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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 m1/2) 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. [ABSTRACT FROM AUTHOR]

Epidural adhesion is a great clinical challenge after laminectomy. In the present study, two types of hydroxyapatite (HA) laminas with distinct surface microstructures were prepared by cold isostatic pressing (CIP) and slip casting (SC) techniques, and investigated to their anti‐fibrosis/adhesion effects by in vitro and in vivo evaluations. In contrast with the dense HA‐CIP, HA‐SC had a large number of micropores on the surface. After cultured on both HA ceramics, human skin fibroblasts presented the obvious senescent feature, and CCN1 gene expression was significantly up‐regulated. HA‐SC induced higher CCN1 gene expression than HA‐CIP. After used for closing the lost vertebral after laminectomy in rabbits, both HA laminas promoted the recovery of the bony structure as well as prevented the hyperplastic fibrous tissue from penetration into the spinal canal area and inhibited the formation of scar‐like tissue in laminectomy sites to some extent. Besides, thinner layer of fibrous tissue and smaller gap between the implant surface and paravertebral muscles were found in HA‐CIP than HA‐SC. Therefore, HA ceramics could have good anti‐fibrosis/adhesion effect when used in spinal repair, and the dense HA‐CIP could be an ideal choice. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B:2629–2637, 2019. [ABSTRACT FROM AUTHOR]

Nanocrystalline hydroxyapatite (HA) ceramic could have better potential in biomedical application due to its high bioactivity and mechanical strength. This study aimed at investigating on the relationship between the starting HA powders and resultant HA ceramics. The synthesized HA crystals using chemical precipitation showed different morphology, size, and crystallinity under different reaction temperature and aging time. The spray‐dried HA powders from the different HA slurries synthesized at 40, 60, and 80°C had spherical shapes and similar particles size but different specific surface area (SSA). Lower synthesizing temperature resulted in lower crystallinity and need‐like shape of the HA crystals, and thus higher SSA of the spray‐dried HA powders. After cold isostatic pressing of the HA powders, the HA green compacts were sintered at 1000, 1050, and 1150°C, respectively, and they presented different sinterability, compactness, and mechanical strength, which were tightly dependent on the starting HA powders. As compared to 80°C synthesized powders, 40 and 60°C synthesized powders exhibited better sinterability due to the lower crystallinity and higher SSA, leading to the relatively high compactness and mechanical strength, but small grain size below 100 nm of the resultant HA ceramics even at low sintering temperature of 1050°C. [ABSTRACT FROM AUTHOR]

Exploring the long-term filler for minimally invasive plastic surgery has been widely concerned. In the present study, a series of injectable paste composed of hydroxyapatite (HAp) spherical particles and cross-linked sodium hyaluronate (cHA) solution were prepared. The physicochemical properties of cHA as a carrier of high content HAp microspheres (>50%) and as-obtained injectable HAp/cHA paste were studied. The cross-linking degree (DC), viscosity and molecular weight (Mw and Mn) of cHA increased with the increasing of the cross-linker dosage from 7.5 to 17.5 wt% under the certain conditions. HAp/cHA pastes were fabricated by homogeneously blending different sizes of HAp microspheres with cHA solution. The stability, rheological performance and push-out force of the pastes were studied, and the influence factors were discussed. The results indicated that moderate crosslinked cHA with 60% middle size HAp (HAp-M60/cHA-15.0) had appropriate comprehensive property. Finally, the in vitro cell culture approved the paste had no cytotoxicity. Although the biological performance of the pastes still need to be investigated, this preliminary study demonstrates that it is possible to carry high content HAp in cHA, expecting the better volumetric maintenance after long term implantation. [ABSTRACT FROM AUTHOR]