Nanozymes in Nanofibrous Mats with Haloperoxidase-like Activity To Combat Biofouling

Synergistic Effects of Insulin-like Growth Factor-1 and Platelet-Derived Growth Factor-BB in Tendon Healing

Tendon ruptures are common musculoskeletal injuries associated with prolonged healing and complications such as adhesion formation and rerupture. Despite advancements in treatment strategies, full functional recovery remains a challenge. Growth factors (GFs) like insulin-like growth factor-1 (IGF-1) and platelet-derived growth factor-BB (PDGF-BB) play key roles in tendon repair and may have synergistic effects when applied together. To support tendon healing, a bioactive electrospun polymer scaffold made of Degrapol® (DP) was developed, incorporating IGF-1, PDGF-BB, or both. A range of in vitro and in vivo analyses were performed to assess scaffold structure, cell behavior, gene expression, metabolism, and biomechanical and adhesion outcomes three weeks post-surgery. Interestingly, the combined application of IGF-1 and PDGF-BB did not simply amplify individual effects but showed a complex interaction. Depending on the parameter and time point, the combination led to either enhanced or reduced responses compared to single-factor treatments, indicating a synergistic modulation rather than a purely additive effect. These findings suggest that the combination of IGF-1 and PDGF-BB can modulate key cellular and molecular processes in tendon regeneration, making this approach a promising strategy to improve tendon healing.

Improved Antifouling and Anticorrosion Performance of CeO2 Nanocoating Prepared by Mussel-Inspired Chemistry

Biofouling, the accumulation of organisms on submerged surfaces, significantly impairs vessel performance and hinders maritime industry development. The development of effective coatings has become an efficient solution to this problem. Cerium oxide nanoparticles (CeO2NPs) were synthesized on dopamine-modified 5083 aluminum alloy (Al) surfaces by mussel-inspired chemistry. The CeO2NPs can be fully exposed to the coating surface using this method, and CeO2 nanocoating exhibited haloperoxidase-like activity. CeO2 nanocoatings have an excellent ability to inhibit the attachment of P. tricornutum, E. coli, and Bacillussp., and their numbers were reduced by 96.03%, 94.41%, and 88.44%, respectively. The outstanding antiadhesion capability of the coating was attributed to its potent antibacterial properties and quorum quenching effect. Furthermore, the CeO2 nanocoating demonstrated outstanding corrosion resistance, with an impedance modulus 46.9 times higher than that of the Al sample. This approach presents a sustainable and environmentally friendly surface modification model for enhancing the performance of antifouling and anticorrosion in aluminum materials.

Fabrication and Characterization of Electrospun DegraPol® Tubes Releasing TIMP-1 Protein to Modulate Tendon Healing

BACKGROUND

Tendon rupture repair can result from fibrotic scar formation through imbalanced ECM deposition during remodeling. The tissue inhibitors of matrix metalloprotease (TIMPs) not only decrease ECM degradation, regulated by matrix metalloproteases (MMPs), but also restrict TGF-β1 activation and thus diminish fibrosis.

METHODS

Rabbit tenocytes (rbTenocytes) and rabbit adipose-derived stem cells (rbASCs) were cultivated under different TIMP-1 concentrations. Proliferation and gene expression were assessed. TIMP-1 was incorporated into emulsion electrospun DegraPol® (DP) tubes that were characterized by SEM for fiber thickness, pore size, and wall thickness. Static and dynamic water contact angles, FTIR spectra, and TIMP-1 release kinetics were determined.

RESULTS

While the proliferation of rbTenocytes and rbACS was not affected by TIMP-1 supplementation in vitro, the gene expression of Col1A1 was increased in rbTenocytes, the gene expression of ki67 was increased in both cell types, the gene expression of tenomodulin was increased in both cell types at 100 ng/mL TIMP-1, and alkaline phosphatase expression ALP rose significantly in rbASCs. Electrospun TIMP-1/DP fibers had a ~5 μm diameter, a ~10 μm pore size, and a mesh thickness of ~200 μm. TIMP-1/DP meshes were more hydrophilic than pure DP meshes. TIMP-1 was released from the meshes with a sustained release of up to 7 days.

CONCLUSIONS

TIMP-1/DP tubes may be used to modulate the fibrotic tissue reaction when applied around conventionally sutured tendon ruptures.

Electrospun nanofibrous membranes meet antibacterial nanomaterials: From preparation strategies to biomedical applications

Electrospun nanofibrous membranes (eNFMs) have been extensively developed for bio-applications due to their structural and compositional similarity to the natural extracellular matrix. However, the emergence of antibiotic resistance in bacterial infections significantly impedes the further development and applications of eNFMs. The development of antibacterial nanomaterials substantially nourishes the engineering design of antibacterial eNFMs for combating bacterial infections without relying on antibiotics. Herein, a comprehensive review of diverse fabrication techniques for incorporating antibacterial nanomaterials into eNFMs is presented, encompassing an exhaustive introduction to various nanomaterials and their bactericidal mechanisms. Furthermore, the latest achievements and breakthroughs in the application of these antibacterial eNFMs in tissue regenerative therapy, mainly focusing on skin, bone, periodontal and tendon tissues regeneration and repair, are systematically summarized and discussed. In particular, for the treatment of skin infection wounds, we highlight the antibiotic-free antibacterial therapy strategies of antibacterial eNFMs, including (i) single model therapies such as metal ion therapy, chemodynamic therapy, photothermal therapy, and photodynamic therapy; and (ii) multi-model therapies involving arbitrary combinations of these single models. Additionally, the limitations, challenges and future opportunities of antibacterial eNFMs in biomedical applications are also discussed. We anticipate that this comprehensive review will provide novel insights for the design and utilization of antibacterial eNFMs in future research.

