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Combining treatment and diagnosis, called theranostics, which is achieved within single nanoparticle is an ultimate goal of many studies. Herein, we developed a new nanotheranostic agent − Nd3+-sensitized upconversion nanoparticles core for dual modal imaging (i.e., upconversion luminescence imaging and magnetic resonance imaging) and antimony nanoshell for photothermal therapy (PTT). The core-shell-shell upconversion nanoparticles (NaYF4:Yb,Er@NaYF4:Yb,Nd@NaGdF4:Nd, named as UCNP) were firstly synthesized using thermal decomposition method and then were coated by antimony shell over the surface of UCNP using simple cost and time effective new method. Furthermore, the surface of UCNP@Sb nanostructures was modified with DSPE-PEG in order to enhance the water solubility and biocompatibility. The final nanotheranostic agent, named as UCNP@Sb-PEG, exhibits very low toxicity, good biocompatibility, very good photothermal therapeutic effect, and efficient upconversion luminescence (UCL) imaging of HeLa cells under only one laser (808 nm) irradiation. The antimony shell is quenching the upconversion emission in pristine nanotheranostic agent, but interestingly, the UCL intensity of the agent recovers progressively under 808 nm laser irradiation due to light induced degradability of antimony shell. Besides, high longitudinal relaxivity (r1) obtained from the experiment approves excellent potential of the nanotheranostic agent for T1-weighted magnetic resonance imaging application.

Manganese-zinc ferrite is a kind of very important magnetic ferrite material. The properties of wide absorption band, sensitivity to ultraviolet (UV) light and tumor H2O2 promise it to be possibly used as a photothermal therapy (PTT), photodynamic therapy (PDT) and chemodynamic therapy (CDT) agent. Based on the unique advantages of rare-earth doped nanoparticles, an Er3+, Tm3+ co-doped upconversion-mediated nanosystem with manganese-zinc ferrite shell (named as UCNPS@M) was developed through a facile thermal co-decomposition method. The final nanosystems were surface-modified by using dopamine hydrochloride (DA) in order to warrant good biocompatibility (named as UCNPS@M@DA). Under irradiation of near-infrared (NIR) light, UCNPS emit both ultraviolet and visible light. The UV light is mostly absorbed by manganese-zinc ferrite shell to produce reactive oxygen species (ROS), which is essential to the potential PDT and CDT effect of nanosystems, and at the same time, Mn0.5Zn0.5Fe2O4 can further react with H2O2 to promote the efficiency of •OH-generation. It is expected that UCNPS@M@DA can act as upconversion luminescence imaging guidance due to the visible emission from UCNPS. In addition, the energy absorbed by the nanosystems can be transferred to heat to realize photothermal effect. Moreover, UCNPS@M@DA was successfully applied as a T1/T2-weighted magnetic resonance imaging (MRI) contrast agent due to the existence of Gd, Mn, and Fe elements. In light of the upconversion luminescence (UCL) imaging from the UCNPS as well as potential PTT, PDT, CDT effect mentioned above, this work provides a possibility to realize cancer multi-model bioimaging guided treatment by using an all-in-one diagnosis and therapy nanosystem through a simple yet powerful strategy.

Under the requirement of the force controller of hydraulic quadruped robots, the goal of this work is to accurately track the force commands at the level of the hydraulic drive unit. The main contribution focuses on the development of a force-controlled compensation scheme, which is specifically aimed at the key issues affecting the hydraulic quadrupedal locomotion. With this idea, based on a P-Q valve-controlled asymmetric cylinder, we first establish a mathematical model for the hydraulic drive unit force control system. With the desired force commands, a force feed-forward algorithm is presented to improve the dynamic performance of the system. Meanwhile, we propose a disturbance compensation algorithm to reduce the influence induced by external disturbances due to foot-ground impacts. Afterwards, combining with a variable gain PI controller, a series of experiments are implemented on a force control performance test platform to verify the proposed scheme. The results demonstrate that the force-controlled compensation scheme has the ability to notably improve the force tracking accuracy, reduce the response time and redundant force.

With the fast development of nanomedicine, the imaging-guided and photo-induced cancer monotherapies can efficiently eliminate tumor lesions, which are strongly dependent on the construction of versatile theranostic nanoplatforms. Among diverse photo-converting nanoplatforms, silver chalcogenide nanoparticles feature high biocompatibility, narrow band gaps, and tunable optical properties, yet Ag2Te-based nanosystems are still at a proof-of-concept stage, and the exploration of Ag2Te-based nanosystems suitable for photonic tumor hyperthermia is challenging. Herein, we report on the construction of versatile ultrasmall Ag2Te quantum dots (QDs) via a facile biomineralization strategy. Especially, these Ag2Te QDs with negligible toxicity and excellent biocompatibility were developed for X-ray computed tomography (CT) imaging-guided photonic tumor hyperthermia by near-infrared (NIR) activation. The fabricated Ag2Te QDs exhibited a high tumor suppression rate (94.3%) on 4T1 breast tumor animal models due to the high photothermal-conversion efficiency (50.5%). Mechanistically, Ag2Te QDs were promising potential CT imaging agents for imaging guidance and monitoring during photonic hyperthermia. Importantly, Ag2Te QDs were rapidly eliminated from the body via feces and urine because of their ultrasmall sizes. This work not only broadens the biomedical applications of silver chalcogenide-based theranostic nanosystems but also provides the paradigm of theranostic nanosystems with a photonic tumor hyperthermia effect and outstanding contrast enhancement of high-performance CT imaging.

During the dry post-machining processing of selective laser melting (SLM)-produced stainless steel with TiAlN coated tool, the elements of stainless steel chips can diffuse and adhere into the coated tool surface, causing serious adhesive wear. In this study, to inhibit the adhesion problem at the tool-chip interface, surface textures with different scales (micro-, nano- and micro/nano-textures) are produced on tool rake face by laser processing before and after physical vapor deposition (PVD) TiAlN coatings deposition. To investigate the cutting performance of these developed coated tools, dry machining tests of the SLM-produced stainless steel are carried out. And, the mechanical properties of textured TiAlN coatings such as the hardness, elastic modulus and critical load are also studied to explain the results from the machining tests. It can be found that the anti-adhesive wear performance of TiAlN coated tool is improved by laser surface texturing. The texture dimension significantly affects the mechanical properties and dry cutting performance of the TiAlN coated tool, and the micro/nano-textures are found to be optimum. Meanwhile, the sequence of surface textures also has an effect on the wear performance of the developed TiAlN coated tools. In the experiment, laser surface texturing before coatings is effective in acting as a barrier against flaking of the TiAlN film, providing a higher active surface for the subsequent TiAlN coatings and presenting a higher compressive residual stress. Thus, the developed cutting tool which is textured before TiAlN coatings deposition presents a milder wear compared to the developed one which is textured after TiAlN coatings deposition.

