The Development of Aptamer-Coupled Microelectrode Fiber Sensors (apta-µFS) for Highly Selective Neurochemical Sensing.

The selective and sensitive sensing of neurochemicals is essential to decipher in-brain chemistry underlying brain pathophysiology. The recent development of flexible and multifunctional polymer-based fibers has been shown useful in recording and modulating neural activities, primarily electrical ones. In this study, we were able to realize fiber-based neurochemical sensing with high sensitivity and selectivity. We achieved a generalizable method to couple aptamers, a type of synthetic receptors on the carbon composites within fibers, as microsensors for highly selective neurochemical detection. Such an aptamer-coupled microelectrode fiber sensor (apta-µFS) enables simple, label-free, and sensitive dopamine (DA) detection down to 5 nM with ultrahigh specificity across major interferents. We succeeded in monitoring DA selectively within the living brain using our apta-µFS. We further showed the proof-of-concept of using microelectronic fiber-based toolsets to target neural pathways across electrical and chemical modalities. In summary, such fiber-based toolsets hold great potential to advance multimodal mechanistic understanding of brain pathophysiology.

Unraveling the Influence of Thermal Drawing Parameters on the Microstructure and Thermo-Mechanical Properties of Multimaterial Fibers.

Multimaterial thermally drawn fibers are becoming important building blocks in several foreseen applications in surgical probes, protective gears, or medical textiles. Here, the influence of the thermal drawing parameters on the degree of polymer chain orientation, the related thermal shrinkage behavior, and the mechanical properties of the final fibers is investigated via thermo-mechanical testing and small- and wide-angle X-ray scattering (SAXS and WAXS) analyses. This study on polyetherimide fibers reveals that the drawing stress, which depends on the drawing speed and temperature, controls the thermal shrinkage behavior and mechanical properties. Furthermore, SAXS and WAXS analyses show that the degree of chain orientation increases with drawing stresses below 8 MPa and then saturates, which correlates with the amount of observed shrinkage. The use of this process-dependent polymer chain alignment to tune the mechanical and shrinkage properties of the fibers is highlighted and controlled bending multimaterial fibers made of two polymethyl methacrylates having different molecular weights are developed. Finally, a heat treatment procedure is proposed to relax the chain alignment and increase the dimensional stability of devices such as temperature sensors. This deeper understanding can serve as a guide for the processing of complex fibers requiring specific mechanical properties or enhanced thermal stability.

Thermally Drawn Elastomer Nanocomposites for Soft Mechanical Sensors.

Stretchable and conductive nanocomposites are emerging as important constituents of soft mechanical sensors for health monitoring, human-machine interactions, and soft robotics. However, tuning the materials' properties and sensor structures to the targeted mode and range of mechanical stimulation is limited by current fabrication approaches, particularly in scalable polymer melt techniques. Here, thermoplastic elastomer-based nanocomposites are engineered and novel rheological requirements are proposed for their compatibility with fiber processing technologies, yielding meters-long, soft, and highly versatile stretchable fiber devices. Based on microstructural changes in the nanofiller arrangement, the resistivity of the nanocomposite is tailored in its final device architecture across an entire order of magnitude as well as its sensitivity to strain via tuning thermal drawing processing parameters alone. Moreover, the prescribed electrical properties are coupled with suitable device designs and several fiber-based sensors are proposed aimed at specific types of deformations: i) a robotic fiber with an integrated bending mechanism where changes as small as 5° are monitored by piezoresistive nanocomposite elements, ii) a pressure-sensing fiber based on a geometrically controlled resistive signal that responds with a sub-newton resolution to changes in pressing forces, and iii) a strain-sensing fiber that tracks changes in capacitance up to 100% elongation.

Soft Multimaterial Magnetic Fibers and Textiles.