Mechanical, water contact angle and fiber thickness data for Insulin-like growth gactor-1 (IGF-1) incorporated in electrospun random DegraPolⓇ fibers and IGF-1 impact on tenocyte aspect ratio and gene expression data

The first set of data refers to Insulin-like Growth Factor-1 (IGF-1) protein incorporation via emulsion electrospinning into a DegraPolⓇ random fiber mesh and its characterization. Specifically, the fiber thickness was assessed and compared to pure DegraPolⓇ fibers without IGF-1 (control). Furthermore, the mechanical properties of these meshes were assessed and data on ultimate tensile stress, Young's modulus and ultimate fracture strain are presented for ring specimen and rectangular pieces taken from electrospun tubes in the transverse direction as well as rectangular pieces taken in the axial direction of the electrospun tube. Moreover, the static and the dynamic water contact angles were determined. The second set of data represents morphological aspects, such as the cytoskeletal aspect ratio (i.e. length of the cell divided by its width) for rabbit Achilles tenocytes stimulated in vitro with 1, 10, and 100 ng/mL IGF-1 supplementation compared to the corresponding cell culture without IGF-1 (control). Furthermore, qPCR was performed and collagen I, ki67 and tenomodulin gene expression data are presented for rabbit Achilles tenocytes in vitro with 0.1, 1 and 10 ng/mL IGF-1 supplementation, respectively, as well as with a supplementation of released IGF-1 from the DegraPol mesh (concentration was 1 ng/mL).

Defect Engineered Bi2Te3 Nanosheets with Enhanced Haloperoxidase Activity for Marine Antibiofouling

Defective bismuth telluride (Bi2Te3) nanosheets, an artificial nanozyme mimicking haloperoxidase activity (hPOD), show promise as eco-friendly, bactericidal, and antimicrofouling materials by enhancing cytotoxic hypohalous acid production from halides and H2O2. Microscopic and spectroscopic characterization reveals that controlled NaOH (upto X = 250 µL) etching of the nearly inactive non-transition metal chalcogenide Bi2Te3 nanosheets creates controlled defects (d), such as Bi3+species, in d-Bi2Te3-X that induces enhanced hPOD activity. d-Bi2Te3-250 exhibits approximately eight-fold improved hPOD than the as-grown Bi2Te3 nanosheets. The antibacterial activity of d-Bi2Te3-250 nanozymes, studied by bacterial viability, show 1, and 45% viability for Staphylococcus aureus and Pseudomonas aeruginosa, respectively, prevalent in marine environments. The hPOD mechanism is confirmed using scavengers, implicating HOBr and singlet oxygen for the effect. The antimicrofouling property of the d-Bi2Te3-250 nanozyme has been studied on Pseudomonas aeruginosa biofilm in a lab setting by multiple assays, and also on titanium (Ti) plates coated with the nanozyme mixed commercial paint, exposed to seawater in a real setting. All studies, including direct microscopic evidence, exhibit inhibition of microfouling, up to ≈73%, in the presence of nanozymes. This approach showcases that defect engineering can induce antibacterial, and antimicrofouling activity in non-transition metal chalcogenides, offering an inexpensive alternative to noble metals.

Nanozymes and their biomolecular conjugates as next-generation antibacterial agents: A comprehensive review

Antimicrobial resistance (AMR), the ability of bacterial species to develop resistance against exposed antibiotics, has gained immense global attention in the past few years. Bacterial infections are serious health concerns affecting millions of people annually worldwide. Therefore, developing novel antibacterial agents that are highly effective and avoid resistance development is imperative. Among various strategies, recent developments in nanozyme technology have shown promising results as antibacterials in several antibiotic-sensitive and resistant bacterial species. Nanozymes offer several advantages over corresponding natural enzymes, such as inexpensive, stable, multifunctional, tunable catalytic properties, etc. Although the use of nanozymes as antibacterial agents has provided promising results, the specific biomolecule-conjugated nanozymes have shown further improvement in catalytic performance and associated antibacterial efficacy. The exclusive design of functional nanozymes with theranostic potential is found to simultaneously inhibit the growth and image of AMR bacterial species. This review comprehensively summarizes the history of nanozymes, their classification, biomolecules conjugated nanozyme, and their mechanism of enzyme-mimetic activity and associated antibacterial activity in antibiotic-sensitive and resistant species. The futureneeds to effectively engineer the existing or new nanozymes to curb AMR have also been discussed.

Ceria nanoparticles immobilized with self-assembling peptide for biocatalytic applications

Peptide-based artificial enzymes exhibit structure and catalytic mechanisms comparable to natural enzymes but they suffer from limited reusability due to their existence in homogenous solutions. Immobilization of self-assembling peptides on the surface of nanoparticles can be used to overcome limitations associated with artificial enzymes. A high, local density of peptides can be obtained on nanoparticles to exert cooperative or synergistic effects, resulting in an accelerated rate of reaction, distinct catalytic properties, and excellent biocompatibility. In this work, we have immobilized a branched, self-assembled, and nanofibrous catalytic peptide, (C12-SHD)2KK(Alloc)-NH2, onto thiolated ceria nanoparticles to generate a heterogeneous catalyst with an enhanced number of catalytic sites. This artificial enzyme mimics the activities of esterase, phosphatase, and haloperoxidase enzymes and the catalytic efficiency remains nearly unaltered when reused. The enzyme-mimicking property is investigated for pesticide detection, bone regeneration, and antibiofouling applications. Overall, this work presents a facile approach to develop a multifunctional heterogeneous biocatalyst that addresses the challenges associated with unstable peptide-based homogeneous catalysts and, thus, shows a strong potential for industrial applications.

Hyaluronic acid/PEO electrospun tube reduces tendon adhesion to levels comparable to native tendons - An in vitro and in vivo study

A major problem after tendon injury is adhesion formation to the surrounding tissue leading to a limited range of motion. A viable strategy to reduce adhesion extent is the use of physical barriers that limit the contact between the tendon and the adjacent tissue. The purpose of this study was to fabricate an electrospun bilayered tube of hyaluronic acid/polyethylene oxide (HA/PEO) and biodegradable DegraPol® (DP) to improve the anti-adhesive effect of the implant in a rabbit Achilles tendon full laceration model compared to a pure DP tube. Additionally, the attachment of rabbit tenocytes on pure DP and HA/PEO containing scaffolds was tested and Scanning Electron Microscopy, Fourier-transform Infrared Spectroscopy, Differential Scanning Calorimetry, Water Contact Angle measurements, and testing of mechanical properties were used to characterize the scaffolds. In vivo assessment after three weeks showed that the implant containing a second HA/PEO layer significantly reduced adhesion extent reaching levels comparable to native tendons, compared with a pure DP implant that reduced adhesion formation only by 20 %. Tenocytes were able to attach to and migrate into every scaffold, but cell number was reduced over two weeks. Implants containing HA/PEO showed better mechanical properties than pure DP tubes and with the ability to entirely reduce adhesion extent makes this implant a promising candidate for clinical application in tendon repair.

