Flexible Filaments Research Articles

Experimental investigation on the role of turbulent buffeting on the dynamics of a flexible filament in airflow

This paper documents the results of an experiment conceived to explore and quantitatively assess the role of turbulent buffeting on the dynamics of a flexible filament exposed to airflow. In the experiment, a circular cross-section flexible filament was tested in a wind tunnel where the turbulence level was modified with a square-mesh grid. Measurements were carried out with and without the grid to assess the role of turbulent buffeting on the dynamics of the filament. A hot wire anemometer was used to measure the turbulent airflow, whilst fast video imaging was employed to resolve the filament motion in 3D. The inclusion of the grid and subsequent increase in turbulence level yielded a higher amplitude of motion during the post-flutter regime, thus providing evidence of the role of turbulent buffeting on the flapping dynamics of the filament, hence confirming a conjecture advanced in previous research but not proved yet. Interestingly, the higher amplitude of motion due to turbulent fluctuation was confined only to the vertical plane, suggesting a role of the filament attachment angle in the propagation of disturbances from turbulent fluctuations. No detectable role of turbulent buffeting was observed on the onset of flapping which, based on a comparison with literature data, has been classified as a fluid-elastic instability. Finally, no detectable role of turbulent buffeting was observed in the qualitative dynamics of the filament during flutter and post-flutter.

Additive manufacturing of zirconia ceramic by fused filament fabrication

Fused filament fabrication (FFF) technology will facilitate the standardization of consumables and printing equipment for the additive manufacturing of engineered ceramics. In this study, a thermoplastic elastic binder based on styrene ethylene butylene styrene (SEBS) was optimized to realize the preparation of flexible filaments with solid loading of 43 vol%. The rheology, stress-strain behavior, and printing performance of the filament were systematically evaluated, and the feasibility of the fabrication of complex-shaped parts was verified. A microstructure model of the filament was innovatively established. The printed parts are suitable for solvent debinding at 40 °C, followed by thermal debinding and sintering to obtain dense zirconia ceramic materials. Microstructural analysis revealed two types of typical defects, interlayer bonding defects with a scale of about 1 μm and triangular voids at path intersections with a scale of about 10 μm. Zirconia ceramics with a relative density of 99.1% and a flexural strength of 492.8 ± 40 MPa was obtained by the FFF method.

Investigation of coupling loss caused by misalignment in optical fiber

In a fiber optic communication system, optical fiber is used as a transmission medium consisting of a flexible filament that guides the optical signal to be transmitted from the transmitter to the receiver or vice versa. Like any other communication medium, the optical fiber cable faces some losses that can be caused by the material and length of the fiber. One of the main reasons for losses in optical communication systems is misalignment during the fiber to fiber joining process. This type of loss is also known as coupling loss, which is caused by an imperfect physical connection between two fibers. The coupling losses are most often caused by three misalignment issues: end gap displacement, lateral displacement, and angular displacement. The main goal of this article is to investigate coupling loss caused by misalignment in optical fiber using the Modicom 6 module. Before we can find a way to reduce the coupling losses in the fiber optic system, we need to have a concrete idea about the nature of coupling losses due to misalignment. An ideal fiber coupler should not lose light and should be insensitive to light dispersion.

Magnetically activated 3D printable polylactic acid/polycaprolactone/magnetite composites for magnetic induction heating generation

