Polymerization Of Filaments Research Articles

Fabrication of Architectured Biomaterials by Multilayer Co‐Extrusion and Additive Manufacturing

AbstractTissue engineering benefits from advances in 3D printing and multi‐material assembly to attain certain functional benefits over existing man‐made materials. Multilayered tissue engineering constructs might unlock a unique combination of properties, but their fabrication remains challenging. Herein, a facile process is reported to manufacture biomaterials with an engineered multilayer architecture, via a combination of co‐extrusion and 3D printing. Polymer filaments containing 5, 17, or 129 alternating layers of poly(lactic acid)/thermoplastic polyurethane (PLA/TPU) are produced, and explored for their use in fused deposition modeling (FDM) to fabricate scaffolds for cardiomyocyte culture. The co‐extruded filaments exhibit a layered architecture in their cross‐section with a continuous interface, and the integrity and alignment of the layers are preserved after 3D printing. The 17 alternating layers PLA/TPU composites exhibit excellent mechanical properties. It is envisaged that the multilayered architecture of the fabricated scaffolds can be beneficial for aligning cardiomyocytes in culture. It is found that the 17 alternating layers PLA/TPU significantly improve cardiomyocyte morphology and functionality compared to single phase materials. It is believed that this biomaterials fabrication scheme, combining a top‐down and bottom‐up approach, offers tremendous flexibility in producing a broad class of novel‐architectured materials with tunable structural design for tissue engineering applications and beyond.

A Tale of 12 Tails: Katanin Severing Activity Affected by Carboxy-Terminal Tail Sequences.

In cells, microtubule location, length, and dynamics are regulated by a host of microtubule-associated proteins and enzymes that read where to bind and act based on the microtubule "tubulin code," which is predominantly encoded in the tubulin carboxy-terminal tail (CTT). Katanin is a highly conserved AAA ATPase enzyme that binds to the tubulin CTTs to remove dimers and sever microtubules. We have previously demonstrated that short CTT peptides are able to inhibit katanin severing. Here, we examine the effects of CTT sequences on this inhibition activity. Specifically, we examine CTT sequences found in nature, alpha1A (TUBA1A), detyrosinated alpha1A, Δ2 alpha1A, beta5 (TUBB/TUBB5), beta2a (TUBB2A), beta3 (TUBB3), and beta4b (TUBB4b). We find that these natural CTTs have distinct abilities to inhibit, most noticeably beta3 CTT cannot inhibit katanin. Two non-native CTT tail constructs are also unable to inhibit, despite having 94% sequence identity with alpha1 or beta5 sequences. Surprisingly, we demonstrate that poly-E and poly-D peptides are capable of inhibiting katanin significantly. An analysis of the hydrophobicity of the CTT constructs indicates that more hydrophobic polypeptides are less inhibitory than more polar polypeptides. These experiments not only demonstrate inhibition, but also likely interaction and targeting of katanin to these various CTTs when they are part of a polymerized microtubule filament.

Additive manufacturing of customized automotive components using novel cellulose fiber reinforced abs polymer filament

Additive manufacturing of customized automotive components using novel cellulose fiber reinforced abs polymer filament

Modification of 3D Printable Polymer Filaments for Radiation Shielding Applications

There is a growing need to develop lead-free shielding materials that are safe, low weight, durable, environmentally friendly, chemically and mechanically stable and customizable for specific applications. Fused deposition modeling (FDM), an additive manufacturing technique based on the extrusion of a thermoplastic filament into a 3D printed object one layer at a time, could be employed well in applications involving ionizing radiation due to its relatively low cost, design flexibility and high manufacturing precision. This study aimed at developing 3D printing composites that contain Titanium dioxide as a filler agent for shielding in a medical radiation environment. First, the effect of low-dose ionizing radiation (up to 15 Gy) on the mechanical properties of common 3D printing polymers, ABS, ULTRAT, PLA, NYLON, ASA and PETG, was investigated. Since ABS experienced the lowest variation in its ultimate tensile strength (±5%) and Young's modulus (-5%/+11%), it was chosen as a matrix for a new extruded 3D filament containing TiO2 at 1 wt.%, 3 wt.%, and 5 wt.%. With the incorporation of TiO2 at different filler contents, the UTS of the ABS composites varied between 24.1 MPa and 28.4 MPa, with the highest value recorded for 3 wt.% TiO2. Young's modulus values were dependent on both the TiO2 concentration and on the irradiation dose. In addition, the ABS/TiO2 composites with a higher filler content (3 wt.% and 5 wt.%) maintained their attenuation ability even after exposure to a radiation dose of 100 Gy as opposed to pure ABS, which exhibited a ~2.5% reduction in its mass attenuation coefficient after exposure to the same dose of radiation. The pilot investigation performed demonstrated that the newly developed ABS/TiO2 composite containing 5 wt.% of filler can be successfully employed to shield electronic devices operating in a radiotherapy room.

