*4.3.10 Hydroxyapatite*

Natural bone ECM consists of organic and inorganic phases and the base of the organic phase is calcium phosphate, especially hydroxyapatite [90]. Therefore, hydroxyapatite is one of the most studied materials in bone regeneration applications [91–94]. The hydroxyapatite can be used alone, synthetically, porously, in a resorbable form, or combined with natural or synthetic materials such as β-TCP, PRP, collagen, and bioactive glass [95]. Walsh et al. [96] showed a high potential of hydroxyapatite-collagen scaffold for the treatment of critical-sized bone defects with 28-fold and 7-fold increments in the bone volume and new bone area after 4 weeks.