Magnetically responsive soft materials are promising building blocks for the next generation of soft robotics, prosthesis, surgical tools, and smart textiles. To date, however, the fabrication of highly integrated magnetic fibers with extreme aspect ratios, that can be used as steerable catheters, endoscopes, or within functional textiles remains challenging. Here, multimaterial thermal drawing is proposed as a material and processing platform to realize 10s of meters long soft, ultrastretchable, yet highly resilient magnetic fibers. Fibers with a diameter as low as 300 µm and an aspect ratio of 105 are demonstrated, integrating nanocomposite domains with ferromagnetic microparticles embedded in a soft elastomeric matrix. With the proper choice of filler content that must strike the right balance between magnetization density and mechanical stiffness, fibers withstanding strains of >1000% are shown, which can be magnetically actuated and lift up to 370 times their own weight. Magnetic fibers can also integrate other functionalities like microfluidic channels, and be weaved into conventional textiles. It is shown that the novel magnetic textiles can be washed and sustain extreme mechanical constraints, as well as be folded into arbitrary shapes when magnetically actuated, paving the way toward novel intriguing opportunities in medical textiles and soft magnetic systems.

Highly Integrated Multi-Material Fibers for Soft Robotics.

Soft robots are envisioned as the next generation of safe biomedical devices in minimally invasive procedures. Yet, the difficulty of processing soft materials currently limits the size, aspect-ratio, manufacturing throughput, as well as, the design complexity and hence capabilities of soft robots. Multi-material thermal drawing is introduced as a material and processing platform to create soft robotic fibers imparted with multiple actuations and sensing modalities. Several thermoplastic and elastomeric material options for the fibers are presented, which all exhibit the rheological processing attributes for thermal drawing but varying mechanical properties, resulting in adaptable actuation performance. Moreover, numerous different fiber designs with intricate internal architectures, outer diameters of 700 µm, aspect ratios of 103 , and a fabrication at a scale of 10s of meters of length are demonstrated. A modular tendon-driven mechanism enables 3-dimensional (3D) motion, and embedded optical guides, electrical wires, and microfluidic channels give rise to multifunctionality. The fibers can perceive and autonomously adapt to their environments, as well as, probe electrical properties, and deliver fluids and mechanical tools to spatially distributed targets.

Enhanced chemiluminescent detection scheme for trace vapor sensing in pneumatically-tuned hollow core photonic bandgap fibers.

We demonstrate an in-fiber gas phase chemical detection architecture in which a chemiluminescent (CL) reaction is spatially and spectrally matched to the core modes of hollow photonic bandgap (PBG) fibers in order to enhance detection efficiency. A peroxide-sensitive CL material is annularly shaped and centered within the fiber's hollow core, thereby increasing the overlap between the emission intensity and the intensity distribution of the low-loss fiber modes. This configuration improves the sensitivity by 0.9 dB/cm compared to coating the material directly on the inner fiber surface, where coupling to both higher loss core modes and cladding modes is enhanced. By integrating the former configuration with a custom-built optofluidic system designed for concomitant controlled vapor delivery and emission measurement, we achieve a limit-of-detection of 100 parts per billion (ppb) for hydrogen peroxide vapor. The PBG fibers are produced by a new fabrication method whereby external gas pressure is used as a control knob to actively tune the transmission bandgaps through the entire visible range during the thermal drawing process.

Controlled filamentation instability as a scalable fabrication approach to flexible metamaterials.

Long and flexible arrays of nanowires find impactful applications in sensing, photonics, and energy harvesting. Conventional manufacturing relies largely on lithographic methods limited in wafer size, rigidity, and machine write time. Here, we report a scalable process to generate encapsulated flexible nanowire arrays with high aspect ratios and excellent tunable size and periodicity. Our strategy is to control nanowire self-assembly into 2D and 3D architectures via the filamentation of a textured thin film under anisotropic stretching. This is achieved by coupling soft lithography, glancing angle deposition, and thermal drawing to obtain well-ordered meters-long nanowires with diameters down to 50 nanometers. We demonstrate that the nanowire diameter and period of the array can be decoupled and manipulated independently. We propose a filamentation criterion and perform numerical simulations implementing destabilizing long-range Van der Waals interactions. Applied to high-index chalcogenide glasses, we show that this decoupling allows for tuning diffraction. Finally, harnessing Mie resonance, we demonstrate the possibility of manufacturing macroscopic meta-grating superstructures for nanophotonic applications.

3D stretchable and self-encapsulated multimaterial triboelectric fibers.

