Mechanical evaluation of polymeric filaments and their corresponding 3D printed samples

3D printing technologies permits to produce functional parts with complex geometries, optimized topologies or enhanced internal structures. The relationship between mechanical performance and manufacturing parameters should be exhaustively analyzed to warrant the long term success of printed products. In this work, the mechanical performance of filaments based on acrylonitrile butadiene styrene (ABS), polylactic acid (PLA) and polylactic acid/polyhydroxyalkanoate (PLA/PHA) was investigated and also compared with their corresponding 3D printed samples. In general, the specimen dimensional deviations were found to be within the tolerances defined by the standard testing protocols. Density values revealed a high level of filament fusion promoting a nearly solid internal structure. The filaments exhibited improved tensile performance with respect to their corresponding printed samples. Tensile and bending performance looked quite independent of the raster angle. Izod impact behavior was increased, for ABS systems printed with the ±45° raster orientation. Quasi-static fracture tests displayed improved crack initiation resistance with the 0°/90° raster angle. The crack propagation observed for the ±45° specimens, through the bonding of the inter-layers, suggests weak entanglements.     

3D printed biodegradable composites: An insight into mechanical properties of PLA/chitosan scaffold

Three-dimensional (3D) printing is a frontier manufacturing approach with great potential to benefit biomedical and patient care sectors. In the last decades, different types of biomedical materials were investigated in purpose of developing medical tools and devices. The present study attempts to assess mechanical performances (namely: tensile, compression, and flexural) of the newly developed chitosan-reinforced poly-lactic-acid (PLA) scaffolds by using fused filament fabrication (FFF) based 3D printing technology. Specifically, the effects of chitosan loading, infill density and annealing temperature on mechanical behavior of PLA composite scaffolds are investigated via design of experiments. Moreover, fracture behavior under various load types is studied with the help of selective electron microscopy. It is found that the strength of the produced composite samples depends significantly on the loading of chitosan and infill density, while annealing temperature does not affect mechanical response. Overall, the developed PLA composite scaffolds are mechanically efficient and they appear suitable for clinical purposes.     

A method for more accurate FEA results on a medical device developed by 3D technologies

At present, 3‐dimensional models of all additive manufactured objects (AMOs) are accepted as a solid model for finite element analysis (FEA). FEA of AMOs may not reveal the real results because mechanical properties of default materials in CAD software and newly built AMOs are not equal to each other. This may produce problems especially for the end user due to unexpected failure or wear off. The aim of this study was to compare FEA results of an additive manufactured Ankle Foot Orthosis model under 2 different value sets, namely default material‐based mechanical properties and measured mechanical properties. In order to determine the real mechanical properties of the additive manufactured Ankle Foot Orthosis, 3‐dimensional printed test specimens with different infill densities were prepared and tested according to the recommended standards. Mechanical test results were then loaded in the CAD software and FEA was performed. This study illustrated that default mechanical properties of existing materials in CAD software produce misleading simulation results for AMOs, ie, real mechanical properties should be used to get more accurate results.     

Experimental analysis of the tensile property of FFF-printed elastomers

Designing and manufacturing functional parts with enhanced mechanical property is a major goal of fused filament fabrication (FFF) for polymeric elastomers, which exhibits major advantages in producing such parts with a range of structures. But the unsatisfactory mechanical performance constrains greatly its real application and there is yet no consensus in the mechanical characterization of printed samples. This work takes the nozzle height as the considered factor and tests the tensile property of FFF-printed thermoplastic polyurethane (TPU). Rheological property of the TPU melt, represented here by die swell behavior and shear viscosity, were measured initially to obtain a preliminary assessment of the material suitability and an optimization of melt extrusion conditions for FFF processing. Then correlation between the cross-section profile of deposited bead and the tensile performance of printed sample were evaluated. Both the shape of deposited bead and the bonding strength of two adjacent beads are emphasized when explaining the measured tensile strength. The significance of molecular permeation efficiency at bead-bead interfaces, and bonding-releasing patterns between adjacent beads to the tensile failure of printed objects is discussed.     

Investigation of infill-patterns on mechanical response of 3D printed poly-lactic-acid

This paper presents the effect of infill patterns (IPs) on the mechanical response of 3D printed specimens by conducting the low-velocity impact test (LVI) and compression test. The poly-lactic acid (PLA, purity 98 wt% >) material has selected and printed using fused deposition modeling (FDM, speed 20 mm/s, layer height 0.2 mm, no of layers 30, extruded at 200 °C) with four different IPs: triangle, grid, quarter cubic, and tri-hexagon. The LVI test on velocity-time, energy-time and force-displacement, and the compression responses have examined and presented in this study. The LVI test was carried out to determine the penetration energy level, energy absorption capacity (toughness), stiffness, and strength of PLA porous parts (60% infill density) for implant/tissue/recyclable product applications. The results have shown that the triangular pattern has produced the highest absorbed energy in LVI test (penetration energy 7.5 J, and stiffness 668.82 N/mm) due to more sheared/contact layers’ perpendicular to impactor (hemispherical insert); while the grid pattern exhibited the highest compressive strength (72 MPa) due to more layers aligned along the compressive loading direction The SEM fracture surface image of Triangular IP has produced effective raster and layer bonding, less number of voids, more amount of circular beach markings, and absence of ratchet lines leading to possess improved mechanical properties.     

