Controlled synthesis of hydroxyapatite crystals templated by novel surfactants and their enhanced bioactivity

In this paper, we report that hydroxyapatite (HAP) nanocrystals with various shape and size have been successfully prepared by a dual template-assisted hydrothermal synthesis approach in isopropanol/water mixed solvents. Herein, we chose 4-aminobenzenesulfonic acid (ABSA) and polyethylene glycol 4000 (PEG-4000) as structure-directed templates, respectively. By gradually changing the mass ratios (R) of PEG-4000 to ABSA, the obtained HAP samples can undergo distinct morphological evolution accordingly. A class of unique sheet-like HAP sample could be formed when only using ABSA as template. Moreover, when the R value was changed to 1/4, uniform and high-yielding HAP plate-shaped structure can be obtained. When only using PEG-4000 as a template, almost novel and wedge-shaped HAP samples can be obtained. The results demonstrated that the obtained plate-like HAP sample has single-crystalline behavior and uniform distribution in both size and shape. Additionally, we perform and evaluate the bioactivity of HAP in simulated body fluid (SBF), indicating that the two obtained HAP samples can possess apparently improved bioactivity compared to previous literature reports, and bone-like apatite could be readily formed on the HAP surface through different soaking periods in SBF. Notably, for the first time, a novel method for evaluating the in vitro bioactivity of HAP has been proposed. Therefore, the presented synthetic route for HAP is well-controlled and facilitated, which could be extended to the preparation of other biomaterials with specific morphologies and architectures.