Comparative studies on micromechanical properties and biological performances in hydroxyapatite ceramics with micro/nanocrystalline

Abstract Further enhancing the comprehensive properties of hydroxyapatite (HA) bioceramics is still a hot topic in biomedical field. The present study was mainly aimed at investigating the special effect of nanoscale feature on the micromechanical properties and biological performances of HA bioceramics. Three kinds of HA bioceramics with micro‐ to nanocrystalline were fabricated by adopting different sintering technologies, that is, conventional sintering (CS), two‐step sintering (TSS), and microwave assisted sintering (MAS). The average grain sizes of HA‐CS, HA‐TSS, and HA‐MAS were 412.49, 264.24, and 122.49 nm, respectively. Among them, HA‐MAS nanoceramics had the lowest water contact angle (28.35°) and the highest surface roughness (92.30 nm). Interestingly, the enhanced crack deflection in HA‐MAS transferred from transgranular cracking to intergranular cracking, resulting into its fracture toughness (1.64 MPa m 1/2 ) increased by 84% compared to HA‐CS. Besides, HA‐MAS underwent the elastic‐plastic deformation without pop‐in cracking, and exhibited no indentation size effect (ISE) phenomenon during the nanoindentation tests. The in vitro biological performances showed that HA‐MAS could promote the bone‐like apatite formation and the osteogenic differentiation of BMSCs. In summary, the construction of nanocrystalline is indeed an effective way to simultaneously improve the micromechanical properties and biological performances of HA bioceramics.