Additive manufacturing technology has attracted the attention of industrial and technological sectors due to the versatility of the design and the easy manufacture of structural and functional elements based on composite materials. The embedding of magnetic nanoparticles in the polymeric matrix enables the development of an easy manufacturing process of low-cost magnetically active novel polymeric composites. In this work, we report a series of magnetic composites prepared by solution casting method combining 5 to 60 wt.% of 140 pm 50 nm commercial Fe3O4 nanoparticles, with a semi-crystalline, biocompatible, and biodegradable polymeric blend made of polylactic acid (PLA) and polycaprolactone (PCL). The composites were extruded, obtaining 1.5 pm 0.2 mm diameter continuous and flexible filaments for fused deposition modelling 3D printing. The chemical, magnetic, and calorimetric properties of the obtained filaments were investigated by differential scanning calorimetry, thermogravimetric analysis, magnetometry, and scanning electron microscopy. Furthermore, taking advantage of the magnetic character of the filaments, their capability to generate heat under the application of low-frequency alternating magnetic fields (magnetic induction heating) was analyzed. The obtained results expose the versatility of these easy manufacturing and low-cost filaments, where selecting a desired composition, the heating capacity can be properly adjusted for those applications where magnetic induction plays a key role (i.e., magnetic hyperthermia, drug release, heterogeneous catalysis, water electrolysis, gas capture, or materials synthesis).Graphical This paper presents the manufacture of novel magnetically activated 3D printable filaments, low cost and easy to manufacture, whereby selecting the desired composition, the heating capacity (ρ) generated under the application of an alternating magnetic field (Happ) can be adjusted to the needs of the user.

3D printing of high solid loading zirconia feedstock via screw-based material extrusion

Zirconia ceramic (3Y-TZP) feedstocks with solid loadings from 50 vol% to 68 vol%, in a 60:40 paraffin wax to LDPE ratio binder system, were prepared and printed using a screw-based material extrusion printer. A two-step debinding process involving solvent debinding (cyclohexane + ethanol) and thermal debinding (140 °C–600 °C at 0.2 °C/min) followed by sintering at 1500 °C for 2 h was employed. Tests performed include TGA, density test, Vickers hardness and fracture toughness, XRD, and SEM. The TGA result showed two significant drops in weight starting at 180 °C and 380 °C, which corresponds to the decomposition of paraffin wax and LDPE, respectively. A minimum of 40 wt% of soluble binder was removed from the green sample after solvent immersion for 3 h at 40 °C for solid loadings ≥55 vol%. High solid loading feedstocks produced samples with comparable density, Vickers hardness and fracture toughness, which are 97.5%, ∼12.3 GPa, and ∼5.5 MPa m1/2, respectively; while XRD and SEM shows no adverse tetragonal to monoclinic phase transformation and grain growth, respectively. This study demonstrates that 3D printing of granular 3Y-TZP ceramic feedstock via screw-based material extrusion technique is feasible even with high solid loadings, which is usually difficult to fabricate into flexible filaments and print due to high viscosity.

Vacuum Thermoforming for Packaging Flexible Electronics and Sensors in E-Textiles

Packaging of flexible electronics is essential for e-textile applications to reduce degradation of the performance caused by mechanical stress, environmental effects and to have increased durability. Conformal coatings for packaging have the advantage of reducing rigidity and can be seamlessly integrated into fabrics. Vacuum forming is a technique for packaging electronic devices with thermoplastic films of various thicknesses providing uniform coating. Polyurethane is a widely used thermoplastic material in e-textile and can be easily processed by vacuum forming for packaging. In this paper, a detailed explanation of the working of Formech 450DT vacuum former is discussed for packaging small electronic chip for e-textile application with thermoplastic polyurethane (TPU). Two types of flexible circuits were packaged; a Carbon monoxide gas sensor and a series of resistors on flexible PCB. The packaged CO flexible sensor and series resistors endured 5.3 times and 1.7 times respectively, more bending cycles than unpackaged flexible electronic filament samples. For the washing cycles, the packaged flexible strips with CO sensor and series resistors endured 1.5 times.

Morphological transformations of vesicles with confined flexible filaments

A fundamental understanding of cell shaping with confined flexible filaments, including microtubules, actin filaments, and engineered nanotubes, has been limited by the complex interplay between the cell membrane and encapsulated filaments. Here, combining theoretical modeling and molecular dynamics simulations, we investigate the packing of an open or closed filament inside a vesicle. Depending on the relative stiffness and size of the filament to the vesicle as well as the osmotic pressure, the vesicle could evolve from an axisymmetric configuration to a general configuration with a maximum of three reflection planes, and the filament could bend in or out of plane or even coil up. A plethora of system morphologies are determined. Morphological phase diagrams predicting conditions of shape and symmetry transitions are established. Organization of actin filaments or bundles, microtubules, and nanotube rings inside vesicles, liposomes, or cells are discussed. Our results provide a theoretical basis to understand cell shaping and cellular stability and to help guide the development and design of artificial cells and biohybrid microrobots.

