This study presents a comprehensive review of the history of research and development of different damage-detection methods in the realm of composite structures. Different fields of engineering, such ...as mechanical, architectural, civil, and aerospace engineering, benefit excellent mechanical properties of composite materials. Due to their heterogeneous nature, composite materials can suffer from several complex nonlinear damage modes, including impact damage, delamination, matrix crack, fiber breakage, and voids. Therefore, early damage detection of composite structures can help avoid catastrophic events and tragic consequences, such as airplane crashes, further demanding the development of robust structural health monitoring (SHM) algorithms. This study first reviews different non-destructive damage testing techniques, then investigates vibration-based damage-detection methods along with their respective pros and cons, and concludes with a thorough discussion of a nonlinear hybrid method termed the Vibro-Acoustic Modulation technique. Advanced signal processing, machine learning, and deep learning have been widely employed for solving damage-detection problems of composite structures. Therefore, all of these methods have been fully studied. Considering the wide use of a new generation of smart composites in different applications, a section is dedicated to these materials. At the end of this paper, some final remarks and suggestions for future work are presented.
Phosphorene and antimonene, single‐ or few‐layered (FL) semiconductor materials, have recently attracted enormous attention due to their unique properties, provided by their extreme thinness. Here, a ...liquid‐phase exfoliation (LPE) procedure to prepare FL arsenene, another member of pnictogens, assisted by sonication and without any additional surfactant is reported. The exfoliation process is performed in various solvents. Among those, N‐methylpyrrolidone is found to provide the highest concentration of stable arsenene sheets. Spectroscopic and microscopic analyses confirm the formation of high‐quality few‐layer arsenene nanosheets with large lateral dimensions. An application of this material for construction of vapor sensor based on electrochemical impedance spectroscopy is demonstrated. The device detects selectively methanol or acetone vapors depending on the selected resonance frequency. The results are highly reproducible, and the vapor sensor has long‐term stability.
A liquid‐phase exfoliation procedure to prepare 2D‐arsenene via sonication is reported, and the formation of high‐quality few‐layer arsenene nanosheets with large lateral dimensions is confirmed. A vapor sensing using arsenene nanosheets is demonstrated, which can selectively detect methanol or acetone vapors depending on the selected resonance frequency. The results are highly reproducible, and the sensor has long‐term stability.
Nano/micromachines with autonomous motion are the frontier of nanotechnology and nanomaterial research. These self‐propelled nano/micromachines convert chemical energy obtained from their ...surroundings to propulsion. They have shown great potential in diagnostic and therapeutic applications. This work introduces a high‐speed tubular electrically conductive micromachine based on reduced nanographene oxide (n‐rGO) as a platform for drug delivery and platinum (Pt) as the catalytic inner layer. n‐rGO/Pt micromachines are loaded with doxorubicin (DOX) by a simple physical adsorption with a very high loading efficiency, displaying single‐ or multistrand wrapping of DOX monomers on the micromachine cylinders. More importantly, it is found that electron injection into DOX@n‐rGO/Pt micromachines via electrochemistry leads to expulsion of DOX from micromachines in motion within only a few seconds. An in vitro study confirms this efficient release mechanism in the presence of cancerous cells. The unique properties of the n‐rGO/Pt micromotor enable the effective management of DOX release at the tumor site and thus enhances the therapeutic efficiency and reduces the side toxicity toward the healthy tissue. These micromachine drug carriers combine the high loading capacity of conventional carbon‐based drug carriers with a fast and efficient electrochemical drug‐release mechanism.
An active platform for an electrochemically triggered drug delivery system based on microrobots is demonstrated. Graphene‐based micromachines are loaded with doxorubicin (DOX). Their ability to deliver an anticancer drug is demonstrated in combination with an on‐demand electrochemical release method. The electron injection into micromachines leads to the controlled release of DOX from micromachines in motion within only a few seconds.