Chemically Modulating Ceria-Based Artificial Haloperoxidase for Enhanced Antibacterial Activity and Biofilm Inhibition

Ceria (CeO2) nanoparticles with haloperoxidase (HPO)-like activity have gained attention as a biologically benign antifoulant. 3,4-Dihydroxy-l-phenylalanine (DOPA), a main composition in mussel foot proteins, plays a crucial role in the biofouling process. However, the impact on the HPO-like activity and antifouling performance of CeO2 nanoparticles when DOPA molecules adsorb on them remains unexplored. This interesting question warrants investigation, particularly considering that it may occur in an actual marine environment. Herein, the interaction between DOPA and CeO2 is explored. Despite the higher Ce3+ fractions and the lower band gap energies due to the electron transfer from DOPA to the CeO2 surface, DOPA still had a slightly negative effect on the HPO-like activity of CeO2 since they decreased the exposed Ce3+ sites. The DOPA-CeO2 nanocomposites with HPO-like activities could kill bacteria and trigger quorum-sensing signaling quenching, achieving a biofilm inhibition performance. Amazingly, 0.1% DOPA-CeO2 nanocomposite exhibited higher antibacterial activity and better biofilm suppression activities due to its HPO-like activity and positive zeta potential. The remarkable results demonstrated that DOPA, as a participant in the biofouling process, could enhance the antibacterial activity and antifouling performance of CeO2 nanoparticles at an appropriate concentration.

Nanomaterials with Enzyme-like Properties for Combatting Foodborne Pathogen Infections: Classifications, Mechanisms, and Applications in Food Preservation

During the transportation and storage of food, foodborne spoilage caused by bacterial and biofilm infection is prone to occur, leading to issues such as short shelf life, economic loss, and sensory quality instability. Therefore, the development of novel and efficient antibacterial agents capable of efficiently inhibiting bacteria throughout various stages of food processing, transportation, and storage is strongly recommended by researchers. The emergence of nanozymes is considered to be an effective candidate for inhibiting foodborne bacteria agents in the food industry. As potent antibacterial agents, nanozymes have the advantages of low cost, high stability, strong broad-spectrum antibacterial ability, and biocompatibility. Herein, we aim to summarize the classification status of various nanozymes. Furthermore, the general catalytic bacteriostatic mechanism of nanozymes against intracellular bacteria, planktonic bacteria, and biofilm activities are highlighted, mainly concerning the destruction of cell walls and/or membranes, reactive oxygen species regulation, HOBr/Cl generation, damage of intracellular components, and so forth. In particular, the review focuses on the pivotal role of nanozymes as antibacterial agents and delivery vehicles in the fields of food preservation applications. We look forward to the future prospects, especially in the field of food preservation, to promote broader applications based on antimicrobial nanozymes.

Multi-Enzyme Activity of MIL-101 (Fe)-Derived Cascade Nano-Enzymes for Antitumor and Antimicrobial Therapy

The clinical application of oncology therapy is hampered by high glutathione concentrations, hypoxia, and inefficient activation of cell death mechanisms in cancer cells. In this study, Fe and Mo bimetallic sulfide nanomaterial (FeS2@MoS2) based on metal-organic framework structure is rationally prepared with peroxidase (POD)-, catalase (CAT)-, superoxide dismutase (SOD)-like activities and glutathione depletion ability, which can confer versatility for treating tumors and mending wounds. In the lesion area, FeS2@MoS2 with SOD-like activity can facilitate the transformation of superoxide anions (O2 -) to hydrogen peroxide (H2O2), and then the resulting H2O2 serves as a substrate for the Fenton reaction with FMS to produce highly toxic hydroxyl radicals (∙OH). Simultaneously, FeS2@MoS2 has an ability to deplete glutathione (GSH) and catalyze the decomposition of nicotinamide adenine dinucleotide phosphate (NADPH) to curb the regeneration of GSH from the source. Thus it can realize effective tumor elimination through synergistic apoptosis-ferroptosis strategy. Based on the alteration of the H2O2 system, free radical production, glutathione depletion and the alleviation of hypoxia in the tumor microenvironment, FeS2@MoS2 NPS can not only significantly inhibit tumors in vivo and in vitro, but also inhibit multidrug-resistant bacteria and hasten wound healing. It may open the door to the development of cascade nanoplatforms for effective tumor treatment and overcoming wound infection.

Disruption of Communication: Recent Advances in Antibiofilm Materials with Anti-Quorum Sensing Properties

Biofilm contamination presents a significant threat to public health, the food industry, and aquatic/marine-related applications. In recent decades, although various methods have emerged to combat biofilm contamination, the intricate and persistent nature of biofilms makes complete eradication challenging. Therefore, innovative alternative solutions are imperative for addressing biofilm formation. Instead of solely focusing on the eradication of mature biofilms, strategically advantageous measures involve the delay or prevention of biofilm formation on surfaces. Quorum sensing, a communication system enabling bacteria to coordinate their behavior based on population density, plays a pivotal role in biofilm formation for numerous microbial species. Materials possessing antibiofilm properties that target quorum sensing have gained considerable attention for their potential to prevent biofilm formation. This Review consolidates recent research progress on the utilization of materials with antiquorum sensing properties for combating biofilm formation. These materials can be categorized into three distinct types: (i) antibiofilm nanomaterials, (ii) antibiofilm surfaces, and (iii) antibiofilm hydrogels with antiquorum sensing capabilities. Finally, the Review concludes with a brief discussion of current challenges and outlines potential avenues for future research.

Polyoxometalate-Guanosine Monophosphate Hydrogels with Haloperoxidase-like Activity for Antibacterial Performance

Haloperoxidases represent an important class of enzymes that nature adopts as a defense mechanism to combat the colonial buildup of microorganisms on surfaces, commonly known as biofouling. Subsequently, there has been tremendous focus on the development of artificial haloperoxidase mimics that can catalyze the oxidation of X- (halide ion) in the presence of H2O2 to form HOX. The natural intermediate HOX disrupts the bacterial quorum sensing, thus preventing biofilm formation. Herein, we report a simple method for the formation of supramolecular hydrogels through the self-assembly of Keggin-structured polyoxometalates, phosphotungstic acid, and silicotungstic acid with the small biomolecule guanosine monophosphate (GMP) in an aqueous medium. The polyoxometalate-GMP hydrogels that contained highly entangled nanofibers were mechanically robust and showed thixotropic properties. The gelation of the polyoxometalates with GMP not only rendered manifold enhancement in biocompatibility but also the fibril network in the hydrogel provided high water wettability and the polyoxometalates acted as an efficient haloperoxidase mimic to trigger oxidative iodination, as demonstrated by a haloperoxidase assay. The antifouling activity of the phosphotungstic acid-GMP hydrogel was demonstrated against both Gram-positive and Gram-negative bacteria, which showed enhanced antibacterial performance of the hydrogel as compared to the polyoxometalate alone. We envision that the polyoxometalate-GMP hydrogels may facilitate mechanically robust coatings in a simple pathway that can be useful for antifouling applications.

