Figure 3. Chemical interaction models of 10-methacryloyloxydecyl dihydrogen phosphate (MDP) with hydroxyapatite (HAp). (I,II) The ionic binding models of MDP interacting electrostatically with the Ca²⁺ ions of HAp, where either one of the P-OH groups of MDP dissociated H⁺ to form one P-O^– group, or two of the P-OH groups of MDP dissociated H⁺ to form two P-O^– groups during chemical interaction with HAp, respectively. (III) The covalent binding model of MDP condensation with the PO₄^3– ions of HAp to form pyrophosphate groups.