Future Thread: Printing Electronics on Fibers.

This article introduces a methodology to increase the integration density of functional electronic features on fibers/threads/wires through additive deposition of functional materials via printed electronics. It opens the possibility to create a multifunctional intelligent system on a single fiber/thread/wire while combining the advantages of existing approaches, i.e., the scalability of coating techniques and the microfeatures of semiconductor-based fabrication. By directly printing on threads (of diameters ranging from 90 to 1000 µm), micropatterned electronic devices and multifunctional electronic systems could be formed. Contact and noncontact printing methods were utilized to create various shapes from serpentines and meanders to planar coils and interdigitated electrodes, as well as complex multilayer structures for thermal and light actuators, humidity, and temperature sensors. We demonstrate the practicality of the method by integrating a multifunctional thread into a FFP mask for breath monitoring. Printing technologies provide virtually unrestricted choices for the types of threads, materials, and devices used. They are scalable via roll-to-roll processes and offer a resource-efficient way to democratize electronics across textile products.

Wearable sensors for monitoring marine environments and their inhabitants.

Human societies depend on marine ecosystems, but their degradation continues. Toward mitigating this decline, new and more effective ways to precisely measure the status and condition of marine environments are needed alongside existing rebuilding strategies. Here, we provide an overview of how sensors and wearable technology developed for humans could be adapted to improve marine monitoring. We describe barriers that have slowed the transition of this technology from land to sea, update on the developments in sensors to advance ocean observation and advocate for more widespread use of wearables on marine organisms in the wild and in aquaculture. We propose that large-scale use of wearables could facilitate the concept of an 'internet of marine life' that might contribute to a more robust and effective observation system for the oceans and commercial aquaculture operations. These observations may aid in rationalizing strategies toward conservation and restoration of marine communities and habitats.

Current-induced zero-field domain wall depinning in cylindrical nanowires.

Multi-segmented cylindrical nanowires have properties that make them attractive for high-density, high-speed logic and memory applications. Investigations of the current-induced domain wall motion in cylindrical nanowires have, so far, typically been conducted with a background magnetic field. However, if performed at zero external field, they would be much more viable for their use in prospective electronic devices. Here, we present an all-magneto electrical method to consistently pin domain walls in multi-segmented nanowires and induce their de-pinning using current pulses. The experiments were conducted with compositionally modulated three-segmented nickel/cobalt/nickel and two-segmented cobalt/nickel nanowires of 190 and 150 nm diameter, respectively, where the soft/hard magnetic texture has been fairly studied. We find that for the 3 segmented nanowire, the domain wall can be de-pinned independent of the polarity of the pulse, while for the 2 segmented nanowire the domain wall de-pins only for one polarity. Applying current pulses of 1 × 1012 A/m2, we use a pulse width of 22 ns to estimate a lower boundary for the domain wall speed of 634.54 m/s in cobalt. We study the resistive heating effect from the DC measurement current to find a temperature increase of no more than 2 °C after more than 20 h of tests.

Smartphone-Based Multiplexed Biosensing Tools for Health Monitoring.

Many emerging technologies have the potential to improve health care by providing more personalized approaches or early diagnostic methods. In this review, we cover smartphone-based multiplexed sensors as affordable and portable sensing platforms for point-of-care devices. Multiplexing has been gaining attention recently for clinical diagnosis considering certain diseases require analysis of complex biological networks instead of single-marker analysis. Smartphones offer tremendous possibilities for on-site detection analysis due to their portability, high accessibility, fast sample processing, and robust imaging capabilities. Straightforward digital analysis and convenient user interfaces support networked health care systems and individualized health monitoring. Detailed biomarker profiling provides fast and accurate analysis for disease diagnosis for limited sample volume collection. Here, multiplexed smartphone-based assays with optical and electrochemical components are covered. Possible wireless or wired communication actuators and portable and wearable sensing integration for various sensing applications are discussed. The crucial features and the weaknesses of these devices are critically evaluated.

Minimally-invasive, real-time, non-destructive, species-independent phytohormone biosensor for precision farming.

