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Wireless on-demand drug delivery systems exploit exogenous stimuli—acoustic waves, electric fields, magnetic fields and electromagnetic radiation—to trigger drug carriers. The approach allows drugs to be delivered with controlled release profiles and minimal off-target effects. Recent advances in electronics and materials engineering have led to the development of sophisticated systems designed for specific applications. Here we review the development of wireless on-demand drug delivery systems. We examine the working mechanisms, applications, advantages and limitations of systems that are triggered by electric fields, magnetic fields or electromagnetic radiation. We also provide design guidelines for the development of such systems, including key metrics for evaluating the practicality of different smart drug delivery systems. This Review examines wireless on-demand drug delivery systems that are triggered by electric fields, magnetic fields or electromagnetic radiation, and provides design guidelines for the development of such systems.

On-demand delivery of substances has been demonstrated for various applications in the fields of chemistry and biomedical engineering. Single-pulse release profile has been shown previously for micro/nanoparticles in different form factors. However, to obtain a sustained release, a pulsatile release profile is needed. Here, we demonstrate such a release profile from polymer magnetic nanocomposite microspheres loaded with chemicals. By exciting the microactuators with AC magnetic fields, we could achieve up to 61% cumulative release over a five-day period. One of the main advantages of using a magnetic stimulus is that the properties of the environment (e.g., transparency, density, and depth) in which the particles are located do not affect the performance. The operating magnitude of the magnetic field used in this work is safe and does not interact with any nonmetallic materials. The proposed approach can potentially be used in microchemistry, drug delivery, lab-on-chip, and microrobots for drug delivery.

The advances in micro/nanofabrication techniques have enabled miniaturization of printed circuit boards (PCBs) for various applications such as portable devices, smart sensors, and IoTs, to name a few. PCBs provide electrical connectivity between the components as well as mechanical support. Down-scaling of PCBs is crucial for miniaturization of large systems and devices. Currently, microtraces down to 25 μm can be microfabricated with the current microfabrication processes at an industrial scale. In the present work, we report a new approach for microfabrication of PCBs with trace widths down to 3 μm on commercially available PCB substrates. We used electroplating/electroetching, sputtering, and photolithography to achieve these fine trace sizes. The proposed fabrication technique can be used in microelectronics, system on chip, MEMS, and miniaturized circuits and systems in general.

Stimuli‐responsive materials have been lately employed in soft robotics enabling new classes of robots that can emulate biological systems. The untethered operation of soft materials with high power light, magnetic field, and electric field has been previously demonstrated. While electric and magnetic fields can be stimulants for untethered actuation, their rapid decay as a function of distance limits their efficacy for long‐range operations. In contrast, light—in the form of sunlight or collimated from an artificial source (e.g., laser, Xenon lamps)—does not decay rapidly, making it suitable for long‐range excitation of untethered soft robots. In this work, an approach to harnessing sunlight for the untethered operation of soft robots is presented. By employing a selective solar absorber film and a low‐boiling point (34 °C) fluid, light‐operated soft robotic grippers are demonstrated, grasping and lifting objects almost 25 times the mass of the fluid in a controllable fashion. The method addresses one of the salient challenges in the field of untethered soft robotics. It precludes the use of bulky peripheral components (e.g., compressors, valves, or pressurized gas tank) and enables the untethered long‐range operation of soft robots., While offering immense potential for disruptive applications, pneumatically driven soft robots require bulky, heavy, and pricy peripherals, such as gas tanks, compressors, and valves, to operate. Here, a technique to fabricate untethered soft robots that are directly powered by solar energy is presented.

