Thermal Drawing Process Research Articles

Laser Machined Fiber-based Microprobe: Application in Microscale Electroporation.

Microscale electroporation devices are mostly restricted to in vitro experiments (i.e., microchannel and microcapillary). Novel fiber-based microprobes can enable in vivo microscale electroporation and arbitrarily select the cell groups of interest to electroporate. We developed a flexible, fiber-based microscale electroporation device through a thermal drawing process and femtosecond laser micromachining techniques. The fiber consists of four copper electrodes (80 μm), one microfluidic channel (30 μm), and has an overall diameter of 400 μm. The dimensions of the exposed electrodes and channel were customizable through a delicate femtosecond laser setup. The feasibility of the fiber probe was validated through numerical simulations and in vitro experiments. Successful reversible and irreversible microscale electroporation was observed in a 3D collagen scaffold (seeded with U251 human glioma cells) using fluorescent staining. The ablation regions were estimated by performing the covariance error ellipse method and compared with the numerical simulations. The computational and experimental results of the working fiber-based microprobe suggest the feasibility of in vivo microscale electroporation in space-sensitive areas, such as the deep brain.

Single fibre enables acoustic fabrics via nanometre-scale vibrations.

Fabrics, by virtue of their composition and structure, have traditionally been used as acoustic absorbers1,2. Here, inspired by the auditory system3, we introduce a fabric that operates as a sensitive audible microphone while retaining the traditional qualities of fabrics, such as machine washability and draping. The fabric medium is composed of high-Young'smodulus textile yarns in the weft of a cotton warp, converting tenuous 10-7-atmosphere pressure waves at audible frequencies into lower-order mechanical vibration modes. Woven into the fabric is a thermally drawn composite piezoelectric fibre that conforms to the fabric and converts the mechanical vibrations into electrical signals. Key to the fibre sensitivity is an elastomeric cladding that concentrates the mechanical stress in a piezocomposite layerwith a high piezoelectric charge coefficient of approximately 46 picocoulombs per newton, a result of the thermal drawing process. Concurrent measurements of electric output and spatial vibration patterns in response to audible acoustic excitation reveal that fabric vibrational modes with nanometre amplitude displacement are the source of the electrical output of the fibre. With the fibre subsuming less than 0.1% of the fabric by volume, a single fibre draw enables tens of square metres of fabric microphone. Three different applications exemplify the usefulness of this study: a woven shirt with dual acoustic fibres measures the precise direction of an acoustic impulse, bidirectional communications are established between two fabrics working as sound emitters and receivers, and a shirt auscultates cardiac sound signals.

Self-Plugging Microneedle (SPM) for Intravitreal Drug Delivery.

Intravitreal injection (IVI) is a common technology which is used to treat ophthalmic diseases inside eyeballs by delivering various drugs into the vitreous cavity using hypodermic needles. However, in some cases, there are possible side effects such as ocular tissue damage due to repeated injection or eyeball infection through the hole created during the needle retraction process. The best scenario of IVI is a one-time injection of drugs without needle retraction, keeping the system of the eyeball closed. Microneedles (MNs) have been applied to ocular tissues over 10 years, and no serious side effects on ocular tissue due to MN injection have been reported. Therefore, a self-plugging MN (SPM) is developed to perform intraocular drug delivery and to seal the scleral puncture simultaneously. The SPMs are fabricated by a thermal drawing process and then coated with a polymeric carrier of drugs and a hydrogel-based scleral plugging component. Each coated functional layer is characterized and demonstrated by in vitro and ex vivo experiments. Finally, in vivo tests using a porcine model confirms prompt sealing of SPM and sustained intraocular drug delivery.