A robust power device for wearable technologies and soft electronics must feature good encapsulation, high deformability, and reliable electrical outputs. Despite substantial progress in materials and architectures for two-dimensional (2D) planar power configurations, fiber-based systems remain limited to relatively simple configurations and low performance due to challenges in processing methods. Here, we extend complex 2D triboelectric nanogenerator configurations to 3D fiber formats based on scalable thermal processing of water-resistant thermoplastic elastomers and composites. We perform mechanical analysis using finite element modeling to understand the fiber's deformation and the level of control and engineering on its mechanical behavior and thus to guide its dimensional designs for enhanced electrical performance. With microtexture patterned functional surfaces, the resulting fibers can reliably produce state-of-the-art electrical outputs from various mechanical deformations, even under harsh conditions. These mechanical and electrical attributes allow their integration with large and stretchable surfaces for electricity generation of hundreds of microamperes.

Thermally Drawn CNT-Based Hybrid Nanocomposite Fiber for Electrochemical Sensing.

Nowadays, bioelectronic devices are evolving from rigid to flexible materials and substrates, among which thermally-drawn-fiber-based bioelectronics represent promising technologies thanks to their inherent flexibility and seamless integration of multi-functionalities. However, electrochemical sensing within fibers remains a poorly explored area, as it imposes new demands for material properties-both the electrochemical sensitivity and the thermomechanical compatibility with the fiber drawing process. Here, we designed and fabricated microelectrode fibers made of carbon nanotube (CNT)-based hybrid nanocomposites and further evaluated their detailed electrochemical sensing performances. Carbon-black-impregnated polyethylene (CB-CPE) was chosen as the base material, into which CNT was loaded homogeneously in a concentration range of 3.8 to 10 wt%. First, electrical impedance characterization of CNT nanocomposites showed a remarkable decrease of the resistance with the increase in CNT loading ratio, suggesting that CNTs notably increased the effective electrical current pathways inside the composites. In addition, the proof-of-principle performance of fiber-based microelectrodes was characterized for the detection of ferrocenemethanol (FcMeOH) and dopamine (DA), exhibiting an ultra-high sensitivity. Additionally, we further examined the long-term stability of such composite-based electrode in exposure to the aqueous environment, mimicking the in vivo or in vitro settings. Later, we functionalized the surface of the microelectrode fiber with ion-sensitive membranes (ISM) for the selective sensing of Na+ ions. The miniature fiber-based electrochemical sensor developed here holds great potential for standalone point-of-care sensing applications. In the future, taking full advantage of the thermal drawing process, the electrical, optical, chemical, and electrochemical modalities can be all integrated together within a thin strand of fiber. This single fiber can be useful for fundamental multi-mechanistic studies for biological applications and the weaved fibers can be further applied for daily health monitoring as functional textiles.

Novel insights into the design of stretchable electrical systems.

Soft electronics have recently gathered considerable interest because of their biomechanical compatibility. An important feature of deformable conductors is their electrical response to strain. While development of stretchable materials with high gauge factors has attracted considerable attention, there is a growing need for stretchable conductors whose response to deformation can be accurately engineered to provide arbitrary resistance-strain relationships. Rare studies addressing this issue have focused on deterministic geometries of single rigid materials, limiting the scope of these strategies. We introduce the novel concept of periodic stretchable patterns combining multiple conductive materials to produce tailored responses. Using shortest path algorithms, we establish a computationally efficient selection method to obtain the required resistance-strain relationship. Using this algorithm, we identify and experimentally demonstrate constant resistance-strain responses up to 50% elongation using a single microtextured material. Last, we demonstrate counterintuitive sinusoidal responses by integrating three materials, with interesting applications in sensing and soft robotics.

Resolving optical illumination distributions along an axially symmetric photodetecting fiber.

Photodetecting fibers of arbitrary length with internal metal, semiconductor and insulator domains have recently been demonstrated. These semiconductor devices exhibit a continuous translational symmetry which presents challenges to the extraction of spatially resolved information. Here, we overcome this seemingly fundamental limitation and achieve the detection and spatial localization of a single incident optical beam at sub-centimeter resolution, along a one-meter fiber section. Using an approach that breaks the axial symmetry through the constuction of a convex electrical potential along the fiber axis, we demonstrate the full reconstruction of an arbitrary rectangular optical wave profile. Finally, the localization of up to three points of illumination simultaneously incident on a photodetecting fiber is achieved.

Metal-insulator-semiconductor optoelectronic fibres.

