title: Mechanical properties of zona pellucida hardening.
abstract: We have investigated the changes in the mechanical properties of the zona pellucida (ZP), a multilayer glycoprotein coat that surrounds mammalian eggs, that occur after the maturation and fertilization process of the bovine oocyte by using atomic force spectroscopy. The response of the ZP to mechanical stress has been recovered according to a modified Hertz model. ZP of immature oocytes shows a pure elastic behavior. However, for ZPs of matured and fertilized oocyte, a transition from a purely elastic behavior, which occurs when low stress forces are applied, towards a plastic behavior has been observed. The high critical force necessary to induce deformations, which supports the noncovalent long interaction lifetimes of polymers, increases after the cortical reaction. Atomic force microscopy (AFM) images show that oocyte ZP surface appears to be composed mainly of a dense, random meshwork of nonuniformly arranged fibril bundles. More wrinkled surface characterizes matured oocytes compared with immature and fertilized oocytes. From a mechanical point of view, the transition of the matured ZP membrane toward fertilized ZP, through the hardening process, consists of the recovery of the elasticity of the immature ZP while maintaining a plastic transition that, however, occurs with a much higher force compared with that required in matured ZP.
authors.affiliation: Istituto di Fisica, Università Cattolica del S. Cuore, Largo F. Vito 1, Rome, Italy.
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Papi
authors.forename: Roberto
authors.initials: R
authors.lastname: Brunelli
authors.forename: Lakamy
authors.initials: L
authors.lastname: Sylla
authors.forename: Tiziana
authors.initials: T
authors.lastname: Parasassi
authors.forename: Maurizio
authors.initials: M
authors.lastname: Monaci
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Maulucci
authors.forename: Mauro
authors.initials: M
authors.lastname: Missori
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Arcovito
authors.forename: Fulvio
authors.initials: F
authors.lastname: Ursini
authors.forename: Marco
authors.initials: M
authors.lastname: De Spirito
mesh_terms: D000818:Animals; D002417:Cattle; D003198:Computer Simulation; D004548:Elasticity / Q000502:physiology*; D005306:Fertilization / Q000502:physiology; D005307:Fertilization in Vitro; D006023:Glycoproteins / Q000737:chemistry; D009865:Oocytes / Q000737:chemistry*; D010063:Ovum / Q000737:chemistry*; D013314:Stress, Mechanical; D013499:Surface Properties; D013552:Swine; D014817:Vitelline Membrane / Q000737:chemistry*; D015044:Zona Pellucida / Q000737:chemistry*
chemical_list: D006023:Glycoproteins