To keep up with population growth, precision farming technologies must be implemented to sustainably increase agricultural output. The impact of such technologies can be expanded by monitoring phytohormones, such as salicylic acid. In this study, we present a plant-wearable electrochemical sensor for in situ detection of salicylic acid. The sensor utilizes microneedle-based electrodes that are functionalized with a layer of salicylic acid selective magnetic molecularly imprinted polymers. The sensor's capability to detect the phytohormone is demonstrated both in vitro and in vivo with a limit of detection of 2.74 µM and a range of detection that can reach as high as 150 µM. Furthermore, the selectivity of the sensor is verified by testing the sensor on commonly occurring phytohormones. Finally, we demonstrate the capability of the sensor to detect the onset of fungal infestation in Tobacco 5 min post-inoculation. This work shows that the sensor could serve as a promising platform for continuous and non-destructive monitoring in the field and as a fundamental research tool when coupled with a portable potentiostat.

Distinguishing Local Demagnetization Contribution to the Magnetization Process in Multisegmented Nanowires.

Cylindrical magnetic nanowires are promising materials that have the potential to be used in a wide range of applications. The versatility of these nanostructures is based on the tunability of their magnetic properties, which is achieved by appropriately selecting their composition and morphology. In addition, stochastic behavior has attracted attention in the development of neuromorphic devices relying on probabilistic magnetization switching. Here, we present a study of the magnetization reversal process in multisegmented CoNi/Cu nanowires. Nonstandard 2D magnetic maps, recorded under an in-plane magnetic field, produce datasets that correlate with magnetoresistance measurements and micromagnetic simulations. From this process, the contribution of the individual segments to the demagnetization process can be distinguished. The results show that the magnetization reversal in these nanowires does not occur through a single Barkhausen jump, but rather by multistep switching, as individual CoNi segments in the NW undergo a magnetization reversal. The existence of vortex states is confirmed by their footprint in the magnetoresistance and 2D MFM maps. In addition, the stochasticity of the magnetization reversal is analysed. On the one hand, we observe different switching fields among the segments due to a slight variation in geometrical parameters or magnetic anisotropy. On the other hand, the stochasticity is observed in a series of repetitions of the magnetization reversal processes for the same NW under the same conditions.

Modulated nanowire scaffold for highly efficient differentiation of mesenchymal stem cells.

BACKGROUND: Nanotopographical cues play a critical role as drivers of mesenchymal stem cell differentiation. Nanowire scaffolds, in this regard, provide unique and adaptable nanostructured surfaces with focal points for adhesion and with elastic properties determined by nanowire stiffness. RESULTS: We show that a scaffold of nanowires, which are remotely actuated by a magnetic field, mechanically stimulates mesenchymal stem cells. Osteopontin, a marker of osteogenesis onset, was expressed after cells were cultured for 1 week on top of the scaffold. Applying a magnetic field significantly boosted differentiation due to mechanical stimulation of the cells by the active deflection of the nanowire tips. The onset of differentiation was reduced to 2 days of culture based on the upregulation of several osteogenesis markers. Moreover, this was observed in the absence of any external differentiation factors. CONCLUSIONS: The magneto-mechanically modulated nanosurface enhanced the osteogenic differentiation capabilities of mesenchymal stem cells, and it provides a customizable tool for stem cell research and tissue engineering.

Robust, Long-Term, and Exceptionally Sensitive Microneedle-Based Bioimpedance Sensor for Precision Farming.

Precision farming has the potential to increase global food production capacity whilst minimizing traditional inputs. However, the adoption and impact of precision farming are contingent on the availability of sensors that can discern the state of crops, while not interfering with their growth. Electrical impedance spectroscopy offers an avenue for nondestructive monitoring of crops. To that end, it is reported on the deployment of impedimetric sensors utilizing microneedles (MNs) that can be used to pierce the waxy exterior of plants to obtain sensitive impedance spectra in open-air settings with an average relative noise value of 3.83%. The sensors are fabricated using a novel micromolding and release method that is compatible with UV photocurable and thermosetting polymers. Assessments of the quality of the MNs under scanning electron microscopy show that the replication process is high in fidelity to the original design of the master mold and that it can be used for upward of 20 replication cycles. The sensor's performance is validated against conventional planar sensors for obtaining the impedance values of Arabidopsis thaliana. As a change is detected in impedance due to lighting and hydration, this raises the possibility for their widespread use in precision farming.

Integrated Magnetohydrodynamic Pump with Magnetic Composite Substrate and Laser-Induced Graphene Electrodes.