Scaling behavior for the detachment of a self-propelling filament from an attractive surface.

Desorption of a self-propelling filament from an attractive surface is studied by computer simulations and the influence of activity, chain length, and chain rigidity is explored. For the flexible filament, we find three scaling regimes of desorption time vs activity with various scaling exponents. At low activity, the scaling law results from the spiral-like detachment kinetics. And at high activity, by theoretical analysis, the desorption is reminiscent of the escaping mechanism of a super-diffusive blob from a potential well at a short time scale. Additionally, the desorption time decreases first and then increases with chain length at low activity, since it is hard to form a spiral for short filaments due to the limited volume repulsion. For high activities, the desorption time approximately scales with chain length, with a scaling exponent ∼0.5, which can be explained by the theory and numerically fitting scaling law between the end-to-end distance of the "globule-like" filament and chain length. Furthermore, a non-monotonic behavior is observed between the desorption time and the chain stiffness. Desorption time slightly decreases first and then rapidly increases with stiffness due to the opposed effects of increasing rigidity on headiing-up time and leaving-away time. In contrast to traditional polymers, the scaling behavior suggests unique desorption characteristics of active polymers.

A Light Scattering Investigation of Enzymatic Gelation in Self-Assembling Peptides.

Self-assembling peptides (SAPs) have been increasingly studied as hydrogel-former gelators because they can create biocompatible environments. A common strategy to trigger gelation, is to use a pH variation, but most methods result in a change in pH that is too rapid, leading to gels with hardly reproducible properties. Here, we use the urea-urease reaction to tune gel properties, by a slow and uniform pH increase. We were able to produce very homogeneous and transparent gels at several SAP concentrations, ranging from c=1g/L to c=10g/L. In addition, by exploiting such a pH control strategy, and combining photon correlation imaging with dynamic light scattering measurements, we managed to unravel the mechanism by which gelation occurs in solutions of (LDLK)3-based SAPs. We found that, in diluted and concentrated solutions, gelation follows different pathways. This leads to gels with different microscopic dynamics and capability of trapping nanoparticles. At high concentrations, a strong gel is formed, made of relatively thick and rigid branches that firmly entrap nanoparticles. By contrast, the gel formed in dilute conditions is weaker, characterized by entanglements and crosslinks of very thin and flexible filaments. The gel is still able to entrap nanoparticles, but their motion is not completely arrested. These different gel morphologies can potentially be exploited for controlled multiple drug release.

Carbonic Anhydrase Enhanced UV-Crosslinked PEG-DA/PEO Extruded Hydrogel Flexible Filaments and Durable Grids for CO2 Capture.

In this study, poly (ethylene glycol) diacrylate/poly (ethylene oxide) (PEG-DA/PEO) interpenetrating polymer network hydrogels (IPNH) were extruded into 1D filaments and 2D grids. The suitability of this system for enzyme immobilization and CO2 capture application was validated. IPNH chemical composition was verified spectroscopically using FTIR. The extruded filament had an average tensile strength of 6.5 MPa and elongation at break of 80%. IPNH filament can be twisted and bent and therefore is suitable for further processing using conventional textile fabrication methods. Initial activity recovery of the entrapped carbonic anhydrase (CA) calculated from esterase activity, showed a decrease with an increase in enzyme dose, while activity retention of high enzyme dose samples was over 87% after 150 days of repeated washing and testing. IPNH 2D grids that were assembled into spiral roll structured packings exhibited increased CO2 capture efficiency with increasing enzyme dose. Long-term CO2 capture performance of the CA immobilized IPNH structured packing was tested in a continuous solvent recirculation experiment for 1032 h, where 52% of the initial CO2 capture performance and 34% of the enzyme contribution were retained. These results demonstrate the feasibility of using rapid UV-crosslinking to form enzyme-immobilized hydrogels by a geometrically-controllable extrusion process that uses analogous linear polymers for both viscosity enhancement and chain entanglement purposes, and achieves high activity retention and performance stability of the immobilized CA. Potential uses for this system extend to 3D printing inks and enzyme immobilization matrices for such diverse applications as biocatalytic reactors and biosensor fabrication.