Adaptive polymer fiber neural device for drug delivery and enlarged illumination angle for neuromodulation

Objective. Optical fiber devices constitute significant tools for the modulation and interrogation of neuronal circuitry in the mid and deep brain regions. The illuminated brain area during neuromodulation has a direct impact on the spatio-temporal properties of the brain activity and depends solely on the material and geometrical characteristics of the optical fibers. In the present work, we developed two different flexible polymer optical fibers (POFs) with integrated microfluidic channels (MFCs) and an ultra-high numerical aperture (UHNA) for enlarging the illumination angle to achieve efficient neuromodulation. Approach. Three distinct thermoplastic polymers: polysulfone, polycarbonate, and fluorinated ethylene propylene were used to fabricate two step-index UHNA POF neural devices using a scalable thermal drawing process. The POFs were characterized in terms of their illumination map as well as their fluid delivery capability in phantom and adult rat brain slices. Main results. A 100-fold reduced bending stiffness of the proposed fiber devices compared to their commercially available counterparts has been found. The integrated MFCs can controllably deliver dye (trypan blue) on-demand over a wide range of injection rates spanning from 10 nl min−1 to 1000 nl min−1. Compared with commercial silica fibers, the proposed UHNA POFs exhibited an increased illumination area by 17% and 21% under 470 and 650 nm wavelength, respectively. In addition, a fluorescent light recording experiment has been conducted to demonstrate the ability of our UHNA POFs to be used as optical waveguides in fiber photometry. Significance. Our results overcome the current technological limitations of fiber implants that have limited illumination area and we suggest that soft neural fiber devices can be developed using different custom designs for illumination, collection, and photometry applications. We anticipate our work to pave the way towards the development of next-generation functional optical fibers for neuroscience.

Thermally‐Drawn Multi‐Electrode Fibers for Bipolar Electrochemistry and Magnified Electrochemical Imaging

AbstractImaging systems using closed bipolar electrode (cBPE) arrays and electrochemiluminescence (ECL) have attracted great attention in recent years as a 2D imaging platform with high spatiotemporal resolution. However, the fabrication techniques for cBPE arrays involve complicated procedures. Therefore, a new fabrication scheme enabling the mass production of cBPE arrays with high precision, reproducibility, and yield, is desired. Here, the use of a versatile and scalable thermal drawing process as a novel fabrication method for fiber‐based cBPEs with feature sizes down to micro‐/nanoscales is proposed. First, a single‐electrode fiber consisting of a carbon‐based composite as the electrode material is produced by thermal drawing. The fundamental electrical properties of the single‐electrode fiber are characterized, and its applicability to the cBPE‐ECL system is demonstrated. A multielectrode fiber is fabricated by subjecting a bundle of 104 single‐electrode fibers to thermal drawing. Its usability as a cBPE array for ECL imaging is confirmed with a functional rate of 99%. Further the multielectrode fiber, utilizing the principle of thermal drawing, for magnified electrochemical imaging is tapered. This work establishes a novel mass‐production method for cBPE arrays, as well as a proof of concept for magnified electrochemical imaging using a thermally‐drawn electrode array fiber.

Microstructured multimaterial fibers for efficient optical detection

AbstractFlexible optoelectronic fibers are recognized as one type of important building block for the system of wearable electronics and advanced functional textiles. The thermal drawing process offers promise for scalable construction of optoelectronic fibers, while they are generally characterized by the continuous cylindrical structure and poor electrical property. Here, we report the fabrication and characterization of the flexible structured multimaterial fibers thermally drawn from the combination of metal‐semiconductor‐polymer, and control of their inner structure via fluid Plateau‐Rayleigh instability. A trapezoidal electrical connection configuration with the semiconductor spheres clamped by two metal electrodes inside the fiber is successfully achieved based on this fluid instability. The obtained structured multimaterial fiber shows better photoresponse properties than that of the as drawn multimaterial fiber. The findings open new opportunity to develop fiber devices for efficient optical detection.

Computational and Histological Analyses for Investigating Mechanical Interaction of Thermally Drawn Fiber Implants with Brain Tissue.

