Back to Basics: Exploiting the Innate Physico‐chemical Characteristics of Nanomaterials for Biomedical Applications

In nanomedicine design, emphasis is centered on the engineered impacts of the nanomaterials (NMs). However, failure to understand the unintended effects of nanomaterials on the cell biology can affect the overall performance, approval, and adoption in the clinic. Much of these unintended effects arise from unique physico‐chemical properties of the NMs. This feature article discusses some of the key physico‐chemical parameters of NMs and highlights how they could cause unexpected and novel biological responses, with some insights into their underlying mechanisms.     

Vanadium‐Based Nanomaterials: A Promising Family for Emerging Metal‐Ion Batteries

The emerging electrochemical energy storage systems beyond Li‐ion batteries, including Na/K/Mg/Ca/Zn/Al‐ion batteries, attract extensive interest as the development of Li‐ion batteries is seriously hindered by the scarce lithium resources. During the past years, large amounts of studies have focused on the investigation of various electrode materials toward emerging metal‐ion batteries to realize high energy density, high power density, and a long cycle life. In particular, vanadium‐based nanomaterials have received great attention. Vanadium‐based compounds have a big family with different structures, chemical compositions, and electrochemical properties, which provide huge possibilities for the development of emerging electrochemical energy storage. In this review, a comprehensive overview of the recent progresses of promising vanadium‐based nanomaterials for emerging metal‐ion batteries is presented. The vanadium‐based materials are classified into four groups: vanadium oxides, vanadates, vanadium phosphates, and oxygen‐free vanadium‐based compounds. The structures, electrochemical properties, and modification strategies are discussed. The structure–performance relationships and charge storage mechanisms are focused on. Finally, the perspectives about future directions of vanadium‐based nanomaterials for emerging energy storage devices are proposed. This review will provide comprehensive knowledge of vanadium‐based nanomaterials and shed light on their potential applications in emerging energy storage.     

Multimodal Magneto‐Plasmonic Nanoclusters for Biomedical Applications

Multimodal nanostructures can help solve many problems in the biomedical field including sensitive molecular imaging, highly specific therapy, and early cancer detection. However, the synthesis of densely packed, multicomponent nanostructures with multimodal functionality represents a significant challenge. Here, a new type of hybrid magneto‐plasmonic nanoparticles is developed using an oil‐in‐water microemulsion method. The nanostructures are synthetized by self‐assembly of primary 6 nm iron oxide core‐gold shell particles resulting into densely packed spherical nanoclusters. The dense packing of primary particles does not change their superparamagnetic behavior; however, the close proximity of the constituent particles in the nanocluster leads to strong near‐infrared (NIR) plasmon resonances. The synthesis is optimized to eliminate nanocluster cytotoxicity. Immunotargeted nanoclusters are also developed using directional conjugation chemistry through the Fc antibody moiety, leaving the Fab antigen recognizing region available for targeting. Cancer cells labeled with immunotargeted nanoclusters produce a strong photoacoustic signal in the NIR that is optimum for tissue imaging. Furthermore, the labeled cells can be efficiently captured using an external magnetic field. The biocompatible magneto‐plasmonic nanoparticles can make a significant impact in development of point‐of‐care assays for detection of circulating tumor cells, as well as in cell therapy with magnetic cell guidance and imaging monitoring.     

Multifunctional and Stimuli‐Responsive Polydopamine Nanoparticle‐Based Platform for Targeted Antimicrobial Applications

The rising threat of antimicrobial resistance is a crisis of a global scale. If not addressed, it can lead to health care system problems worldwide. This warrants alternative therapeutic approaches whose mechanism of action starkly differs from conventional antibiotic‐based therapies. Here, a multifunctional and stimuli‐responsive (NIR laser‐activated) antimicrobial platform is engineered by combining the intrinsic photothermal capability and excellent biocompatibility of polydopamine nanoparticles (PdNPs), with the membrane targeting and lytic activities of an antimicrobial peptide (AMP). The resulting PdNP‐AMP nanosystem can specifically target and destabilize the mechanical integrity of the outer membrane of Escherichia coli, as measured using the atomic force microscope. Furthermore, the laser‐induced nano‐localized heating of PdNP—in close proximity to the already compromised bacterial envelope—induces further membrane damage. This results in a more efficient, laser‐activated, bacterial killing action of PdNP‐AMP. The antimicrobial platform developed in this work is shown to be effective against a drug‐resistant E. coli. Overall, this work highlights the advantage and strength of combining multiple and coordinated biocidal mechanisms, into one nanomaterial‐based system and its promise in treating drug‐resistant pathogens.     