An efficient large-deformation fluid-structure interaction model for flow induced oscillation of an elastic thin structure

An efficient large-deformation fluid-structure interaction (FSI) model with GPU parallel framework is presented to simulate flow induced oscillation of an elastic slender structure, even light-weight and high-rigidity structures. A grid refinement and asynchronous advancement strategy is developed to ensure the matching of the different time-steps and grid sizes by flexibly coupling the fluid solver of a multi-direct forcing immersed boundary method (IBM) and the structure solver of a geometrically accurate Euler-Bernoulli beam model. This strategy can achieve good numerical stability and improve the computational performance of the present model. Free falling of a flexible pendulum, uniform flows around a stationary cylinder, and the flow induced oscillation of a flexible filament are simulated to validate the accuracy and capability of the structure solver, the fluid solver, and the coupled model, respectively. The results show that the present model can predict the large-displacement and large-deformation coupled responses of the elastic boundary. Also, the present model can obtain near 100 of acceleration ratio compared with the corresponding CPU version. Further, the effects of the density ratio and the bending coefficient on the flapping mode, the motion trajectory, and the fluid field are examined.

A Typical Workflow to Simulate Cytoskeletal Systems.

Many cytoskeletal systems are now sufficiently well known to permit their precise quantitative modeling. Microtubule and actin filaments are well characterized, and the associated proteins are often known, as well as their abundance and the interactions between these elements. Thus, computer simulations can be used to investigate the collective behavior of the system precisely, in a way that is complementary to experiments. Cytosim is an Open Source cytoskeleton simulation suite designed to handle large systems of flexible filaments with associated proteins such as molecular motors. It also offers the possibility to simulate passive crosslinkers, diffusible crosslinkers, nucleators, cutters, and discrete versions of the motors that only step on unoccupied lattice sites on a filament. Other objects complement the filaments by offering spherical or more complicated geometry that can be used to represent chromosomes, the nucleus, or vesicles in the cell. Cytosim offers simple command-line tools for running a simulation and displaying its results, which are versatile and do not require programming skills. In this workflow, step-by-step instructions are given to i) install the necessary environment on a new computer, ii) configure Cytosim to simulate the contraction of a 2D actomyosin network, and iii) produce a visual representation of the system. Next, the system is probed by systematically varying a key parameter: the number of crosslinkers. Finally, the visual representation of the system is complemented by the numerical quantification of contractility to view, in a graph, how contractility depends on the composition of the system. Overall, these different steps constitute a typical workflow that can be applied with few modifications to tackle many other problems in the cytoskeletal field.

Mode transition of a coupled rigid–flexible system in a uniform flow

The interaction between a rigid–flexible system and ambient fluid was simulated numerically at Re = 300 by the immersed boundary method. The rigid–flexible system consists of a stationary rigid plate upstream and a closed flexible filament downstream. For different filament lengths, four typical regimes for the motions of the flexible filament were observed. As the length increases, the flexible filament successively experiences the plate-like (P) mode, the cylinder-like (C) mode, the slender-shape (S) mode and finally enters the wriggling (W) mode. It was demonstrated by the frequency spectra that when the filament length increases up to a critical value, the second harmonic becomes dominant, corresponding to the transition from the S mode to the W mode, and at the transition point, the drag exerted on the rigid–flexible system becomes minimum. The occurrence of the S–W mode transition was found to be caused by the increased inertia of the filament.

