The Antibacterial Applications of Graphene and Its Derivatives

Graphene materials have unique structures and outstanding thermal, optical, mechanical and electronic properties. In the last decade, these materials have attracted substantial interest in the field of nanomaterials, with applications ranging from biosensors to biomedicine. Among these applications, great advances have been made in the field of antibacterial agents. Here, recent advancements in the use of graphene and its derivatives as antibacterial agents are reviewed. Graphene is used in three forms: the pristine form; mixed with other antibacterial agents, such as Ag and chitosan; or with a base material, such as poly (N‐vinylcarbazole) (PVK) and poly (lactic acid) (PLA). The main mechanisms proposed to explain the antibacterial behaviors of graphene and its derivatives are the membrane stress hypothesis, the oxidative stress hypothesis, the entrapment hypothesis, the electron transfer hypothesis and the photothermal hypothesis. This review describes contributions to improving these promising materials for antibacterial applications.     

Polyphenol‐Inspired Facile Construction of Smart Assemblies for ATP‐ and pH‐Responsive Tumor MR/Optical Imaging and Photothermal Therapy

Smart assemblies have attracted increased interest in various areas, especially in developing novel stimuli‐responsive theranostics. Herein, commercially available, natural tannic acid (TA) and iron oxide nanoparticles (Fe₃O₄ NPs) are utilized as models to construct smart magnetic assemblies based on polyphenol‐inspired NPs–phenolic self‐assembly between NPs and TA. Interestingly, the magnetic assemblies can be specially disassembled by adenosine triphosphate, which shows a stronger affinity to Fe₃O₄ NPs than that of TA and partly replaces the surface coordinated TA. The disassembly can further be facilitated by the acidic environment hence causing the remarkable change of the transverse relaxivity and potent “turn‐on” of fluorescence (FL) signals. Therefore, the assemblies for specific and sensitive tumor magnetic resonance and FL dual‐modal imaging and photothermal therapy after intravenous injection of the assemblies are successfully employed. This work not only provides understandings on the self‐assembly between NPs and polyphenols, but also will open new insights for facilely constructing versatile assemblies and extending their biomedical applications.     

“Smart” Surface Capsules for Delivery Devices

This review describes emerging trends, basic principles, applications, and future challenges for designing next generation responsive “smart” surface capsules. Advances and importance of “surface” capsules which are not deposited onto the surface but are built into the surface are highlighted for selective applications with specific examples of surface sponge structures formed by high intensity ultrasonic surface treatment (HIUS). Surface capsules can be adapted for biomedical applications, membrane materials, lab‐on‐chip, organ‐on‐chip, and for template synthesis. They provide attractive self‐healing anticorrosion and antifouling prospects. Nowadays delivery systems are built from inorganic, organic, hybrid, biological materials to deliver various drugs from low molecular weight substances to large protein molecules and even live cells. It is important that capsules are designed to have time prolonged release features. Available stimuli to control capsule opening are physical, chemical and biological ones. Understanding the underlying mechanisms of capsule opening by different stimuli is essential for developing new methods of encapsulation, release, and targeting. Development of “smart” surface capsules is preferable to respond to multiple stimuli. More and more often a new generation of “smart” capsules is designed by a bio‐inspired approach.     

Energy‐Converting Nanomedicine

Serious side effects to surrounding normal tissues and unsatisfactory therapeutic efficacy hamper the further clinic applications of conventional cancer‐therapeutic strategies, such as chemotherapy and surgery. The fast development of nanotechnology provides unprecedented superiorities for cancer therapeutics. Externally activatable therapeutic modalities mediated by nanomaterials, relying on highly effective energy transformation to release therapeutic elements/effects (cytotoxic reactive oxygen species, thermal effect, photoelectric effect, Compton effect, cavitation effect, mechanical effect or chemotherapeutic drug) for cancer therapies, categorized and termed as “energy‐converting nanomedicine,” have arouse considerable concern due to their noninvasiveness, desirable tissue‐penetration depth, and accurate modulation of therapeutic dose. This review summarizes the recent advances in the engineering of intelligent functional nanotherapeutics for energy‐converting nanomedicine, including photo‐based, radiation‐based, ultrasound‐based, magnetic field‐based, microwave‐based, electric field‐based, and radiofrequency‐based nanomedicines, which are enabled by external stimuli (light, radiation, ultrasound, magnetic field, microwave, electric field, and radiofrequency). Furthermore, biosafety issues of energy‐converting nanomedicine related to future clinical translation are also addressed. Finally, the potential challenges and prospects of energy‐converting nanomedicine for future clinical translation are discussed.     