Graphene has gained substantial research interest in many fields due to its remarkable properties among many other two-dimensional materials. In this study, we propose a wireless electrochemical ...approach, bipolar electrochemistry, for the precise modification of single layers of graphene at predefined locations, such as distinct edges or corners, with a variety of metals or polymers, thus enabling the elaboration of multi-functional monolayer graphene sheets. We illustrate the concept e.g. by depositing multiple metals, or platinum and a catalyst-containing porous polymer on the same graphene sheet, but at separate corners. This configuration allows activating chemiluminescence on the polymer spot, and simultaneously generates the driving force for autonomous motion on the Pt side through the catalytic decomposition of hydrogen peroxide into oxygen bubbles. This integration of different chemical features on the same object, exemplified by these proof-of-principle experiments, enhances the functionality of two-dimensional materials, paving the way for the use of these hybrid materials for a variety of applications, ranging from sensing and catalysis to targeted delivery.
Spatial confinement of chemical reactions or physical effects may lead to original phenomena and new properties. Here, the generation of electrochemiluminescence (ECL) in confined free-standing 2D ...spaces, exemplified by surfactant-based air bubbles is reported. For this, the ultrathin walls of the bubbles (typically in the range of 100-700 nm) are chosen as a host where graphene sheets, acting as bipolar ECL-emitting electrodes, are trapped and dispersed. The proposed system demonstrates that the required potential for the generation of ECL is up to three orders of magnitude smaller compared to conventional systems, due to the nanoconfinement of the potential drop. This proof-of-concept study demonstrates the key advantages of a 2D environment, allowing a wireless activation of ECL at rather low potentials, compatible with (bio)analytical systems.
2D nanoconfinement in the walls of a soap bubble can reduce the electric field required for the wireless generation of electrochemiluminescence by up to three orders of magnitude, which is critical in sensitive environments such as those for bio-imaging.
The surface of steel S235 was oxidized by Cl2 gas and checked for its electrocatalytic efficiency regarding oxygen formation in aqueous solution. If exposed to humid Cl2 gas for 110 min, steel S235 ...became an electrocatalyst that exhibits an overpotential for the oxygen evolution reaction (OER) of 462 mV at 1 mA cm−2 at pH 7. The OER activity of the same sample at pH 13 was moderate (347 mV overpotential at 2.0 mA cm−2 current density) in comparison with OER electrocatalysts developed recently. Potential versus time plots measured at a constant current demonstrate the sufficient stability of all samples under catalysis conditions at pH 7 and 13 for tens of hours. High‐resolution X‐ray photoelectron spectra could be reasonably resolved with the proviso that Fe2O3, FeO(OH), MnO(OH), and Mn2O3 are the predominant Fe and Mn species on the surface of the oxidized steel S235.
Anode of steel: Exposure to chlorine gas at room temperature converts standard carbon manganese steel (S235) into an oxygen evolution electrocatalyst that exhibits a surprisingly high catalytic activity in a neutral regime. This is shown by the strong voltage current behavior derived from long‐term chronopotentiometry measurements: 462 mV overpotential at 1 mA cm−2 in 0.1 M KH2PO4/K2KHPO4 buffer solution.
It has been more than a decade since nano/micromachines (NMMs) have received the particular attention of scientists in different research fields. They are able to convert chemical energy into ...mechanical motion in their surrounding environment. Herein, a powerful, efficient and fast strategy of using nanosized reduced graphene oxide flake (n-rGO)-based self-propelled tubular micromachines for the removal of nitroaromatic compounds (NACs) is described. This method relies on the integration of the rGO as a well-known adsorbent of aromatic compounds with chemically powered engines for the removal of explosive compounds such as 2,4,6-trinitrotoluene (TNT), 2,4,6-trinitrophenol (TNP) and 2,4-dinitrotoluene (DNT). Nanographene oxide reduced electrochemically inside the pores of the polycarbonate membrane to form an outer layer (n-rGO, adsorbent layer) of the micromachines. Subsequent electrodeposition of nickel (Ni, magnetic layer) and platinum (Pt, catalytic layer) resulted in the formation of n-rGO/Ni/Pt micromachines. Notably, the bubble-propelled micromachines were able to remove nitroaromatic compounds with high efficiency (∼90-92%) compared to the efficiency of magnetic-guided (22-42%) and static (2.5-7%) micromachines. Most importantly, the micromachines were regenerated and reused several times. The regeneration is based on an electrochemical method in which electron injection into the machine causes the expulsion of contaminants from the outer layer of the micromachines within a few seconds. The integration of the powerful self-propulsion, high adsorbent capacity of rGO and the introduced ultrafast regeneration procedure are beneficial for the realization of an active platform for water remediation.
