Advanced Materials and BioEngineering Research

Two-dimensional (2D) transition metal carbides and nitrides (MXenes) have shown outstanding performances in electrochemical energy storage and many other applications. Delamination of MXene flakes in water produces colloidal solutions that are used to manufacture all kinds of products (thin films, coatings, and electrodes, etc.). However, the stability of MXene colloidal solutions, which is of critical importance to their application, remains largely unexplored. Here we report on the degradation of delaminated-Ti 3 C 2 T x colloidal solutions (T represents the surface functionalities) and outline protocols to improve their stability. Ti 3 C 2 T x MXene solutions in open vials degraded by 42%, 85%, and 100% after 5, 10, and 15 days, respectively, leading to the formation of cloudy-white colloidal solutionss containing primarily anatase (TiO 2 ). On the other hand, the solution could be well-preserved when Ti 3 C 2 T x MXene colloidal solutionss were stored in hermetic Ar-filled bottles at 5 °C, because dissolved oxygen, the main oxidant of the MXene flakes, was eliminated. Under such a recipe, the time constant of the solution was dramatically increased. We have found that the degradation starts at the edges and its kinetics follows the single-exponential decay quite well. Moreover, we performed size selection of the MXene solution via a cascade technique and showed that the degradation process is also size-dependent, with the small flakes being the least stable. Furthermore, a dependence between the degradation time constants and the flake size allows us to determine the size of the nanosheets in situ from UV–vis spectra and vice versa . Finally, the proposed method of storing the MXene colloidal solution in Ar-filled vials was applied to Ti 2 CT x to improve its stability and time constant, demonstrating the validity of this protocol in improving the lifetime of different MXene solutions.

Adhesion to wet and dynamic surfaces, including biological tissues, is important in many fields but has proven to be extremely challenging. Existing adhesives are cytotoxic, adhere weakly to tissues, or cannot be used in wet environments. We report a bioinspired design for adhesives consisting of two layers: an adhesive surface and a dissipative matrix. The former adheres to the substrate by electrostatic interactions, covalent bonds, and physical interpenetration. The latter amplifies energy dissipation through hysteresis. The two layers synergistically lead to higher adhesion energies on wet surfaces as compared with those of existing adhesives. Adhesion occurs within minutes, independent of blood exposure and compatible with in vivo dynamic movements. This family of adhesives may be useful in many areas of application, including tissue adhesives, wound dressings, and tissue repair.

2D transition‐metal carbides and nitrides, known as MXenes, have displayed promising properties in numerous applications, such as energy storage, electromagnetic interference shielding, and catalysis. Titanium carbide MXene (Ti 3 C 2 T x ), in particular, has shown significant energy‐storage capability. However, previously, only micrometer‐thick, nontransparent films were studied. Here, highly transparent and conductive Ti 3 C 2 T x films and their application as transparent, solid‐state supercapacitors are reported. Transparent films are fabricated via spin‐casting of Ti 3 C 2 T x nanosheet colloidal solutions, followed by vacuum annealing at 200 °C. Films with transmittance of 93% (≈4 nm) and 29% (≈88 nm) demonstrate DC conductivity of ≈5736 and ≈9880 S cm −1 , respectively. Such highly transparent, conductive Ti 3 C 2 T x films display impressive volumetric capacitance (676 F cm −3 ) combined with fast response. Transparent solid‐state, asymmetric supercapacitors (72% transmittance) based on Ti 3 C 2 T x and single‐walled carbon nanotube (SWCNT) films are also fabricated. These electrodes exhibit high capacitance (1.6 mF cm −2 ) and energy density (0.05 µW h cm −2 ), and long lifetime (no capacitance decay over 20 000 cycles), exceeding that of graphene or SWCNT‐based transparent supercapacitor devices. Collectively, the Ti 3 C 2 T x films are among the state‐of‐the‐art for future transparent, conductive, capacitive electrodes, and translate into technologically viable devices for next‐generation wearable, portable electronics.