Tailoring the Surface and Composition of Nanozymes for Enhanced Bacterial Binding and Antibacterial Activity

With the advantages of diverse structures, tunable enzymatic activity, and high stability, nanozymes are widely used in medicine, chemistry, food, environment, and other fields. As an alternative to traditional antibiotics, nanozymes attract more and more attention from the scientific researchers in recent years. Developing nanozymes-based antibacterial materials opens up a new avenue for the bacterial disinfection and sterilization. In this review, the classification of nanozymes and their antibacterial mechanisms are discussed. The surface and composition of nanozymes are critical for the antibacterial efficacy, which can be tailored to enhance both the bacterial binding and the antibacterial activity. On the one hand, the surface modification of nanozymes enables binding and targeting of bacteria that improves the antibacterial performance of nanozymes including the biochemical recognition, the surface charge, and the surface topography. On the other hand, the composition of nanozymes can be modulated to achieve enhanced antibacterial performance including the single nanozyme-mediated synergistic and multiple nanozymes-mediated cascade catalytic antibacterial applications. In addition, the current challenges and future prospects of tailoring nanozymes for antibacterial applications are discussed. This review can provide insights into the design of future nanozymes-based materials for the antibacterial treatments.

Light-gated specific oxidase-like activity of a self-assembled Pt(II) nanozyme for environmental remediation

Artificial enzyme equivalents, also known as nanozymes, are a practical tool for environmental remediation when compared to their natural counterparts due to their high operational stability, efficiency, and cost-effectiveness. Specific oxidase mimicking nanozymes are well suited to degrade toxic chemicals from industrial waste such as phenols and azo dyes. Therefore, photocatalytic nanozymes using visible/sunlight would provide a viable strategy for sustainable environmental remediation. Herein, we introduce an aggregation-induced emissive Pt(II) complex, which self-assembles in water providing NanoPtA nanotapes. These structures exhibit a specific oxidase-like nanozyme activity driven by light. The NanoPtA structure assists in the photogeneration of singlet oxygen in water via a triplet excited 3MMLCT state, leading to a specific oxidase-like activity instead of a peroxidase-like activity. The self-assembled nanozyme showed great stability under harsh environmental conditions and exhibited photo-induced specific oxidase-mimetic activity, which was considerably more efficient than the natural enzyme or other specific nanozymes. We demonstrated efficient NanoPtA-induced photocatalytic degradation of various phenolic compounds and azo dyes within 5-10 minutes of light irradiation. Notably, the system operates under sunlight and exhibits reusability over twenty cycles of catalytic reactions. Another fascinating aspect of NanoPtA is the unaltered catalytic performance for more than 75 days, providing a robust enzyme-equivalent for practical sustainable environmental remediation.

Recent Advances in Nanozyme-Mediated Strategies for Pathogen Detection and Control

Pathogen detection and control have long presented formidable challenges in the domains of medicine and public health. This review paper underscores the potential of nanozymes as emerging bio-mimetic enzymes that hold promise in effectively tackling these challenges. The key features and advantages of nanozymes are introduced, encompassing their comparable catalytic activity to natural enzymes, enhanced stability and reliability, cost effectiveness, and straightforward preparation methods. Subsequently, the paper delves into the detailed utilization of nanozymes for pathogen detection. This includes their application as biosensors, facilitating rapid and sensitive identification of diverse pathogens, including bacteria, viruses, and plasmodium. Furthermore, the paper explores strategies employing nanozymes for pathogen control, such as the regulation of reactive oxygen species (ROS), HOBr/Cl regulation, and clearance of extracellular DNA to impede pathogen growth and transmission. The review underscores the vast potential of nanozymes in pathogen detection and control through numerous specific examples and case studies. The authors highlight the efficiency, rapidity, and specificity of pathogen detection achieved with nanozymes, employing various strategies. They also demonstrate the feasibility of nanozymes in hindering pathogen growth and transmission. These innovative approaches employing nanozymes are projected to provide novel options for early disease diagnoses, treatment, and prevention. Through a comprehensive discourse on the characteristics and advantages of nanozymes, as well as diverse application approaches, this paper serves as a crucial reference and guide for further research and development in nanozyme technology. The expectation is that such advancements will significantly contribute to enhancing disease control measures and improving public health outcomes.

Electrospun PA6 Nanofibers Bearing the CeO2 Dephosphorylation Catalyst

Two types of CeO₂ nanoparticles (CeNPs) prepared by low-temperature (<100 °C) precipitation methods in water were successfully immobilized in a matrix of electrospun PA6 nanofibers. The colloidal solutions of CeNPs in AcOH were directly mixed with the polymer solution before the needle electrospinning process, thereby achieving their good dispersion in the nanofibers. CeNPs embedded in the structure and on the surface of nanofibers exposing their reactive surfaces showed robust dephosphorylation catalytic activity, as demonstrated by monitoring the hydrolytic cleavage of three phosphodiester molecules (p-NP-TMP, p-NPPC, BNPP) in water by the HPLC method. This procedure allowed us to study the kinetics and mechanism of the hydrolytic cleavage and the ability of immobilized CeNPs to cleave different types of P-O bonds. One of the main hydrolysis products, p-nitrophenol, was effectively adsorbed on PA6 nanofibers, which may allow the selective separation of the degradation products after hydrolysis.