Ni foils with various thickness were used as interlayer to achieve the laser tailored welding of 22MnB5 press-hardened steel (PHS) with Al-Si coating. The effect of Ni content on the microstructure, hardness and strength were studied. The results showed that Ni reduced the content of solidified primary δ phase in the fusion zone, and promoted the transformation from δ phase into γ phase. δ ferrite was absent with the Ni content of 4.7–19.5 wt.%. In addition, the fusion zone was in γ phase region during post-weld heat treatment at 950℃ because Ni can reduce the Ac3 temperature (the temperature at all ferrite was transformed into austenite). The microstructure of fusion zone after post-weld heat treatment was lath martensite with the Ni content of 4.7–11.2 wt.%. The average hardness was similar to base metal, and the tensile strength of welded joint was increased by ∼22% of as-received joint. Ni was effective to suppress the formation of δ ferrite in Al-rich fusion zone, which is potential to achieve the laser welding of PHS with Al-Si coating.

Microrobots have attracted considerable attention due to their immense potential for biomedical and engineering applications in recent years. Inspired by human walks, a bipedal microwalker capable of standing and walking like humans regulated by external weak magnetic fields was reported in this paper. The walker has a submillimeter size and a simple arrowhead shape. Its standing and walking locomotion is controlled by external oscillating magnetic fields generated by orthogonal electromagnetic coil pairs. The walking speeds of the microwalker are controlled using magnetic fields with varying parameters. The walking speeds on a glass substrate immersed in water could reach up to 2.2 mm s−1. Designed walking paths of the microwalker on a horizontal substrate are also demonstrated. Besides walking on horizontal flat surfaces, the microwalker can climb up slopes and walk freely in circular microtubes. The microwalker is of interest in fundamental robotic gait research and for micromanipulation applications.

Liquid metal shows great potential in the fields of consumer electronics, wearable devices, and electronic skin, etc. At the same time, the liquid metal of the micro-Nano structure can also be used to obtain structures such as nanowires. However, traditional direct writing methods are difficult to achieve high precision due to the nozzle diameter, and the viscosity of the liquid metal. In order to overcome that, this paper proposes an innovative direct writing processing method based on a flexible nozzle. A self-made flexible glass nozzle is used in this method. The liquid metal extrusion direction and the nozzle movement direction are collinear during processing, thus making full use of the momentum while the contact area of the liquid metal with the substrate increases. A system was designed and built, the liquid metal dot features and line features were characterized based on this system. The manufacturing resolution of liquid metal is greatly improved, the resolution of spheres and lines can reach 28 μm and 10 μm, respectively. The experiment results demonstrate that the system has the advantages of dimensional stability, structure simplicity, and cost efficiency. In addition, a silicon nanowire structure is obtained through SLS mechanism with liquid metal line. The result indicates that the liquid metal wire produced is small enough to catalyze the growth of silicon nanowires. Overall, this method further improves the accuracy of the liquid metal direct writing. It shows great application potential in the field of flexible electronics Nanowire preparation and Nano technology.

This paper proposed a high-performance magnetic-coupled nonlinear electromagnetic generator (MNL-EMG). A high-permeability iron core is incorporated to the coil. The strong coupling between the iron core and the vibrating magnets lead to significantly improved output power and a broadened operating bandwidth. The magnetic force of the iron core to the permanent magnets and the magnetic flux density inside the iron core are simulated, and the dimension parameters of the MNL-EMG are optimized. Under acceleration of 1.5 g, the MNL-EMG can maintain high output performance in a wide frequency range of 17~30 Hz, which is 4.3 times wider than that of linear electromagnetic generator (EMG) without an iron core. The maximum output power of MNL-EMG reaches 174 mW under the optimal load of 35 Ω, which is higher than those of most vibration generators with frequency less than 30 Hz. The maximum 360 parallel-connected LEDs were successfully lit by the prototype. Moreover, the prototype has an excellent charging performance such that a 1.2 V, 900 mAh Ni-MH battery was charged from 0.95 V to 0.98 V in 240 s. Both the simulation and experiments verify that the proposed bistable EMG device based on magnetic coupling has advantages of wide operating bandwidth and high output power, which could be sufficient to power micro electronic devices.

In order to achieve effective physical human–robot interaction, human dynamic characteristics needs to be considered in admittance control. This paper proposes a variable admittance control method for physical human–robot interaction based on trajectory prediction of human hand motion. By predicting the moving direction of the robot end tool under human guidance, the admittance control parameters are adjusted to reduce the interaction force. The end tool trajectory of the robot under human guidance is used for offline training of long and short-term memory neural network to generate trajectory predictors. Then the trajectory predictors are used in variable admittance control to predict the trajectory and movement direction of the robot end tool in real time. The variable admittance controller adjusts the damping matrix to reduce the damping value in the moving direction. Experiment results show that, using the constant admittance method as a benchmark, the interaction force of the proposed method is reduced by 23%, the trajectory error is reduced by 51%, and the operating jerk is reduced by at least 21%, which proves that the proposed method improves the accuracy and compliance of the operation.

Determining the metallicity and semiconductivity of a multi-walled carbon nanotube (MWCNT) bundle plays a particularly vital role in its interconnection with the metal electrode of an integrated circuit. In this paper, an effective method is proposed to determine the electrical transport properties of an MWCNT bundle using a current–voltage characteristic curve during its electrical breakdown. We established the reliable electrical nanoscale contact between the MWCNT bundle and metal electrode using a robotic manipulation system under scanning electron microscope (SEM) vacuum conditions. The experimental results show that the current–voltage curve appears as saw-tooth-like current changes including up and down steps, which signify the conductance and breakdown of carbon shells in the MWCNT bundle, respectively. Additionally, the power law nonlinear behavior of the current–voltage curve indicates that the MWCNT bundle is semiconducting. The molecular dynamics simulation explains that the electron transport between the inner carbon shells, between the outermost carbon shells and gold metal electrode and between the outermost carbons shells of two adjacent individual three-walled carbon nanotubes (TWCNTs) is through their radial deformation. Density functional theory (DFT) calculations elucidate the electron transport mechanism between the gold surface and double-wall carbon nanotube (DWCNT) and between the inner and outermost carbon shells of DWCNT using the charge density difference, electrostatic potential and partial density of states.