Development of crab shell particle reinforced polylactic acid filaments for 3D printing application

In the polymeric 3D printing process, composite material development is based on preparing feedstock material such as polymeric filaments. The present work focuses on recycling crab shell particles as bio fillers for developing Polylactic Acid feedstock material. The extruded filament's intrinsic properties, such as tensile strength, diameter deviation, and surface roughness, were measured to its crab shell composition of 0, 2, 4, 6, 8, and 10 wt%. The results depict that the maximum tensile strength of 61.3 MPa was achieved on the 8% crab shell -reinforced PLA polymeric filaments. A minimum diameter deviation of 0.001 was observed on the 2% crab shell-reinforced PLA filaments. The surface morphology of the extruded PLA/crab shell filaments of 8% possesses uniform distribution of added particles in the polymeric matrix. From the overall results, the PLA/crab shell filament of 8% composition is an optimal composition feedstock material for the 3D printing application to develop biomaterials like bio-scaffolds.

Experimental-theoretical comparative analysis of PLA-based 3D lattice

Lattice materials are one of the most desirable and widely used materials due to the characteristics derived from their geometrical formation as opposed to their chemical composition. In this article, a lattice material has been designed and printed using polymer filament wire made of polylactic acid (PLA) and fused deposition modelling (FDM), followed by mechanical testing. In addition, tensile testing of the PLA printed samples has also been carried out to ascertain the tensile properties of the material in use, and the material has shown 38–40 MPa tensile strength with a Young’s modulus value of 1538 ± 120 MPa. The lattice was designed using 3D CAD software, and numerical results were obtained using the Autodesk Inventor simulation module. In addition to the experimental test, theoretical tests were also conducted, and the results were compared to the experimental results. With this methodology, the lattice material failure process can be comprehended. Along with the lattices, the PLA tensile test samples were also prepared and tested to check the feasibility of the PLA being used and ascertain the properties. In addition, it has been observed that after a specific load and deformation, the material’s resistance increases due to its increased density and repeated cell interference. The major purpose of the study is to explore the aspects and feasibility of the PLA printed lattice material with complex shapes and explore the application potential of such shapes.

Actin based motility unveiled: How chemical energy is converted into motion

Actin-based motility is a complex process in which the actin-polymerization is the primary force-generating motor machinery. It can produce protrusive forces through actin filaments polymerization and cross-link during lamellipodia protrusion in migrating cells and it is responsible for the intracellular motion of certain pathogens in infected host cells. We propose a multi-physics model for actin-based motility, stemming from continuity equations that account for the actin chemical kinetics. Thermodynamic restrictions are identified, moving from the multiplicative decomposition of the deformation gradient into chemical and elastic parts. Constitutive theory and chemical kinetics are prescribed to finally write governing equations for the multi-physics problem. The field equations are solved numerically with the finite element method. As a proof of concept, a one-dimensional model for actin-based motility of bacteria pathogens is studied.

Millimeter-Wave Near-Field Evaluations of Polylactic Acid (PLA) Filament Used in Polymer-Based Additive Manufacturing (AM)

ABSTRACT Additive manufacturing (AM) remains to be a rapidly growing industry with applications that are extended beyond metals and to other materials, such as polymers, ceramics, and concrete, to name a few. However, advancement in the development of inspection techniques, particularly in-line nondestructive testing (NDT) methods, lags significantly. Most of the research in developing such methods has focused on metal-based AM. This paper investigates the efficacy of three high-resolution near-field millimeter-wave probes for detecting small voids in the feedstock polymeric filaments used for AM. The electromagnetic (EM) design and optimization of these probes are discussed in this paper. The design of the probes is based on concentrating the interrogating electric field of an open-ended waveguide in a small region corresponding to the area of a thin dielectric slab insert. This results in achieving a higher spatial resolution than when using only the open-ended waveguide. Extending the dielectric slab to an optimum value out of the waveguide makes the electric field more concentrated and potentially further improves the spatial resolution. These modifications also reduce the detection sensitivity as a function of increasing standoff distance. However, the spatial resolution of these probes varies more rapidly as the standoff distance increases. Subsequently, the efficacy of these three probes was studied and compared using a comprehensive set of numerical EM simulations at V-band (50–75 GHz). Afterward, three such probes were fabricated, at V-band (50–75 GHz), and were used to measure the reflection responses of the stock Polylactic Acid (PLA) filaments with a very small hemispherical surface void. Root-Mean-Squared-Error (RMSE), between reference and defective filaments and over the simulated and measured frequency range, was calculated as a criterion to compare the detection capability of the three probes in the entire frequency band. The results showed that at V-band (50–75 GHz) the spatial resolution of the standard open-ended rectangular waveguide is deemed sufficient detecting small surface voids of the stock PLA filaments.