Configurational dynamics of flexible filaments in bacterial active baths

Biopolymers with microscale length and nanoscale cross-sections subjected to active forces is a common non-equilibrium phenomenon in living creatures. It is therefore crucial to intuitively present and investigate the detailed dynamics of such flexible filaments in an active bath full of living matter. Hence, by introducing fluorescent actin filament into an active suspension of motile bacteria at different number densities in a quasi-two-dimensional chamber, we directly visualize the detailed interaction processes and find that bacteria deform a fluctuating filament by relative motion perpendicular to its principal axis of the filament and straighten a filament by parallel motions. We analyzed the evolution of bending energy in dilute and dense bacterial baths with gradual compact or coiled shapes. We successfully introduce a dimensionless number , named as active elasto-viscous number, which governs the generic deformation of filaments in the bacterial baths by comparing the viscous force generated in the bacterial active baths to the elastic restoring force of filaments. The persistence length measuring the tangential correlation of the flexible filament is found to be proportional to . Finally, an effective temperature of the bacterial bath is given through the relation between constant stiffness and loading forces instead of the popularly used Einstein relation. Our findings provide detailed information and specific scaling of flexible filaments interplay with active forces and in response to living and crowded environments.

Low-cost and open-source three-dimensional (3D) printing in neurosurgery: A pilot experiment using direct drive modification to produce multi-material neuroanatomical models

Background3-dimensional (3D) printing carries a genuine potential for pre-operative planning in neurosurgery. Entry-level 3D printers offer practicality in low resource settings, but are often limited by the range of filament materials as well as the capability of open-source segmentation software. ObjectiveWe intended to demonstrate that 3D printing of neuroanatomical structures is possible using an entry-level 3D printer equipped with the direct drive (DD) modification, which supported flexible filaments, with the models segmented using an open-source software. MethodsA DD system was installed onto the Ender 3 Pro printer. An attempt to print neurosurgical models using a low-cost 3D printer was conducted, where four patient-based neuroanatomical models were printed: skull base-vasculature, skull base-tumour, cervical spine, and ventricular system. The results were discussed and compared to similar endeavours in past literature. ResultsAlthough DD installation was challenging and led to vibration and longer print time, which ultimately warranted an inferior printing speed, DD system enabled the printing with thermoplastic polyurethane (TPU), a versatile elastomer; in addition to producing equal amount of detail to those printed with high-end printers and advanced image segmentation software. Fitting the frame well, changing infill type, and avoiding warping and stringing will improve print quality with the DD system. Conclusion3D printing with entry-level 3D printers equipped with DD system has been proven to be a reliable way of accurately reproducing patient-specific neuroanatomical constructs. Follow-up studies are necessary to implement 3D printing for neurosurgical planning in low-resource settings.

A new era: 3D printing as an aesthetic language and creative tool in fashion and textile design

Purpose This study aims to produce textile-like surfaces using fused deposition modelling (FDM) 3D printers and create a garment collection. Design/methodology/approach Experiments were conducted using different types of materials in FDM 3D printers until the sufficient flexibility was achieved to create textile-like structures. During the research, properties of polylactic acid (PLA), acrylonitrile butadiene styrene (ABS) and thermoplastic polyurethane (TPU) were observed. Geometrical patterns were printed and each of them gave a different result depending on the pattern. Based on the information obtained from the experiments, a garment collection with four total looks was designed inspired by Vivaldi’s “Four Seasons”. Findings Among the materials used, TPU, a flexible filament, yielded the best results. Because of the rigid properties of PLA and ABS, chain-like structures were printed to create relatively flexible surfaces, but the results were still not successful enough to create a clothing material. Therefore, TPU was preferred for the garment material selection. Originality/value In this study, combinations of 3D printed flexible structures and different types of fabrics were used to create a garment collection. It was concluded that, with the right material selection, 3D printing can be used as an alternative method to create a new aesthetic language in fashion design.

Drag reduction by flapping a pair of flexible filaments behind a cylinder

The hydrodynamic mechanism of drag reduction by flapping a pair of flexible filaments behind a cylinder was explored using the penalty immersed boundary method. The effects of the phase difference between two filaments, the attachment height, and the flapping amplitude on drag reduction were examined. The flapping filaments weaken the vortex shedding via the destructive interaction between the vortices with the opposite signal. The clapping (out-of-phase) flexible filaments experience a lower friction drag and reduce a form drag of the cylinder, showing a better drag reduction than the snaking (in-phase) flexible filaments and the clapping rigid filaments. A minimum drag is obtained at an appropriate attachment height and flapping amplitude that avoid collision of the filaments and weaken the shear-layer–filaments interaction. The effectiveness ratio of the clapping filaments is higher than that of the snaking filaments. Energy saving can be achieved by avoiding the shear layer–filament interaction at a low flapping amplitude, whereas the filaments can further reduce the drag with greater energy consumption at an appropriate flapping amplitude. In addition, the total drag decreases with increasing Reynolds number, accompanied by a transition of the wake pattern from the 2S mode to the P + S mode.