Summary This article proposed a high-performance triboelectric-electromagnetic hybrid wind energy harvester (WEH). By adopting the revolution and rotation movements of tapered rollers, which serve as both the rotor of the electromagnetic generator (EMG) part and freestanding layers of the triboelectric nanogenerator (TENG) part, the WEH can work as a sustainable power source and a self-powered wind speed sensor. When the wind speed is 12 m/s, super-high open-circuit voltage peaks of 47.4 and 683 V can be achieved by the EMG and TENG, respectively, corresponding to the high-power outputs of 62 and 1.8 mW. It was demonstrated that the WEH can easily light up over 600 red light-emitting diodes and even a 5-W globe light. A self-powered wireless temperature and humidity sensing network was also systematically demonstrated. In summary, the proposed WEH exhibits bright future toward IoT applications, such as in border detection, smart buildings, and so on., Graphical abstract, Highlights • A triboelectric-electromagnetic hybrid generator based on tapered rollers is proposed • The high-performance WEH has been systematically optimized and tested • A self-powered anemometer system has been successfully established • The WEH shows bright prospect in future IoT applications, Electromagnetics ; Energy Resources ; Energy Systems ; Device

Strut collisions can occur in tensegrity structures and seriously change the general mechanical behaviors of the structures. For many years, there have been few investigations into this topic. This paper systematically addresses the issue of strut collision modeling in tensegrity mechanical analyses. A general and efficient rigid body model for strut collision analysis is presented. A two-strut collision model is formulated using contact force methods. The normal contact force and the tangential friction force are evaluated by using the Lankarani–Nikravesh model and the modified Coulomb's friction law, respectively. Exact formulations of the generalized force vectors and the related tangent stiffness and tangent damping matrices are analytically derived. Fundamental issues related to collision detection and stiffness coefficient determination, are also addressed. Two representative examples involving both classical and clustered tensegrity structures are presented to demonstrate the effectiveness of the general framework, as well as to make a detailed study into the influence of collisions effects. Outcomes presented in this work will broaden the research discipline on tensegrity systems.

Rare earth doped upconversion nanoparticles can be considered as the spice of research in the field of luminescence nanomaterials due to their unique optical properties such as near-infrared excitation. Enormous works have been reported about biomedical applications of 980 nm excited and Yb3+-sensitized upconversion nanoparticles. However, 980 nm excitation wavelength overlaps with the absorption band of water molecules in the biological environment, leading to overheating effect that can induce thermal damages of normal cells and tissues. Recently, Nd3+-sensitized upconversion nanoparticles which can be excited with 808 nm has been widely investigated as alternative nanoparticles that can surmount this issue of overheating effect. Even though Nd3+-sensitized upconversion nanoparticles can reduce the overheating effect by 20 fold as compared to Yb3+-sensitized counterpart, there are several factors that reduce the upconversion luminescence intensity. In this review article, photon energy harvesting and transferring mechanisms in Nd3+, Yb3+ and emitter ions co-doped upconversion nanoparticles under 808 nm excitation are briefly discussed. Factors that affect upconversion luminescence intensity and quantum yield of Nd3+-sensitized upconversion nanoparticles are also addressed. Besides, some of the important strategies that have been recently utilized to boost upconversion luminescence intensity of Nd3+ sensitized upconversion nanoparticles are thoroughly summarized. Lastly, the future challenges in the area and our perspectives are in sight.

In order to achieve the nano-operation in a limited space, a precision motion platform with a cubic centimeter volume based on the principle of inertial stick–slip driving is proposed in this paper. The mechanical structure and the operating principle are discussed. Kinematic models are used to analyze the performance of the prototype. To investigate the working performance of the prototype, a series of experiments are carried out. Experimental results show that the displacement outputs is related to the parameters of the electrical signal. The maximum moving speed of the platform reaches 13.1 mm/s when the driving frequency is 3.1 kHz. The maximum single step displacement reaches 4.8 μm. Through proper driving voltage and frequency, the proposed prototype can produce a satisfactory velocity.

Sensors based on triboelectric nanogenerators have been widely used for energy harvesting and sensing applications, however, the applications of multidimensional information perception and interactive control are insufficient. In this paper, we present an ultra-stretchable triboelectric strip sensor (TSS) using triboelectric mechanism for controlling the objects in three-dimensional space. This facile and low-cost TSS is mainly composed of a parallel structure including three symmetric sensor strips fixed on the base and a mobile stage connected with them. Based on the coupling effect of triboelectrification and electrostatic induction, the length changes of each strip with the same finger contacting point generate different signal output ratios from two terminal electrodes, functioning as the interactive interface for multi-dimensional sensing and controlling. Hence, the parallel sensor strips structure can realize the sensing and controlling in three degrees of freedom of linear motion and two degrees of freedom of rotational motion, and resultant sensing ranges are X, Y, Z, α and β (20 mm, 20 mm, 30 mm, 36°, and 36°). In terms of manipulation, this is simpler than the conventional controller with rigid structure and includes additional space dimensions. Furthermore, demonstration of the TSS as human-nanomachine terminal to control the nanomanipulator in scanning electron microscope (SEM) is successfully realized with the accuracy of 10 nm. The proposed TSS shows great potential for the applications in automated control, robotics control, and Internet of Things (IoT).

Selective Laser Melting (SLM) technique applied to the stainless steel has been developing rapidly in the biomedical and aerospace industries. However, a post-machining is still needed to efficiently improve the surface finish and dimensional precision of the SLM-produced stainless steel parts. Dry machining (machining without the using of cutting fluid) is attracting interest around the world, which can reach green manufacturing without water pollution, residue on the swarf, and danger to health. In this work, to achieve the green finishing machining of SLM-produced AISI 316 L stainless steel, the hard coated tools with a nanotextured substrate were designed, and the key preparation methods of this developed tools were presented. First, a periodic nano-ripple structure (nanotexture) was induced by femtosecond laser scanning on the WC/Co substrate tool with different processing parameters, then TiAlN film was deposited on the nanotextured substrate surface using the cathode arc-evaporation technique without employing any interlayer. The surface micro-topography and mechanical property of the nanotextured TiAlN coated surface were studied. Machining tests without cutting fluid were performed on the SLM-produced stainless steel using the developed tool, and the cutting tool without laser pretreatment was also employed for the comparison. The obtained results demonstrate that, the TiAlN coatings adhesiveness is significantly enhanced by the femtosecond laser-induced periodic structure on the WC/Co substrate, and the critical load of the TiAlN coatings is increased from 57 to 73 N. The improved machining performances of nanotextured tools in drying cutting SLM 316 L stainless steel are achieved, resulting in a decrease of 10–20% in cutting forces, a decrease of 10–15% in cutting temperature and a high surface quality of the machined workpieces at the high cutting speed. The possible mechanisms for the effects of femtosecond laser pretreatment are discussed.