Few-layer black phosphorus (BP) is a new two-dimensional material which is of great interest for applications, mainly in electronics. However, its lack of environmental stability severely limits its synthesis and processing. Here we demonstrate that high-quality, few-layer BP nanosheets, with controllable size and observable photoluminescence, can be produced in large quantities by liquid phase exfoliation under ambient conditions in solvents such as N-cyclohexyl-2-pyrrolidone (CHP). Nanosheets are surprisingly stable in CHP, probably due to the solvation shell protecting the nanosheets from reacting with water or oxygen. Experiments, supported by simulations, show reactions to occur only at the nanosheet edge, with the rate and extent of the reaction dependent on the water/oxygen content. We demonstrate that liquid-exfoliated BP nanosheets are potentially useful in a range of applications from ultrafast saturable absorbers to gas sensors to fillers for composite reinforcement.

Abstract Direct printing of functional inks is critical for applications in diverse areas including electrochemical energy storage, smart electronics and healthcare. However, the available printable ink formulations are far from ideal. Either surfactants/additives are typically involved or the ink concentration is low, which add complexity to the manufacturing and compromises the printing resolution. Here, we demonstrate two types of two-dimensional titanium carbide (Ti 3 C 2 T x ) MXene inks, aqueous and organic in the absence of any additive or binary-solvent systems, for extrusion printing and inkjet printing, respectively. We show examples of all-MXene-printed structures, such as micro-supercapacitors, conductive tracks and ohmic resistors on untreated plastic and paper substrates, with high printing resolution and spatial uniformity. The volumetric capacitance and energy density of the all-MXene-printed micro-supercapacitors are orders of magnitude greater than existing inkjet/extrusion-printed active materials. The versatile direct-ink-printing technique highlights the promise of additive-free MXene inks for scalable fabrication of easy-to-integrate components of printable electronics.

Transition metal nitrides (TMNs), by virtue of their unique electronic structure, high electrical conductivity, superior chemical stability, and excellent mechanical robustness, have triggered tremendous research interest over the past decade, and showed great potential for electrochemical energy conversion and storage. However, bulk TMNs usually suffer from limited numbers of active sites and sluggish ionic kinetics, and eventually ordinary electrochemical performance. Designing nanostructured TMNs with tailored morphology and good dispersity has proved an effective strategy to address these issues, which provides a larger specific surface area, more abundant active sites, and shorter ion and mass transport distances over the bulk counterparts. Herein, the most up-to-date progress on TMN-based nanomaterials is comprehensively reviewed, focusing on geometric-structure design, electronic-structure engineering, and applications in electrochemical energy conversion and storage, including electrocatalysis, supercapacitors, and rechargeable batteries. Finally, we outline the future challenges of TMN-based nanomaterials and their possible research directions beyond electrochemical energy applications.

The hybrid halide perovskite CH3NH3PbI3 has enabled solar cells to reach an efficiency of about 20%, demonstrating a pace for improvements with no precedents in the solar energy arena. Despite such explosive progress, the microscopic origin behind the success of such material is still debated, with the role played by the organic cations in the light-harvesting process remaining unclear. Here van der Waals-corrected density functional theory calculations reveal that the orientation of the organic molecules plays a fundamental role in determining the material electronic properties. For instance, if CH3NH3 orients along a (011)-like direction, the PbI6 octahedral cage will distort and the bandgap will become indirect. Our results suggest that molecular rotations, with the consequent dynamical change of the band structure, might be at the origin of the slow carrier recombination and the superior conversion efficiency of CH3NH3PbI3.

In this work, multiwalled carbon nanotubes were investigated as potential mechanical reinforcement agents in two hosts, polyvinyl alcohol (PVA) and poly(9-vinyl carbazole) (PVK). It was found that, by adding various concentrations of nanotubes, both Young’s modulus and hardness increased by factors of 1.8 and 1.6 at 1 wt % in PVA and 2.8 and 2.0 at 8 wt % in PVK, in reasonable agreement with the Halpin–Tsai theory. Furthermore, the presence of the nanotubes was found to nucleate crystallization of the PVA. This crystal growth is thought to enhance matrix-nanotube stress transfer. In addition, microscopy studies suggest extremely strong interfacial bonding in the PVA-based composite. This is manifested by the fracture of the polymer rather that the polymer-nanotube interface.