The development of a compliant neural probe is necessary to achieve chronic implantation with minimal signal loss. Although fiber-based neural probes fabricated by the thermal drawing process have been proposed as a solution, their long-term effect on the brain has not been thoroughly investigated. Here, we examined the mechanical interaction of thermally drawn fiber implants with neural tissue through computational and histological analyses. Specifically, finite element analysis and immunohistochemistry were conducted to evaluate the biocompatibility of various fiber implants made with different base materials (steel, silica, polycarbonate, and hydrogel). Moreover, the effects of the coefficient of friction and geometric factors including aspect ratio and the shape of the cross-section on the strain were investigated with the finite element model. As a result, we observed that the fiber implants fabricated with extremely softer material such as hydrogel exhibited significantly lower strain distribution and elicited a reduced immune response. In addition, the implants with higher coefficient of friction (COF) and/or circular cross-sections showed a lower strain distribution and smaller critical volume. This work suggests the materials and design factors that need to be carefully considered to develop future fiber-based neural probes to minimize mechanical invasiveness.

Thermally Drawn Stretchable Electrical and Optical Fiber Sensors for Multimodal Extreme Deformation Sensing

AbstractHighly stretchable fiber sensors have attracted significant interest recently due to their applications in wearable electronics, human–machine interfaces, and biomedical implantable devices. Here, a scalable approach for fabricating stretchable multifunctional electrical and optical fiber sensors using a thermal drawing process is reported. The fiber sensors can sustain at least 580% strain and up to 750% strain with a helix structure. The electrical fiber sensor simultaneously exhibits ultrahigh stretchability (400%), high gauge factors (≈1960), and excellent durability during 1000 stretching and bending cycles. It is also shown that the stretchable step‐index optical fibers facilitate detection of bending and stretching deformation through changes in the light transmission. By combining both electrical and optical detection schemes, multifunctional fibers can be used for quantifying and distinguishing multimodal deformations such as bending and stretching. The fibers’ utility and functionality in sensing and control applications are demonstrated in a smart glove for controlling a virtual hand model, a wrist brace for wrist motion tracking, fiber meshes for strain mapping, and real‐time monitoring of multiaxial expansion and shrinkage of porcine bladders. These results demonstrate that the fiber sensors can be promising candidates for smart textiles, robotics, prosthetics, and biomedical implantable devices.

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.

Improved mechanical and biological properties of biodegradable thinner poly(l-lactic acid) tubes by bi-directional drawing

Fully biodegradable polymer stents still suffer from weak mechanical properties and thick stent struts, which could induce thrombosis under in vivo clinical applications. To address these problems, we fabricated a thinner poly(l-lactic acid) (PLLA) tube with improved mechanical properties through a thermal drawing process and characterized the tubes using several analytical tools. The mechanical properties of the tubes showed that the optimized conditions for the axial drawing were at 65°C (A65) and 95°C (A95), and those for the radial drawing process were also at 65°C (R65) and 95°C (R95). The bi-directional drawing process (A65/R95), performed at 65°C for axial and then at 95°C for radial drawings, demonstrated an excellent way to reduce the thickness of the tubes while reinforcing the mechanical properties. In addition, it reduced the amount of adsorbed fibrinogen and increased the albumin/fibrinogen ratio. Moreover, the platelet adhesion exhibited lower number and activity with completely round morphology. It also promoted the adhesion and proliferation of endothelial cells with stretched morphology and a significant increase of filopodial outgrowth. From these results, it can be seen that a combination of the axial and radial processes may be a promising strategy for improving the physicochemical, mechanical, and biological properties of PLLA tubes to be used for the fabrication of fully biodegradable polymeric stents.