In this work, a trans-scale precision positioning stage without guideway based on the inertial stick-slip driving is proposed, which can provide nano-scale resolution ratio and output long-range motion. The stage consists of an encapsulated piezoelectric actuator, a connection block, a base, a pair of ceramic bars, and magnets, and the volume is 25 mm × 17 mm × 13.5 mm. The structure and the principle are introduced in detail. To investigate the locomotion characteristics, a prototype is manufactured, and a series of experiments are carried out. The velocity can reach 13 mm/s when the driving frequency is 2.5 kHz and the resolution is 2 nm. The experimental results confirm that the prototype based on the inertial stick-slip driving is valid through magnets. The good linear relationships exist between the displacement curves and time under various driving voltages and frequencies.

The stick–slip driving is widely used in the field of nanotechnology because of its high resolution and theoretically unlimited displacement. However, it suffers from such problems as low velocity and one-step displacement instability. In this paper, a method to improve the performance of inertial stick–slip movement from the perspective of overturning moment is proposed. Firstly, modeling and mechanical analysis of the inertial stick–slip platform structure. Then analyzing the influence of overturning moment through the conservation of energy and getting calculation results. Finally, building an experimental system for verification and finding that the height of the inertial force dropped by 5 mm, and the prototype single step displacement increased by 26%. Through theoretical calculation and experiment, the influence of overturning moment on inertial stick–slip motion is verified, which provides further guidance for inertial stick–slip motion platform design.

In this paper, a large thrust trans-scale precision positioning stage based on the inertial stick–slip driving is proposed, which can output long range motion. The stage consists of a piezoelectric actuator, a cross roller guide, a pair of cantilever beams, the flexure hinge system and the gather system of grating ruler, and the volume is 30 mm (L) × 17 mm (W) × 17.5 mm (H). The structure and the driving principle are introduced in detail. To investigate the working performance, a prototype is fabricated and a series of experiments is carried out. Experimental results demonstrate that the displacement outputs under various driving voltages, various driving frequencies and various step response time show good linear relationships with the time. The maximum thrust and the maximum load capacity are 6.1 N and 2500 g. The displacement and the driving resolution can reach 20 mm and 5 nm. The velocity can reach 12 mm/s when the driving frequency is 2.5 kHz. The experimental results also confirm that the designed stage can achieve various speeds by changing the driving voltage and driving frequency.

This note proposes a novel linear-rotary piezoelectric positioning stage which utilizes a double octagon driving module to produce rectangular driving trajectories of a surface. A rotational pair is embedded into a translational pair to constitute the 2-DOF output end (mover/rotor). With the circulating driving trajectories, the device can deliver translational and rotational motions step by step. The two motion modes can be switched by controlling a piezo-stack, which contributes to the elimination of the interference between translational and rotational motions. Experimental results show that the stage can work in a stable manner. The working strokes/stepping resolution of the translational and rotational motions are 50 mm/19.85 nm and infinite/1.32 μrad, respectively. The maximum velocities/load capacity values are 1023.4 μm/s/10.78 N and 98210 μrad/s/13.72 N, respectively.

Nanocomposites have been playing an increasingly significant role in the bioimaging-guided visualization of cancer physiotherapy. However, it has been a challenge to explore new diagnosis and treatment reagents with small size, good stability, and high photothermal conversion efficiency. Herein, we report a novel preparation of nanocomposites based on the heterogeneous growth of nano-palladium on the surface of upconversion nanoparticles (UCNPs). The final poly vinylpyrrolidone (PVP) modified UCNPs@Pd nanocomposites possess a small size and exhibit good monodispersity, biocompatibility and high photothermal conversion efficiency. In addition, relevant cellular assays show that based on the growth of palladium, the UCNPs@Pd-PVP nanocomposites can effectively kill HeLa cells under 808 nm laser irradiation. The nanocomposites also present effective upconversion luminescence imaging and T1 signal enhancement capability based on Er3+ and Gd3+ ions, respectively. Therefore, the nanocomposites successfully integrate upconversion luminescence imaging, magnetic resonance imaging, and photothermal therapy. This work provides new insights for the future development of multi-application materials based on the multicomponent heterogeneous growth of nanocomposites.

The piezoelectrically-actuated inertial stick-slip device (PAISSD) is widely used in the field of nanotechnology because of its high resolution and theoretically unlimited displacement. However, it suffers from such problems as a small driving force and low velocity. In this paper, an optimized driving waveform is proposed to increase the velocity. The optimized driving waveform includes a second order driving waveform, the step response of the waveform, and a buffer waveform that can effectively improve the velocity. First, the driving waveform optimization is proposed and a kinematic model of inertial stick-slip driving is established. Then the effects of various waveform parameters on PAISSD performance are determined and optimal parameters are selected via simulation. Finally, the kinematic model is validated and the effectiveness of the driving waveform optimization is demonstrated experimentally. We achieve higher velocities and larger single-step displacements than those provided by the traditional driving waveform, a sawtooth wave. Results show that the waveform optimization-driven single-step displacement and velocity are remarkably effective.

Ocean wave is one of the promising renewable energy sources all around the world. In this paper, an electromagnetic ocean wave energy harvester (OWEH) based on efficient swing body mechanism is presented. A swing body senses the ultra-low frequency wave motion and drive the rotor of an electromagnetic power module (EPM) rotating at high speed through transmission gears. A series of electromagnetic and dynamic simulations were carried out to optimize the power generation capability of the OWEH. Additionally, the power management circuit is specially designed such that the generated power is able to charge a lithium battery and discharge an external load automatically. The OWEH is installed inside an ocean buoy and tested in the Yellow China Sea. When the peak wave height is greater than 0.6 m, the maximum peak-to-peak output voltage is 15.9 V. The corresponding output power is as high as 0.13 W and the maximum power density is 0.21 mW/cm3, where the internal resistance of the OWEH is 122 Ω. Due to the high performance and adaptability, the OWEH can potentially power many low power components, which opens a promising way for improving the life of ocean buoys. Considering the small dimension of 10 × 10 × 6.3 cm3, this OWEH can be mounted inside most buoys easily and realize the self-powered ocean buoys in the near future.

Recent progress of untethered mobile micromotors has shown immense potential for targeted drug delivery in vivo. However, designing a wireless micromotor with high maneuverability and biocompatibility and achieving controlled drug release with high efficiency at a specific position remains a great challenge. Herein, we present a pine pollen-based micromotor (PPBM) and demonstrate its potential application as a cargo carrier for targeted drug delivery. These multifunctional biohybrid micromotors were massively and inexpensively fabricated by the encapsulation of magnetic particles (Fe3O4) and medicine into the two hollow air sacs of pine pollen, via vacuum loading. PPBMs successfully inherit the intrinsic functionalities of pine pollen: structural uniformity, morphological stability, biocompatibility, autofluorescence (AF) and physicochemical robustness. Under an external magnetic field, the loaded Fe3O4 enables individual and swarm PPBMs to propel precisely in complex biological fluids. Capitalizing on the magnetic nanoparticle aggregation phenomenon under a powerful magnetic field, controlled release of the therapeutic cargo is achieved using a fluid field generated by the rotating magnetic agglomerate. The biohybrid micromotors reported here turn natural pine pollen into active and controllable cargo carriers for biomedical applications.