One of the main challenges associated with mechanical ventilators is their limited availability in pandemics and other emergencies. Therefore, there is a great demand for mechanical ventilators to address this issue. In this work, we propose a low-cost, portable, yet high-performance design for a volume-controlled mechanical ventilator. We are employing pneumatic artificial muscles, such as air cylinders, in the reverse mode of operation to achieve mechanical ventilation. The current design of the device can operate in two modes: controlled mode and assisted mode. Unlike most ICU ventilators, our device does not need a high-pressure air pipeline to operate. With the current design, mechanical ventilation for respiration rate ranging from 10 b/min to 30 b/min with a tidal volume range of 150 mL to 1000 mL and I:E ratio of 1:1 to 1:5 can be performed. We achieved a total cost of less $400 USD to make one device. We estimate the device to cost less than $250 USD when produced in larger volumes.

Torsional artificial muscles made of multiwalled carbon nanotube/niobium nanowire yarns have shown remarkable torsional speed and gravimetric torque. The muscle structure consists of a twisted yarn with half of its length infiltrated with a stimuli-responsive guest material such as paraffin wax. The volumetric expansion of the guest material creates the torsional actuation in the yarn. In the present work, we show that this type of actuation is not unique to wax-infiltrated carbon multiwalled nanotube (MWCNT) or niobium nanowire yarns and that twisted yarn of NiTi alloy fibers also produces fast torsional actuation. By gold-plating half the length of a NiTi twisted yarn and Joule heating it, we achieved a fully reversible torsional actuation of up to 16°/mm with peak torsional speed of 10 500 rpm and gravimetric torque of 8 N·m/kg. These results favorably compare to those of MWCNTs and niobium nanowire yarns.

Pneumatic artificial muscles have been widely used in industry because of their simple and relatively high-performance design. The emerging field of soft robotics has also been using pneumatic actuation mechanisms since its formation. However, these actuators/soft robots often require bulky peripheral components to operate. Here, we report a simple mechanism and design for actuating pneumatic artificial muscles and soft robotic grippers without the use of compressors, valves, or pressurized gas tanks. The actuation mechanism involves a magnetically induced liquid-to-gas phase transition of a liquid that assists the formation of pressure inside the artificial muscle. The volumetric expansion in the liquid-to-gas phase transition develops sufficient pressure inside the muscle for mechanical operations. We integrated this actuation mechanism into a McKibben-type artificial muscle and soft robotic arms. The untethered McKibben artificial muscle generated actuation strains of up to 20% (in 10 seconds) with associated work density of 40 kilojoules/meter3, which favorably compares with the peak strain and peak energy density of skeletal muscle. The untethered soft robotic arms demonstrated lifting objects with an input energy supply from only two Li-ion batteries.

The area of artificial muscle is a highly interdisciplinary field of research that has evolved rapidly in the last 30 years. Recent advances in nanomaterial fabrication and characterization, specifically carbon nanotubes and nanowires, have had major contributions in the development of artificial muscles. However, what can artificial muscles really do for humans? This question is considered here by first examining nature's solutions to this design problem and then discussing the structure, actuation mechanism, applications, and limitations of recently developed artificial muscles, including highly oriented semicrystalline polymer fibers; nanocomposite actuators; twisted nanofiber yarns; thermally activated shape-memory alloys; ionic-polymer/metal composites; dielectric-elastomer actuators; conducting polymers; stimuli-responsive gels; piezoelectric, electrostrictive, magnetostrictive, and photostrictive actuators; photoexcited actuators; electrostatic actuators; and pneumatic actuators.

Nitinol microwires of 25 μm in diameter can have tensile actuation of up to 4.5% in less than 100 ms. A work density of up to 480 MPa can be achieved from these microwires. In the present work, we are showing that by twisting the microwires in form of closed-loop two-ply yarn we can create a torsional actuator. We achieved a revisable torsional stroke of 46°/mm with peak rotational speed of up to 10,000 rpm. We measured a gravimetric torque of up to 28.5 N•m/kg which is higher than the 3 – 6 N•m/kg for direct-drive commercial electric motors. These remarkable performance results are comparable to those of guest-infiltrated carbon nanotube twisted yarns.