Stimulus Responsive 3D Assembly for Spatially Resolved Bifunctional Sensors

3D electronic/optoelectronic devices have shown great potentials for various applications due to their unique properties inherited not only from functional materials, but also from 3D architectures. Although a variety of fabrication methods including mechanically guided assembly have been reported, the resulting 3D devices show no stimuli‐responsive functions or are not free standing, thereby limiting their applications. Herein, the stimulus responsive assembly of complex 3D structures driven by temperature‐responsive hydrogels is demonstrated for applications in 3D multifunctional sensors. The assembly driving force, compressive buckling, arises from the volume shrinkage of the responsive hydrogel substrates when they are heated above the lower critical solution temperature. Driven by the compressive buckling force, the 2D‐formed membrane materials, which are pre‐defined and selectively bonded to the substrates, are then assembled to 3D structures. They include “tent,” “tower,” “two‐floor pavilion,” “dome,” “basket,” and “nested‐cages” with delicate geometries. Moreover, the demonstrated 3D bifunctional sensors based on laser induced graphene show capability of spatially resolved tactile sensing and temperature sensing. These multifunctional 3D sensors would open new applications in soft robotics, bioelectronics, micro‐electromechanical systems, and others.     

Vanadium Dioxide: The Multistimuli Responsive Material and Its Applications

The reversible, ultrafast, and multistimuli responsive phase transition of vanadium dioxide (VO₂) makes it an intriguing “smart” material. Its crystallographic transition from the monoclinic to tetragonal phases can be triggered by diverse stimuli including optical, thermal, electrical, electrochemical, mechanical, or magnetic perturbations. Consequently, the development of high‐performance smart devices based on VO₂ grows rapidly. This review systematically summarizes VO₂‐based emerging technologies by classifying different stimuli (inputs) with their corresponding responses (outputs) including consideration of the mechanisms at play. The potential applications of such devices are vast and include switches, memories, photodetectors, actuators, smart windows, camouflages, passive radiators, resonators, sensors, field effect transistors, magnetic refrigeration, and oscillators. Finally, the challenges of integrating VO₂ into smart devices are discussed and future developments in this area are considered.     

Dynamically PEGylated and Borate‐Coordination‐Polymer‐Coated Polydopamine Nanoparticles for Synergetic Tumor‐Targeted,Chemo‐Photothermal Combination Therapy

Multifunctional nanomaterials with efficient tumor‐targeting and high antitumor activity are highly anticipated in the field of cancer therapy. In this work, a synergetic tumor‐targeted, chemo‐photothermal combined therapeutic nanoplatform based on a dynamically PEGylated, borate‐coordination‐polymer‐coated polydopamine nanoparticle (PDA@CP‐PEG) is developed. PEGylation on the multifunctional nanoparticles is dynamically achieved via the reversible covalent interaction between the surface phenylboronic acid (PBA) group and a catechol‐containing poly(ethylene glycol) (PEG) molecule. Due to the acid‐labile PBA/catechol complex and the weak‐acid‐stable PBA/sialic acid (SA) complex, the nanoparticles can exhibit a synergetic targeting property for the SA‐overexpressed tumor cells, i.e., the PEG‐caused “passive targeting” and PBA‐triggered “active targeting” under the weakly acidic tumor microenvironment. In addition, the photothermal effect of the polydopamine core and the doxorubicin‐loading capacity of the porous coordination polymer layer endow the nanoparticles with the potential for chemo‐photothermal combination therapy. As expected, the in vitro and in vivo studies both verify that the multifunctional nanoparticles possess relatively lower systematic toxicity, efficient tumor targeting ability, and excellent chemo‐photothermal activity for tumor inhibition. It is believed that these multifunctional nanoparticles with synergetic tumor targeting property and combined therapeutic strategies would provide an insight into the design of a high‐efficiency antitumor nanoplatform for potential clinical applications.     

