**2.3 Calcium phosphate nanoparticles**

With the introduction of smaller calcium phosphate particles, it has become possible to use them in advanced fields of biomedicine. Calcium phosphate nanoparticles, with a size about 100 nm, are highly biocompatible. These particles are able to penetrate the outer membrane of cells and bacteria. Calcium phosphate nanoparticles could be utilized in different fields of biomedicine such as drug delivery, gene delivery, and imaging (Epple et al., 2010). Also, to produce high quality HAp bioceramics for artificial bone substitution, ultrafine HAp powder is usually employed. Nano-HAp powder results in easy handling, casting, and sintering leading to an excellent sintered body in the bioceramics preparation process (Cao et al., 2005).
