novel biomembrane mechanical model. By visually extracting biomembrane deformations during loading, geometry changes can be used to estimate applied forces using a biomembrane mechanical model and the determined elastic modulus. Forces on a biomembrane can be visually observed and controlled, thus creating a framework for vision and force assimilated cell manipulation. The experimental results quantitatively describe a stiffness increase seen in the mouse zona pellucida (ZP) after fertilization. Understanding this stiffness increase, referred to as "zona hardening", helps provide an understanding of ZP protein structure development, i.e., an increase in the number of cross links of protein ZP1 between ZP2 and ZP3 units that is conjectured to be responsible for zona hardening. Furthermore, the system, technique, and model presented in this paper can be applied to investigating mechanical properties of other biomembranes and other cell types, which has the potential to facilitate many biological studies, such as cell injury and recovery where biomembrane mechanical property changes need to be monitored.