Digital microfluidics technology based on the electrowetting-on-dielectric (EWOD) effect is a popular emerging technology whose objects of manipulation are individual droplets on the micro-liter or even nano-liter scales. It has the unique advantages such as rapid reaction, low reagent consumption, and high integration, which have drawn extensive attention and application in the fields of biology, medicine, and chemistry. However, there has been no a complete mechanism by which the droplets transition from stillness to motion in EWOD chip, leaving the proper mechanism for droplet movement uncertain. At this point in time, we studied the EWOD theory and polarization mechanism underlying solid-liquid interface, thus building upon previous research. The theoretical derivation and numerical analyses of EWOD driving force were presented. Then, the process and mechanism of droplet movement from stillness to motion was comprehensively analyzed, the results obtained from the simulation and discussion were in agreement with experimental results. It is our hope that this work will inspire new research into less understood EWOD regimes and help design useful EWOD devices.

Digital microfluidics technology based on the electrowetting-on-dielectric effect is a popular emerging technology whose objects of control are individual droplets on the microliter or even nano-liter scales. It has unique advantages such as rapid response, low reagent consumption, and high integration, so it has drawn widespread attention and use in the biological, medical, and chemical fields. However, to date, there has been relatively little research conducted on the mechanism of droplets transition from stillness to motion by electrowetting-on-dielectric actuation. Here, we studied the polarization mechanism underlying solid–liquid contact surface, thus building upon the previous research. The electric field in chip, internal pressure, and flow field of droplet were modeled and simulated numerically. Then, the process and mechanism of droplet transition from stillness to motion was comprehensively analyzed, and the results obtained from the simulation and discussion were in close agreement with experimental results. It is here shown that the process of droplet from stillness to motion involves four successive steps, which helps to better understand electrowetting-on-dielectric-induced droplet motions and physics of digital microfluidics systems. The aim of this work was to research basic physical mechanisms of electrowetting-on-dielectric droplet motion on a common ground so that the researchers may form a clear picture of the fundamentals.

Bridge-type mechanism is one of the most widely used displacement amplifiers in micro scale applications due to its compact and symmetrical structure. However, a drawback of the bridge-type mechanism that restricts its further applications is the limited amplification ratio. To solve this problem, a bridge-lever-type displacement amplifier is developed and analyzed in this paper. Compared with the conventional design, the proposed amplifier not only maintains a compact and symmetrical structure, but also features a high amplification ratio and high load capacity. To reduce the displacement loss of the amplifier and enhance its load capacity, the hybrid flexure hinges are employed in the novel design. Furthermore, the kineto-static model based on the compliance matrix method and the dynamic model based on Lagrangian method are established to analyze the bridge-lever-type amplifier. Finally, a prototype is fabricated whose amplification ratio is approximately 48 and 34 in the case of zero load and 30 N load respectively, which is confirmed by FEA simulation and experimental study.

Biological microdissection has a wide range of applications in the field of molecular pathology. The current laser-assisted dissection technology is expensive. As an economical microdissection method, piezoelectric ultrasonic microdissection has broad application prospects. However, the performance of the current piezoelectric ultrasonic microdissection technology is unsatisfactory. This paper aims to solve the problems of the low dissecting precision and excessive wear of the dissecting needle caused by the harmful lateral vibration of the present piezoelectric ultrasonic microdissection device. A piezoelectric ultrasonic microdissection device based on a novel flexure mechanism is proposed. By analyzing the flexure hinge flexibility, the type of flexure beam and the optimal design parameters are determined. Through harmonic response simulation analysis, the newly designed microdissection device with a vibration-suppressing mechanism achieves the best vibration effect when the driving frequency is 28 kHz. Under this driving frequency, the lateral vibration suppression effect is improved by 68% compared to the traditional effect without vibration suppression. Then, based on 3D printing technology, a prototype of a novel microdissection device is produced, and its performance is tested. Experiments on dissecting needle vibration tests show that the flexure mechanism does indeed suppress the lateral vibration of the needle tip. We conducted various tissue dissection experiments on paraffin tissue sections. First, we determine the optimal dissecting parameters (driving voltage, frequency, feed speed, cutting angle) of the new equipment through various parameter dissecting experiments. Then, we adopt these optimal dissecting parameters to perform three kinds of dissecting experiments on mouse tissue paraffin section (liver, lung, bone), dissecting experiments on tissue sections of different thicknesses (3 μm, 4 μm, 5 μm), sampling and extraction experiments on complete tissue. The new device has a better dissecting performance for paraffin tissue sections below a 5 μm thickness and can complete various dissecting tasks. Finally, we compare the wear of the dissecting needles of the new and old devices after the same dissecting tasks. The results prove that the suppression of harmful lateral vibration not only significantly improves the dissecting effect but also increases the service life and durability of the dissecting needle, which is beneficial for reducing the equipment costs.

In situ scanning electron microscope (SEM) characterization have enabled the stretching, compression, and bending of micro/nanomaterials and have greatly expanded our understanding of small-scale phenomena. However, as one of the fundamental approaches for material analytics, torsion tests at a small scale remain a major challenge due to the lack of an ultrahigh precise torque sensor and the delicate sample assembly strategy. Herein, we present a microelectromechanical resonant torque sensor with an ultrahigh resolution of up to 4.78 fN∙m within an ultrawide dynamic range of 123 dB. Moreover, we propose a nanorobotic system to realize the precise assembly of microscale specimens with nanoscale positioning accuracy and to conduct repeatable in situ pure torsion tests for the first time. As a demonstration, we characterized the mechanical properties of Si microbeams through torsion tests and found that these microbeams were five-fold stronger than their bulk counterparts. The proposed torsion characterization system pushes the limit of mechanical torsion tests, overcomes the deficiencies in current in situ characterization techniques, and expands our knowledge regarding the behavior of micro/nanomaterials at various loads, which is expected to have significant implications for the eventual development and implementation of materials science. A microelectromechanical resonant sensor is proposed for small-scale torsion tests and demonstrated for the testing of silicon microbeams. It is important to understand the mechanical properties of small-scale materials used in MEMS and NEMS. Various systems have been reported for this under a range of loading conditions, but the application of torque to small-scale samples is particularly hard to measure. Here, a joint team led by Xueyong Wei from Xi’an Jiaotong University and Yajing Shen from City University of Hong Kong reports a MEMS-based resonator sensor that can measure bending and torsion over a wide dynamic range with a high force resolution. They demonstrate their system for the testing of silicon microbeams, which are found to be five times stronger than bulk silicon under pure torsion.