Plasmonic Pt Superstructures with Boosted Near‐Infrared Absorption and Photothermal Conversion Efficiency in the Second Biowindow for Cancer Therapy

Photothermal therapy triggered by near‐infrared light in the second biowindow (NIR‐II) has attracted extensive interest owing to its deeper penetration depth of biological tissue, lower photon scattering, and higher maximum permissible exposure. In spite of noble metals showing great potential as the photothermal agents due to the tunable localized surface plasmon resonance, the biological applications of platinum are rarely explored. Herein, a monocomponent hollow Pt nanoframe (“Pt Spirals”), whose superstructure is assembled with three levels (3D frame, 2D layered shells, and 1D nanowires), is reported. Pt Spirals exhibit outstanding photothermal conversion efficiency (52.5%) and molar extinction coefficients (228.7 m² mol^?1) in NIR‐II, which are much higher than those of solid Pt cubes. Simulations indicate that the unique superstructure can be a significant cause for improving both adsorption and the photothermal effect simultaneously in NIR‐II. The excellent photothermal effect is achieved and subsequently verified in in vitro and in vivo experiments, along with superb heat‐resistance properties, excellent photostability, and a prominent effect on computed tomography (CT) imaging, demonstrating that Pt Spirals are promising as effective theranostic platforms for CT imaging‐guided photothermal therapy.     

Laser–Material Interactions for Flexible Applications

The use of lasers for industrial, scientific, and medical applications has received an enormous amount of attention due to the advantageous ability of precise parameter control for heat transfer. Laser‐beam‐induced photothermal heating and reactions can modify nanomaterials such as nanoparticles, nanowires, and two‐dimensional materials including graphene, in a controlled manner. There have been numerous efforts to incorporate lasers into advanced electronic processing, especially for inorganic‐based flexible electronics. In order to resolve temperature issues with plastic substrates, laser–material processing has been adopted for various applications in flexible electronics including energy devices, processors, displays, and other peripheral electronic components. Here, recent advances in laser–material interactions for inorganic‐based flexible applications with regard to both materials and processes are presented.     

Shock Exfoliation of Graphene Fluoride in Microwave

An unprecedented microwave‐based strategy is developed to facilitate solid‐phase, instantaneous delamination and decomposition of graphite fluoride (GF) into few‐layer, partially fluorinated graphene. The shock reaction occurs (and completes in few seconds) under microwave irradiation upon exposing GF to either “microwave‐induced plasma” generated in vacuum or “catalyst effect” caused by intense sparking of graphite at ambient conditions. A detailed analysis of the structural and compositional transformations in these processes indicates that the GF experiences considerable exfoliation and defluorination, during which sp²‐bonded carbon is partially recovered despite significant structural defects being introduced. The exfoliated fluorinated graphene shows excellent electrochemical performance as anode materials in potassium ion batteries and as catalysts for the conversion of O₂ to H₂O₂. This simple and scalable method requires minimal energy input and does not involve the use of other chemicals, which is attractive for extensive research in fluorine‐containing graphene and its derivatives in laboratories and industrial applications.     

Graphene Quantum Dots‐Capped Magnetic Mesoporous Silica Nanoparticles as a Multifunctional Platform for Controlled Drug Delivery,Magnetic Hyperthermia,and Photothermal Therapy

A multifunctional platform is reported for synergistic therapy with controlled drug release, magnetic hyperthermia, and photothermal therapy, which is composed of graphene quantum dots (GQDs) as caps and local photothermal generators and magnetic mesoporous silica nanoparticles (MMSN) as drug carriers and magnetic thermoseeds. The structure, drug release behavior, magnetic hyperthermia capacity, photothermal effect, and synergistic therapeutic efficiency of the MMSN/GQDs nanoparticles are investigated. The results show that monodisperse MMSN/GQDs nanoparticles with the particle size of 100 nm can load doxorubicin (DOX) and trigger DOX release by low pH environment. Furthermore, the MMSN/GQDs nanoparticles can efficiently generate heat to the hyperthermia temperature under an alternating magnetic field or by near infrared irradiation. More importantly, breast cancer 4T1 cells as a model cellular system, the results indicate that compared with chemotherapy, magnetic hyperthermia or photothermal therapy alone, the combined chemo‐magnetic hyperthermia therapy or chemo‐photothermal therapy with the DOX‐loaded MMSN/GQDs nanosystem exhibits a significant synergistic effect, resulting in a higher efficacy to kill cancer cells. Therefore, the MMSN/GQDs multifunctional platform has great potential in cancer therapy for enhancing the therapeutic efficiency.     