The combination of conductors, semiconductors and insulators with well-defined geometries and at prescribed length scales, while forming intimate interfaces, is essential in most functional electronic and optoelectronic devices. These are typically produced using a variety of elaborate wafer-based processes, which allow for small features, but are restricted to planar geometries and limited coverage area. In contrast, the technique of fibre drawing from a preformed reel or tube is simpler and yields extended lengths of highly uniform fibres with well-controlled geometries and good optical transport characteristics. So far, this technique has been restricted to particular materials and larger features. Here we report on the design, fabrication and characterization of fibres made of conducting, semiconducting and insulating materials in intimate contact and in a variety of geometries. We demonstrate that this approach can be used to construct a tunable fibre photodetector comprising an amorphous semiconductor core contacted by metallic microwires, and surrounded by a cylindrical-shell resonant optical cavity. Such a fibre is sensitive to illumination along its entire length (tens of meters), thus forming a photodetecting element of dimensionality one. We also construct a grid of such fibres that can identify the location of an illumination point. The advantage of this type of photodetector array is that it needs a number of elements of only order N, in contrast to the conventional order N2 for detector arrays made of photodetecting elements of dimensionality zero.

Exploiting collective effects of multiple optoelectronic devices integrated in a single fiber.

The opportunities and challenges of realizing sophisticated functionality by assembling many nanoscale devices, while covering large areas, remain for the most part unrealized and unresolved. In this work, we demonstrate the successful fabrication of an eight-device cascaded optoelectronic fiber structure in which components down to 100 nm are individually electrically addressed and can operate collectively to deliver novel functionality over large area coverage. We show that a tandem arrangement of subwavelength photodetecting devices integrated in a single fiber enables the extraction of information on the direction, wavelength, and potentially even color of incident radiation over a wide spectral range in the visible regime. Finally, we fabricated a 0.1 square meter single plane fiber assembly which uses polychromatic illumination to extract images without the use of a lens, representing an important step toward ambient light imaging fabrics.

Facile Fabrication of Microfluidic Chips for 3D Hydrodynamic Focusing and Wet Spinning of Polymeric Fibers.

Microfluidic wet spinning has gained increasing interest in recent years as an alternative to conventional wet spinning by offering higher control in fiber morphology and a gateway for the development of multi-material fibers. Conventionally, microfluidic chips used to create such fibers are fabricated by soft lithography, a method that requires both time and investment in necessary cleanroom facilities. Recently, additive manufacturing techniques were investigated for rapid and cost-efficient prototyping. However, these microfluidic devices are not yet matching the resolutions and tolerances offered by soft lithography. Herein, we report a facile and rapid method using selected arrays of hypodermic needles as templates within a silicone elastomer matrix. The produced microfluidic spinnerets display co-axially aligned circular channels. By simulation and flow experiments, we prove that these devices can maintain laminar flow conditions and achieve precise 3D hydrodynamic focusing. The devices were tested with a commercial polyurethane formulation to demonstrate that fibers with desired morphologies can be produced by varying the degree of hydrodynamic focusing. Thanks to the adaptability of this concept to different microfluidic spinneret designs-as well as to its transparency, ease of fabrication, and cost-efficient procedure-this device sets the ground for transferring microfluidic wet spinning towards industrial textile settings.

High-efficiency super-elastic liquid metal based triboelectric fibers and textiles.

Fibers that harvest mechanical energy via the triboelectric effect are excellent candidates as power sources for wearable electronics and functional textiles. Thus far however, their fabrication remains complex, and exhibited performances are below the state-of-the-art of 2D planar configurations, making them impractical. Here, we demonstrate the scalable fabrication of micro-structured stretchable triboelectric fibers with efficiencies on par with planar systems. We use the thermal drawing process to fabricate advanced elastomer fibers that combine a micro-textured surface with the integration of several liquid metal electrodes. Such fibers exhibit high electrical outputs regardless of repeated large deformations, and can sustain strains up to 560%. They can also be woven into deformable machine-washable textiles with high electrical outputs up to 490 V, 175 nC. In addition to energy harvesting, we demonstrate self-powered breathing monitoring and gesture sensing capabilities, making this triboelectric fiber platform an exciting avenue for multi-functional wearable systems and smart textiles.

Structured nanoscale metallic glass fibres with extreme aspect ratios.