Planar micro-supercapacitors are attractive for system on chip technologies and surface mount devices due to their large areal capacitance and energy/power density compared to the traditional oxide-based capacitors. In the present work, a novel material, niobium nanowires, in form of vertically aligned electrodes for application in high performance planar micro-supercapacitors is introduced. Specific capacitance of up to 1 kF m-2 (100 mF cm-2 ) with peak energy and power density of 2 kJ m-2 (6.2 MJ m-3 or 1.7 mWh cm-3 ) and 150 kW m-2 (480 MW m-3 or 480 W cm-3 ), respectively, is achieved. This remarkable power density, originating from the extremely low equivalent series resistance value of 0.27 Ω (2.49 µΩ m2 or 24.9 mΩ cm2 ) and large specific capacitance, is among the highest for planar micro-supercapacitors electrodes made of nanomaterials.

Highly efficient light absorption and charge separation within the photosystem and reaction center (RC) complexes of photosynthetic plants and bacteria are of great interest for solar cell and photo detector applications, since they offer almost unity quantum yield and expected ultimate power conversion efficiencies of more than 18% and 12%, respectively. In addition, the charge separated states created by these protein complexes are very long lived compared to conventional semiconductor solar cells. In this work, a novel technique is presented for the deposition of photosynthetic protein complexes, by electrospraying RCs of Rhodobacter sphaeroides onto highly ordered pyrolytic graphite (HOPG) electrodes. Remarkably, it is shown that the RCs not only survive exposure to the high electric fields but also yield peak photocurrent densities of up to 7 μA cm−2, which is equal to the highest value reported to date.

Metal nanowires are twisted to form yarns that are strong (0.4 to 1.1 GPa), pliable, and more conductive (3 × 106 S m−1) than carbon nanotube yarns. Niobium nanowire fibers are extracted by etching a copper-niobium nano-composite material fabricated using the severe plastic deformation process. When impregnated with paraffin wax, the niobium (Nb) nanowire yarns produce fast rotational actuation as the wax is heated. The heated wax expands, untwisting the yarn, which then re-twists upon cooling. Normalized to yarn length, 12 deg mm−1 of torsional rotation was achieved along with twist rates in excess of 1800 rpm. Tensile modulus of 19 ± 5 GPa was measured for the Nb yarns, which is very similar to those of carbon multiwalled nanotubes.

A bending actuator and methods for making and using the same. A beam of anisotropic polymer material, such as nylon, characterized by a greater degree of molecular orientation along a longitudinal axis than transverse to the longitudinal axis, has a heating element in thermal contact with at least one of a pair of opposing faces parallel to the longitudinal axis of the beam. The heating element in certain embodiments provides for photothermal activation of the bending actuator.

Natural Sciences and Engineering Research Council of Canada (Alexander Graham Bell Graduate Fellowship)

The large-ion-accessible surface area of carbon nanotubes (CNTs) and graphene sheets formed as yarns, forests, and films enables miniature high-performance supercapacitors with power densities exceeding those of electrolytics while achieving energy densities equaling those of batteries. Capacitance and energy density can be enhanced by depositing highly pseudocapacitive materials such as conductive polymers on them. Yarns formed from carbon nanotubes are proposed for use in wearable supercapacitors. In this work, we show that high power, energy density, and capacitance in yarn form are not unique to carbon materials, and we introduce niobium nanowires as an alternative. These yarns show higher capacitance and energy per volume and are stronger and 100 times more conductive than similarly spun carbon multiwalled nanotube (MWNT) and graphene yarns. The long niobium nanowires, formed by repeated extrusion and drawing, achieve device volumetric peak power and energy densities of 55 MW·m(-3) (55 W·cm(-3)) and 25 MJ·m(-3) (7 mWh·cm(-3)), 2 and 5 times higher than that for state-of-the-art CNT yarns, respectively. The capacitance per volume of Nb nanowire yarn is lower than the 158 MF·m(-3) (158 F·cm(-3)) reported for carbon-based materials such as reduced graphene oxide (RGO) and CNT wet-spun yarns, but the peak power and energy densities are 200 and 2 times higher, respectively. Achieving high power in long yarns is made possible by the high conductivity of the metal, and achievement of high energy density is possible thanks to the high internal surface area. No additional metal backing is needed, unlike for CNT yarns and supercapacitors in general, saving substantial space. As the yarn is infiltrated with pseudocapacitive materials such as poly(3,4-ethylenedioxythiophene) (PEDOT), the energy density is further increased to 10 MJ·m(-3) (2.8 mWh·cm(-3)). Similar to CNT yarns, niobium nanowire yarns are highly flexible and show potential for weaving into textiles and use in wearable devices.