Abstract The fast growth of portable smart electronics and internet of things have greatly stimulated the demand for miniaturized energy storage devices. Micro‐supercapacitors (MSCs), which can provide high power density and a long lifetime, are ideal stand‐alone power sources for smart microelectronics. However, relatively few MSCs exhibit both high areal and volumetric capacitance. Here rapid production of flexible MSCs is demonstrated through a scalable, low‐cost stamping strategy. Combining 3D‐printed stamps with arbitrary shapes and 2D titanium carbide or carbonitride inks (Ti 3 C 2 T x and Ti 3 CNT x , respectively, known as MXenes), flexible all‐MXene MSCs with controlled architectures are produced. The interdigitated Ti 3 C 2 T x MSC exhibits high areal capacitance: 61 mF cm −2 at 25 µA cm −2 and 50 mF cm −2 as the current density increases by 32 fold. The Ti 3 C 2 T x MSCs also showcase capacitive charge storage properties, good cycling lifetime, high energy and power densities, etc. The production of such high‐performance Ti 3 C 2 T x MSCs can be easily scaled up by designing pad or cylindrical stamps, followed by a cold rolling process. Collectively, the rapid, efficient production of flexible all‐MXene MSCs with state‐of‐the‐art performance opens new exciting opportunities for future applications in wearable and portable electronics.

Abstract Polymer–multiwalled carbon nanotube composite films were fabricated using two types of polymer matrices, namely poly(vinyl alcohol), (PVA) and chlorinated polypropylene. In the first case, the PVA was observed to form a crystalline coating around the nanotubes, maximising interfacial stress transfer. In the second case the interface was engineered by covalently attaching chlorinated polypropylene chains to the nanotubes, again resulting in large stress transfer. Increases in Young's modulus, tensile strength, and toughness of × 3.7, × 4.3, and × 1.7, respectively were observed for the PVA‐based materials at less than 1 wt.‐% nanotubes. Similarily for the polypropylene‐based composites, increases in Young's modulus, tensile strength and toughness of × 3.1, × 3.9, and × 4.4, respectively, were observed at equivalent nanotube loading levels. In addition, a model to describe composite strength was derived. This model shows that the tensile strength increases in proportion to the thickness of the interface region. This suggests that composite strength can be optimized by maximising the thickness of the crystalline coating or the thickness of the interfacial volume partially occupied by functional groups.

. In this review, we describe current fluorescent probes designed for the detection and quantification of key bioactive molecules associated with common diseases, such as organ damage, inflammation, cancers, cardiovascular diseases, and brain disorders. We emphasize the strategies behind the design of fluorescent probes capable of disease biomarker detection and diagnosis and cover some aspects of combined diagnostic/therapeutic strategies based on regulating disease-related molecules. This review concludes with a discussion of the challenges and outlook for fluorescent probes, highlighting future avenues of research that should enable these probes to achieve accurate detection and identification of disease-related biomarkers for biomedical research and clinical applications.

High-performance sensors based on molybdenum disulfide (MoS2 ) grown by sulfurization of sputtered molybdenum layers are presented. Using a simple integration scheme, it is found that the electrical conductivity of MoS2 films is highly sensitive to NH3 adsorption, consistent with n-type semiconducting behavior. A sensitivity of 300 ppb at room temperature is achieved, showing the high potential of 2D transition metal-dichalcogenides for sensing.

Abstract 2D transition metal carbides and/or nitrides (MXenes), by virtue of high electrical conductivity, abundant surface functional groups and excellent dispersion in various solvents, are attracting increasing attention and showing competitive performance in energy storage and conversion applications. However, like other 2D materials, MXene nanosheets incline to stack together via van der Waals interactions, which lead to limited number of active sites, sluggish ionic kinetics, and finally ordinary performance of MXene materials/devices. Constructing 2D MXene nanosheets into 3D architectures has been proven to be an effective strategy to reduce restacking, thus providing larger specific surface area, higher porosity, and shorter ion and mass transport distance over normal 1D and 2D structures. In this review, the commonly used strategies for manufacturing 3D MXene architectures (3D MXenes and 3D MXene‐based composites) are summarized, such as template, assembly, 3D printing, and other methods. Special attention is also given to the structure–property relationships of 3D MXene architectures and their applications in electrochemical energy storage and conversion, including supercapacitors, rechargeable batteries, and electrocatalysis. Finally, the authors propose a brief perspective on future opportunities and challenges for 3D MXene architectures/devices.