In the fast tool servo (FTS) system for microstructure surface cutting, the dynamic voltage hysteresis of piezoelectric actuators (PEAs) and the cutting force produced in the manufacturing affect the driving accuracy and the cutting performance. For a multi-input-single-output (MISO) cutting system, in this paper, a dynamic hysteresis model based on a rate-dependent Prandtl&ndash, Ishlinskii model is proposed. A backpropagation neural network (BPNN) is established to describe the cross-coupling effect between the applied voltage and external load. An inverse dynamic model is developed to compensate the nonlinearity of PEAs. The accuracy of the model and its inverse is discussed and the performance of the inverse feedforward compensator is validated through experiments.

Energy-converting biomaterials (ECBs)-mediated cancer-therapeutic modalities have been extensively explored, which have achieved remarkable benefits to overwhelm the obstacles of traditional cancer-treatment modalities. Energy-driven cancer-therapeutic modalities feature their distinctive merits, including noninvasiveness, low mammalian toxicity, adequate therapeutic outcome, and optimistical synergistic therapeutics. In this advanced review, the prevailing mainstream ECBs can be divided into two sections: Reactive oxygen species (ROS)-associated energy-converting biomaterials (ROS-ECBs) and hyperthermia-related energy-converting biomaterials (H-ECBs). On the one hand, ROS-ECBs can transfer exogenous or endogenous energy (such as light, radiation, ultrasound, or chemical) to generate and release highly toxic ROS for inducing tumor cell apoptosis/necrosis, including photo-driven ROS-ECBs for photodynamic therapy, radiation-driven ROS-ECBs for radiotherapy, ultrasound-driven ROS-ECBs for sonodynamic therapy, and chemical-driven ROS-ECBs for chemodynamic therapy. On the other hand, H-ECBs could translate the external energy (such as light and magnetic) into heat for killing tumor cells, including photo-converted H-ECBs for photothermal therapy and magnetic-converted H-ECBs for magnetic hyperthermia therapy. Additionally, the biosafety issues of ECBs are expounded preliminarily, guaranteeing the ever-stringent requirements of clinical translation. Finally, we discussed the prospects and facing challenges for constructing the new-generation ECBs for establishing intriguing energy-driven cancer-therapeutic modalities. This article is categorized under: Nanotechnology Approaches to Biology >Nanoscale Systems in Biology.

Gallium-based liquid metals exhibit excellent locomotion and deformation capabilities under external stimuli and has potential in developing intelligent robots. Programing the locomotion and morphology of the Liquid metal (LM) to endow it with functionalities and intelligence as robots is charming but remains challenging. In this study, we develop a programmable digital LM (PDLM) control platform that can realize versatile locomotion and morphological manipulation of magnetic LM (MLM) droplets using arrays of electromagnets. We demonstrate on-demand transportation, deformation, breakup, and merging of multiple MLM droplets simultaneously and precisely. We find that the intriguing behaviors of MLM under a magnetic field are due to the interplay of surface tension and magnetic forces. Furthermore, we present a functional cooperative droplet robot by equipping the MLM droplets with three-dimensionally printed microtool modules. We show that both the position and orientation of a rod-shaped object can be precisely manipulated by the cooperation of the MLM droplet robots. More interestingly, we explore the capability of the MLM droplet robots for cooperatively handling a copper wire to connect and disconnect electronic circuits. Finally, we demonstrate that the PDLM control platform is capable of programing a group of MLM droplets to accomplish a digital display task. We believe that the PDLM control system presents a promising potential in developing LM-based reconfigurable circuits, digital display systems, and biomimetic soft robotic systems with high controllability, multifunctionalities, and intelligence.

Vertical data collected by Scanning Electron Microscopy (SEM) are important for sample characterization, 3D reconstruction, and flex manipulation. Traditional methods are limited by the extent to which the probe obstructs the view of the sample along the vertical axis. Herein, we propose a novel SEM microprobe for measuring the vertical distance between the probe and substrate. To form a semi-transparent hole that is set as the objective regions in processing of the SEM images, an epoxy film was embedded in the through-hole at the tip of the microforce probe with 3D printing. The film can be modified with a focused ion beam (FIB) system. The motion of the modified probe along the vertical axis is controlled by a nanopositioner and the process is recorded by taking a real-time SEM video. The change in gray contrast caused by the semi-transparent epoxy is corrected during the SEM image processing of the video. By comparing the gray contrast with the nanopositioner motion data, we find that the change in gray contrast can provide feedback for adjusting the displacement between the probe and the substrate, and the resolution can be up to 100 nm. We propose a novel and simple method for measuring vertical distances in the SEM, which is useful for in-situ measurements and nanomanipulations.

In order to improve the response speed and output force of the camera focusing mechanism, the authors proposed a novelty micro focusing mechanism based on piezoelectric driving, which has the characteristics of rapid response, high precision positioning and large displacement focusing. In this paper, the operating principle of the proposed focusing mechanism is presented. Using the piezoelectric output characteristic, the movable tooth drive theory and the screw drive theory, the electromechanical coupling mechanical model and equations of the piezoelectric focusing mechanism are established. Through MATLAB simulation, the output characteristics of the piezoelectric focusing mechanism are calculated. The results indicate that the maximum thrust force of the lens and the maximum output torque of the movable tooth drive for the piezoelectric focusing mechanism are 562.5 N and 1.16 Nm, respectively. Furthermore, the driving voltage directly affects the output performance of the piezoelectric focusing mechanism. These results can be utilized both to optimize the dimensions and improve the overall performance of the piezo-driven focusing mechanism.

Some applications are very sensitive to the weight of the robot, such as space manipulation or any untethered mobile manipulation. In this article, we designed a five-module unilaterally bending serial manipulator with length of 32 cm and a weight of only 18 g. The manipulator is driven by dielectric elastomer actuators (DEAs). Each module consists of a spatially closed tubular structure, which has the capability of large deformation while simultaneously maintaining torsional rigidity. The design is based on the buckling of columns. To achieve global deformation continuously, each module was controlled independently by a multichannel high-voltage power supply. As a demo, the manipulator was able to enter and exit a narrow L-shaped pipe. Experiments demonstrate that the manipulator driven by spatial DEAs can be super lightweight and can realize large continuous deformation.

