Abstract
Given their wide range of biomedical applications, hydroxyapatite (HA) nanoparticles are an attractive material widely used in many fields. Therefore, a simple, inexpensive, and stable process for the synthesis of HA nanoparticles is necessary to meet current needs. Herein, we studied HA synthesis assisted by four surfactants, namely cation, anion, non-ionic, and zwitterion templates, to verify the synthesis phase, aspect ratio, morphology, and biocompatibility under different environments (i.e., pH 4 and 9) before and after calcination. Results showed that before calcination, the surfactant-free groups could not produce HA but showed an abundant dicalcium phosphate anhydrous (DCPA) phase at pH 4. Except for the anionic group containing a small amount of DCPA, all surfactant-assistant groups presented single-phase HA in acidic and alkaline environments. The diameter of HA synthesized at pH 4 was significantly larger than that of HA synthesized at pH 9, and the effect of aspect ratio changes after calcination was more significant than that before calcination. The uncalcined rod-shaped HA synthesized with a non-ionic template at pH 4 demonstrated excellent cell viability, whereas anionic, cationic, and non-ionic surfactants exhibited biocompatibility only after calcination. At pH 9, non-ionic and uncalcined zwitterion-assisted rod-shaped HA showed excellent biocompatibility. In conclusion, the uncalcined HA rod-shaped nanoparticles synthesized from the non-ionic template at pH 4 and 9 and the zwitterion template at pH 9, as well as all surfactant-assisted HA after calcination, had no cytotoxicity. These tailor-made non-toxic HA types can meet the different requirements of apatite composite materials in biomedical applications.
Highlights
Hydroxyapatite (HA) is the crystalline form of apatite
When using SDS as a nucleation template at pH 4, the diffraction peak was based on the dicalcium phosphate anhydrous (DCPA) structure, it contained a small amount of HA diffraction at 31.7◦
When using a nucleating agent CTAB, F127, or CTAB as a nucleation template, HA planes of (2 1 1), (1 1 2), and (300) (HA: JCPDS 09-0432) had the highest diffraction density at 31.7◦, 32.2◦, and 32.9◦, respectively, indicating that HA can be successfully synthesized even at pH 4 when surfactants CTAB, F127, and cocamidopropyl betaine (CAPB) are used as nucleation templates
Summary
Almost all chemicals in the apatite family can promote bone growth by introducing bone-derived mechanisms. It does not cause local or systemic toxicity and foreign-body reactions [1,2]. When HA is implanted, it binds to bone tissue through chemical bonds, so it has good bone repairability. It is highly suitable as a repair material for bone defects. The main challenge in the synthesis of apatite powder is to precisely control the growth of HA crystals before manufacturing the required scaffolds for various tissues [3,4], which directly affects the size and geometry of the final nanoparticles [5]. The microscopic shape, size, and size distribution of HA can significantly affect the mechanical properties, processing conditions, surface chemistry, biocompatibility, and biological activity of HA [6,7]
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