Bioactive and Elastic Emulsion Electrospun DegraPol Tubes Delivering IGF-1 for Tendon Rupture Repair

Tendon injuries can result in two major drawbacks. Adhesions to the surrounding tissue may limit the range of motion, while fibrovascular scar formation can lead to poor biomechanical outcomes. Prosthetic devices may help to mitigate those problems. Emulsion electrospinning was used to develop a novel three-layer tube based on the polymer DegraPol (DP), with incorporated insulin-like growth factor-1 (IGF-1) in the middle layer. Scanning electron microscopy was utilized to assess the fiber diameter in IGF-1 containing pure DP meshes. Further characterization was performed with Fourier Transformed Infrared Spectroscopy, Differential Scanning Calorimetry, and water contact angle, as well as through the assessment of mechanical properties and release kinetics from ELISA, and the bioactivity of IGF-1 by qPCR of collagen I, ki67, and tenomodulin in rabbit Achilles tenocytes. The IGF-1-containing tubes exhibited a sustained release of the growth factor up to 4 days and showed bioactivity by significantly upregulated ki67 and tenomodulin gene expression. Moreover, they proved to be mechanically superior to pure DP tubes (significantly higher fracture strain, failure stress, and elastic modulus). The novel three-layer tubes intended to be applied over conventionally sutured tendons after a rupture may help accelerate the healing process. The release of IGF-1 stimulates proliferation and matrix synthesis of cells at the repair site. In addition, adhesion formation to surrounding tissue can be reduced due to the physical barrier.

One stone, two birds: A Cu-S cluster as a laccase-mimicking nanozyme and sulfite activator for phenol remediation in marine environments

Phenols are infamous pollutants in marine environments and present a grave danger to human health, which makes their efficient detection and removal serious issues. Colorimetry is a simple method for detecting phenols in water because phenols can be oxidized by natural laccase and generate a brown product. However, high cost and poor stability impede the wide-spread implementation of natural laccase in phenol detection. To reverse this adverse situation, a nanoscale Cu-S cluster, Cu₄(MPPM)₄ (Cu₄S₄, MPPM = 2-mercapto-5-n-propylpyrimidine), is synthesized. As a stable and inexpensive nanozyme, Cu₄S₄ shows excellent laccase-mimicking activity and prompts the oxidation of phenols. This characteristic makes Cu₄S₄ a perfect option for phenol detection with colorimetry. In addition, Cu₄S₄ also exhibits sulfite activation properties. It can degrade phenols and other pollutants with advanced oxidation processes (AOPs). Theoretical calculations show good laccase-mimicking and sulfite activation properties originating from appropriate interactions between Cu₄S₄ and substrates. We anticipate that the phenol detection and degradation characteristics of Cu₄S₄ make it a promising material to be used for practical phenol remediation in water environments.

N-Doped Carbon/CeO2 Composite as a Biomimetic Catalyst for Antibacterial Application

Exploring new and high efficiency mimic enzymes is a vital and novel strategy for antibacterial application. Haloperoxidase-like enzymes have attracted wide attention thanks to their amazing catalytic property for hypohalous acid generation from hydrogen peroxide and halides. However, few materials have displayed halogenating catalytic performance until now. Herein, we synthesized N-doped C/CeO₂ (N-C/CeO₂) composite materials by a combination of the liquid and solid-state method. N-C/CeO₂ can possess haloperoxidase-like catalytic activity by catalyzing the bromination of organic signaling compounds (phenol red) with H₂O₂ at a wide range of temperatures (20 °C to 55 °C), with a solution color changing from yellow to blue. Meanwhile, it exhibits high catalytic stability/recyclability in the catalytic reaction. The synthesized N-C/CeO₂ composite can effectively catalyze the oxidation of Br^- with H₂O₂ to produce HBrO without the presence of phenol red. The produced HBrO can resist typical marine bacteria like Pseudomonas aeruginosa. This study provides an efficient biomimetic haloperoxidase and a novel sustainable method for antibacterial application.

Nanozyme-based pollutant sensing and environmental treatment: Trends, challenges, and perspectives

Nanozymes are defined as nanomaterials exhibiting enzyme-like properties, and they possess both catalytic functions and nanomaterial's unique physicochemical characteristics. Due to the excellent stability and improved catalytic activity in comparison to natural enzymes, nanozymes have established a wide base for applications in environmental pollutants monitoring and remediation. Nanozymes have been applied in the detection of heavy metal ions, molecules, and organic compounds, both quantitatively and qualitatively. Additionally, within the natural environment, nanozymes can be employed for the degradation of organic and persistent pollutants such as antibiotics, phenols, and textile dyes. Further, the potential sphere of applications for nanozymes traverses from indoor air purification to anti-biofouling agents, and even they show promise in combatting pathogenic bacteria. However, nanozymes may have inherent toxicity, which can restrict their widespread utility. Thus, it is important to evaluate and monitor the interaction and transformation of nanozymes towards biosphere damage when employed within the natural environment in a cradle-to-grave manner, to assure their utmost safety. In this context, various studies have concluded that the green synthesis of nanozymes can efficiently overcome the toxicity limitations in real life applications, and nanozymes can be well utilized in the sensing and degradation of several toxic pollutants including metal ions, pesticides, and chemical warfare agents. In this seminal review, we have explored the great potential of nanozymes, whilst addressing a range of concerns, which have often been overlooked and currently restrict widespread applications and commercialization of nanozymes.

Nanomaterials against intracellular bacterial infection: from drug delivery to intrinsic biofunction

Fighting intracellular bacteria with strong antibiotics evading remains a long-standing challenge. Responding to and regulating the infectious microenvironment is crucial for treating intracellular infections. Sophisticated nanomaterials with unique physicochemical properties exhibit great potential for precise drug delivery towards infection sites, along with modulating infectious microenvironment via their instinct bioactivity. In this review, we first identify the key characters and therapeutic targets of intracellular infection microenvironment. Next, we illustrate how the nanomaterials physicochemical properties, such as size, charge, shape and functionalization affect the interaction between nanomaterials, cells and bacteria. We also introduce the recent progress of nanomaterial-based targeted delivery and controlled release of antibiotics in intracellular infection microenvironment. Notably, we highlight the nanomaterials with unique intrinsic properties, such as metal toxicity and enzyme-like activity for the treatment of intracellular bacteria. Finally, we discuss the opportunities and challenges of bioactive nanomaterials in addressing intracellular infections.