This paper presents a multiparameter water quality sensor chip with temperature compensation. The sensor chip was manufactured using microelectromechanical system (MEMS) technology. The surface of the chip integrated pH, dissolved oxygen (DO), ammonia nitrogen, and temperature sensors. To compensate for the solution temperature, the chip was also designed with a sandwich, plate-type serpentine Pt resistance heater. The experimental results showed that the pH sensor had a high sensitivity of 0.288 mA/pH with good linearity ( R 2 = 0.9998 ), the sensitivity of the temperature sensor was 0.949 Ω/°C, the sensitivity of the ammonia nitrogen sensor was 0.1139 mA/ppm, the sensitivity of the dissolved oxygen (DO) sensor was 2.22 μA/ppm, and the sensitivity of the temperature changes with respect to the heater power was 0.3126°C/mW. Compared with a single water quality parameter sensor, the as-prepared sensor chip could simultaneously detect multiple parameters of a water sample and had a good temperature compensation effect. Moreover, the sensor chip was small in size, rugged, and highly accurate.

The mechanical properties of cells are closely related to their physiological functions and states. Analyzing and measuring these properties are beneficial to understanding cell mechanisms. However, most measurement methods only involve the unidirectional analysis of cellular mechanical properties and thus result in the incomplete measurement of these properties. In this study, a microfluidic platform was established, and an innovative microfluidic chip was designed to measure the multiangle cellular mechanical properties by using dielectrophoresis (DEP) force. Three unsymmetrical indium tin oxide (ITO) microelectrodes were designed and combined with the microfluidic chip, which were utilized to generate DEP force and stretch cell from different angles. A series of experiments was performed to measure and analyze the multiangle mechanical properties of red blood cells of mice. This work provided a new tool for the comprehensive and accurate measurement of multiangle cellular mechanical properties. The results may contribute to the exploration of the internal physiological structures of cells and the building of accurate cell models.

Triboelectric nanogenerators and sensors have been widely adopted for diversified energy harvesting and sensing applications, but the demonstrations of 3D information sensing and controlling are very limited. In this paper, we present a novel self-powered virtual reality 3D-control sensor (VR-3D-CS) based on triboelectric mechanism for controlling the attitude (both the position and rotation) of object in 3D virtual space. This innovative, cost-effective, simple-designed sensor has a symmetric 3D structure with eight separated sensing electrodes and two touching spheres as the interactive interface with human fingers for 3D force information sensing and VR controlling. Based on the coupling effect of triboelectrification and electrostatic induction, the VR-3D-CS generates different electric output signals in response to different operation manner that can be used to control the attitude of objects in 3D virtual space. The symmetrical 3D configuration design of the sensor enables the detection of 3D force from both the normal direction and shear direction. By employing vector properties of force and signal analysis from the eight sensing electrodes, detection of six-axis directions in 3D space is achieved by triboelectric mechanism for the first time. The VR-3D-CS has been demonstrated to be able to detect normal force in the range of 0–18 N. It can resolve the shear force direction with step resolution of at least 15°. Besides, due to the positive output voltage and low internal impedance, the VR-3D-CS is readily compatible with commercial portable signal processing system for signal analysis and controlling. Demonstration of the VR-3D-CS as interactive interface for Augmented Reality (AR) control is successfully realized. The robust structure, stable output performance and self-powered sensing property enable the device as an ideal human machine interface towards AR interface, batteryless and energy saving applications.

Recently, much attention has been paid to the lanthanide luminescent materials based on the visible-light sensitization for their potential applications in the fields of bio-imaging and optical devices. In this work, the lanthanide complexes have been covalently bonded to the ordered mesoporous titania (OMT) matrix, and the resulting titania-based hybrid ordered mesoporous materials (named as LnDB-OMT, Ln = Eu, Sm, Yb, Nd) were characterized by using Fourier-transform infrared (FT-IR) spectroscopy, small-angle X-ray powder diffraction (SAXD), N2 adsorption–desorption isotherms, transmission electron microscopy (TEM), fluorescence spectroscopy, and thermogravimetric analysis. Generally, exciting with visible light is advantageous over UV excitation. Of importance here is that, under excitation with visible light, the LnDB-OMT all show characteristic visible (Eu3+, Sm3+) as well as near-infrared (Sm3+, Yb3+, Nd3+) luminescence of the corresponding Ln3+ ions (multicolor emission covered from 500 to 1400 nm spectral region), which is attributed to the energy transfer from the ligands to the Ln3+ ions via an antenna effect.

Flexible electronic devices are developing rapidly, especially in medical applications. This paper reports an arrayed flexible piezoelectric micromachined ultrasonic transducer (FPMUT) with a sandwich structure for adjuvant treatment of bone injury. To make the device conformable and stretchable for attaching to the skin surface, the flexible substrate of polydimethylsiloxane (PDMS) was combined with the flexible metal line interconnection between the bulk lead zirconate titanate (PZT) arrays. Simulations and experiments were carried out to verify the resonant frequency and tensile property of the reported FPMUT device. The device had a resonant frequency of 321.15 KHz and a maximum sound pressure level (SPL) of 180.19 dB at the distance of 5 cm in water. In addition, detailed experiments were carried out to test its acoustic performance with different pork tissues, and the results indicated good ultrasound penetration. These findings confirm that the FPMUT shows unique advantages for adjuvant treatment of bone injury.

A novel drug-delivery nanosystem based on near-infrared (NIR) light-degradable antimony nanoparticles (AMNP) have been developed for synergistic chemo-phototherapy in vitro. The monodispersed AMNP were synthesized by using a simple and cost-effective method. Positively charged doxorubicin hydrochloride (DOX) was loaded onto the negatively charged surface of AMNP via electrostatic interaction and finally modified by polyacrylic acid (PAA) to enhance biocompatibility. Under NIR (808 nm) laser irradiation of the AMNP-DOX-PAA nanosystem, not only was high photothermal conversion efficiency of AMNP achieved but also pH-dependent DOX release was enhanced due to laser-induced hyperthermia. As a consequence, almost all of the HeLa cells (around 97%) were killed because of the combined effects of chemotherapy and photothermal therapy. More interestingly, AMNP showed very fast (about 10 min) laser-induced degradation that may help to minimize long-term toxicity after therapy by using same-wavelength NIR laser irradiation (808 nm). Computational total energy calculations and molecular dynamics simulations based on density functional theory (DFT) suggest that the NIR laser irradiation induces a photothermally activated reaction on the surface of AMNP in water, which can lead to surface degradation via the formation of Sb-H bonds first and then Sb-OH bonds upon further increase of temperature. This work demonstrates a simple platform that has potential applications for synergistic and highly effective chemo-photothermal therapy based on photodegradable nanoparticles.

