Continuous Extrusion Research Articles

Feasible Regions of Bioink Composition, Extrusion Pressure, and Needle Size for Continuous Extrusion-Based Bioprinting

Abstract Bioprinting has many potential applications in drug screening, tissue engineering, and regenerative medicine. In extrusion-based bioprinting, the extruded strand is the fundamental building block for printed constructs and needs to be of good quality and continuous in structure. In recent years, many studies have been conducted on extrusion-based bioprinting. However, values of process parameters leading to continuous extrusion of strands have rarely been reported. In this paper, feasible regions of bioink composition, extrusion pressure, and needle size for continuous strand extrusion have been evaluated. The information on feasible regions for extruding continuous strands, provided in this paper, can be useful in deciding appropriate extrusion pressure and needle size for the bioink of different compositions (ratios of alginate:methylcellulose) in extrusion-based bioprinting.

Test parameters optimization for constrained spray forming of aluminum alloy based on artificial neural network

Spray deposition with following continuous extrusion (SD-CE) forming technique is a novel technology that combines spray forming and continuous extrusion. Optimization of test parameters for spray deposition is an important part of SD-CE. In this study, Al-20Si alloy was produced by spray forming at different melt temperature and gas pressure, and obtained grain diameter of 8 group primary silicon phase. Based on the experimental results, an Artificial Neural Network (ANN) with single hidden layers composing of 10 neurons was employed to simulate optimizing of test parameters for spray deposition. The inputs of the model are melt temperature and gas pressure. The output of the model is grain diameter. Finally, the minimum relative error of grain diameter is 0.09%, the maximum relative error is 8.38%, and error majority concentrate within 3.80%, the average absolute relative error(AARE) is 1.04%, R is 0.097, the error is small. The optimal test parameters for spray deposition are melt temperature(829 °C) and gas pressure(0.2 MPa). The results indicate that the ANN model is an easy and practical method to optimize the test parameters for spray deposition of Al-20Si alloy. Thereby this model is a useful reference for optimizing the test parameters of SD-CE

Integrated Computational and Experimental Design of Ductile, Abrasion-Resistant Thermoplastic Polyurethane/Graphene Oxide Nanocomposites

Polymer nanocomposites are widely studied for improving and developing novel materials. Incorporation of nanofillers in polymer matrices impart strong behavioral changes, with the extent of dispersion of fillers in polymers playing a key role. This not only limits the amount of filler one can incorporate but also often leads to enhancement of some material properties at the expense of others. Herein, for the first time, thermoplastic polyurethane (TPU) graphene oxide (GO) nanocomposites with improved abrasion resistance and ductility are produced by integrating mesoscale modeling and a solvent-free continuous and upscalable extrusion process. The role of GO in hard segment crystallization is established via dissipative particle dynamics simulations, which then informs processing in twin-screw extrusion involving extensional mixing elements to achieve desired deagglomeration and dispersion of GO. This approach allows a tough yet highly ductile composite suitable for high abrasion resistant applications to be produced. In comparison with composites obtained from conventional processing, ductility improved by more than 300%, strength increased by 80%, toughness enhanced by more than 500%, and abrasion resistance improved by 45%. Insights into the gradient of TPU hard block crystallinity, role of deagglomeration, and phase separation are also discussed.

Hot Deformation Behavior of Cu-Sn-La Polycrystalline Alloy Prepared by Upcasting.

In this study, the hot deformation of a Cu–0.55Sn–0.08La (wt.%) alloy was studied using a Gleeble-3180 testing machine at deformation temperatures of 400–700 °C and various strain rates. The stress–strain curve showed that the hot deformation behavior of the Cu–0.55Sn–0.08La (wt.%) alloy was significantly affected by work hardening, dynamic recovery, and dynamic recrystallization. The activation energy Q was 261.649 kJ·mol−1 and hot compression constitutive equation was determined as The microstructural evolution of the alloy during deformation at 400 °C revealed the presence of both slip and shear bands in the grains. At 700 °C, dynamic recrystallization grains were observed, but recrystallization was incomplete. In summary, these results provide the theoretical basis for the continuous extrusion process of alloys with promising application prospects in the future.