All-printed transistors consisting of interconnected networks of various types of two-dimensional nanosheets are an important goal in nanoscience. Using electrolytic gating, we demonstrate all-printed, vertically stacked transistors with graphene source, drain, and gate electrodes, a transition metal dichalcogenide channel, and a boron nitride (BN) separator, all formed from nanosheet networks. The BN network contains an ionic liquid within its porous interior that allows electrolytic gating in a solid-like structure. Nanosheet network channels display on:off ratios of up to 600, transconductances exceeding 5 millisiemens, and mobilities of >0.1 square centimeters per volt per second. Unusually, the on-currents scaled with network thickness and volumetric capacitance. In contrast to other devices with comparable mobility, large capacitances, while hindering switching speeds, allow these devices to carry higher currents at relatively low drive voltages.

This work describes silicon nanoparticle-based lithium-ion battery negative electrodes where multiple nonactive electrode additives (usually carbon black and an inert polymer binder) are replaced with a single conductive binder, in this case, the conducting polymer PEDOT: PSS. While enabling the production of well-mixed slurry-cast electrodes with high silicon content (up to 95 wt %), this combination eliminates the well-known occurrence of capacity losses due to physical separation of the silicon and traditional inorganic conductive additives during repeated lithiation/delithiation processes. Using an in situ secondary doping treatment of the PEDOT: PSS with small quantities of formic acid, electrodes containing 80 wt % SiNPs can be prepared with electrical conductivity as high as 4.2 S/cm. Even at the relatively high areal loading of 1 mg/cm(2), this system demonstrated a first cycle lithiation capacity of 3685 mA·h/g (based on the SiNP mass) and a first cycle efficiency of ∼78%. After 100 repeated cycles at 1 A/g this electrode was still able to store an impressive 1950 mA·h/g normalized to Si mass (∼75% capacity retention), corresponding to 1542 mA·h/g when the capacity is normalized by the total electrode mass. At the maximum electrode thickness studied (∼1.5 mg/cm(2)), a high areal capacity of 3 mA·h/cm(2) was achieved. Importantly, these electrodes are based on commercially available components and are produced by the standard slurry coating methods required for large-scale electrode production. Hence, the results presented here are highly relevant for the realization of commercial LiB negative electrodes that surpass the performance of current graphite-based negative electrode systems.

In order to fulfill their potential for applications, it will be necessary to develop large-scale production methods for two-dimensional (2D) inorganic nanosheets. Here we demonstrate the large-scale shear-exfoliation of molybdenum disulfide nanosheets in aqueous surfactant solution using a kitchen blender. Using standard procedures, we measure how the MoS 2 concentration and production rate scale with processing parameters. However, we also use recently developed methods based on optical spectroscopy to simultaneously measure both nanosheet lateral size and thickness, allowing us to also study the dependence of nanosheet dimensions on processing parameters. We found the nanosheet concentration and production rates to depend sensitively on the mixing parameters (the MoS 2 concentration, C i; the mixing time, t; the liquid volume, V; and the rotor speed, N ). By optimizing mixing parameters, we achieved concentrations and production rates as high as 0.4 mg/mL and 1.3 mg/min, respectively. Conversely, the nanosheet size and thickness were largely invariant with these parameters. The nanosheet concentration is also extremely sensitive to the surfactant concentration. However, more interestingly the nanosheet lateral size and thickness also varied strongly with the surfactant concentration. This allows the mean nanosheet dimensions to be controlled during shear exfoliation at least in the range ∼40–220 nm for length and ∼2–12 layers for thickness. We demonstrate the importance of this by showing that the MoS 2 nanosheets prepared using different surfactant concentrations, and so displaying different nanosheets sizes, perform differently when used as hydrogen evolution catalysts. We find the nanosheets produced using high surfactant concentrations, which gives smaller flake sizes, perform significantly better, consistent with catalysis occurring at nanosheet edges. Finally, we also demonstrate that shear exfoliation using a kitchen blender is not limited to MoS 2 but can also be achieved for boron nitride and tungsten disulfide.