An integrated polymer-based magnetohydrodynamic (MHD) pump that can actuate saline fluids in closed-channel devices is presented. MHD pumps are attractive for lab-on-chip applications, due to their ability to provide high propulsive force without any moving parts. Unlike other MHD devices, a high level of integration is demonstrated by incorporating both laser-induced graphene (LIG) electrodes as well as a NdFeB magnetic-flux source in the NdFeB-polydimethylsiloxane permanent magnetic composite substrate. The effects of transferring the LIG film from polyimide to the magnetic composite substrate were studied. Operation of the integrated magneto hydrodynamic pump without disruptive bubbles was achieved. In the studied case, the pump produces a flow rate of 28.1 µL/min. while consuming ~1 mW power.

3D Printed Microneedle Array for Electroporation.

In-vitro transfection of cells by electroporation is a widely used approach in cell biology and medicine. The transfection method is highly dependent on the cell culture's electrical resistance, which is strongly determined by differences in the membranes, but also on the morphology of the electrodes. Microneedle (MN)-based electrodes have been used to concentrate the electrical field during electroporation, and therefore maximize its effect on cell membrane permeability. So far, the methods used for the fabrication of MN electrodes have been relatively limited with respect to the needle design. In this work, we provide a method to fabricate MNs using 3D printing, which is a technology that provides a high degree of flexibility with respect to geometry and dimensions. Pyramidal-shaped MN designs were fabricated and tested on HCT116 cancer cells. Customization of the tips of the pyramids permits tailoring of the electrical field in the vicinity of the cell membranes. The fabricated device enables low-voltage (2 V) electroporation, eliminating the need for the use of specialized chemical buffers. The results show the potential of this method, which can be exploited and optimized for many different applications, and offer a very accessible approach for in-vitro electroporation and cell studies. The MNs can be customized to create complex structures, for example, for a multi-culture cell environment.

Strain-induced Differentiation of Mesenchymal Stem Cells.

Directing the fate of human mesenchymal stem/stromal cells (hMSCs) toward bone formation using mechanical strain is a promising approach in regenerative medicine related to bone diseases. Numerous studies have evaluated the effects of vibration or cyclic tensile strain on MSCs towards developing a mechanically-based method for stimulating differentiation. Here, we study the differentiation of hMSCs cultured on elastic polydimethylsiloxane (PDMS) membrane, which is magnetically actuated to induce periodically varying strain. The strain distribution across the membrane was calculated by finite-element modeling and demonstrates three main areas of different strain amplitudes. The strain effect on the hMSCs was evaluated by measuring the mineralization of differentiated hMSCs using Alizarin S red stain. The results indicate a strain-dependent differentiation of hMSCs, where the highest region of strain on the membrane resulted in the most accelerated differentiation. Osteogenic differentiation was achieved as early as two weeks, which is significantly sooner than control hMSCs treated with osteogenic media alone.

Biofunctionalization of Magnetic Nanomaterials.

Magnetic nanomaterials have received great attention in different biomedical applications. Biofunctionalizing these nanomaterials with specific targeting agents is a crucial aspect to enhance their efficacy in diagnostics and treatments while minimizing the side effects. The benefit of magnetic nanomaterials compared to non-magnetic ones is their ability to respond to magnetic fields in a contact-free manner and over large distances. This allows to guide or accumulate them, while they can also be monitored. Recently, magnetic nanowires (NWs) with unique features were developed for biomedical applications. The large magnetic moment of these NWs enables a more efficient remote control of their movement by a magnetic field. This has been utilized with great success in cancer treatment, drug delivery, cell tracing, stem cell differentiation or magnetic resonance imaging. In addition, the NW fabrication by template-assisted electrochemical deposition provides a versatile method with tight control over the NW properties. Especially iron NWs and iron-iron oxide (core-shell) NWs are suitable for biomedical applications, due to their high magnetization and low toxicity. In this work, we provide a method to biofunctionalize iron/iron oxide NWs with specific antibodies directed against a specific cell surface marker that is overexpressed in a large number of cancer cells. Since the method utilizes the properties of the iron oxide surface, it is also applicable to superparamagnetic iron oxide nanoparticles. The NWs are first coated with 3-aminopropyl-tri-ethoxy-silane (APTES) acting as a linker, which the antibodies are covalently attached to. The APTES coating and the antibody biofunctionalization are proven by electron energy loss spectroscopy (EELS) and zeta potential measurements. In addition, the antigenicity of the antibodies on the NWs is tested by using immunoprecipitation and western blot. The specific targeting of the biofunctionalized NWs and their biocompatibility are studied by confocal microscopy and a cell viability assay.

Laser-Printed, Flexible Graphene Pressure Sensors.

