**6.1.11. Silver-substituted apatite**

The favorable biocompatibility of hydroxyapatite (HA) makes it a popular bone graft material as well as a coating layer on metallic implant. One common and accepted strategy to pre‐ vent the implant-related infections is to create antibacterial properties for the implant. Silver ions can be either incorporated into the apatite during the co-precipitation process (AgHAP-CP) or subjected to the ion exchange with calcium ions in apatite (AgHAP-IE). The incorpo‐ ration of silver ions into apatite is based on the equation [51]:

$$\begin{aligned} \text{(10-y)}\ \text{Ca}^{2+}+\text{y Ag}^{+}+\text{6 PO}\_{4}^{3+}+\text{(2-y)OH}^{-}\rightarrow\\ \text{Ca}\_{10-\text{y Ag}}\text{(PO}\_{4}\text{)}\_{6}\text{(OH)}\_{2-\text{y}} \end{aligned} \tag{20}$$

where *y* is the molar amount of silver to be incorporated. However, the distribution of silver ions in AgHAP-CP and AgHAP-IE was different, thus affecting the antibacterial action.