Workplace Exposure Measurements of Emission from Industrial 3D Printing.

Particle and gaseous contaminants from industrial scale additive manufacturing (AM) machines were studied in three different work environments. Workplaces utilized powder bed fusion, material extrusion, and binder jetting techniques with metal and polymer powders, polymer filaments, and gypsum powder, respectively. The AM processes were studied from operator's point of view to identify exposure events and possible safety risks. Total number of particle concentrations were measured in the range of 10 nm to 300 nm from operator's breathing zone using portable devices and in the range of 2.5 nm to 10 µm from close vicinity of the AM machines using stationary measurement devices. Gas-phase compounds were measured with photoionization, electrochemical sensors, and an active air sampling method which were eventually followed by laboratory analyses. The duration of the measurements varied from 3 to 5 days during which the manufacturing processes were practically continuous. We identified several work phases in which an operator can potentially be exposed by inhalation (pulmonary exposure) to airborne emissions. A skin exposure was also identified as a potential risk factor based on the observations made on work tasks related to the AM process. The results confirmed that nanosized particles were present in the breathing air of the workspace when the ventilation of the AM machine was inadequate. Metal powders were not measured from the workstation air thanks to the closed system and suitable risk control procedures. Still, handling of metal powders and AM materials that can act as skin irritants such as epoxy resins were found to pose a potential risk for workers. This emphasizes the importance of appropriate control measures for ventilation and material handling that should be addressed in AM operations and environment.

Experimental and numerical analysis of additively manufactured foamed sandwich beams

This work examines the feasibility of using foamable polymer filaments to create lightweight composite beams using additive manufacturing. To accomplish this, monolithic and sandwich beams, with non-foamed face sheets and a foam core were fabricated using MEX 3D printers. The non-foamed and foamed PLA components were created by extruding foamable PLA with nozzle temperatures of 200 °C and 220 °C, respectively. Tensile testing samples were printed and tested and used to provide data for numerical models. A range of different sandwich structures were printed and tested in 3-point bending and their performance was compared to monolithic non-foamed and foam beams and to analytical and numerical models.The stiffness, yield load, and maximum load of sandwich beams with non-foamed face sheets and foamed cores are much greater than those of pure foamed beams. With sandwich foam beams, weight reductions of around 30 % are both observed and predicted compared to non-foamed beams with equivalent stiffness. Analytical and numerical models using experimental data show value in aiding the design of sandwich structures of this type.

Design and fabrication of multi-material broadband electromagnetic absorbers for use in cavity-backed antennas

We investigated the feasibility of designing and fabricating novel broadband radiofrequency (RF) absorbers for use in cavity-backed antennas. Fabricating the absorber involved a multi-material additive manufacturing (AM) approach that combined two polymer filaments: a low-loss dielectric filament and a lossy carbon-loaded filament. An iterative optimization algorithm was developed to deploy these filaments and create gradient distributions of material properties that minimize reflectance over a desired frequency band and a range of incident angles to achieve wideband electromagnetic absorption. The chosen material profiles were effectively realized using a spatially varying subwavelength lattice structure printed via fused filament fabrication. Experimentally, validation results demonstrated low reflectance over a wide frequency band, 10 to 40 GHz, and a range of incident angles, 0°–50°. Finally, this printed multi-material absorber was integrated within a cavity-backed spiral antenna and used to suppress backlobe radiation while maintaining an acceptable radiation pattern in the forward direction. While this study investigated cavity-backed antennas, these computational and experimental methods are potentially useful for a wide range of other applications.

First steps of the melting of an amorphous polymer through a hot-end of a material extrusion additive manufacturing

The melting of an amorphous polymer filament through the hot end of a material extrusion process is addressed using computational multiphase fluid dynamics coupled to heat transfer. Only the flow through the heat block is investigated. The air gap between the filament and the interior of the extruder is accounted for. The polymer/air interface is implicitly tracked by a level-set method. The system of equations is solved using a finite element method with a time-marching method. Three extrusion velocities are investigated. For the lowest velocity, after the contact of the polymer with the extruder on the nozzle, the air gap disappears with time. The transient regime lasts a few tens of seconds. For the two larger velocities, even if the air gap is more and more reduced with time, it persists for a long time. The extension of the air gap increases with the velocity. The feeding force needed to push the filament is obtained by the integration of the tension on the surface of the extruder. After a transient regime driven by the heat transfer, a steady-state regime is observed for the three velocities. Roughly, the feeding force increases linearly with the extrusion velocity. A good agreement is found with experimental results for the two smallest velocities.