Cartilage is a dense connective tissue with limited self-repair capabilities. Mesenchymal stem cell (MSC) laden hydrogels are commonly used for fibrocartilage and articular cartilage tissue engineering, however they typically lack the mechanical integrity for implantation into high load bearing environments. This has led to increased interested in 3D bioprinting of cell laden hydrogel bioinks reinforced with stiffer polymer fibres. The objective of this study was to compare a range of commonly used hydrogel bioinks (agarose, alginate, GelMA and BioINK™) for their printing properties and capacity to support the development of either hyaline cartilage or fibrocartilage in vitro . Each hydrogel was seeded with MSCs, cultured for 28 days in the presence of TGF- β 3 and then analysed for markers indicative of differentiation towards either a fibrocartilaginous or hyaline cartilage-like phenotype. Alginate and agarose hydrogels best supported the development of hyaline-like cartilage, as evident by the development of a tissue staining predominantly for type II collagen. In contrast, GelMA and BioINK ™ (a PEGMA based hydrogel) supported the development of a more fibrocartilage-like tissue, as evident by the development of a tissue containing both type I and type II collagen. GelMA demonstrated superior printability, generating structures with greater fidelity, followed by the alginate and agarose bioinks. High levels of MSC viability were observed in all bioinks post-printing (∼80%). Finally we demonstrate that it is possible to engineer mechanically reinforced hydrogels with high cell viability by co-depositing a hydrogel bioink with polycaprolactone filaments, generating composites with bulk compressive moduli comparable to articular cartilage. This study demonstrates the importance of the choice of bioink when bioprinting different cartilaginous tissues for musculoskeletal applications.

We present here a perspective detailing the current state-of-the-art technologies for the characterisation of nanoparticles (NPs) in liquid suspension. We detail the technologies involved and assess their applications in the determination of NP size and concentration. We also investigate the parameters that can influence the results and put forward a cause and effect analysis of the principle factors influencing the measurement of NP size and concentration by NP tracking analysis and dynamic light scattering, to identify areas where uncertainties in the measurement can arise. Also included are technologies capable of characterising NPs in solution, whose measurements are not based on light scattering. It is hoped that the manuscript, with its detailed description of the methodologies involved, will assist scientists in selecting the appropriate technology for characterising their materials and enabling them to comply with regulatory agencies' demands for accurate and reliable NP size and concentration data.

Layered two-dimensional (2D) materials display great potential for a range of applications, particularly in electronics. We report the large-scale synthesis of thin films of platinum diselenide (PtSe 2 ), a thus far scarcely investigated transition metal dichalcogenide. Importantly, the synthesis by thermally assisted conversion is performed at 400 °C, representing a breakthrough for the direct integration of this material with silicon (Si) technology. Besides the thorough characterization of this 2D material, we demonstrate its promise for applications in high-performance gas sensing with extremely short response and recovery times observed due to the 2D nature of the films. Furthermore, we realized vertically stacked heterostructures of PtSe 2 on Si which act as both photodiodes and photovoltaic cells. Thus, this study establishes PtSe 2 as a potential candidate for next-generation sensors and (opto-)electronic devices, using fabrication protocols compatible with established Si technologies.

Abstract The ever-increasing demands for advanced lithium-ion batteries have greatly stimulated the quest for robust electrodes with a high areal capacity. Producing thick electrodes from a high-performance active material would maximize this parameter. However, above a critical thickness, solution-processed films typically encounter electrical/mechanical problems, limiting the achievable areal capacity and rate performance as a result. Herein, we show that two-dimensional titanium carbide or carbonitride nanosheets, known as MXenes, can be used as a conductive binder for silicon electrodes produced by a simple and scalable slurry-casting technique without the need of any other additives. The nanosheets form a continuous metallic network, enable fast charge transport and provide good mechanical reinforcement for the thick electrode (up to 450 µm). Consequently, very high areal capacity anodes (up to 23.3 mAh cm −2 ) have been demonstrated.