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carrier with an extremely high energy density (approximately 142 MJ kg −1 ) and zero-carbon content, has been regarded as a promising clean fuel. [1,2] In this context, electrochemical water splitting, which converts electricity into storable hydrogen, is a viable and efficient solution to mitigate severe energy shortages and greenhouse gas emissions. [3] Among these strategies, hydrogen and oxygen evolution reactions, which occur on the cathode and anode, respectively, in a water electrolyzer, are considered as two critical half-reactions of the water-splitting process. [4] Theoretically, water splitting requires a thermodynamic Gibbs free energy (ΔG) of approximately 237.2 kJ mol −1 , corresponding to a standard potential (ΔE) of 1.23 V versus a reversible hydrogen electrode (RHE), which allows the thermodynamically uphill reaction to occur in the electrolyzer. [5] However, the unfavorable thermodynamics and resulting large overpotential are the main barriers to the scalable implementation of water electrolysis for hydrogen generation. [6,7] Currently, noble metal-based electrocatalysts exhibit the most efficient activity for water splitting, particularly Pt-based hydrogen evolution reaction (HER) catalysts and Ir/Ru-based oxygen evolution reaction (OER) catalysts. [8,9] Nevertheless, the scarcity and high price of precious metals severely impede their widespread use in commercial water-splitting applications. Taking these limitations into Electrochemical water splitting has attracted significant attention as a key pathway for the development of renewable energy systems. Fabricating efficient electrocatalysts for these processes is intensely desired to reduce their overpotentials and facilitate practical applications. Recently, metal-organic framework (MOF) nanoarchitectures featuring ultrahigh surface areas, tunable nanostructures, and excellent porosities have emerged as promising materials for the development of highly active catalysts for electrochemical water splitting. Herein, the most pivotal advances in recent research on engineering MOF nanoarchitectures for efficient electrochemical water splitting are presented. First, the design of catalytic centers for MOF-based/derived electrocatalysts is summarized and compared from the aspects of chemical composition optimization and structural functionalization at the atomic and molecular levels. Subsequently, the fast-growing breakthroughs in catalytic activities, identification of highly active sites, and fundamental mechanisms are thoroughly discussed. Finally, a comprehensive commentary on the current primary challenges and future perspectives in water splitting and its commercialization for hydrogen production is provided. Hereby, new insights into the synthetic principles and electrocatalysis for designing MOF nanoarchitectures for the practical utilization of water splitting are offered, thus further promoting their future prosperity for a wide range of applications.

An intense stimulus can cause death of odontoblasts and initiate odontoblastic differentiation of stem/progenitor cell populations of dental pulp cells (DPCs), which is followed by reparative dentin formation. However, the mechanism of odontoblastic differentiation during reparative dentin formation remains unclear. This study was to determine the role of β-catenin, a key player in tooth development, in reparative dentin formation, especially in odontoblastic differentiation. We found that β-catenin was expressed in odontoblast-like cells and DPCs beneath the perforation site during reparative dentin formation after direct pulp capping. The expression of β-catenin was also significantly upregulated during odontoblastic differentiation of in vitro cultured DPCs. The expression pattern of runt-related transcription factor 2 (Runx2) was similar to that of β-catenin. Immunofluorescence staining indicated that Runx2 was also expressed in β-catenin–positive odontoblast-like cells and DPCs during reparative dentin formation. Knockdown of β-catenin disrupted odontoblastic differentiation, which was accompanied by a reduction in β-catenin binding to the Runx2 promoter and diminished expression of Runx2. In contrast, lithium chloride (LiCl) induced accumulation of β-catenin produced the opposite effect to that caused by β-catenin knockdown. In conclusion, it was reported in this study for the first time that β-catenin can enhance the odontoblastic differentiation of DPCs through activation of Runx2, which might be the mechanism involved in odontoblastic differentiation during reparative dentin formation.