Biomedical Applications of DNA‐Based Hydrogels

Nucleic acids are gaining significant attention as versatile building blocks for the next generation of soft materials. Due to significant advances in the chemical synthesis and biotechnological production, DNA becomes more widely available enabling its usage as bulk material in various applications. This has prompted researchers to actively explore the unique features offered by DNA‐containing materials like hydrogels. In this review article, recent developments in the field of hydrogels that feature DNA as a component either in the construction of the material or as functional unit within the construct and their biomedical applications are discussed in detail. First, different synthetic approaches for obtaining DNA hydrogels are summarized, which allows classification of DNA materials according to their structure. Then, new concepts, properties, and applications are highlighted such as DNA‐based biosensor devices, drug delivery platforms, and cell scaffolds. With the 2018 Nobel Prize in Physiology or Medicine being awarded to cancer immunotherapy underscoring the importance of this therapy, DNA hydrogel systems designed to modulate the immune system are introduced. This review aims to give the reader a timely overview of the most important and recent developments in this emerging class of therapeutically useful materials of DNA‐based hydrogels.     

Molybdenum Disulfide‐Based Tubular Microengines: Toward Biomedical Applications

2D molybdenum disulfide (MoS₂) is herein explored as an advanced surface material in the fabrication of powerful tubular microengines. The new catalytic self‐propelled open‐tube bilayer microengines have been fabricated using a template electrodeposition and couple the unique properties of sp² hybridized MoS₂ with highly reactive inner granular Pt catalytic structures. The MoS₂/metal microengines display extremely efficient bubble propulsion, reflecting the granular structure of the inner catalytic platinum or gold layers (compared to the smooth metal surfaces of common micromotors). The efficient movement of functionalized MoS₂ micromotors can address challenges imposed by slow mass transport processes involved in various applications of MoS_2. The delocalized electron network of the MoS₂ outer layer facilitates π–π stacking interactions and endows the tubular microengines with a diverse array of capabilities. These are demonstrated here for efficient loading and release of the drug doxorubicin, and rapid and sensitive “OFF–ON” fluorescent detection of important nucleic acids (miRNA‐21) and proteins (thrombin) using microengines modified with dye‐labeled single‐stranded DNA and aptamer, respectively. Such coupling of the attractive capabilities of 2D‐MoS₂ nanosheets with rapidly moving microengines provides an opportunity to develop multifunctional micromachines for diverse biomedical applications ranging from efficient drug delivery to the detection of important bioanalytes.     

Fabrication of CdSe‐Nanofibers with Potential for Biomedical Applications

The design and synthesis of nanostructured functional hybrid biomaterials are essential for the next generation of advanced diagnostics and the treatment of disease. A simple route to fabricate semiconductor nanofibers by self‐assembled, elastin‐like polymer (ELP)‐templated semiconductor nanoparticles is reported. Core–shell nanostructures of CdSe nanoparticles with a shell of ELPs are used as building blocks to fabricate functional one‐dimensional (1D) nanostructures. The CdSe particles are generated in situ within the ELP matrix at room temperature. The ELP controls the size and the size‐distribution of the CdSe nanoparticles in an aqueous medium and simultaneously directs the self‐assembly of core–shell building blocks into fibril architectures. It was found that the self‐assembly of core–shell building blocks into nanofibers is strongly dependent on the pH value of the medium. Results of cytotoxicity and antiproliferation of the CdSe‐ELP nanofibers demonstrate that the CdSe‐ELP does not exhibit any toxicity towards B14 cells. Moreover, these are found to be markedly capable of crossing the cell membrane of B14. In contrast, unmodified CdSe nanoparticles with ELPs cause a strong toxic response and reduction in the cell proliferation. This concept is valid for the fabrication of a variety of metallic and semiconductor 1D‐architectures. Therefore, it is believed that these could be used not only for biomedical purposes but for application in a wide range of advanced miniaturized devices.     