Compared with the electrowetting on dielectric (EWOD) microfluidic device, optoelectrowetting (OEW) microfluidic device does not need to control the on-off of single electrode, but only needs to change the lighting condition to control the droplet, simplifying the peripheral control device and improving the stability of the device. The contradiction between the operating voltage and the driving force exists in the existing OEW device. To solve this problem, this paper proposes an OEW device based on diode structure, which uses the photoelectric effect of the diode connected in the DC circuit to control the movement state of the droplet. In this paper, the feasibility of the OEW device with pn structure is theoretically analyzed. Compared with the previous OEW device, under the same applied voltage and the same illumination difference, the potential difference between the diodes in the new device will be significantly larger than the potential difference between the photoresistors, which will effectively improve the driving force of the DC drive.

A magnetic urchin-like microswimmer based on sunflower pollen grain (SPG) that can pierce the cancer cell membrane and actively deliver therapeutic drugs is reported. These drug loaded microperforators are fabricated on a large scale by sequentially treating the natural SPGs with acidolysis, sputtering, and vacuum loading. The microswimmers exhibit precise autonomous navigation and obstacle avoidance in complex environments via association with artificial intelligence. Assemblies of microswimmers can further enhance individual motion performance and adaptability to complicated environments. Additionally, the experimental results demonstrate that microswimmers with nanospikes can accomplish single-cell perforation for direct delivery under an external rotating magnetic field. Drugs encapsulated in the inner cavity of the microperforators can be accurately delivered to a specific site via remote control. These dual-action microswimmers demonstrate good biocompatibility, high intelligence, precision in single-cell targeting, and sufficient drug loading, presenting a promising avenue for many varieties of biomedical applications.

In this letter, a dynamic atomic force microscopy approach using a magnetic bead probe (MBP) is presented for in situ quantification of the complex Poisson's ratio of single cells. The MBP is fabricated as a double-bead probe comprising a polystyrene bead and a magnetic bead superimposed thereon. The polystyrene bead is molded into a flat bottom to apply accurate global force to individual cells. The magnetic bead is magnetized at a certain angle to the longitudinal axis of the cantilever, which can simultaneously bend and twist the probe at off-resonant frequencies up to tens of kiloHertz. This allows for the dynamic measurement of viscoelastic properties of a single cell in the directions of shear and stretching, obtaining its complex Poisson's ratio. The performance of the proposed method was tested by measuring the complex Poisson's ratio of individual cells at different excitation frequencies and compression ratios. The experimental results show that the developed method has a wide range of applications for the field of cell mechanics.

In this letter, a new open-loop amplitude modulation Kelvin probe force microscopy is presented for nanoscale mapping of the surface potential. In this method, measurement of the contact potential difference (CPD) is performed with a normal probe under two electrostatic excitations. One excitation oscillates the probe in its second resonance mode with an amplitude of less than 5 nm and the other nonresonant excitation modulates this oscillation at a frequency much lower than the probe's first resonant frequency. With this approach, the probe-sample CPD can be measured directly from the periodic variations of the modulated amplitude and the phase without feedback control. Nanoscale mapping of the surface potential of the graphene-on-silicon sample shows that the proposed method has comparable performance to the conventional amplitude modulation Kelvin probe force microscopy. Further experimental results demonstrate that the proposed method can accurately map the surface potentials of various conductor, semiconductor and insulator materials.

Electrospinning is a technique for creating continuous nanofibrous networks that can architecturally be similar to the structure of extracellular matrix. In this work, a simple and semiautomatic electrostatic spinning system is designed, and a method of multilayer composite electrostatic spinning is adopted, which is called the hierarchical construction (sandwich mode). Then, a kind of PLGA/silk fibroin composite electrospinning nanofibrous scaffolds is proposed for the growth of skin cells in combination with the good characters of silk fibroin and PLGA. The SEM experiment of the silk fibroin/PLGA composite nanofibers indicated that the prepared nanofibers are smooth, uniform in size, and have good porosity. The wrinkled contrast test shows that this nanofiber scaffold remains flat in the culture medium as the original, and is basically not shrink. The water absorption experimental results show that the composite nanofiber scaffold has good hydrophilicity, and the increase in water absorption with time is not obvious. The cell culture experiment is also shown that the skin cells can proliterate on the scaffold.

Lanthanide-doped upconversion nanoparticles (UCNPs) which could show unique upconversion photoluminescence (UCPL) have attracted considerable attention due to their excellent chemical and optical characteristics. Compared with down-shifting luminescence, UCPL shows its bright future in the bioapplication where sequential absorption of multiple low-energy photons (such as near-infrared (NIR) excitation) by the ladder-like energy levels of the lanthanide ions (Ln3+) leads to the production of higher energy photons (such as ultraviolet, visible light). UCPL shows a variety of advantages such as large anti-Stokes shifts, sharp emissions, long luminescence lifetimes, and high resistance to photobleaching. Furthermore, NIR irradiation has lower photo damage effect, a large penetration depth in tissues, and at the same time, it can avoid the auto-fluorescence interference of biological sample and light scattering phenomenon, which can reduce the background light and improve the signal-to-noise ratio. Thus, UCNPs have emerged as more appropriate nanomaterials for bioapplications. To date, many scientists have focused on the research of the bioapplications of UCNPs, including bioimaging, drug release, and therapies after the special surface modification. In this critical review, recent advances regarding the mechanism, synthesis, modification, and promising bioapplications of UCNPs are reviewed. In particular, the studies related to sensing and bioimaging (UCPL, MR, CT, PET and SPECT), drug release, and therapies (photothermal therapy, photodynamic therapy, and radiotherapy) are presented in detail. For specific bioapplication, tailored UCNPs can be designed and synthesized according to the different synthesis and modification methods as summarized in this review. Finally, we discuss the prospects and challenges of UCNPs in the biomedical and biotechnological fields.

Catalytic micro- and nanorobots exhibit self-propulsion in the presence of chemical fuels such as glucose, hydrogen peroxide. Generally, swimmers incorporate a catalyst as a part of their structure for the decomposition of a chemical fuel. Several applications such as active drug delivery, minimally invasive surgery, and water remediation, have been envisaged. In this letter, we investigated the influence of geometric variable of catalytic microrobot to their swimming behaviors in hydrogen peroxide (H2O2) solutions. V-shaped microrobots with various opening angles (45°, 90°, and 135°), and triangle-shaped microrobots that have similar dimensions with V-shaped microrobots, have been fabricated by focused-ion-beam etching on commercial platinum microwires. Swimming tests were performed in 15% and 30% H2O2 solutions. We have found that V-shaped microrobot with 45° opening angle showed a superior swimming speed of 4.3 μm/s in 15% H2O 2 solution, while 90° microrobot exhibits a speed of 1.52 μm/s. The 135° V-shaped microrobot and all triangle-shaped microrobots have not shown any obvious motions in 30% H2O2 solution. Our observation that the swimming performances of various shaped microrobots change in tandem proves the necessity of structural asymmetry in designing catalytic micro- and nanorobots.