Because of the high catalytic activities and substrate specificity, natural enzymes have been widely used in industrial, medical, and biological fields, etc. Although promising, they often suffer from intrinsic shortcomings such as high cost, low operational stability, and difficulties of recycling. To overcome these shortcomings, researchers have been devoted to the exploration of artificial enzyme mimics for a long time. Since the discovery of ferromagnetic nanoparticles with intrinsic horseradish peroxidase-like activity in 2007, a large amount of studies on nanozymes have been constantly emerging in the next decade. Nanozymes are one kind of nanomaterials with enzymatic catalytic properties. Compared with natural enzymes, nanozymes have the advantages such as low cost, high stability and durability, which have been widely used in industrial, medical, and biological fields. A thorough understanding of the possible catalytic mechanisms will contribute to the development of novel and high-efficient nanozymes, and the rational regulations of the activities of nanozymes are of great significance. In this review, we systematically introduce the classification, catalytic mechanism, activity regulation as well as recent research progress of nanozymes in the field of biosensing, environmental protection, and disease treatments, etc. in the past years. We also propose the current challenges of nanozymes as well as their future research focus. We anticipate this review may be of significance for the field to understand the properties of nanozymes and the development of novel nanomaterials with enzyme mimicking activities.

Nanozymes: Classification, Catalytic Mechanisms, Activity Regulation, and Applications

Tissue engineering has become a promising strategy for repairing damaged cartilage and bone tissue Among the scaffolds for tissue-engineering applications, injectable hydrogels have demonstrated great potential for use as three-dimensional cell culture scaffolds in cartilage and bone tissue engineering, owing to their high water content, similarity to the natural extracellular matrix (ECM), porous framework for cell transplantation and proliferation, minimal invasive properties, and ability to match irregular defects In this review, we describe the selection of appropriate biomaterials and fabrication methods to prepare novel injectable hydrogels for cartilage and bone tissue engineering In addition, the biology of cartilage and the bony ECM is also summarized Finally, future perspectives for injectable hydrogels in cartilage and bone tissue engineering are discussed

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Injectable hydrogels for cartilage and bone tissue engineering.

Glucose is a key energy supplier and nutrient for tumor growth. Herein, inspired by the glucose oxidase (GOx)-assisted conversion of glucose into gluconic acid and toxic H2 O2 , a novel treatment paradigm of starving-like therapy is developed for significant tumor-killing effects, more effective than conventional starving therapy by only cutting off the energy supply. Furthermore, the generated acidic H2 O2 can oxidize l-Arginine (l-Arg) into NO for enhanced gas therapy. By using hollow mesoporous organosilica nanoparticle (HMON) as a biocompatible/biodegradable nanocarrier for the co-delivery of GOx and l-Arg, a novel glucose-responsive nanomedicine (l-Arg-HMON-GOx) has been for the first time constructed for synergistic cancer starving-like/gas therapy without the need of external excitation, which yields a remarkable H2 O2 -NO cooperative anticancer effect with minimal adverse effect.

Glucose-Responsive Sequential Generation of Hydrogen Peroxide and Nitric Oxide for Synergistic Cancer Starving-Like/Gas Therapy.

The rising dangers of bacterial infections have created an urgent need for the development of a new generation of antibacterial nanoagents and therapeutics. A new near-infrared 808 nm laser-mediated nitric oxide (NO)-releasing nanovehicle (MoS2 -BNN6) is reported through the simple assembly of α-cyclodextrin-modified MoS2 nanosheets with a heat-sensitive NO donor N,N'-di-sec-butyl-N,N'-dinitroso-1,4-phenylenediamine (BNN6) for the rapid and effective treatment of three typical Gram-negative and Gram-positive bacteria (ampicillin-resistant Escherichia coli, heat-resistant Escherichia faecalis, and pathogen Staphylococcus aureus). This MoS2 -BNN6 nanovehicle has good biocompatibility and can be captured by bacteria to increase opportunities of NO diffusion to the bacterial surface. Once stimulated by 808 nm laser irradiation, the MoS2 -BNN6 nanovehicle not only exhibits photothermal therapy (PTT) efficacy but also can precisely control NO release, generating oxidative/nitrosative stress. The temperature-enhanced catalytic function of MoS2 induced by 808 nm laser irradiation simultaneously accelerates the oxidation of glutathione. This acceleration disrupts the balance of antioxidants, ultimately resulting in significant DNA damage to the bacteria. Within 10 min, the MoS2 -BNN6 with enhanced PTT/NO synergetic antibacterial function achieves >97.2% inactivation of bacteria. The safe synergetic therapy strategy can also effectively repair wounds through the formation of collagen fibers and elimination of inflammation during tissue reconstruction.

Functionalized MoS2 Nanovehicle with Near-Infrared Laser-Mediated Nitric Oxide Release and Photothermal Activities for Advanced Bacteria-Infected Wound Therapy.

Featuring high biocompatibility, the emerging field of gas therapy has attracted extensive attention in the medical and scientific communities. Currently, considerable research has focused on the gasotransmitter nitric oxide (NO) owing to its unparalleled dual roles in directly killing cancer cells at high concentrations and cooperatively sensitizing cancer cells to other treatments for synergistic therapy. Of particular note, recent state-of-the-art studies have turned our attention to the chemical design of various endogenous/exogenous stimuli-responsive NO-releasing nanomedicines and their biomedical applications for on-demand NO-sensitized synergistic cancer therapy, which are discussed in this Minireview. Moreover, the potential challenges regarding NO gas therapy are also described, aiming to advance the development of NO nanomedicines as well as usher in new frontiers in this fertile research area.

Stimuli‐Responsive NO Release for On‐Demand Gas‐Sensitized Synergistic Cancer Therapy

A novel sandwich nanomedicine (GO-BNN6) for near-infrared (NIR) light responsive release of nitric oxide (NO) has been constructed by self-assembly of graphene oxide (GO) nanosheets and a NO donor BNN6 through the π-π stacking interaction. The GO-BNN6 nanomedicine has an extraordinarily high drug loading capacity (1.2 mg BNN6 per mg GO), good thermal stability, and high NIR responsiveness. The NO release from GO-BNN6 can be easily triggered and effectively controlled by adjusting the switching, irradiation time and power density of NIR laser. The intracellular NIR-responsive release of NO from the GO-BNN6 nanomedicine causes a remarkable anti-cancer effect.

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Nongyue He

Papers

A novel self-assembled sandwich nanomedicine for NIR-responsive release of NO