Scalable, washable and lightweight triboelectric-energy-generating fibers by the thermal drawing process for industrial loom weaving

Abstract In the era of the internet of things (IoTs), it is desired to equip the decentralized electronics with distributed power sources. The fiber-based triboelectric nanogenerator (FTENG) provides one of the soundest solutions due to its high efficiency, easy deployment, excellent wearability, low cost, and eco-friendliness. Compared with other forms of TENGs, it can be woven into fabrics as wearable devices, offering good compactness and comfortability. However, the industrial-loom-compatible FTENGs have yet to be fabricated; the fiber diameter and length are typical challenges in the large scale weaving. In this paper, the thermal drawing process (TDP) is introduced to produce FTENGs that are compatible with industrial looms. The diameter of the polymer-cladding and metal-core fiber has been reduced to ~350 μm, and the length of a single fiber has been scaled up to sub-kilometer. Both hand-woven and loom-woven swatches are demonstrated, showing good flexibility, stretchability, power density, stability, washability, and breathability. Besides serving as power sources, such swatches have been used as self-powered sensors for body motion monitoring and communication. These applications show that the thermally drawn FTENGs can serve as powerful and reliable wearable devices in modern electronics.

Microstructured Biodegradable Fibers for Advanced Control Delivery

AbstractBiodegradable polymers are increasingly employed at the heart of therapeutic devices. Particularly in the form of thin and elongated fibers, they offer an effective strategy for controlled release in a variety of biomedical configurations such as sutures, scaffolds, wound dressings, surgical or imaging probes, and smart textiles. So far however, the fabrication of fiber‐based drug delivery systems has been unable to fulfill significant requirements of medicated fibers such as multifunctionality, adequate mechanical strength, drug loading capability, and complex release profiles of multiple substances. Here, a novel paradigm in the design and fabrication of microstructured biodegradable fibers with tailored mechanical properties and capable of predefined release patterns from multiple reservoirs is proposed. Different biodegradable polymers compatible with the scalable thermal drawing process are identified, and their release properties as thin films of various thicknesses in the fiber form are experimentally investigated and modeled. Multimaterial microstructured fibers with predictable complex release profiles of potentially different substances are then designed and fabricated. Moreover, the tunability of the mechanical properties via tailoring the drawing process parameters is demonstrated, as well as the ability to weave such fibers. This work establishes a novel platform for biodegradable microstructured fibers for applications in implants, sutures, wound dressing, or tissue scaffolds.

Tailored morphology and highly enhanced phonon transport in polymer fibers: a multiscale computational framework

Although tremendous efforts have been devoted to enhance thermal conductivity in polymer fibers, correlation between the thermal-drawing conditions and the resulting chain alignment, crystallinity, and phonon transport properties have remained obscure. Using a carefully trained coarse-grained force field, we systematically interrogate the thermal-drawing conditions of bulk polyethylene samples using large-scale molecular dynamics simulations. An optimal combination of moderate drawing temperature and strain rate is found to achieve highest degrees of chain alignment, crystallinity, and the resulting thermal conductivity. Such combination is rationalized by competing effects in viscoelastic relaxation and condensed to the Deborah number, a predictive metric for the thermal-drawing protocols, showing a delicate balance between stress localizations and chain diffusions. Upon tensile deformation, the thermal conductivity of amorphous polyethylene is enhanced to 80% of the theoretical limit, that is, its pure crystalline counterpart. An effective-medium-theory model, based on the serial-parallel heat conducting nature of semicrystalline polymers, is developed here to predict the impacts from both chain alignment and crystallinity on thermal conductivity. The enhancement in thermal conductivity is mainly attributed to the increases in the intrinsic phonon mean free path and the longitudinal group velocity. This work provides fundamental insights into the polymer thermal-drawing process and establishes a complete process–structure–property relationship for enhanced phonon transport in all-organic electronic devices and efficiency of polymeric heat dissipaters.

Efficient coupling of a quantum cascade laser to a few-mode chalcogenide fiber.