While the outstanding properties of graphene have attracted a lot of attention, one of the major bottlenecks of its widespread usage is its availability in large volumes. Laser printing graphene on polyimide films is an efficient single-step fabrication process that can remedy this issue. A laser-printed, flexible pressure sensor is developed utilizing the piezoresistive effect of 3D porous graphene. The pressure sensors performance can be easily adjusted via the geometrical parameters. They have a sensitivity in the range of 1.23 × 10-3 kPa and feature a high resolution with a detection limit of 10 Pa in combination with an extremely wide dynamic range of at least 20 MPa. They also provide excellent long-term stability of at least 15 000 cycles. The biocompatibility of laser-induced graphene is also evaluated by cytotoxicity assays and fluorescent staining, which show an insignificant drop in viability. Polymethyl methacrylate coating is particularly useful for underwater applications, protecting the sensors from biofouling and shunt currents, and enable operation at a depth of 2 km in highly saline Red Sea water. Due to its features, the sensors are a prime choice for multiple healthcare applications; for example, they are used for heart rate monitoring, plantar pressure measurements, and tactile sensing.

Magnetic core-shell nanowires as MRI contrast agents for cell tracking.

BACKGROUND: Identifying the precise location of cells and their migration dynamics is of utmost importance for achieving the therapeutic potential of cells after implantation into a host. Magnetic resonance imaging is a suitable, non-invasive technique for cell monitoring when used in combination with contrast agents. RESULTS: This work shows that nanowires with an iron core and an iron oxide shell are excellent materials for this application, due to their customizable magnetic properties and biocompatibility. The longitudinal and transverse magnetic relaxivities of the core-shell nanowires were evaluated at 1.5 T, revealing a high performance as T2 contrast agents. Different levels of oxidation and various surface coatings were tested at 7 T. Their effects on the T2 contrast were reflected in the tailored transverse relaxivities. Finally, the detection of nanowire-labeled breast cancer cells was demonstrated in T2-weighted images of cells implanted in both, in vitro in tissue-mimicking phantoms and in vivo in mouse brain. Labeling the cells with a nanowire concentration of 0.8 µg of Fe/mL allowed the detection of 25 cells/µL in vitro, diminishing the possibility of side effects. This performance enabled an efficient labelling for high-resolution cell detection after in vivo implantation (~ 10 nanowire-labeled cells) over a minimum of 40 days. CONCLUSIONS: Iron-iron oxide core-shell nanowires enabled the efficient and longitudinal cellular detection through magnetic resonance imaging acting as T2 contrast agents. Combined with the possibility of magnetic guidance as well as triggering of cellular responses, for instance by the recently discovered strong photothermal response, opens the door to new horizons in cell therapy and make iron-iron oxide core-shell nanowires a promising theranostic platform.

Direct imaging of an inhomogeneous electric current distribution using the trajectory of magnetic half-skyrmions.

The direct imaging of current density vector distributions in thin films has remained a daring challenge. Here, we report that an inhomogeneous current distribution can be mapped directly by the trajectories of magnetic half-skyrmions driven by an electrical current in Pt/Co/Ta trilayer, using polar magneto-optical Kerr microscopy. The half-skyrmion carries a topological charge of 0.5 due to the presence of Dzyaloshinskii-Moriya interaction, which leads to the half-skyrmion Hall effect. The Hall angle of half-skyrmions is independent of current density and can be reduced to as small as 4° by tuning the thickness of the Co layer. The Hall angle is so small that the elongation path of half-skyrmion approximately delineates the invisible current flow as demonstrated in both a continuous film and a curved track. Our work provides a practical technique to directly map inhomogeneous current distribution even in complex geometries for both fundamental research and industrial applications.

Functionalization of Magnetic Nanowires for Active Targeting and Enhanced Cell-Killing Efficacy.

Conventional chemotherapy and radiation therapy are often insufficient in eliminating cancer and are accompanied by severe side effects, due to a lack in the specificity of their targeting. Magnetic iron nanowires have made a great contribution to the nanomedicine field because of their low toxicity and ease of manipulation with the magnetic field. Recently, they have been used in magnetic resonance imaging and wireless magnetomechanical and photothermal treatments. The addition of active targeting moieties to these nanowires thus creates a multifunctional tool that can boost therapeutic efficacies through the combination of different treatments toward a specific target. Colon cancer is the third most commonly occurring cancer, and 90 ± 2.5% of colon cancer cells express the glycoprotein CD44. Iron nanowires with an iron oxide surface are biocompatible, multifunctional materials that can be controlled by magnetic fields and heated by laser irradiation. Here, they were functionalized with anti-CD44 antibodies and used in a combination therapy that included magnetomechanical and photothermal treatments on colon cancer cells. The functionalization resulted in a 3-fold increase of nanowire internalization in colon cancer cells compared to control cells and did not affect the antigenicity and magnetic properties. It also increased the efficacy of killing from 35 ± 1% to more than 71 ± 2%, showing that the combination therapy was more effective than individual therapies alone.

