Figure 11. The behavior of the ζ -potential of hydroxyapatite (HAp) ( a ), 7ZnHAp ( b ), and 20ZnHAp ( c ) Figure 11. The behavior of the ζ -potential of hydroxyapatite (HAp) ( a ), 7ZnHAp ( b ), and 20ZnHAp particle suspensions. ZnHAp: zinc-doped ( c ) particle suspensions. ZnHAp: zinc-doped hydroxyapatite.