Their extraordinary mechanical properties are due to a special hierarchical
arrangement of the constituent carbonated calcium-deficient
hydroxyapatite (‘‘bioapatite’’) crystals (Al-Sawalmih et al., 2008;
Dunlop and Fratzl, 2010; Fabritius et al., 2009; Wang and Weiner,
1998a,b; Weiner and Addadi, 1997).