Effects of pressure drop rate and CO2 content on the foaming behavior of newly developed high-melt-strength polypropylene in continuous extrusion

We report systematic studies on the foamability of our novel high-melt-strength long-chain branched polypropylene under supercritical CO2. Continuous foaming experiments were conducted using a tandem extrusion system and a set of filamentary dies with similar pressure drops but different pressure drop rates. The foam expansion was controlled by varying the temperature at the die exit. Under identical CO2 loadings, the expansion ratio plotted as a function of die temperature exhibited similar shapes across multiple pressure drop rates. However, the shape of the curve varied across different amounts of CO2, under which the highest achievable expansion ratio occurred at a lower die temperature with increasing CO2 content. The cell density displayed strong dependence on both the pressure drop rate and the amount of dissolved CO2. The effect of the latter became more apparent at lower pressure drop rates. The average cell size decreased with increasing CO2 loading but generally showed weak dependence on pressure drop rate except at the highest value.

On the suitability of induction heating system for metal additive manufacturing

Induction heating is a non-contact-based energy source that has the potential to quickly melt the metal and become the alternate energy source that can be used for additive manufacturing. At present, induction heating is widely used in various industrial applications such as melting, preheating, heat treatment, welding, and brazing. The potential of this source has not been explored in the additive manufacturing domain. However, the use of induction heating in additive manufacturing could lead to low-cost part fabrication as compared to other energy sources such as laser or electron beam. Therefore, this study explores the feasibility of this energy source in additive manufacturing for fabricating parts of metallic materials. An experimental system has been developed by modifying an existing delta three-dimensional printer. An induction heater coil has been incorporated to extruder head for semi-solid processing of the metal alloy. In order to test the viability of the developed system, aluminium material in the filament form has been processed. Obtained results have shown that the induction heating–based energy source is capable of processing metallic materials having a melting point up to 1000° C. The continuous extrusion of the material has been achieved by controlling the extruder temperature using a proportional integral derivative–based controller and k-type thermocouple. The study also discusses various issues and challenges that occurred during the melting of metal with induction heating. The outcomes of this study may be a breakthrough in the area of metal-based additive manufacturing.

Recycling of Titanium Alloy Powders and Swarf through Continuous Extrusion (ConformTM) into Affordable Wire for Additive Manufacturing

Over the last 20 years, there has been growing research and development investment to exploit the benefits of wire deposition additive manufacturing (AM) for the production of near-net shape components in aircraft and space applications. The wire feedstock for these processes is a significant part of the overall process costs, especially for high-value materials such as alloyed titanium. Powders for powder-based AM have tight specifications regarding size and morphology, resulting in a significant amount of waste during the powder production. In the aerospace sector, up to 95% of forged billet can be machined away, and with increasing aircraft orders, stockpiles of such machining swarf are increasing. In this study, the continuous extrusion process—ConformTM—was employed to consolidate waste titanium alloy feedstocks in the forms of gas atomised powder and machining swarf into wire. Samples of wire were further cold-drawn down to 40% reduction, using conventional wiredrawing equipment. As close to 100% of the waste powder can be converted to wire by using the ConformTM process. This technology offers an attractive addition to the circular economy for manufacturers and, with further development, could be an important addition as industries move toward more sustainable supply chains.

Effects of Bi and Ce addition on tensile properties and corrosion resistance of Zn-15Al alloys by continuous casting and extrusion

The effect of Bi or Ce as alloy elements were added into the Zn-15Al alloys by continuous casting and extrusion (CASTEX) to improve the tensile properties and corrosion resistance was investigated. The results indicated that the addition of Bi or Ce to CASTEX Zn-15Al alloys could not form new phase. The distribution of Bi was homogeneous in the alloys, but the Ce focused on the Zn-rich η phase. The refinement effect of Ce was better than that of Bi for CASTEX Zn-15Al alloys. The result of tensile test indicated that the CASTEX Zn-15Al alloys by adding Ce element led to higher ultimate tensile strength and ductility. Corrosion behavior of CASTEX Zn-15Al-0.2Bi and Zn-15Al-0.2Ce alloys was investigated in 3.5 wt% NaCl solution using electrochemical measurements. The results show that CASTEX Zn-15Al-0.2Ce alloys have higher corrosion resistance.