3D Printing in LMICs: Functional Design for Upper Limb Prosthetics in Uganda

Meeting the needs of persons with upper limb loss in Uganda requires an understanding of the needs and desires of the local population. The limitations of resources and accessibility for the individual gave rise to a focused design methodology for delivering a culturally acceptable solution using 3D Printing technology. A series of co-design activities were held in Uganda and provided direct feedback to drive the design of two prototypes based on acceptable aesthetics and priority Activities of Daily Living. Two terminal device prototypes were 3D printed in the UK. These can be directly attached to a standard proximal socket thread. The passive hand was printed in a flexible filament and the prehensor was printed in a durable impact resistant material. Local researchers in Uganda have similar 3D printers, filaments, and assembly hardware, which allowed for concurrent development and refinement of the prototypes. Local participation provides a rich user feedback environment to understand which elements of prosthetic device design are integral to delivering acceptable prosthetics solutions for fabrication in Uganda. 3D printing can provide a viable route to addressing the needs of the user. The proposed terminal devices are now in the process of being printed locally for field testing.

Symmetry breaking of a closed flexible filament behind a rigid plate at low Reynolds numbers

In this paper, the motion modes transition and dynamic performance of the flow past a rigid–flexible coupling system were investigated at low Reynolds numbers. The coupling system consisted of a rigid plate and a trailing closed flexible filament and was simulated numerically using the immersed boundary method. According to whether the filament moves and the symmetry of its movement, six motion modes have been identified for different filament lengths and Reynolds numbers (Re), i.e., the symmetric and stationary mode, the asymmetric and stationary (AS) mode, the regular and unilateral flap (RUF) mode, the transition motion (TM) mode, the symmetric and bilateral flap mode, and the asymmetric and bilateral flap (ABF) mode. Moreover, symmetry breaking occurred in the AS mode, RUF mode, and ABF mode. Drag reduction was found at Re≥40, which was mainly influenced by the pressure behind the filament. However, drag reduction was weakened for the filament with Lr≥2.57 because of the large width suffered to the flow, where Lr is the ratio of the length of the filament to the width of the plate. The time-averaged lift was also found to be directly dependent on the symmetry of the filament. In addition, the motion modes were significantly affected by the bending coefficient of the filament. Symmetry breaking was prevented by the reduction of the bending coefficient before vortex shedding. Moreover, if the filament was symmetric before vortex shedding, the RUF mode and the TM mode did not appear with the increase in Re.

3D-Printed Polycaprolactone Implants Modified with Bioglass and Zn-Doped Bioglass.

In this work, composite filaments in the form of sticks and 3D-printed scaffolds were investigated as a future component of an osteochondral implant. The first part of the work focused on the development of a filament modified with bioglass (BG) and Zn-doped BG obtained by injection molding. The main outcome was the manufacture of bioactive, strong, and flexible filament sticks of the required length, diameter, and properties. Then, sticks were used for scaffold production. We investigated the effect of bioglass addition on the samples mechanical and biological properties. The samples were analyzed by scanning electron microscopy, optical microscopy, infrared spectroscopy, and microtomography. The effect of bioglass addition on changes in the SBF mineralization process and cell morphology was evaluated. The presence of a spatial microstructure within the scaffolds affects their mechanical properties by reducing them. The tensile strength of the scaffolds compared to filaments was lower by 58-61%. In vitro mineralization experiments showed that apatite formed on scaffolds modified with BG after 7 days of immersion in SBF. Scaffold with Zn-doped BG showed a retarded apatite formation. Innovative 3D-printing filaments containing bioglasses have been successfully applied to print bioactive scaffolds with the surface suitable for cell attachment and proliferation.