We report efficient coupling of a quantum cascade laser (QCL) into step-index chalcogenide fibers (As 2S 3). Mechanically robust and low-loss chalcogenide fibers were fabricated using a hybrid, multi-material thermal drawing process. With suitable free-space optics, more than 160 mW of optical power was coupled into the fiber with predominantly single-mode excitation. Antireflection coatings on the fiber facets enabled 88.9% transmission with strong core confinement. By accurately tailoring the core diameter and antireflection-coating thickness, these fibers offer a versatile platform for high-power and low-loss transmission across the infrared spectrum. This work introduces an attractive alternative to the use of hollow-core fibers or multimode solid-core fibers for diffraction-limited infrared beam delivery.

Ethylene polymerization to branched thermoplastic elastomers through proper activation of heterogeneous nickel (II) α-diimine complex and thermal drawing process

Ethylene polymerization with heterogeneous nickel (II) α-diimine complex, covalently attached to silica, under various conditions revealed effective control over polymer structure and activity. NMR, WAXD, thermal and mechanical characterization techniques provide the relationship between crystallinity and elastic properties and polymer microstructure. Catalytic activation with high ethylaluminium sesquichloride (EASC) amount (Al/Ni = 1500 and 2000) can improve productivity and induce long-chain branch formation. Increasing temperature, changes polyethylene behavior from properties characteristics of thermoplastics toward elastomers by only ethylene polymerization. Moreover, uniaxial stretching at melting, crystallization and onset of crystallization temperatures showed to have significant impact on crystallization behavior and mechanical properties enhancement. In particular, drawing at Tc resulted in formation of interlamellar crystallites followed by improving stress-at-break up to 200% and crystalline index to 80%.

Effects of drawing process on crimp formation-ability of side-by-side bicomponent filament yarns produced from recycled, fiber-grade and bottle-grade PET

In this study, side-by-side bicomponent filaments from recycled poly(ethylene) terephthalate (R-PET) from post-consumer bottles, fiber-grade PET (FG-PET) and bottle-grade PET (BG-PET) successfully were extruded. The bicomponent fibers in the forms of FG/R, BG/R and FG/BG were produced in a spinning machine and drawn by a thermal drawing process to improve their mechanical properties using draw ratios between ‘2.5 and 2.8’. The effects of conditions on the fiber structure, physical properties and crimp formation of resultant fibers were evaluated. The birefringence, shrinkage and mechanical properties, such as tensile strength and tensile modulus, increased and elongation at break decreased for the drawn fibers, and this was attributed to the fiber orientation. Distinct crimp formation was observed from drawn bicomponent fibers after thermal treatment. There were significant birefringence and shrinkage difference between two components in drawn bicomponent fibers caused to severe crimp formation.

Insights into the fabrication of sub-100 nm textured thermally drawn fibers

The preform-to-fiber thermal drawing process has been recently proposed for the fabrication of fibers and microchannels with submicrometer surface textures. To better control the final architecture and reach small feature size down to tens of nanometers however, a proper understanding and modeling of the fluids dynamics at play during the fabrication of the texture is needed. Here, we present an analytical model describing comprehensively the reflow of periodic polymer micropatterns of arbitrary shape in isothermal annealing as well as in a fiber drawing process. Experiments on square-grooved thermoplastic plates subjected to both treatments show excellent agreement with the calculated theoretical values. Based on this model, we could identify a strategy and the corresponding materials to fabricate sub-100 nm surface-patterned fibers. These results deepen the understanding and control of thermal-based approaches for polymer surface texturing and open novel opportunities for textured fibers and microchannels in bioengineering, microfluidics, or smart textiles.

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.

Diode fibres for fabric-based optical communications.

