1. Nanoscale characterization of the biomechanical hardening of bovine zona pellucida by Antonio Boccaccio, Maria Cristina Frassanito, Luciano Lamberti, Roberto Brunelli, Giuseppe Maulucci, Maurizio Monaci, Massimiliano Papi, Carmine Pappalettere, Tiziana Parasassi, Lakamy Sylla, Fulvio Ursini, and Marco De Spirito Interface Volume ():rsif20120269 June 6, 2012 ©2012 by The Royal Society

2. Finite element model simulating the AFM nanoindentation process and typical deformation field for 200-nm indentation. Antonio Boccaccio et al. J. R. Soc. Interface doi:10.1098/rsif.2012.0269 ©2012 by The Royal Society

3. Flowchart of the hybrid identification procedure. Antonio Boccaccio et al. J. R. Soc. Interface doi:10.1098/rsif.2012.0269 ©2012 by The Royal Society

4. Abaqus finite element model of the indented ZP, including a heterogeneous distribution of elastic properties across membrane thickness: two layers with linearly variable elastic properties are considered. Antonio Boccaccio et al. J. R. Soc. Interface doi:10.1098/rsif.2012.0269 ©2012 by The Royal Society

5. Force–indentation curves acquired experimentally and corresponding numerical curves obtained with the hybrid identification procedure: (a) mature oocyte's ZP; (b) fertilized oocyte's ZP outer layer; (c) fertilized oocyte's ZP inner layer (the figure shows o... Antonio Boccaccio et al. J. R. Soc. Interface doi:10.1098/rsif.2012.0269 ©2012 by The Royal Society

6. Variation of the Young modulus ‘optimized’ by Abaqus through indentation depth. Antonio Boccaccio et al. J. R. Soc. Interface doi:10.1098/rsif.2012.0269 ©2012 by The Royal Society

7. (a) Schematic of the model of zona pellucida filamentous structure hypothesized by Wassarman [5]; (b) increase in number of inter-filament cross-links after fertilization as hypothesized by Green [6]. Antonio Boccaccio et al. J. R. Soc. Interface doi:10.1098/rsif.2012.0269 ©2012 by The Royal Society