High-performance artificial muscles have been produced from fibers having highly anisotropic thermal expansion. Inserting twist into these precursor fibers enables thermally-driven torsional actuation and can cause the formation of helical coils. Such coiled structures provide giant-stroke tensile actuation exceeding the 20% in-vivo contraction of natural muscles. This contraction is highly reversible, with over one million cycles demonstrated, and can occur without the hysteresis that plagues competing shape-memory and piezoelectric muscles. Several materials and composites are investigated, including low-cost, commercially-available muscle precursors, potentially facilitating thermally-responsive textiles that change porosity to provide wearer comfort.

Twisted carbon nanotube yarns have been shown to develop useful torsional and tensile actuation. Particularly useful are those hybrid yarns that incorporate a volume-changing guest material into the yarn pore space. Changing guest volume causes concomitant untwisting and shortening of the twisted yarn. Intriguingly, the magnitude of the tensile actuation can be increased by an order of magnitude by inserting such high twist into the fiber as to cause coiling. The mechanism of coil-induced stroke enhancement is investigated using ordinary spring mechanics and it is shown that tensile actuation can be adequately predicted from the coil and yarn geometries.

Highly oriented nylon and polyethylene fibres shrink in length when heated and expand in diameter. By twisting and then coiling monofilaments of these materials to form helical springs, the anisotropic thermal expansion has recently been shown to enable tensile actuation of up to 49% upon heating. Joule heating, by passing a current through a conductive coating on the surface of the filament, is a convenient method of controlling actuation. In previously reported work this has been done using highly flexible carbon nanotube sheets or commercially available silver coated fibres. In this work silver paint is used as the Joule heating element at the surface of the muscle. Up to 29% linear actuation is observed with energy and power densities reaching 840 kJ m-3 (528 J kg-1) and 1.1 kW kg-1 (operating at 0.1 Hz, 4% strain, 1.4 kg load). This simple coating method is readily accessible and can be applied to any polymer filament. Effective use of this technique relies on uniform coating to avoid temperature gradients.

not Available.

Photosynthetic reaction centres (RCs) convert light into separated charges with nearly perfect quantum efficiency, and have been used to generate photocurrent. Previous work has shown that electron tunnelling rates between redox centres in proteins depend exponentially on the tunnelling distance. In this work the RC from Rhodobacter sphaeroides was genetically modified with the aim of achieving the shortest tunnelling distances yet demonstrated between the RC's electron-accepting P site and underlying graphite and gold electrodes, and between the electron donor Q site and graphite electrodes. Opposite charges are carried to counter electrodes using mobile mediators, as in dye-sensitised solar cells. Native RCs are bound to graphite surfaces through N-(1-pyrene)iodoacetamide. Although the linker's length is only 4 A, the electron transfer pathway between the Q electron donor site on the RC and the electrode surface is still too large for current to be significant. A mutant version with the electron acceptor P side close to the graphite surface produced currents of 15 nA cm−2 upon illumination. Direct binding of RCs to a gold surface is shown, resulting in currents of 5 nA cm−2. In both cases the current was unaffected by mediator concentration but increased with illumination, suggesting that direct electron transfer was achieved. The engineering of an RC to achieve direct electron transfer will help with long term efforts to demonstrate RC-based photovoltaic devices.