Micro- and nanoscale metallic glasses offer exciting opportunities for both fundamental research and applications in healthcare, micro-engineering, optics and electronics. The scientific and technological challenges associated with the fabrication and utilization of nanoscale metallic glasses, however, remain unresolved. Here, we present a simple and scalable approach for the fabrication of metallic glass fibres with nanoscale architectures based on their thermal co-drawing within a polymer matrix with matched rheological properties. Our method yields well-ordered and uniform metallic glasses with controllable feature sizes down to a few tens of nanometres, and aspect ratios greater than 1010. We combine fluid dynamics and advanced in situ transmission electron microscopy analysis to elucidate the interplay between fluid instability and crystallization kinetics that determines the achievable feature sizes. Our approach yields complex fibre architectures that, combined with other functional materials, enable new advanced all-in-fibre devices. We demonstrate in particular an implantable metallic glass-based fibre probe tested in vivo for a stable brain-machine interface that paves the way towards innovative high-performance and multifunctional neuro-probes.

Microstructured Fibers for the Production of Food.

Food engineering faces the difficult challenge of combining taste, i.e., tailoring texture and rheology of food matrices with the balanced intake of healthy nutrients. In materials science, fiber suspensions and composites have been developed as a versatile and successful approach to tailor rheology while imparting materials with added functionalities. Structures based on such types of physical (micro)fibers are however rare in food production mainly due to a lack of food-grade materials and processes allowing for the fabrication of fibers with controlled sizes and microstructures. Here, the controlled fabrication of multi-material microstructured edible fibers is demonstrated using a food compatible process based on preform-to-fiber thermal drawing. It is shown that different material systems based on gelatin or casein, with plasticizers such as glycerol, can be thermally drawn into fibers with various geometries and cross-sectional structures. It is demonstrated that fibers can exhibit tailored mechanical properties post-drawing, and can encapsulate nutrients to control their release. The versatility of fiber materials is also exploited to demonstrate the fabrication of food-grade fabrics and scaffolds for food growth. The end results establish a new field in food production that relies on fiber-based simple and eco-friendly processes to realize enjoyable yet healthy and nutritious products.

Advanced Multimaterial Electronic and Optoelectronic Fibers and Textiles.

The ability to integrate complex electronic and optoelectronic functionalities within soft and thin fibers is one of today's key advanced manufacturing challenges. Multifunctional and connected fiber devices will be at the heart of the development of smart textiles and wearable devices. These devices also offer novel opportunities for surgical probes and tools, robotics and prostheses, communication systems, and portable energy harvesters. Among the various fiber-processing methods, the preform-to-fiber thermal drawing technique is a very promising process that is used to fabricate multimaterial fibers with complex architectures at micro- and nanoscale feature sizes. Recently, a series of scientific and technological breakthroughs have significantly advanced the field of multimaterial fibers, allowing a wider range of functionalities, better performance, and novel applications. Here, these breakthroughs, in the fundamental understanding of the fluid dynamics, rheology, and tailoring of materials microstructures at play in the thermal drawing process, are presented and critically discussed. The impact of these advances on the research landscape in this field and how they offer significant new opportunities for this rapidly growing scientific and technological platform are also discussed.

Publisher Correction: Self-assembly of nanostructured glass metasurfaces via templated fluid instabilities.

In the version of this Article originally published, the volume, article number and year of ref. 32 were incorrect; they should have read 31, 1802348 (2019). This has now been corrected.

Self-assembly of nanostructured glass metasurfaces via templated fluid instabilities.

Modern devices require the tuning of the size, shape and spatial arrangement of nano-objects and their assemblies with nanometre-scale precision, over large-area and sometimes soft substrates. Such stringent requirements are beyond the reach of conventional lithographic techniques or self-assembly approaches. Here, we show nanoscale control over the fluid instabilities of optical thin glass films for the fabrication of self-assembled all-dielectric optical metasurfaces. We show and model the tailoring of the position, shape and size of nano-objects with feature sizes below 100 nm and with interparticle distances down to 10 nm. This approach can generate optical nanostructures over rigid and soft substrates that are more than tens of centimetres in size, with optical performance and resolution on a par with advanced traditional lithography-based processes. To underline the potential of our approach, which reconciles high-performance optical metasurfaces and simple self-assembly fabrication approaches, we demonstrate experimentally and via numerical simulation sharp Fano resonances with a quality factor, Q, as high as ∼300 in the visible for all-dielectric nanostructures, to realize protein monolayer detection.