high sensitivity to surroundings, and difficulties in recycling and reuse, limit their further applications. Thus, this situation has promoted the rapid exploration and development of various artificial enzyme mimics, including fullerenes, porphyrins, biomolecules, metal complexes, polymers, and functional nanomaterials. [3-6] Among these enzyme-mimetic catalysts (Enz-Cats, also defined as nanozymes in some systems), [4,5,7,8] alkaline metals, transition metals, and lanthanoid components [9-11] have been devoted to extending their applications in the fields of disease diagnosis, [12,13] wound disinfection, [14] and tumor treatments. [15-17] In particular, synthesizing metal-based nanomaterials to engineer Enz-Cats by precisely modulating their catalytic metal centers, sizes, structures, porosities, and compositions has been a long-standing objective, which provides tremendous opportunities to explore highly efficient Enz-Cats and reveal the essential catalytic mechanisms. [18-21] Although some developed Enz-Cats have exhibited efficient in vitro activities, the catalytic performances and selectivity in diverse physiological environments are still vital considerations during the exploration of their further application in biomedical areas. [22-24] Furthermore, the inherent physicochemical characteristics of these Enz-Cats may yield multiple catalytic reactions, such as generating or scavenging reactive oxygen species (ROS) under internal microenvironments Nanomaterial-based enzyme-mimetic catalysts (Enz-Cats) have received considerable attention because of their optimized and enhanced catalytic performances and selectivities in diverse physiological environments compared with natural enzymes. Recently, owing to their molecular/atomic-level catalytic centers, high porosity, large surface area, high loading capacity, and homogeneous structure, metal-organic frameworks (MOFs) have emerged as one of the most promising materials in engineering Enz-Cats. Here, the recent advances in the design of MOF-engineered Enz-Cats, including their preparation methods, composite constructions, structural characterizations, and biomedical applications, are highlighted and commented upon. In particular, the performance, selectivities, essential mechanisms, and potential structure-property relations of these MOF-engineered Enz-Cats in accelerating catalytic reactions are discussed. Some potential biomedical applications of these MOF-engineered Enz-Cats are also breifly proposed. These applications include, for example, tumor therapies, bacterial disinfection, tissue regeneration, and biosensors. Finally, the future opportunities and challenges in emerging research frontiers are thoroughly discussed. Thereby, potential pathways and perspectives for designing future state-of-the-art Enz-Cats in biomedical sciences are offered.

Recent emerged metal–organic frameworks (MOFs), as superior drug carriers, provide novel strategies to combat pathogenic bacterial infections. Although various antibacterial metal ions can be easily introduced in MOFs for chemical bacterial ablation, such a single-model bactericidal method suffers from high-dose use, limited antibacterial efficiency, and slow sterilization rate. Hence, developing a dual bactericidal system is urgently required. Herein, we report an MOF/Ag-derived nanocomposite with efficient metal-ion-releasing capability and robust photo-to-thermal conversion effect for synergistic sterilization. The MOF-derived nanocarbon consisting of metallic zinc and a graphitic-like carbon framework is first synthesized, and then Ag nanoparticles (AgNPs) are evenly introduced via the displacement reaction between Zn and Ag+. Upon near-infrared irradiation, the fabricated nanoagents can generate massive heat to destroy bacterial membranes. Meanwhile, abundant Zn2+ and Ag+ ions are released to make chemical damage to bacterial intracellular substances. Systematic antibacterial experiments reveal that such dual-antibacterial effort can endow the nanoagents with nearly 100% bactericidal ratio for highly concentrated bacteria at a very low dosage (0.16 mg/mL). Furthermore, the nanoagents exhibit less cytotoxicity, which provides potential possibilities for the applications in the biological field. In vivo assessment indicates that the nanocomposites can realize rapid and safe wound sterilization and are expected to be an alternative to antibiotics. Overall, we present an easily fabricated structure-engineered nanocomposite with chemical and photothermal effects for broad-spectrum bacterial sterilization.

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MicroRNAs (miRs) play an important role in regulating gene expression. Limited by their instabilities, miR therapeutics require delivery vehicles. Tetrahedral framework nucleic acids (tFNAs) are potentially applicable to drug delivery because they prominently penetrate tissue and are taken up by cells. However, tFNA‐based miR delivery strategies have failed to separate the miRs after they enter cells, affecting miR efficiency. In this study, an RNase H‐responsive sequence is applied to connect a sticky‐end tFNA (stFNA) and miR‐2861, which is a model miR, to target the expression of histone deacetylase 5 (HDAC5) in bone marrow mesenchymal stem cells. The resultant bioswitchable nanocomposite (stFNA–miR) enables efficient miR‐2861 unloading and deployment after intracellular delivery, thereby inhibiting the expression of HDAC5 and promoting osteogenic differentiation. stFNA–miR also facilitated ideal bone repair via topical injection. In conclusion, a versatile miR delivery strategy is offered for various biomedical applications that necessitate modulation of gene expression.