Three-Dimensional Printing of Recycled Polypropylene and Activated Carbon Coatings for Harmful Gas Adsorption and Antibacterial Properties.

In recent years, the utilization of three-dimensional (3D) printing has been expanding due to advances in technology and economic efficiency. One of the 3D printing technologies is fused deposition modeling, which can be used to create different kinds of products or prototypes from various polymer filaments. In this study, the activated carbon (AC) coating was introduced to the 3D outputs printed using recycled polymer materials to impart multi-functions such as adsorption of harmful gas and antimicrobial activities. A filament of uniform diameter (1.75 μm) and a filter template in the form of a 3D fabric shape were prepared through the extrusion and 3D printing processes, respectively, of the recycled polymer. In the next process, the 3D filter was developed by coating the nanoporous AC, produced from the pyrolysis fuel oil and waste PET, on the 3D filter template through direct coating. The 3D filters coated with the nanoporous activated carbon showed the enhanced adsorption capacity of 1038.74 mg of SO2 gas and the antibacterial properties of 49% removal of E. coli bacteria. As a model system, a functional gas mask that has harmful gas adsorption abilities and antibacterial properties has been produced by a 3D printing process.

Dark-induced chloroplast relocation depends on actin filaments in the liverwort Apopellia endiviifolia along with the light- and cold-induced relocations.

Chloroplasts move to the periclinal walls of cells under weak light to harness light energy for photosynthesis and to anticlinal walls to avoid strong light. These responses involve the cytoskeleton components microtubules and/or actin filaments. In the dark, chloroplasts move to the anticlinal cell walls bordering neighbouring cells (dark-positioning response), but this response in various plants normally requires a prolonged dark incubation period, which has hampered analysis. However, we recently demonstrated the dark-positioning response that can be induced after a short period of dark incubation in the liverwort Apopellia endiviifolia. Here, we investigated whether the cytoskeleton components function in the dark-positioning response of A. endiviifolia cells. Microtubules and actin filaments were fluorescentlyvisualised in A. endiviifolia cells and were disrupted following treatment with the microtubule and actin filament polymerisation inhibitors. The dark-positioning response was unaffected in the cells with disrupted microtubules. By contrast, the dark-positioning response was inhibited by the disruption of actin filaments. The disruption of actin filaments also restricted chloroplast mobility during light- and cold-dependent chloroplast movements in A. endiviifolia. Therefore, the dark-positioning response of A. endiviifolia depends solely on an actin filament-associated motility mechanism, as do the light- and cold-dependent chloroplast responses.

Repeatable self-healing of composite’s fatigue delamination

This paper investigates repeatable self-healing of composite laminates to mitigate fatigue delamination where a two-step healing mechanism is employed to heal the delamination cracks in a CFRP composite: (i) close the cracked surfaces by thermally activating dispersed shape memory polymer (SMP) filaments, and (ii) heal the closed crack by melting the thermoplastic healant (PCL) dispersed in the thermoset polymer matrix and allowing it to flow into the cracked region and solidify. Repetitive self-healing is carried out on double cantilever beam (DCB) specimens using macro fiber composite (MFC) actuators bonded to the test specimens, which generate the heat required to activate the thermoplastic healants to heal the delamination in the composite. Fatigue delamination growth rates were obtained for replicate specimens to extract statistically meaningful data on fatigue life under mode-I loading after seven healing cycles, indicating substantial retardation in delamination growth rate resulting in a significant increase in fatigue life.

Towards Self-Reinforced PLA Composites for Fused Filament Fabrication

Aligned with the Sustainability Development Goals (SDGs), we present the complete methodology of preparing bio-based polymer filaments to be used in additive manufacturing, specifically by means of so-called Fused Filament Fabrication (FFF) in 3D printing. Filament production and 3D printing were both developed and optimised in this work. First, we focused on the steps of producing and optimising the extrusion process of unreinforced polylactic acid (PLA) composite filaments. Second, we studied the resulting material properties by discussing the selection of a specimen geometry and the international standards adequate for FFF 3D printing. Moreover, we investigated the process parameters in order to achieve reliable structures. Based on the reinforcement material (stereocomplex fibres (Sc-PLA fibre) and bi-component fibres (bi-co PLA fibre), base-matrices were selected for producing un-reinforced filaments. In this way, we present the complete preparation approach by identifying problems and pitfalls for fostering studies of bio-based polymer filaments.

