Co/Co₃O₄@NC catalyst for the ORR with a low cost and highly stable performance is developed through the pyrolysis of an easy physical mixture containing ZIF-67 as the precursor and poplar flowers as the carbon source.

The understanding of the role of acidic amino acids in the synthesis of calcium phosphate (Ca–P) may provide effective ways for the design of advanced biomaterials. In this work, by employing L-glutamic acid (Glu), a one-step hydrothermal synthesis of porous carbonated hydroxyapatite (CHA) microspheres with high purity, good uniformity, controllable morphology, and large particle size is proposed. The morphology is well controlled by adjusting the concentration of Glu and the hydrothermal treatment time. The presence of Glu alters the growth pattern of Ca–P products and leads to the evolution of particles from ribbons to flower-like microspheres due to adsorption and the subsequent inhibiting action of the active growth sites onto the CHA's surface. It is established that the optimal condition having a predominance of uniform microspheres with an average diameter of about 64 μm is a Glu concentration of 0.06 M (at a Ca²⁺ : PO₄ ³⁻ : Glu molar ratio of 10.8 : 6 : 15). The CHA microspheres may be possibly used as effective carriers for biomedical application.

Commercial poly methyl methacrylate (PMMA)-based cement is currently used in the field of orthopedics. However, it suffers from lack of bioactivity, mechanical weakness, and monomer toxicity. In this study, a PMMA-based cement nanocomposite reinforced with hydroxyapatite (HA) nanofibers and two-dimensional (2D) magnesium phosphate MgP nanosheets was synthesized and optimized in terms of mechanical property and cytocompatibility. The HA nanofibers and the MgP nanosheets were synthesized using a hydrothermal homogeneous precipitation method and tuning the crystallization of the sodium-magnesium-phosphate ternary system, respectively. Compressive strength and MTT assay tests were conducted to evaluate the mechanical property and the cytocompatibility of the PMMA-HA-MgP nanocomposites prepared at different ratios of HA and MgP. To optimize the developed nanocomposites, the standard response surface methodology (RSM) design known as the central composite design (CCD) was employed. Two regression models generated by CCD were analyzed and compared with the experimental results, and good agreement was observed. Statistical analysis revealed the significance of both factors, namely, the HA nanofibers and the MgP nanosheets, in improving the compressive strength and cell viability of the PMMA-MgP-HA nanocomposite. Finally, it was demonstrated that the HA nanofibers of 7.5% wt and the MgP nanosheets of 6.12% wt result in the PMMA-HA-MgP nanocomposite with the optimum compressive strength and cell viability.

The concentration of OH⁻ can directly influence the crystal growth of flexible hydroxyapatite nanofibers in oleic acid-assisted solvothermal reaction systems.