Localized Laser‐Based Photohydrothermal Synthesis of Functionalized Metal‐Oxides

We discuss the rapid in situ hydrothermal synthesis of metal oxide materials based on the photothermal superheating of light‐absorbing metal layers for simple and facile on‐demand placement of semiconductor materials with micrometer‐scale lateral resolution. Localized heating from pulsed and focused laser illumination enables ultrafast growth of metal oxide materials with high spatiotemporal precision in aqueous precursor solution. Among many possible electronic and optoelectronic applications, the proposed method can be used for laser‐based in situ real‐time soldering of separated metal structures and electrodes with functionalized semiconductor materials. Resistive electrical interconnections of metal strip lines as well as sensitive UV detection using photohydrothermally grown metal oxide bumps are experimentally demonstrated.     

Phthalocyanine‐Based 2D Conjugated Metal‐Organic Framework Nanosheets for High‐Performance Micro‐Supercapacitors

2D conjugated metal‐organic frameworks (2D c‐MOFs) are emerging as a novel class of conductive redox‐active materials for electrochemical energy storage. However, developing 2D c‐MOFs as flexible thin‐film electrodes have been largely limited, due to the lack of capability of solution‐processing and integration into nanodevices arising from the rigid powder samples by solvothermal synthesis. Here, the synthesis of phthalocyanine‐based 2D c‐MOF (Ni₂[CuPc(NH)₈]) nanosheets through ball milling mechanical exfoliation method are reported. The nanosheets feature with average lateral size of ≈160 nm and mean thickness of ≈7 nm (≈10 layers), and exhibit high crystallinity and chemical stability as well as a p‐type semiconducting behavior with mobility of ≈1.5 cm² V^?1 s^?1 at room temperature. Benefiting from the ultrathin feature, the nanosheets allow high utilization of active sites and facile solution‐processability. Thus, micro‐supercapacitor (MSC) devices are fabricated mixing Ni₂[CuPc(NH)₈] nanosheets with exfoliated graphene, which display outstanding cycling stability and a high areal capacitance up to 18.9 mF cm^?2; the performance surpasses most of the reported conducting polymers‐based and 2D materials‐based MSCs.     

Copper Sulfide (CuxS) Nanowire‐in‐Carbon Composites Formed from Direct Sulfurization of the Metal‐Organic Framework HKUST‐1 and Their Use as Li‐Ion Battery Cathodes

Li‐ion batteries containing cost‐effective, environmentally benign cathode materials with high specific capacities are in critical demand to deliver the energy density requirements of electric vehicles and next‐generation electronic devices. Here, the phase‐controlled synthesis of copper sulfide (Cu_xS) composites by the temperature‐controlled sulfurization of a prototypal Cu metal‐organic framework (MOF), HKUST‐1 is reported. The tunable formation of different Cu_xS phases within a carbon network represents a simple method for the production of effective composite cathode materials for Li‐ion batteries. A direct link between the sulfurization temperature of the MOF and the resultant Cu_xS phase formed with more Cu‐rich phases favored at higher temperatures is further shown. The Cu_xS/C samples are characterized through X‐ray diffraction (XRD), thermogravimetric analysis (TGA), transmission electron microscopy, and energy dispersive X‐ray spectroscopy (EDX) in addition to testing as Li‐ion cathodes. It is shown that the performance is dependent on both the Cu_xS phase and the crystal morphology with the Cu_1.8S/C‐500 material as a nanowire composite exhibiting the best performance, showing a specific capacity of 220 mAh g^?1 after 200 charge/discharge cycles.     

Polymer‐Based Nitric Oxide Therapies: Recent Insights for Biomedical Applications

Since the discovery of nitric oxide (NO) in the 1980s, this cellular messenger has been shown to participate in diverse biological processes such as cardiovascular homeostasis, immune response, wound healing, bone metabolism, and neurotransmission. Its beneficial effects have prompted increased research in the past two decades, with a focus on the development of materials that can locally release NO. However, significant limitations arise when applying these materials to biomedical applications. This Feature Article focuses on the development of NO‐releasing and NO‐generating polymeric materials (2006–2011) with emphasis on recent in vivo applications. Results are compared and discussed in terms of NO dose, release kinetics, and biological effects, in order to provide a foundation to design and evaluate new NO therapies.     

