The concentrations of the redox pair hydrogen peroxide (HO) and oxygen (O) can promote or decelerate the progression and duration of the wound healing process. Although HO can reach critically high concentrations and prohibit healing, a sufficient O inflow to the wound is commonly desired. Herein, we describe the fabrication and use of a membrane that can contemptuously decrease HO and increase O levels. Therefore, hematite nanozyme particles were integrated into electrospun and cross-linked poly(vinyl alcohol) membranes. Within the dual-compound membrane, the polymeric mesh provides a porous scaffold with high water permeability and the nanozymes act as a catalyst with catalase-like activity that can efficiently convert HO into O, as shown by a catalase assay. When comparing the growth of fibroblasts at an HO concentration of 50 μM, the growth was largely enhanced when applying the nanozyme dressing. Thus, application of the nanozyme dressing can significantly reduce the harmful effect of higher HO concentrations. The described catalytic membranes could be used in the future to provide an improved environment for cell proliferation in wounds and thus applied as advanced wound healing dressings.

We describe elementary concepts, up-to-date developments, and perspectives of the emerging field of nanoparticle enzyme mimics (so-called "nanozymes") at the interface of chemistry, biology, materials, and nanotechnology. The design and synthesis of functional enzyme mimics is a long-standing goal of biomimetic chemistry. Metal complexes, polymers and engineered biomolecules capturing the structure of natural enzymes or their active centers have been made to achieve high rates and enhanced selectivities. Still, the design of new "artificial enzymes" that are not related to proteins but with capacity of production and stability at industrial level, remains a goal. Inorganic nanoparticles bear this potential. Although it seems counterintuitive to compare nanoparticles and natural enzymes because they appear very different they share many common features: nano-size, irregular shape, and rich surface chemistry. These features enable nanomaterials to mimic reactions of natural enzymes. Representative examples with biomedical and environmental applications are given.

MnO nanoparticles decompose superoxide and hydrogen peroxide in an enzyme-like manner leading to enhanced MRI contrast.

Superoxide dismutases (SOD) are a group of enzymes that catalyze the dismutation of superoxide (O) radicals into molecular oxygen (O) and HO as a first line of defense against oxidative stress. Here, we show that glycine-functionalized copper(ii) hydroxide nanoparticles (Gly-Cu(OH) NPs) are functional SOD mimics, whereas bulk Cu(OH) is insoluble in water and catalytically inactive. In contrast, Gly-Cu(OH) NPs form water-dispersible mesocrystals with a SOD-like activity that is larger than that of their natural CuZn enzyme counterpart. Based on this finding, we devised an application where Gly-Cu(OH) NPs were incorporated into cigarette filters. Cigarette smoke contains high concentrations of toxic reactive oxygen species (ROS, >10 molecules per puff) including superoxide and reactive nitrogen species which lead to the development of chronic and degenerative diseases via oxidative damage and subsequent cell death. Embedded in cigarette filters Gly-Cu(OH) NPs efficiently removed ROS from smoke, thereby protecting lung cancer cell lines from cytotoxic effects. Their stability, ease of production and versatility make them a powerful tool for a wide range of applications in environmental chemistry, biotechnology and medicine.

The large-scale production and ecotoxicity of urea make its removal from wastewater a health and environmental challenge. Whereas the industrial removal of urea relies on hydrolysis at elevated temperatures and high pressure, nature solves the urea disposal problem with the enzyme urease under ambient conditions. We show that CeO2-x nanorods (NRs) act as the first and efficient green urease mimic that catalyzes the hydrolysis of urea under ambient conditions with an activity (kcat = 9.58 × 101 s-1) about one order of magnitude lower than that of the native jack bean urease. The surface properties of CeO2-x NRs were probed by varying the Ce4+/Ce3+ ratio through La doping. Although La substitution increased the number of surface defects, the reduced number of Ce4+ sites with higher Lewis acidity led to a slight decrease of their catalytic activity. CeO2-x NRs are stable against pH changes and even to the presence of transition metal ions like Cu2+, one of the strongest urease inhibitors. The low costs and environmental compatibility make CeO2-x NRs a green urease substitute that may be applied in polymer membranes for water processing or filters for the waste water reclamation. The biomimicry approach allows the application of CeO2-x NRs as functional enzyme mimics where the use of native or recombinant enzyme is hampered because of its costs or operational stability.

Electrospun polymer mats are widely used in tissue engineering, wearable electronics, and water purification. However, in many environments, the polymer nanofibers prepared by electrospinning suffer from biofouling during long-term usage, resulting in persistent infections and device damage. Herein, we describe the fabrication of polymer mats with CeO 2−x nanorods that can prevent biofouling in an aqueous environment. The embedded CeO 2−x nanorods are functional mimics of natural haloperoxidases that catalyze the oxidative bromination of Br − and H 2 O 2 to HOBr. The generated HOBr, a natural signaling molecule, disrupted the bacterial quorum sensing, a critical step in biofilm formation. The polymer fibers provide porous structures with high water wettability, and the embedded cerium oxide nanozymes act as a catalyst that can efficiently trigger oxidative bromination, as shown by a haloperoxidase assay. Additionally, the embedded nanozymes enhance the mechanical property of polymer mats, as shown by a single-fiber bending test using atomic force microscopy. We envision that the fabricated polymer mats with CeO 2−x nanorods may be used to provide mechanically robust coatings with antibiofouling properties.

Compared to conventional deposition techniques for the epitaxial growth of metal oxide structures on a bulk metal substrate, wet-chemical synthesis based on a dispersible template offers advantages such as low cost, high throughput, and the capability to prepare metal/metal oxide nanostructures with controllable size and morphology. However, the synthesis of such organized multicomponent architectures is difficult because the size and morphology of the components are dictated by the interplay of interfacial strain and facet-specific reactivity. Here we show that solution-processable two-dimensional Pd nanotetrahedra and nanoplates can be used to direct the epitaxial growth of γ-Fe 2 O 3 nanorods. The interfacial strain at the Pd−γ-Fe 2 O 3 interface is minimized by the formation of an Fe x Pd "buffer phase" facilitating the growth of the nanorods. The γ-Fe 2 O 3 nanorods show a (111) orientation on the Pd(111) surface. Importantly, the Pd@γ-Fe 2 O 3 hybrid nanomaterials exhibit enhanced peroxidase activity compared to that of isolated Fe 2 O 3 nanorods with comparable surface area because of a synergistic effect for the charge separation and electron transport. The metal-templated epitaxial growth of nanostructures via wet-chemical reactions appears to be a promising strategy for the facile and high-yield synthesis of novel functional materials.

Cerium dioxide nanoparticles and nanorods were found to exhibit much stronger scavenging activity than ·OH generation in quasi-physiological conditions.