Temporally Controlled Multienzyme Catalysis Using a Dissipative Supramolecular Nanozyme

The development of superior functional enzyme mimics (nanozymes) is essential for practical applications, including point-of-care diagnostics, biotechnological applications, biofuels, and environmental remediation. Nanozymes with the ability to control their catalytic activity in response to external fuels offer functionally valuable platforms mimicking nonequilibrium systems in nature. Herein, we fabricated a supramolecular coordination bonding-based dynamic vesicle that exhibits multienzymatic activity. The supramolecular nanozyme shows effective laccase-like catalytic activity with a K_M value better than the native enzyme and higher stability in harsh conditions. Besides, the nanostructure demonstrates an efficient peroxidase-like activity with NADH peroxidase-like properties. Generation of luminescence from luminol and oxidation of dopamine are efficiently catalyzed by the nanozyme with high sensitivity, which is useful for point-of-care detections. Notably, the active nanozyme exhibits dynamic laccase-mimetic activity in response to pH variation, which has never been explored before. While a neutral/high pH leads to the self-assembly, a low pH disintegrates the assembled nanostructures and consequently turns off the nanozyme activity. Altogether, the self-assembled Cu²⁺-based vesicular nanostructure presents a pH-fueled dissipative system demonstrating effective temporally controlled multienzymatic activity.

Tuning ceria catalysts in aqueous media at the nanoscale: how do surface charge and surface defects determine peroxidase- and haloperoxidase-like reactivity

Designing the shape and size of catalyst particles, and their interfacial charge, at the nanometer scale can radically change their performance. We demonstrate this with ceria nanoparticles. In aqueous media, nanoceria is a functional mimic of haloperoxidases, a group of enzymes that oxidize organic substrates, or of peroxidases that can degrade reactive oxygen species (ROS) such as H₂O₂ by oxidizing an organic substrate. We show that the chemical activity of CeO_2-x nanoparticles in haloperoxidase- and peroxidase-like reactions scales with their active surface area, their surface charge, given by the ζ-potential, and their surface defects (via the Ce³⁺/Ce⁴⁺ ratio). Haloperoxidase-like reactions are controlled through the ζ-potential as they involve the adsorption of charged halide anions to the CeO₂ surface, whereas peroxidase-like reactions without charged substrates are controlled through the specific surface area S_BET. Mesoporous CeO_2-x particles, with large surface areas, were prepared via template-free hydrothermal reactions and characterized by small-angle X-ray scattering. Surface area, ζ-potential and the Ce³⁺/Ce⁴⁺ ratio are controlled in a simple and predictable manner by the synthesis time of the hydrothermal reaction as demonstrated by X-ray photoelectron spectroscopy, sorption and ζ-potential measurements. The surface area increased with synthesis time, whilst the Ce³⁺/Ce⁴⁺ ratio scales inversely with decreasing ζ-potential. In this way the catalytic activity of mesoporous CeO_2-x particles could be tailored selectively for haloperoxidase- and peroxidase-like reactions. The ease of tuning the surface properties of mesoporous CeO_2x particles by varying the synthesis time makes the synthesis a powerful general tool for the preparation of nanocatalysts according to individual needs.

Antifouling coatings can reduce algal growth while preserving coral settlement

In the early stages after larval settlement, coral spat can be rapidly overgrown and outcompeted by algae, reducing overall survival for coral reef replenishment and supply for restoration programs. Here we investigated three antifouling (AF) coatings for their ability to inhibit algal fouling on coral settlement plugs, a commonly-used restoration substrate. Plugs were either fully or partially coated with the AF coatings and incubated in mesocosm systems with partial recirculation for 37 days to track fouling succession. In addition, settlement of Acropora tenuis larvae was measured to determine whether AF coatings were a settlement deterrent. Uncoated control plugs became heavily fouled, yielding only 4–8% bare substrate on upper surfaces after 37 days. During this period, an encapsulated dichlorooctylisothiazolinone (DCOIT)-coating was most effective in reducing fouling, yielding 61–63% bare substrate. Antiadhesive and cerium dioxide (CeO_2−x) nanoparticle (NP) coatings were less effective, yielding 11–17% and 2% bare substrate, respectively. Average settlement of A. tenuis larvae on the three types of AF-coated plugs did not statistically differ from settlement on uncoated controls. However, settlement on the NP-coating was generally the highest and was significantly higher than settlement found on the antiadhesive- and DCOIT-coating. Furthermore, on plugs only partially-covered with AF coatings, larval settlement on coated NP- areas was significantly higher than settlement on coated antiadhesive- and DCOIT-areas. These results demonstrate that AF coatings can reduce fouling intensity on biologically-relevant timescales while preserving robust levels of coral settlement. This represents an important step towards reducing fine-scale competition with benthic fouling organisms in coral breeding and propagation.

Cationized silica ceria nanocomposites to target biofilms in chronic wounds

Altered wound healing is a major challenge faced by both developed and developing nations. Biofilm formation has been identified as one of the causative factors for the progression of chronic wounds. The spread of biofilm is controlled by inhibiting the biofilm formation or disrupting the mature biofilm. Functional nanomaterials/enzymes with antimicrobial effects, such as metal oxides, rare earth metals, and carbon nanoparticles have been investigated to treat biofilm and overcome the drawbacks associated with the antibiotic therapy. Cerium oxide nanoparticles (CNPs) have drawn significant attention as a promising antimicrobial agent owing to their antibacterial, enzyme-mimetic, and crystalline properties but they suffer from poor colloidal stability and dispersity in an aqueous environment and size-dependent function. In this work, we have developed a functionalized silica ceria nanocomposite (FSC), as an antibiotic-free system, to treat biofilms. The FSC possesses a high surface area of mesoporous silica nanoparticles (MSNs) combined with the intrinsic antibacterial activity of cerium oxide for biofilm inhibition. The nanocomposite was fabricated using silica and ceria precursors, and it exhibited a high surface area of 436 m²/g and an average particle size of around 450 nm. The physical and chemical properties of nanocomposite were characterized using FTIR, XRD, UV-Vis, BET, EDX, and XPS analysis. It exhibited a potent antioxidant activity (86%), positive haloperoxidase mimetic property, and broad-spectrum antibacterial activities. It showed 99.9% inhibition against S. aureus (Gram-positive) and 81% inhibition against E. coli (Gram-negative) within 12 and 24 h along with the significant inhibition of biofilm formation (80%) as well as the disruptive effect against the established biofilm (77%) of S. aureus. Cell viability assays indicated the proliferative nature of composite in normal basal conditions and increased cell viability (97%) in the presence of oxidative stress. Despite being a cationic nanomaterial, it showed a good hemocompatibility against human blood and caused complete wound closure in mouse fibroblast cell line within 24 h. The functionalized silica ceria nanocomposite developed has a strong potential in chronic wound healing applications.