High velocity flame spraying of highly-filled ceramic — Polymer filaments (F-HVOF)

A novel technique of spraying fine and ultra-fine powders via high velocity oxy fuel flame spraying (HVOF) is presented based on a highly filled filament as feedstock material – F-HVOF. The polymer material is used as a solid dispersion medium for the desired coating material, similar to the liquid dispersion medium in a suspension. Thus, the polymer works as a transportation medium only and is burned upon entering the combustion zone, thereby releasing the powder material. Within this study two filaments are fabricated and sprayed using Al2O3 and Al2O3-TiO2 87/13 ceramic powders in combination with low-density Polyethylene and Polybutylenadipat-Terephthalat, respectively. The filaments are characterized using TGA and electron as well as light microscopy. Compared to suspension spraying, filament spraying offers several benefits especially from a manufacturing and handling point of view as it is geared similar to a wire flame spraying method. In order to evaluate the potential of the new process, the coatings are characterized with regard to their microstructure, topography, microhardness, surface roughness and phase composition. The obtained results are compared to suspension sprayed samples and literature data.

Polymeric Microfluidic Fuel Cells with Controlled Printed Patterns.

Since its first appearance almost a couple of decades ago, microfluidic fuel cells (MFFCs) have gained considerable research momentum due to their potential applications in portable devices. The main focus has been on the effective fabrication of microfluidic channels with different materials, where the manufacturing limitations proved to be the main stumbling blocks. Paper-based MFFCs have been reported with some success, where the porosity of the flow channel medium drives the reactants, greatly reducing the need for elaborate external devices and complex manufacturing obstacles, although the longevity of these cells remains questionable. The current article addresses this issue by replacing the paper-based flow channels with 3D-printed substrates of different structural forms to serve as pathways for controlled flow and mixing responses of the reactant liquids without the use of other devices, such as micro pumps and valves. The line-by-line material consolidation mechanics of fused filament fabrication and the porous mesostructural responses of a commercial polymer filament are combined to build the microfluidic fuel channels of varying configurations. Numerical and experimental characterizations proved the cells to perform better than the current paper-based counterparts, apart from better longevity and possible new opportunities for future improvements based on more complex micro-, meso-, and macrostructural advances.

Metallothionein-3 attenuates the effect of Cu2+ ions on actin filaments

Metallothionein 3 (MT-3) is a cysteine-rich metal-binding protein that is expressed in the mammalian central nervous system and kidney. Various reports have posited a role for MT-3 in regulating the actin cytoskeleton by promoting the assembly of actin filaments. We generated purified, recombinant mouse MT-3 of known metal compositions, either with zinc (Zn), lead (Pb), or copper/zinc (Cu/Zn) bound. None of these forms of MT-3 accelerated actin filament polymerization in vitro, either with or without the actin binding protein profilin. Furthermore, using a co-sedimentation assay, we did not observe Zn-bound MT-3 in complex with actin filaments. Cu2+ ions on their own induced rapid actin polymerization, an effect that we attribute to filament fragmentation. This effect of Cu2+ is reversed by adding either EGTA or Zn-bound MT-3, indicating that either molecule can chelate Cu2+ from actin. Altogether, our data indicate that purified recombinant MT-3 does not directly bind actin but it does attenuate the Cu-induced fragmentation of actin filaments.

Self-spinning filaments for autonomously linked microfibers

Filamentous bundles are ubiquitous in Nature, achieving highly adaptive functions and structural integrity from assembly of diverse mesoscale supramolecular elements. Engineering routes to synthetic, topologically integrated analogs demands precisely coordinated control of multiple filaments’ shapes and positions, a major challenge when performed without complex machinery or labor-intensive processing. Here, we demonstrate a photocreasing design that encodes local curvature and twist into mesoscale polymer filaments, enabling their programmed transformation into target 3-dimensional geometries. Importantly, patterned photocreasing of filament arrays drives autonomous spinning to form linked filament bundles that are highly entangled and structurally robust. In individual filaments, photocreases unlock paths to arbitrary, 3-dimensional curves in space. Collectively, photocrease-mediated bundling establishes a transformative paradigm enabling smart, self-assembled mesostructures that mimic performance-differentiating structures in Nature (e.g., tendon and muscle fiber) and the macro-engineered world (e.g., rope).