Ultrathin bismuth exhibits promising performance for topological insulators due to its narrow band gap and intrinsic strong spin–orbit coupling, as well as for energy‐related applications because of ...its electronic and mechanical properties. However, large‐scale production of 2D sheets via liquid‐phase exfoliation as an established large‐scale method is restricted by the strong interaction between bismuth layers. Here, a sonication method is utilized to produce ultrahigh‐aspect‐ratio bismuthene microsheets. The studies on the mechanism excludes the exfoliation of the layered bulk bismuth and formation of the microsheets is attributed to the melting of spherical particles (r = 1.5 µm) at a high temperature—generated under the ultrasonic tip—followed by a recrystallization step producing uniformly‐shaped ultrathin microsheets (A = 0.5–2 µm2, t: ≈2 nm). Notably, although the preparation is performed in oxygenated aqueous solution, the sheets are not oxidized, and they are stable under ambient conditions for at least 1 month. The microsheets are used to construct a vapor sensor using electrochemical impedance spectroscopy as detection technique. The device is highly selective, and it shows long‐term stability. Overall, this project exhibits a reproducible method for large‐scale preparation of ultrathin bismuthene microsheets in a benign environment, demonstrating opportunities to realize devices based on bismuthene.
The transformation of bulk bismuth to ultrahigh‐aspect‐ratio 2D bismuthene via a sonication method is demonstrated. The formation of such large sheets is attributed to the recrystallization of bismuth under sonication tip. Despite preparation in oxygenated water, microsheets are not oxidized and are stable in an ambient condition. Overall, this method allows facile preparation of high‐quality bismuthene on a large scale.
The development of fuel‐free light‐powered multi stimuli‐responsive microrobots is becoming a vital field in biomedical research. The challenge is to design biomedical robots with precise motion ...control and novel functionalities such that one day they will stand alongside medical staff as fully fledged partners in the delivery of advanced non‐invasive therapeutic procedures. In this study, a simple one‐step etching/polymerization procedure is used to fabricate crystalline metal‐organic framework structures surface‐coated with a conductive polypyrrole (PPy) layer and then enriched with Methylene Blue sensitizer molecules. Due to the PPy surface charge, the microrobots start to move when exposed to a visible light source, enabling the controllable accumulation of the microrobots at the focal point of the light beam. Furthermore, a self‐regulated motion is achieved by the PPy surface charge also providing a pH‐dependent switch capable of altering microrobot behavior. In vitro study is conducted to test microrobot efficiency against human cervix carcinoma HeLa cells. It is shown that the micromotors are able to penetrate and successfully destroy the cancer cells. The work provides proof‐of‐concept for a novel strategy in which such microrobots can be guided by an optical beam, can self‐regulate movement toward or away from each other, and can perform therapeutic functions with great efficiency.
Fuel‐free light‐powered microrobots with unique combination of materials enables them exceptional self‐regulatory and switchable collective behavior and also to penetrate and destroy cancer cells. Composed of metal‐organic framework crystals functionalized with polypyrrole and Methylene Blue sensitizer molecules, the microrobots show highly responsive light‐controlled motion behavior, rapidly navigating to and accumulating at the focal point of a visible light source.
Holes and knots are common defects that occur in wood that affect its value for both structural and high-end aesthetic applications. When these defects are internal to wood they are rarely evident ...from visual inspection. It is therefore important to develop techniques to detect and analyse these defects both in standing trees prior to harvesting them and in processed timber and/or completed wooden structures. This paper presents an effective method to detect and analyse hole defects in wood. The method uses the recorded output wave signal from an ultrasonic device tested on rectangular wood samples. The ultrasonic wave signal is decomposed into its constructive modes using Empirical Mode Decomposition (EMD). This process decomposes a non-stationary non-linear wave signal into its semi-orthogonal bases known as intrinsic mode functions (IMFs). A matrix of all IMFs (except the residual IMF) is then assembled and its covariance matrix derived. The research demonstrates through several experimental studies that the maximum eigenvalue of the proposed covariance matrix is more sensitive to hole defects in wood than traditionally used measures such as time-of-flight. The results provide evidence that the proposed damage sensitive feature (DSF) can successfully detect hole defects in hardwood samples but further work is recommended on its application to other materials. It is anticipated that this method will have wide applicability in the forestry and timber industries for aiding in product value determination.
PDF