Using chaotic advection for facile high-throughput fabrication of ordered multilayer micro- and nanostructures: continuous chaotic printing

This paper introduces the concept of continuous chaotic printing, i.e. the use of chaotic flows for deterministic and continuous extrusion of fibers with internal multilayered micro- or nanostructures. Two free-flowing materials are coextruded through a printhead containing a miniaturized Kenics static mixer (KSM) composed of multiple helicoidal elements. This produces a fiber with a well-defined internal multilayer microarchitecture at high-throughput (>1.0 m min−1). The number of mixing elements and the printhead diameter determine the number and thickness of the internal lamellae, which are generated according to successive bifurcations that yield a vast amount of inter-material surface area (∼102 cm2 cm−3) at high resolution (∼10 µm). This creates structures with extremely high surface area to volume ratio (SAV). Comparison of experimental and computational results demonstrates that continuous chaotic 3D printing is a robust process with predictable output. In an exciting new development, we demonstrate a method for scaling down these microstructures by 3 orders of magnitude, to the nanoscale level (∼150 nm), by feeding the output of a continuous chaotic 3D printhead into an electrospinner. The simplicity and high resolution of continuous chaotic printing strongly supports its potential use in novel applications, including—but not limited to—bioprinting of multi-scale layered biological structures such as bacterial communities, living tissues composed of organized multiple mammalian cell types, and fabrication of smart multi-material and multilayered constructs for biomedical applications.

Corrigendum to “A physical based empirical model for the accumulated strain in novel Metal Continuous Screw Extrusion (MCSE)” [J. Mater. Process. Technol. 282C (2020) 116670

Corrigendum to “A physical based empirical model for the accumulated strain in novel Metal Continuous Screw Extrusion (MCSE)” [J. Mater. Process. Technol. 282C (2020) 116670

Microstructural and mechanical properties of ZA10 alloy tubes and their weld seams prepared by Conform continuous extrusion

In the present work, Zn–10Al–2Cu–0.05Ti (ZA10) alloy tubes with a diameter of 12.5 mm and wall thickness of 1.2 mm were fabricated by one-pass and double-pass Conform continuous extrusion. A stabilizing heat treatment [350 °C, 30 min (furnace cooling) + 120 °C, 12 h (air cooling)] was also applied to some of the double-pass tubes to improve the quality of their weld seams. The yield strength, ultimate tensile strength, elongation and expansion ratio of the one-pass continuous extrusion tube were 268.4 MPa, 294.3 MPa, 13.8% and 5.5%, respectively. Double-pass continuous extrusion improved these values to 278.4 MPa, 317.2 MPa, 15.4% and 11.4%, respectively. Double-pass tubes also had fewer aggregations of Al-α precipitates along the welding seam, which improved seam quality and caused cracks to appear in the matrix, away from the weld-affected zone, during expansion testing. Heat-treated double-pass tubes exhibited superior yield strength (283.9 MPa) and ultimate tensile strength (328.5 MPa) but lower elongation (10.2%) and expansion ratios (10.3%). Additionally, the heat-treated tubes exhibited markedly lower elongation at room temperature due to the remarkable blockage of dislocation motions by fine-scale lamellar (α + η) eutectoid structures and a lower size effect when stretched.

Additive Manufacturing of Reinforced Concrete—Development of a 3D Printing Technology for Cementitious Composites with Metallic Reinforcement

Reinforced concrete (RC) is by far the most widely used composite material in the world. Despite the enormous economic importance of RC construction, there is a lack of viable concepts for its digital fabrication. While 3D printing of plain concrete has been pushed forward by a growing research community in recent years, methods for integration of steel reinforcement have only scarcely been researched and little attention has been payed to meet the practical requirements of construction sites and prefabrication plants. Therefore, full-scale implementations of current approaches are hardly available. Based on both, a sound review of R&D for digital fabrication of RC structures and an analysis of practical requirements, the present paper proposes a novel 3D printing process for RC structures, called Additive Manufacturing of Reinforced Concrete (AMoRC), viable for real-world application. In this hybrid process, consisting of an intermittent stud welding process and a continuous concrete extrusion process, segmented steel reinforcing bars are joined to form a three-dimensional reinforcement mesh and simultaneously encased with extruded concrete. The paper describes the conceptual design and development of the process and demonstrates the results of preliminary investigations on its feasibility. As AMoRC enables the operation of rebar welding and concrete extrusion process with synchronized feed rates, combination of both processes in one hybrid print head for digital fabrication of RC is a key-advantage of the proposed method.