Semiconductor diodes are basic building blocks of modern computation, communications and sensing1. As such, incorporating them into textile-grade fibres can increase fabric capabilities and functions2, to encompass, for example, fabric-based communications or physiologicalmonitoring. However, processing challenges have so far precluded the realization of semiconducting diodes of high quality in thermally drawn fibres. Here we demonstrate a scalable thermal drawing process of electrically connected diode fibres. We begin by constructing a macroscopic preform that hosts discrete diodesinternal to the structure alongside hollow channels through which conducting copper or tungsten wires are fed. As the preform is heated and drawn into a fibre, the conducting wires approach the diodes until they make electrical contact, resulting in hundreds of diodes connected in parallel inside a single fibre. Two types of in-fibre device are realized: light-emitting and photodetecting p-i-n diodes. An inter-device spacing smaller than 20 centimetres is achieved, as well as light collimation and focusing by a lens designed in the fibre cladding. Diode fibres maintain performance throughout ten machine-wash cycles, indicating the relevance of this approach to apparel applications. To demonstrate the utility of this approach, a three-megahertz bi-directional optical communication link is established between two fabrics containing receiver-emitter fibres. Finally, heart-rate measurements with the diodes indicate their potential for implementation in all-fabric physiological-status monitoring systems. Our approach provides a path to realizing evermore sophisticated functions in fibres, presenting the prospect of a fibre 'Moore's law' analogue through the increase ofdevice density and function in thermally drawn textile-ready fibres.

Multifunctional Fibers as Tools for Neuroscience and Neuroengineering.

Multifunctional devices for modulation and probing of neuronal activity during free behavior facilitate studies of functions and pathologies of the nervous system. Probes composed of stiff materials, such as metals and semiconductors, exhibit elastic and chemical mismatch with the neural tissue, which is hypothesized to contribute to sustained tissue damage and gliosis. Dense glial scars have been found to encapsulate implanted devices, corrode their surfaces, and often yield poor recording quality in long-term experiments. Motivated by the hypothesis that reducing the mechanical stiffness of implanted probes may improve their long-term reliability, a variety of probes based on soft materials have been developed. In addition to enabling electrical neural recording, these probes have been engineered to take advantage of genetic tools for optical neuromodulation. With the emergence of optogenetics, it became possible to optically excite or inhibit genetically identifiable cell types via expression of light-sensitive opsins. Optogenetics experiments often demand implantable multifunctional devices to optically stimulate, deliver viral vectors and drugs, and simultaneously record electrophysiological signals from the specified cells within the nervous system. Recent advances in microcontact printing and microfabrication techniques have equipped flexible probes with microscale light-emitting diodes (μLEDs), waveguides, and microfluidic channels. Complementary to these approaches, fiber drawing has emerged as a scalable route to integration of multiple functional features within miniature and flexible neural probes. The thermal drawing process relies on the fabrication of macroscale models containing the materials of interest, which are then drawn into microstructured fibers with predefined cross-sectional geometries. We have recently applied this approach to produce fibers integrating conductive electrodes for extracellular recording of single- and multineuron potentials, low-loss optical waveguides for optogenetic neuromodulation, and microfluidic channels for drug and viral vector delivery. These devices allowed dynamic investigation of the time course of opsin expression across multiple brain regions and enabled pairing of optical stimulation with local pharmacological intervention in behaving animals. Neural probes designed to interface with the spinal cord, a viscoelastic tissue undergoing repeated strain during normal movement, rely on the integration of soft and flexible materials to avoid injury and device failure. Employing soft substrates, such as parylene C and poly-(dimethylsiloxane), for electrode and μLED arrays permitted stimulation and recording of neural activity on the surface of the spinal cord. Similarly, thermally drawn flexible and stretchable optoelectronic fibers that resemble the fibrous structure of the spinal cord were implanted without any significant inflammatory reaction in the vicinity of the probes. These fibers enabled simultaneous recording and optogenetic stimulation of neural activity in the spinal cord. In this Account, we review the applications of multifunctional fibers and other integrated devices for optoelectronic probing of neural circuits and discuss engineering directions that may facilitate future studies of nerve repair and accelerate the development of bioelectronic medical devices.