Bone regeneration with hydroxyapatite-based biomaterials

Degeneration, trauma, and tumor resection are the main causes of bone loss (Owen et al., J. Biomed. Mater. Res. B Appl. Biomater. 106(6), 2493-2512 (2018), Korkusuz et al., (2014), Kondo et al., Biomaterials. 26, 5600-5608 (2005), Matsumine et al., J. Bone Joint Surg. [Br]. 86-B, 5 (2004), Christensen et al., Knee Surg. Sports Traumatol. Arthrosc. 24, 2380-2387 (2016), Calabrese et al. Scientific Reports. 7(1), 1-11 (2017); Korkusuz et al. (2017), Morimoto et al. Spine J. 15, 1379-1390 (2015); Tang et al. Biomaterials 83, 363-382 (2016)). Autografts are still considered as the golden standard for bone regeneration. Donor site shortage, prolonged surgery time, blood loss, and donor site morbidity are the main drawbacks. Allografts are osteoconductive and to an extent osteoinductive. But they have low osteogenicity, possible immunologic reactions, and low mechanical strength and are associated with ethical or religious concerns. In order to overcome these disadvantages, studies on composites with ideal ranges of porosity, biodegradation rate, bioactivity, osteoinductivity, osteoconductivity, and mechanical properties are a popular research area.Calcium phosphate ceramics (CPCs) are biodegradable, biocompatible, and bioactive materials. Their resemblance to the inorganic part of bone makes them good alternatives to autografts and allografts (Korkusuz et al. (2014), Jeong et al. Biomaterials Research 23, 4 (2019), Rouahi et al., Colloids Surf. B: Biointerf. 47(1), 10-19 (2006)). Throughout CPCs, β-tricalcium phosphate (β-TCP), biphasic calcium phosphates (BCPs), and hydroxyapatite (HA) are frequently used in regeneration studies. Hydroxyapatite [Ca10(PO4)6(OH)2] is the main inorganic component of bones (~ 70% of bone tissue). HA is combined with many different natural or synthetic polymers and/or growth factors/cells to imitate the natural structure of bone in order to achieve bone formation and regeneration by either enhancing its osteoconductivity, osteoinductivity, or both. Nanohydroxyapatite (nHA) has a smaller grain size, and therefore, the increased surface area allows more cells and proteins to adhere on the surface. This therefore increases the ideal properties of a bone substitute. Here in this review, the use of HA in bone regeneration is briefly summarized.