New Horizons for Diagnostics and Therapeutic Applications of Graphene and Graphene Oxide

Graphene, a one‐atom‐thick two‐dimensional (2D) layer of sp²‐bonded carbon, has received worldwide attention owing to its extraordinary physical and chemical properties. Recently, great efforts have been devoted to explore potential applications of graphene and its oxide in life science, especially in disease‐related diagnostics, near‐Infrared (NIR) phototherapy and imaging. Here we will introduce recent advances and new horizons in this area, and focus on the rising progress on NIR photothermal therapy for cancer and Alzheimer's disease (AD), human telomerase detection, stem cell proliferation and differentiation on graphene substrate, diagnosis of cancer cell and related biomarkers, drug/nucleotide/peptide delivery and cell imaging, which have not been comprehensively reviewed. We hope to provide an outlook to the applications of graphene and its oxide, especially on the new horizons in this field, and inspire broader interests across various disciplines.     

MRI‐Visualized,Dual‐Targeting,Combined Tumor Therapy Using Magnetic Graphene‐Based Mesoporous Silica

Targeting peptide‐modified magnetic graphene‐based mesoporous silica (MGMSPI) are synthesized, characterized, and developed as a multifunctional theranostic platform. This system exhibits many merits, such as biocompatibility, high near‐infrared photothermal heating, facile magnetic separation, large T2 relaxation rates (r2), and a high doxorubicin (DOX) loading capacity. In vitro and in vivo results demonstrate that DOX‐loaded MGMSPI (MGMSPID) can integrate magnetic resonance imaging, dual‐targeting recognition (magnetic targeting and receptor‐mediated active targeting), and chemo‐photothermal therapy into a single system for a visualized‐synergistic therapy of glioma. In addition, it is observed that the MGMSPID system has heat‐stimulated, pH‐responsive, sustained release properties. All of these characteristics would provide a robust multifunctional theranostic platform for visualized glioma therapy.     

Graphene Glass from Direct CVD Routes: Production and Applications

Recently, direct chemical vapor deposition (CVD) growth of graphene on various types of glasses has emerged as a promising route to produce graphene glass, with advantages such as tunable quality, excellent film uniformity and potential scalability. Crucial to the performance of this graphene‐coated glass is that the outstanding properties of graphene are fully retained for endowing glass with new surface characteristics, making direct‐CVD‐derived graphene glass versatile enough for developing various applications for daily life. Herein, recent advances in the synthesis of graphene glass, particularly via direct CVD approaches, are presented. Key applications of such graphene materials in transparent conductors, smart windows, simple heating devices, solar‐cell electrodes, cell culture medium, and water harvesters are also highlighted.     

Design and Applications of Photoresponsive Hydrogels

Hydrogels are the most relevant biochemical scaffold due to their tunable properties, inherent biocompatibility, and similarity with tissue and cell environments. Over the past decade, hydrogels have developed from static materials to “smart” responsive materials adapting to various stimuli, such as pH, temperature, chemical, electrical, or light. Light stimulation is particularly interesting for many applications because of the capability of contact‐free remote manipulation of biomaterial properties and inherent spatial and temporal control. Moreover, light can be finely adjusted in its intrinsic properties, such as wavelength and intensity (i.e., the energy of an individual photon as well as the number of photons over time). Water is almost transparent for light in the photochemically relevant range (NIR–UV), thus hydrogels are well‐suited scaffolds for light‐responsive functionality. Hydrogels' chemical and physical variety combined with light responsiveness makes photoresponsive hydrogels ideal candidates for applications in several fields, ranging from biomaterials, medicine to soft robotics. Herein, the progress and new developments in the field of light‐responsive hydrogels are elaborated by first introducing the relevant photochemistries before discussing selected applications in detail.     