Recent Trends in Composite Nanozymes and Their Pro-Oxidative Role in Therapeutics

Nanozymes are inorganic nanostructures whose enzyme mimic activities are increasingly explored in disease treatment, taking inspiration from natural enzymes. The catalytic ability of nanozymes to generate reactive oxygen species can be used for designing effective antimicrobials and antitumor therapeutics. In this context, composite nanozymes are advantageous, particularly because they integrate the properties of various nanomaterials to offer a single multifunctional platform combining photodynamic therapy (PDT), photothermal therapy (PTT), and chemodynamic therapy (CDT). Hence, recent years have witnessed great progress in engineering composite nanozymes for enhanced pro-oxidative activity that can be utilized in therapeutics. Therefore, the present review traverses over the newer strategies to design composite nanozymes as pro-oxidative therapeutics. It provides recent trends in the use of composite nanozymes as antibacterial, antibiofilm, and antitumor agents. This review also analyzes various challenges yet to be overcome by pro-oxidative composite nanozymes before being used in the field.

Defect-controlled halogenating properties of lanthanide-doped ceria nanozymes

Marine organisms combat bacterial colonization by biohalogenation of signaling compounds that interfere with bacterial communication. These reactions are catalyzed by haloperoxidase enzymes, whose activity can be emulated by nanoceria using milli- and micromolar concentrations of Br^- and H₂O₂. We show that the haloperoxidase-like activity of nanoceria can greatly be enhanced by Ln substitution in Ce_1-xLn_xO_2-x/2. Non-agglomerated nanosized Ce_1-xLn_xO_2-x/2 (Ln = Pr, Tb, particle size < 10 nm) was prepared mechanochemically from CeCl₃ and Na₂CO₃ followed by short calcination. Lanthanide metals could be incorporated into the CeO₂ host without solubility limit, as shown for Tb. The distribution of the Ln³⁺ defect sites in the CeO₂ host structure was analyzed by electron spin resonance spectroscopy. Ce³⁺ and superoxide O₂^- species are present at surface sites. Their formation is promoted by increasing dopant concentration. Ce_1-xLn_xO_2-x/2 was prepared in copious amounts by ball-milling. This energy-saving and residue-free method can be upscaled to industrial scale. The surface defect chemistry of Ce_1-xLn_xO_2-x/2 was unravelled by vibrational spectroscopy. It is associated with the mechanochemical preparation and leads to enhanced catalytic activity. Although Ce_0.9Pr_0.1O_1.95 had a lower BET surface area than pure CeO₂, its catalytic activity, calibrated by oxidative bromination of phenol red, was much higher because the ζ-potential increased from 15 mV (for CeO₂) to 30 mV (for Ce_0.9Pr_0.1O_1.95). This facilitates adsorption of Br^- in aqueous conditions and explains the high catalytic activity of the Ln-substituted CeO₂. Ce_1-xLn_xO_2-x/2 is an effective and "green" nanoparticle haloperoxidase mimic for antifouling applications, as no chemicals other than the ubiquitous Br^- and H₂O₂ (generated in daylight) are required, and only natural metabolites are released into the environment.

Insights on catalytic mechanism of CeO2 as multiple nanozymes

CeO₂ with the reversible Ce³⁺/Ce⁴⁺ redox pair exhibits multiple enzyme-like catalytic performance, which has been recognized as a promising nanozyme with potentials for disease diagnosis and treatments. Tailorable surface physicochemical properties of various CeO₂ catalysts with controllable sizes, morphologies, and surface states enable a rich surface chemistry for their interactions with various molecules and species, thus delivering a wide variety of catalytic behaviors under different conditions. Despite the significant progress made in developing CeO₂-based nanozymes and their explorations for practical applications, their catalytic activity and specificity are still uncompetitive to their counterparts of natural enzymes under physiological environments. With the attempt to provide the insights on the rational design of highly performed CeO₂ nanozymes, this review focuses on the recent explorations on the catalytic mechanisms of CeO₂ with multiple enzyme-like performance. Given the detailed discussion and proposed perspectives, we hope this review can raise more interest and stimulate more efforts on this multi-disciplinary field.

Nanofibrous Photocatalytic Membranes Based on Tailored Anisotropic Gold/Ceria Nanoparticles

The combination of plasmonic nanoparticles with semiconductor photocatalysts is a good strategy for synthesizing highly efficient photocatalysts. Such binary nanoparticles have demonstrated enhanced catalytic activity in comparison to either plasmonic catalysts or semiconductor catalysts. However, problematic recovery and limited long-term colloidal stability of those nanoparticles in suspension limit their wide use in catalysis. To palliate to such limitations, we embedded binary nanoparticles in polymer fibers to design photocatalytic membranes. First, we used the selective over-growth of crystalline cerium oxide on the gold nanoparticle template with distinct shapes. Gold nanospheres, gold nanorods, and gold nanotriangles were used as the template for the growth of the cerium oxide domains. Then, the resulting nanoparticles were used to catalyze model reactions in suspensions. The gold nanoparticles covered with patches of cerium oxide outperformed the fully covered and naked nanoparticles in terms of catalytic efficiency. Finally, the most efficient binary nanostructures were successfully embedded in nanofibrous membranes by colloidal electrospinning and used in water remediation experiments in a flow-through reactor.

Biocatalytic Nanomaterials: A New Pathway for Bacterial Disinfection

Clinical treatment of pathogenic infection has emerged as a growing challenge in global public health. Such treatment is currently limited to antibiotics, but abuse of antibiotics have induced multidrug resistance and high fatality rates in anti-infection therapies. Thus, it is vital to develop alternative bactericidal agents to open novel disinfection pathways. Drawing inspiration from elements of the human immune system that show great potential for controlling pathogens or regulating cell apoptosis, the design of biocatalytic nanomaterials (BCNs) have provided unrivaled opportunities for future antibacterial therapies. More significantly, BCNs exhibit various superior properties to immune cells and natural enzymes, such as higher biocatalytic performance, extraordinary stability against harsh conditions, and scalable production. In this review, the most recent efforts toward developing BCN-based biomedical applications in combating bacterial infections are focused upon. BCNs' antibacterial mechanisms, the classification of BCNs, antibacterial activities that can be triggered or augmented by energy conversion, and the eradication of biofilms with BCNs are systematically introduced and discussed. The current challenges and prospects of BCNs for biocatalytic disinfection are also summarized. It is anticipated this review will provide new therapeutic insights into combating bacteria and biofilms and offer significant new inspiration for designing future biocatalytic nanomaterials.

