CeO2 nanoparticles (NPs) have been well demonstrated as an antioxidant in protecting against oxidative stress-induced cellular damages and a potential therapeutic agent for various diseases thanks to their redox enzyme-mimicking activities. The Ce3+/Ce4+ ratio and oxygen vacancies on the surface have been considered as the major originations responsible for the redox enzyme-mimicking activities of CeO2 NPs. Herein, CeO2 nanostructures (nanocubes and nanorods) exposed different facets were synthesized via a facile hydrothermal method. The characterizations by X-ray photoelectron spectroscopy, Raman spectroscopy, and UV-Vis spectroscopy show that the Ce3+/Ce4+ ratio and oxygen vacancy content on the surfaces of as-synthesized CeO2 nanostructures are nearly at the same levels. Meanwhile, the enzymatic activity measurements indicate that the redox enzyme-mimicking activities of as-synthesized CeO2 nanostructures are greatly dependent on their exposed facets. CeO2 nanocubes with exposed {100} facets exhibit a higher peroxidase but lower superoxide dismutase activity than those of the CeO2 nanorods with exposed {110} facets. Our results provide new insights into the redox enzyme-mimicking activities of CeO2 nanostructures, as well as the design and synthesis of inorganic nanomaterials-based artificial enzymes.

Developing efficient non-precious metal hydrogen evolution reaction (HER) electrocatalysts is a great challenge for sustainable hydrogen production from water. In this communication, for the first time, semimetallic MoP2 nanoparticle films on a metal Mo plate (MoP2 NPs/Mo) are fabricated through a facile two-step strategy. When used as a binder-free hydrogen evolution cathode, the as-prepared MoP2 NPs/Mo electrode exhibits superior HER catalytic activity at all pH values. At a current density of 10 mA cm(-2), the catalyst displays overpotentials of 143, 211 and 194 mV in 0.5 M H2SO4, 1.0 M phosphate buffer solution and 1.0 M KOH, respectively. Furthermore, it exhibits excellent stability over a wide pH range. Thus, this in situ route opens up a new avenue for the fabrication of highly efficient, cost-effective and binder-free non-precious catalysts for water splitting and other electrochemical devices.

In the present study, hydroxyapatite (HA, Ca5(PO4)3OH) with different morphologies, such as nanorods, microspheres, hexagonal prisms, and hollow flowerlike structure, were synthesized via a facile hydrothermal route by adjusting reaction parameters. The as-synthesized samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and high resolution transmission electron microscopy. Furthermore, the saturation index of the reaction systems under different conditions was approximately calculated in order to explore the formation mechanism of HA. The results indicate that both the saturation index and the intermediates presented at the initial stage of the reaction play crucial roles in the formation of HA with different morphologies. These results provide a promising strategy for the tunable synthesis of HA and other nanomaterials.

Fe-N-C series catalysts are always attractive for their high catalytic activity towards the oxygen reduction reaction (ORR). However, they usually consist of various components such as iron nitrides, metallic iron, iron carbides, N-doped carbon and Fe-N moieties, leading to controversial contributions of these components to the catalysis of the ORR, especially iron nitrides. In this work, to investigate the function of iron nitrides, FeN nanoparticles (NPs) embedded in mesoporous N-doped carbon without Fe-N moieties are designed and constructed by a simple histidine-assisted method. Herein, the use of histidine can increase the N and Fe contents in the product. The obtained catalyst exhibits excellent ORR catalytic activity which is very close to that of the commercial Pt/C catalyst in alkaline electrolytes. Combining the catalytic activity, structural characterization (especially from Mössbauer spectroscopy), and the results of DFT calculations for adsorption energies of oxygen on the main surfaces of FeN including ε-FeN and ζ-FeN, it can be deduced that FeN NPs as active species make a contribution to the ORR catalysis, of which ε-FeN (x ≤ 2.1) is more active than ζ-FeN. In addition, we find that there exists an obvious synergistic effect between FeN NPs and N-doped carbon, leading to the greatly enhanced ORR catalytic activity.

A stem cell-derived mineralized extracellular matrix (ECM) may be a good strategy to endow scaffolds with a bone microenvironment, thus inducing bone regeneration. However, it also faces some challenges, such as limited number of cells, additional wound for autologous cell isolation, and time consumption of cell expansion. In this study, we designed a novel tissue-derived ECM scaffold fabricated by depositing porcine small intestinal submucosa (SIS) ECM on true bone ceramic (TBC), which was followed by mineralization treatment (mSIS/TBC). In vitro, compared with pure TBC, mSIS/TBC promoted cell proliferation, cell viability, and osteoblastic differentiation of the newly seeded rat bone marrow mesenchymal stem cells (BMSCs), and upregulation of the messenger RNA (mRNA) level of osteogenesis-related genes. Western blot assay revealed that mSIS/TBC enhanced osteoblastic differentiation through activation of phosphorylated Smad1/5/8 and phosphorylated extracellular signal-regulated kinase (ERK), as an underlying mechanism. In vivo, in a rat cranial critical size defect model, mSIS/TBC scaffolds induced greater bone formation than pure TBC scaffolds. Meanwhile, a comparative study on the capacity of bone regeneration was also carried out between mSIS/TBC and BMSC-derived ECM deposited on TBC scaffold in vivo and in vitro. The results demonstrated that mSIS/TBC scaffolds acquired a comparable bone regeneration efficacy to that of BMSC-derived ECM deposited on TBC scaffolds. Collectively, our results demonstrated that mSIS/TBC enhanced bone regeneration by supporting cell proliferation and cell viability, and by activating Smad1/5/8 and ERK1/2 signal pathways of BMSC in vitro and in vivo; thus, mSIS/TBC is an excellent alternative to stem cell-derived ECM scaffold for bone regeneration.