An insight into different phenomena involved in continuous extrusion foaming of biodegradable poly(lactic acid)/expanded graphite nanocomposites

The continuous extrusion foaming of poly(lactic acid) (PLA) has several critical drawbacks that crucially limit the substitution of the renewable foams for the extruded foams based on synthetic plastics. In this work, the foamability of PLA melt through a twin-screw extrusion process was improved by using expanded graphite (EG) nanoplatelets having different aspect ratios and loadings along with an organic peroxide. Morphological observations demonstrated the beneficial influences of adding nanofiller, which resulted in the formation of microcellular foams with larger void content and cell densities. Different phenomena, which are involved in the extrusion foaming of PLA melt, are considerably affected by the presence of EG including rheological behavior, PLA crystallization, thermal chain scission of the matrix, chain extension function of the peroxide and thermal decomposition of foaming agent. To correlate the phenomena affected by EG nanofiller with foam morphology, the linear viscoelastic responses, molecular weight, crystallization kinetics and structural properties of PLA and PLA/EG nanocomposites were evaluated.

Finite element modeling of Conform-HPTE process for a continuous severe plastic deformation path

A novel continuous severe plastic deformation (SPD) approach was proposed by combining continuous extrusion forming (Conform) with high pressure torsion extrusion (HPTE), which is called Conform-HPTE process. Finite element method (FEM) simulations were employed to investigate the severe plastic deformation behavior of aluminum alloys under various processing conditions. The results showed that the novel Conform-HPTE process effectively accumulated large plastic strain after a single deformation pass. During the Conform-HPTE process, the Conform machine not only provided driving power for the whole equipment, but also introduced shear deformation and heating in the specimen for subsequent HPTE process. The subsequent HPTE process further introduced severe plastic deformation in the specimen. And the severe gradient shear deformation condition could lead to the formation of refined and gradient microstructure. Therefore, the novel Conform-HPTE process could be a promising industrial SPD technique to continuously produce advanced engineering materials with the advantages of energy and cost saving and high process efficiency.

3D printable and injectable lactoferrin-loaded carboxymethyl cellulose-glycol chitosan hydrogels for tissue engineering applications.

In this study, carboxymethyl cellulose (CMC)-glycol chitosan (GC) hydrogel, a potential three-dimensional (3D) printing biomaterial ink for tissue engineering applications was synthesized using simple, biocompatible in situ-gelling Schiff's base reaction and ionic interactions. Different grades of hydrogels (C70G30, C50G50 and C30G70) were synthesized at physiological conditions. The oxidation of CMC and imine bond formation in the hydrogel were confirmed spectroscopically. Scanning electron microscopic images revealed the crosslinked interconnected pores in the cross-sectioned hydrogels (dried). Swelling (equilibrium: 1 h), porosity (~75%), in vitro degradation (>30 days) and thermal gravimetric analyses of the dried gels were studied. Initially, cytotoxicity assay was evaluated using mouse osteoblastic cells (MC3T3). These experiments revealed that CMC-GC gels formed stable hydrogel networks and were biocompatible. Particularly, C50G50 gels showed high printability (continuous extrusion) and post-printing stability (without secondary crosslinking). Gel 3D printing was optimized by varying the air pressure, temperature, needle size and nozzle speed, to obtain stable lattice structures (2 to 16 layers). The printed (2 and 5 layers) hydrogels showed high stability in phosphate buffer saline (PBS) solution (1 h), under UV light (1 h) and after autoclaving. The strut dimensions and porosity of the printed gels before and after the stability tests were analyzed. The hydrogel stability may be attributed to both the imine bond and ionic interaction between the cationic and anionic polymer side chains. Lactoferrin (glycoprotein) incorporated C50G50 gels showed sustained release up to 21 days in PBS (pH 7.4) solution and demonstrated increased biocompatibility (>80%) during in vitro cytotoxicity assays (MC3T3 cells and bone marrow mesenchymal stem cells) and Live/Dead assay (MC3T3 cells). A higher number of live osteoblast cells on the C50G50 hydrogels with increasing lactoferrin concentration was observed. These results show that the CMC-GC gels are promising bio-ink candidates for 3D printing and loading proteins or drugs for tissue engineering applications.

Fabrication of high-strength PET fibers modified with graphene oxide of varying lateral size

The large lateral-sized graphene oxide (LGO) was successfully broken into medium- and small lateral-sized graphene oxide (MGO and SGO, respectively), using a self-designed tubular ultrasonic instrument and other different techniques such as centrifugation, ultrasonication, and freeze-drying. Nanocomposite fibers composed of polyester (PET) material modified with various lateral-sized graphene oxide (GO) were prepared by twin-rotor continuous extrusion and melt spinning. The effects of high-speed mixing and GO lateral size on the mechanical and thermal properties of the composite samples were investigated. Compared to the conventional twin-screw extruder, a twin-rotor continuous extruder achieves a more uniform distribution of GO in the PET matrix. Furthermore, the use of SGO yields the best dispersion and interfacial compatibility properties. It also promotes crystallization, which confirms that, compared to LGO and MGO, SGO plays a more important role in the heterogeneous nucleation of PET. Among the investigated samples, PET/SGO fibers loaded with 0.1 wt% SGO show the highest tensile strength (890 MPa) and Young's modulus (30 GPa). Therefore, the high-speed mixing of PET with nanometer-sized SGO using a twin-rotor continuous extruder has broad application prospects in the field of GO-reinforced polymers, on an industrial scale.