High‐Performance Metal‐Free Nanosheets Array Electrocatalyst for Oxygen Evolution Reaction in Acid

Development of low cost electrocatalysts with outstanding catalytic activity and stability for oxygen evolution reaction (OER) in acid is a major challenge to produce hydrogen energy from water splitting. Herein, a novel metal‐free electrocatalyst consisting of a oxygen‐functionalized electrochemically exfoliated graphene (OEEG) nanosheets array is reported. Benefitting from a vertically aligned arrays structure and introducing oxygen functional groups, the metal‐free OEEG nanosheets array exhibits superior electrocatalytic activity and stability toward OER with a low overpotential of 334 mV at 10 mA cm^?2 in acidic electrolyte. Such a high OER performance is thus far the best among all previously reported metal‐free carbon‐based materials, and even superior to commercial Ir/C catalysts (420 mV at 10 mA cm^?2) in acid. Characterization results and electrochemical measurements identify the COOH species in the OEEG acting as active sites for acidic OER, which is further supported by atomic‐scale scanning transmission electron microscopy imaging and electron energy‐loss spectroscopy. Density functional theory calculations reveal that the reaction pathway of dual sites that is mixed by zigzag and armchair edges (COOH‐zig‐corner) is better than the pathway of single site.     

Multifunctional Nano‐Biointerfaces: Cytocompatible Antimicrobial Nanocarriers from Stabilizer‐Free Cubosomes

The rational design of alternative antimicrobial materials with reduced toxicity toward mammalian cells is highly desired due to the growing occurrence of bacteria resistant to conventional antibiotics. A promising approach is the design of lipid‐based antimicrobial nanocarriers. However, most of the commonly used polymer‐stabilized nanocarriers are cytotoxic. Herein, the design of a novel, stabilizer‐free nanocarrier for the human cathelicidin derived antimicrobial peptide LL‐37 that is cytocompatible and promotes cell proliferation for improved wound healing is reported. The nanocarrier is formed through the spontaneous integration of LL‐37 into novel, stabilizer‐free glycerol mono‐oleate (GMO)‐based cubosomes. Transformations in the internal structure of the cubosomes from Pn3m to Im3m‐type and eventually their transition into small vesicles and spherical micelles are demonstrated upon the encapsulation of LL‐37 into their internal bicontinuous cubic structure using small angle X‐ray scattering, cryogenic transmission electron microscopy, and light scattering techniques. Additional in vitro biological assays show the antimicrobial activity of the stabilizer‐free nano‐objects on a variety of bacteria strains, their cytocompatibility, and cell‐proliferation enhancing effect. The results outline a promising strategy for the comprehensive design of antimicrobial, cytocompatible lipid nanocarriers for the protection and delivery of bioactive molecules with potential for application as advanced wound healing materials.     

A Generic Synthetic Approach to Large‐Scale Pristine‐Graphene/Metal‐Nanoparticles Hybrids

The homogeneous attachment of metal‐nanoparticles (metal‐NPs) on pristine‐graphene surface to construct pristine‐graphene/metal‐NPs hybrids is highly expected for application in many fields such as transparent electrodes and conductive composites. However, it remains a great challenge since the pristine‐graphene is highly hydrophobic. Here, an environmentally friendly generic synthetic approach to large‐scale pristine‐graphene/metal‐NPs hybrids is presented, by a combinatorial process of exfoliating expanded graphite in N‐methyl pyrrolidone via sonication and centrifugation to achieve the pristine‐graphene, and attaching pre‐synthesized metal‐NPs on the pristine‐graphene in ethanol via van der Waals interactions between the metal‐NPs and the pristine‐graphene. Nanoparticles of different metals (such as Ag, Au, and Pd) with various morphologies (such as sphere, cube, plate, multi‐angle, and spherical‐particle assembling) can be homogeneously attached on the defect‐free pristine‐graphene with controlled packing densities. Both the pristine‐graphene and the metal‐NPs preserve their original intrinsic structures. The as‐synthesized pristine‐graphene/Ag‐NPs hybrids show very high surface‐enhanced Raman scattering activity due to the combined effects of large surface area of the pristine‐graphene to adsorb more target molecules and the electromagnetic enhancement of the Ag‐NPs. This large‐scale synthesis of the pristine‐graphene/metal‐NPs hybrids with tunable shape and packing density of metal‐NPs opens up opportunities for fundamental research and potential applications ranging from devices to transparent electrodes and conductive composites.     