Iron-Based Core-Shell Nanowires for Combinatorial Drug Delivery and Photothermal and Magnetic Therapy.

Combining different therapies into a single nanomaterial platform is a promising approach for achieving more efficient, less invasive, and personalized treatments. Here, we report on the development of such a platform by utilizing nanowires with an iron core and iron oxide shell as drug carriers and exploiting their optical and magnetic properties. The iron core has a large magnetization, which provides the foundation for low-power magnetic manipulation and magnetomechanical treatment. The iron oxide shell enables functionalization with doxorubicin through a pH-sensitive linker, providing selective intracellular drug delivery. Combined, the core-shell nanostructure features an enhanced light-matter interaction in the near-infrared region, resulting in a high photothermal conversion efficiency of >80% for effective photothermal treatment. Applied to cancer cells, the collective effect of the three modalities results in an extremely efficient treatment with nearly complete cell death (∼90%). In combination with the possibility of guidance and detection, this platform provides powerful tools for the development of advanced treatments.

Electric-Field-Enhanced Bulk Perpendicular Magnetic Anisotropy in GdFe/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 Multiferroic Heterostructure.

Perpendicular magnetic anisotropy is important for increasing the information storage density in the perpendicular magnetic recording media, and for rare-earth-transition-metal alloys with bulk perpendicular magnetic anisotropy that generate great research interest due to their abundant interesting phenomena, such as fast domain wall motion and skyrmion. Here, we deposit amorphous GdFe ferrimagnetic films on Pb(Mg1/3Nb2/3)0.7Ti0.3O3 ferroelectric substrate and investigate the effect of electric-field-induced piezostrain on its bulk perpendicular magnetic anisotropy. The anomalous Hall effect and polar Kerr image measurements suggest an enhanced bulk perpendicular magnetic anisotropy by electric field, which originates from a positive magnetoelastic anisotropy due to the positive magnetostriction coefficient of the GdFe film and the electric-field-induced tensile strain along the z axis in Pb(Mg1/3Nb2/3)0.7Ti0.3O3 ferroelectric substrate. Our results enrich the electrical control of perpendicular magnetic anisotropy and are useful for designing spintronic devices based on perpendicular magnetic anisotropy.

Iron Nanowire Fabrication by Nano-Porous Anodized Aluminum and its Characterization.

Magnetic nanowires possess unique properties that have attracted the interest of different fields of research, including basic physics, biomedicine, and data storage. We demonstrate a fabrication method for iron (Fe) nanowires via electrochemical deposition into anodic alumina oxide (AAO) templates. The templates are fabricated by anodization of aluminum (Al) discs, and the pore length and diameter are controlled by changing the anodizing conditions. Pores with an average diameter of around 120 nm are created using oxalic acid as the electrolyte. Using this method, cylindrical nanowires are synthesized, which are released by dissolving the alumina using a selective chemical etchant.

Design of Intense Nanoscale Stray Fields and Gradients at Magnetic Nanorod Interfaces.

We explore electrodeposited ordered arrays of Fe, Ni, and Co nanorods embedded in anodic alumina membranes as a source of intense magnetic stray field gradients localized at the nanoscale. We perform a multiscale characterization of the stray fields using a combination of experimental methods (magnetooptical Kerr effect and virtual bright field differential phase contrast imaging) and micromagnetic simulations and establish a clear correlation between the stray fields and the magnetic configurations of the nanorods. For uniformly magnetized Fe and Ni wires, the field gradients vary following saturation magnetization of the corresponding metal and the diameter of the wires. In the case of Co nanorods, very localized (∼10 nm) and intense (>1 T) stray field sources are associated with the cores of magnetic vortexes. Confinement of that strong field at extremely small dimensions leads to exceptionally high field gradients up to 108 T/m. These results demonstrate a clear path to design and fine-tune nanoscale magnetic stray field ordered patterns with a broad applicability in key nanotechnologies, such as nanomedicine, nanobiology, nanoplasmonics, and sensors.