Will the Bacteria Survive in the CeO2 Nanozyme-H2O2 System?

As one of the nanostructures with enzyme-like activity, nanozymes have recently attracted extensive attention for their biomedical applications, especially for bacterial disinfection treatment. Nanozymes with high peroxidase activity are considered to be excellent candidates for building bacterial disinfection systems (nanozyme-H2O2), in which the nanozyme will promote the generation of ROS to kill bacteria based on the decomposition of H2O2. According to this criterion, a cerium oxide nanoparticle (Nanoceria, CeO2, a classical nanozyme with high peroxidase activity)-based nanozyme-H2O2 system would be very efficient for bacterial disinfection. However, CeO2 is a nanozyme with multiple enzyme-like activities. In addition to high peroxidase activity, CeO2 nanozymes also possess high superoxide dismutase activity and antioxidant activity, which can act as a ROS scavenger. Considering the fact that CeO2 nanozymes have both the activity to promote ROS production and the opposite activity for ROS scavenging, it is worth exploring which activity will play the dominating role in the CeO2-H2O2 system, as well as whether it will protect bacteria or produce an antibacterial effect. In this work, we focused on this discussion to unveil the role of CeO2 in the CeO2-H2O2 system, so that it can provide valuable knowledge for the design of a nanozyme-H2O2-based antibacterial system.

CeO2 Nanoparticle-Containing Polymers for Biomedical Applications: A Review

The development of advanced composite biomaterials combining the versatility and biodegradability of polymers and the unique characteristics of metal oxide nanoparticles unveils new horizons in emerging biomedical applications, including tissue regeneration, drug delivery and gene therapy, theranostics and medical imaging. Nanocrystalline cerium(IV) oxide, or nanoceria, stands out from a crowd of other metal oxides as being a truly unique material, showing great potential in biomedicine due to its low systemic toxicity and numerous beneficial effects on living systems. The combination of nanoceria with new generations of biomedical polymers, such as PolyHEMA (poly(2-hydroxyethyl methacrylate)-based hydrogels, electrospun nanofibrous polycaprolactone or natural-based chitosan or cellulose, helps to expand the prospective area of applications by facilitating their bioavailability and averting potential negative effects. This review describes recent advances in biomedical polymeric material practices, highlights up-to-the-minute cerium oxide nanoparticle applications, as well as polymer-nanoceria composites, and aims to address the question: how can nanoceria enhance the biomedical potential of modern polymeric materials?

Nanozymes used for antimicrobials and their applications

Bacterial infection-related diseases have been growing year-by-year rapidly and raising health problems globally. The exploitation of novel, high efficiency, and bacteria-binding antibacterial agents are extremely need. As far as now, the most extensive treatment is restricted to antibiotics, which may be overused and misused, leading to increased multidrug resistance. Antibiotics abuse, as well as antibiotic-resistance of bacteria, is a global challenge in the current situation. It is highly recommended and necessary to develop novel bactericide to kill the bacteria effectively without causing further resistance development and biosafety issues. Nanozymes, inorganic nanostructures with intrinsic enzymatic activities, have attracted more and more interest from the researchers owing to their exceptional advantages. Compared to natural enzymes, nanozymes can destroy many Gram-positive, Gram-negative bacteria, which builds an important bridge between biology and nanotechnology. As the potent nanoantibiotics, nanozymes have exciting broad-spectrum antimicrobial properties and negligible biotoxicities. And we summarized and highlighted the recent advances on nanozymes including its antibacterial mechanism and applications. Finally, challenges and limitations for the further improvement of the antibacterial activity are covered to provide future directions for the use of engineered nanozymes with enhanced antibacterial function.

Multifunctional ionic porous frameworks for CO2 conversion and combating microbes

Porous organic frameworks (POFs) with a heteroatom rich ionic backbone have emerged as advanced materials for catalysis, molecular separation, and antimicrobial applications. The loading of metal ions further enhances Lewis acidity, augmenting the activity associated with such frameworks. Metal-loaded ionic POFs, however, often suffer from physicochemical instability, thereby limiting their scope for diverse applications. Herein, we report the fabrication of triaminoguanidinium-based ionic POFs through Schiff base condensation in a cost-effective and scalable manner. The resultant N-rich ionic frameworks facilitate selective CO2 uptake and afford high metal (Zn(ii): 47.2%) loading capacity. Owing to the ionic guanidinium core and ZnO infused mesoporous frameworks, Zn/POFs showed pronounced catalytic activity in the cycloaddition of CO2 and epoxides into cyclic organic carbonates under solvent-free conditions with high catalyst recyclability. The synergistic effect of infused ZnO and cationic triaminoguanidinium frameworks in Zn/POFs led to robust antibacterial (Gram-positive, Staphylococcus aureus and Gram-negative, Escherichia coli) and antiviral activity targeting HIV-1 and VSV-G enveloped lentiviral particles. We thus present triaminoguanidinium-based POFs and Zn/POFs as a new class of multifunctional materials for environmental remediation and biomedical applications.

Recent advances in nanoparticulate biomimetic catalysts for combating bacteria and biofilms

Due to the abuse of antibiotics and the tendency of bacteria to form protective biofilms, the design and development of new efficient agents that can eliminate bacteria and biofilms are still highly desired but remain a great challenge; on the other hand, natural enzymes with unique catalytic characteristics can cause an irreversible damage to the bacteria without inducing drug-resistance in the bacteria. However, the intrinsic drawbacks, such as insufficient stability and high purification cost, of enzymes significantly limit their antimicrobial applications. Therefore, significant research efforts have been devoted towards the development of quality-equivalent or even superior enzyme substitutes with low cost and high stability. In this regard, nanomaterials with extraordinary enzyme-mimetic catalytic activities (termed as nanozymes) are considered as suitable candidates. To date, nanozymes have been proved to be promising materials for combating bacteria and biofilms under mild conditions. In this review, we have summarized the recent progress of nanozymes in this highly active field. The antibacterial mechanisms of nanozymes and the roles of their sizes, morphologies, compositions, surface modifications and microenvironment on their overall performance have been discussed. Moreover, the current challenges and prospects in this research area have been discussed. We believe that nanozymes with unique features and functions can provide a wealth of opportunities via their clinical and industrial applications.