Logic‐Based Delivery of Site‐Specifically Modified Proteins from Environmentally Responsive Hydrogel Biomaterials

The controlled presentation of proteins from and within materials remains of significant interest for many bioengineering applications. Though “smart” platforms offer control over protein release in response to a single external cue, no strategy has been developed to trigger delivery in response to user‐specified combinations of environmental inputs, nor to independently control the release of multiple species from a homogenous material. Here, a modular semisynthetic scheme is introduced to govern the release of site‐specifically modified proteins from hydrogels following Boolean logic. A sortase‐mediated transpeptidation reaction is used to generate recombinant proteins C‐terminally tethered to gels through environmentally sensitive degradable linkers. By varying the connectivity of multiple stimuli‐labile moieties within these customizable linkers, YES/OR/AND control of protein release is exhaustively demonstrated in response to one and two‐input combinations involving enzyme, reductant, and light. Tethering of multiple proteins each through a different stimuli‐sensitive linker permits their independent and sequential release from a common material. It is expected that these methodologies will enable new opportunities in tissue engineering and therapeutic delivery.     

Chemically Integrated Inorganic‐Graphene Two‐Dimensional Hybrid Materials for Flexible Energy Storage Devices

State‐of‐the‐art energy storage devices are capable of delivering reasonably high energy density (lithium ion batteries) or high power density (supercapacitors). There is an increasing need for these power sources with not only superior electrochemical performance, but also exceptional flexibility. Graphene has come on to the scene and advancements are being made in integration of various electrochemically active compounds onto graphene or its derivatives so as to utilize their flexibility. Many innovative synthesis techniques have led to novel graphene‐based hybrid two‐dimensional nanostructures. Here, the chemically integrated inorganic‐graphene hybrid two‐dimensional materials and their applications for energy storage devices are examined. First, the synthesis and characterization of different kinds of inorganic‐graphene hybrid nanostructures are summarized, and then the most relevant applications of inorganic‐graphene hybrid materials in flexible energy storage devices are reviewed. The general design rules of using graphene‐based hybrid 2D materials for energy storage devices and their current limitations and future potential to advance energy storage technologies are also discussed.     

Graphene: An Outstanding Multifunctional Coating for Conventional Materials

As the most significant facilitator of human civilization, materials are eternal jewels in the view of researchers whose brilliance never faded. However, simple conventional materials, which are most commonly used and indispensable today, seem too primitive and insufficiently functional to meet the demands of the future intelligent and informational applications, urging more functions to be integrated. The ideal strategy to achieve the transformations of conventional materials non‐destructively is functionalizing the surface and retaining the original properties at the same time. Graphene, a two‐dimensional material with only atomic‐thickness, has come into the view of the researchers, attributed to its various outstanding properties. In recent years, a large amount of research has been devoted to “wearing” graphene to functionalize the conventional materials, booming a huge “graphene‐X” family. In this concept, representative members are illustrated and their improved functions are demonstrated. Also, the prospects and challenges for this dazzling family are discussed.     

Electrorheological Fluids

Materials that switch from liquid‐like to solid‐like upon application of an electric field are termed electrorheological fluids. The general features and preparation of these smart materials are reviewed before recent advances in the improvement and applications (e.g., sensors, damping devices, inks) of these fluids are described. Materials ranging from aluminosilicate (see Figure) and carbonaceous inorganic materials to liquid‐crystal polymers to semiconductive polymers can be used to fabricate electrorheological fluids.     

Quantum‐Confined‐Superfluidics‐Enabled Moisture Actuation Based on Unilaterally Structured Graphene Oxide Papers

The strong interaction between graphene oxides (GO) and water molecules has trigged enormous research interest in developing GO‐based separation films, sensors, and actuators. However, sophisticated control over the ultrafast water transmission among the GO sheets and the consequent deformation of the entire GO film is still challenging. Inspired from the natural “quantum‐tunneling‐fluidics‐effect,” here quantum‐confined‐superfluidics‐enabled moisture actuation of GO paper by introducing periodic gratings unilaterally is reported. The folded GO nanosheets that act as quantum‐confined‐superfluidics channels can significantly promote water adsorption, enabling controllable and sensitive moisture actuation. Water‐adsorption‐induced expansion along and against the normal direction of a GO paper is investigated both theoretically and experimentally. Featuring state‐of‐the‐art of ultrafast response (1.24 cm^?1 s^?1), large deformation degree, and complex and predictable deformation, the smart GO papers are used for biomimetic mini‐robots including a creeping centipede and a smart leaf that can catch a living ladybug. The reported method is simple and universal for 2D materials, revealing great potential for developing graphene‐based smart robots.