Good extrusion foaming performance of long‐chain branched PET induced by its enhanced crystallization property

AbstractPoly(ethylene terephthalate) (PET) was modified by regulating different contents of branching agent epoxy‐based multifunctional oligomer and chain extender pyromellitic dianhydride in reactive extrusion process. The modified PET with better long‐chain branched (LCB) structure boosted its rheological properties, and its enhancement of melt viscoelasticity resulted in excellent foamability in molten‐state foaming process using supercritical CO2 as blowing agent. More importantly, the branched structures acted as crystal sites to accelerate the crystallization kinetic of LCB PET whether under atmospheric pressure or high‐pressure CO2. The shear and elongation flow inside die further quickly induced the crystallization of LCB PET. The rapidly generated fine crystals could both introduce heterogeneous cell nucleation and suppress CO2 escape, so the cell morphology of LCB PET in continuous extrusion foaming process exhibited a three‐fold increase in cell density and smaller uniform cell size with respect to those of other foam‐grade PET with long‐chain structure.

Dispersion-tunable chalcogenide tri-cladding fiber based on novel continuous two-stage extrusion

A novel robust tri-cladding stepped fiber structure has been proposed for the dispersion tuning, and a systematic simulation has been given for the fibers with different sizes of claddings and cores. The results show that double zero-dispersion wavelength (ZDW) points can be obtained, and the first ZDW is shorter at 3.3 µm and the second ZDW at 9.9 µm. Based on the simulation of the structural optimization, we have prepared a well-structured tri-cladding fiber with a minimum loss of 1.55 dB/m at 6.77 µm by a novel continuous two-stage extrusion method. Moreover, a flattened supercontinuum extending from 1.3 to 12.9 µm pumping at anomalous dispersion wavelength of 5 µm between the two ZDWs can be achieved, which fits well with the simulated results. After all, the optimized fiber consisting of As2Se3, Ge10As22Se68, As2S3 exhibits excellent properties that demonstrate the potential for a simple way to prepare high quality fiber with a tri-cladding structure.

3D printing of a biocompatible low molecular weight supramolecular hydrogel by dimethylsulfoxide water solvent exchange

A fragile and non-thixotropic biocompatible low molecular weight gel is printed in 3D structures by a solvent exchange process. The 3D printing process is based on the continuous extrusion of a solution of a small amphiphile molecule, N-heptyl-d-galactonamide, in dimethylsulfoxide, that forms a gel in contact with water. The diffusion of water in the dimethylsulfoxide / N-heptyl-d-galactonamide solution triggers the self-assembly of the molecule into supramolecular fibers and the setting of the ink. The conditions for getting a well-defined pattern and the dimensions of the constructs have been determined. The resulting constructs can be easily dissolved, orienting its application as a sacrificial ink or a temporary support. This method opens the way to the injection and the 3D printing of other fragile and non-thixotropic supramolecular hydrogels.

A physical based empirical model for the accumulated strain in novel Metal Continuous Screw Extrusion (MCSE)

Abstract This work concerns the novel Metal Continuous Screw Extrusion process (MCSE). The process gives new opportunities for processing metal alloys, composites and novel multi-materials. By principle, one feeds granulated material into the screw extruder which compacts and extrudes the material in a continuous manner. The inherent deformation is very complex and based on empirical knowledge, a comprehensive quantitative model for the strain evolution through the main four stages of the process is formulated for the first time.Data from screw extrusion of an Al-5%Mg alloy using an extrusion die temperature of 410 °C and relatively low feeding rate, showed a total accumulated strain ∼15 in the current prototype set-up for a O10 mm profile. Granule feeding rate and screw rotation speed are considered the most influencing parameters regarding predicted accumulated strain. The latter increases with lower feeding rates and higher rotation speeds of the screw. Further design optimization of the screw extruder might be assisted by the current model.