Metal‐Organic Framework Nanoparticles in Photodynamic Therapy: Current Status and Perspectives

This feature article covers the recent applications of metal‐organic framework nanoparticles (MOF NPs) in photodynamic therapy (PDT) of cancer. It aims at giving the reader an overview about these two current research fields, i.e., MOF and PDT, and at highlighting the potential synergistic effect that could result from their association. After describing the general photophysics and photochemistry that underlie PDT, the relationship between photosensitizer (PS) properties and PDT requirements is discussed throughout the PSs historical development. This development reveals the advantages of using nanotechnology platforms for the creation of the ideal PS and leads us to define the fourth generation of PSs, which includes NPs built from the PS itself as porphysomes or PS‐based MOF NPs. Especially, the precise spatial control over the PS assembly into well‐defined MOF NPs, which keeps the PS in its monomeric form and prevents PS self‐quenching, appears as a notable feature to solve PS solubility and aggregation issues and therefore improves the PDT efficiency. Finally, we discuss the future perspectives of MOF NPs in PDT and shed light on how promising these nanomaterials are.     

Dual‐Mechanism Antimicrobial Polymer–ZnO Nanoparticle and Crystal Violet‐Encapsulated Silicone

The prevalence of healthcare‐associated infection caused by multidrug‐resistant bacteria is of critical concern worldwide. It is reported on the development of a bactericidal surface prepared by use of a simple, upscalable, two‐step dipping strategy to incorporate crystal violet and di(octyl)­phosphinic‐ acid‐capped zinc oxide nanoparticles into medical grade silicone, as a strategy to reduce the risk of infection. The material is characterized by UV–vis absorbance spectroscopy, X‐ray photoelectron spectroscopy (XPS), inductively coupled plasma‐optical emission spectroscopy (ICP‐OES) and transmission electron microscopy (TEM) and confirmed the incorporation of the ZnO nanoparticles in the polymer. The novel system proves to be a highly versatile bactericidal material when tested against both Staphylococcus aureus and Escherichia coli, key causative micro‐organisms for hospital‐acquired infection (HAI). Potent antimicrobial activity is noted under dark conditions, with a significant enhancement exhibits when the surfaces are illuminated with a standard hospital light source. This polymer has the potential to decrease the risk of HAI, by killing bacteria in contact with the surface.     

One‐Dimensional Metal‐Oxide Nanostructures: Recent Developments in Synthesis,Characterization, and Applications

1D metal‐oxide nanostructures have attracted much attention because metal oxides are the most fascinating functional materials. The 1D morphologies can easily enhance the unique properties of the metal‐oxide nanostructures, which make them suitable for a wide variety of applications, including gas sensors, electrochromic devices, light‐emitting diodes, field emitters, supercapacitors, nanoelectronics, and nanogenerators. Therefore, much effort has been made to synthesize and characterize 1D metal‐oxide nanostructures in the forms of nanorods, nanowires, nanotubes, nanobelts, etc. Various physical and chemical deposition techniques and growth mechanisms are exploited and developed to control the morphology, identical shape, uniform size, perfect crystalline structure, defects, and homogenous stoichiometry of the 1D metal‐oxide nanostructures. Here a comprehensive review of recent developments in novel synthesis, exceptional characteristics, and prominent applications of one‐dimensional nanostructures of tungsten oxides, molybdenum oxides, tantalum oxides, vanadium oxides, niobium oxides, titanium oxides, nickel oxides, zinc oxides, bismuth oxides, and tin oxides is provided.