Statistical analysis of mechanical properties of wood-PLA composites prepared via additive manufacturing

Additive manufacturing circumscribes numerous technologies that allow for the construction of three-dimensional parts by superimposing layers of material. These technologies have undergone greater development in recent years. In this work, using 3D additive printing technology, the samples are prepared using biodegradable wood-PLA composite by varying the layer height (0.08?mm, 0.16?mm, and 0.24?mm), infill (30%, 60%, and 90%) and three different patterns such as layer, triangle, and hexagon. Using universal testing machines tensile properties, energy absorption, and toughness of samples are evaluated as per ASTM standards. The results show that better values are achieved with increase in the infill percentage and layer pattern provides better strength and stiffness. A statistical linear regression model was successfully developed to predict the mechanical properties with an accuracy of 96% predicted in layer pattern when compared to other. Linear regression method helps to find the relationships between two sub-properties of mechanical property of different types of materials and helps to predict the properties of unknown materials.     

Multifunctional properties of 3D printed poly(lactic acid)/graphene nanocomposites by fused deposition modeling

In this work, three-dimensional (3D) printing system based on fused deposition modeling (FDM) is used for the fabrication of conductive polymer nanocomposites. This technology consists in the additive multilayer deposition of polymeric nanocomposite based on poly(lactic acid) (PLA) and graphene by means of a in house made low-cost commercial bench-top 3D printer. Further, 3D printed PLA/graphene nanocomposites containing 10 wt% graphene in PLA matrix were characterized for their mechanical, electrical and electromagnetic induction shielding properties of the nanocomposite. Furthermore X-ray computed micro-tomography analyses showed that printed samples have good dimensional accuracy and are significantly closer to the predefined design and the results of scanning electron microscopy (SEM) printed samples showed a uniform dispersion of graphene in PLA matrix The proposed material has uniquely advantageous when implemented in 3D printed structures, because incorporation of multifunctional graphene has been shown to substantially improve the properties of the resulting nanocomposite.     

Three‐dimensional printing of poly(lactic acid) bio‐based composites with sugarcane bagasse fiber: Effect of printing orientation on tensile performance

The cellulose fiber was extracted from the abandoned crop sugarcane bagasse (SCB) by means of chemical treatment methods. Poly(lactic acid) (PLA) bio‐based composites with SCB were prepared through fused deposition modeling (FDM) 3D‐printing technology, and the morphologies, mechanical properties, crystallization properties, and thermal stability of 3D‐printed composites were investigated. Compared with the neat PLA, the incorporation of SCB into PLA reduces the tensile strength and flexural strength of 3D‐printed samples but increases the flexural modulus. The difference in tensile performance and bending performance is that the tensile strength of 3D‐printed samples is best when the SCB content is 6 wt%, while the flexural modulus continuously decreases as the SCB content increases. Furthermore, the effects of various printing methods on the tensile performance of 3D‐printed samples were explored via modifying G‐code of 3D models. The results indicate that the optimum SCB fiber content is identical for all printing methods except method “vertical.” Due to the fibers and molecular chains are oriented to varying degrees with altering raster angle in 3D‐printed samples, the fully oriented sample printed by method “parallel” has a better tensile strength. Besides, SCB exhibits enough high thermal decomposition temperature to meet requirements for melt extrusion processing of PLA composites, and SCB fiber is capable of promoting the crystallization of PLA.     

Effect of surface texturing on friction behaviour of 3D printed polylactic acid (PLA)

Additive manufacturing is gaining a remarkable importance in manufacturing industries because of the ability to build parts with complex and intricate shapes. The most widely used material in additive manufacturing is the polymer. In this paper, circular textures have been 3D printed on the surface of Polylactic Acid (PLA) polymer using fused deposition modelling technique. Experiments were performed under dry and lubricated conditions by varying the texture size. The results were obtained for high and low speeds with varying loads of 10, 20, 30, 40 and 50 N. It was observed that coefficient of friction was minimum for texture T₂ at both high and low speeds under dry sliding conditions. This is due to the less real area of contact than texture T₁ and more effective formation of transfer film in case of texture T_3. The entrapment of wear debris is more effective which helps in the formation of transfer layer that acts as solid lubricant. Under lubricated conditions, it was observed that for low speed, texture T₃ has least coefficient of friction while at high speed texture T₁ resulted in the minimum coefficient of friction. This is mainly due to the more retention of lubricating oil for texture T₃ at low speed in comparison to the high speed. Surface analysis carried out for all the textures under dry sliding conditions revealed that the wear is mainly to adhesive and abrasive action.     

Effect of wood flour content on surface properties of 3D printed materials produced from wood flour/PLA filament

Amount of wood flour was gradually increased from 0 to 50?wt% in the production of polylactic acid (PLA) based filaments with 1.75?mm diameter using twin screw extruder. Surface roughness and wettability were measured of the specimens. Surface roughness of the specimens significantly increased with incorporation of wood flour into PLA filament. Wettability of the specimens significantly decreased with increasing wood flour content. This was mainly attributed to the higher surface free energy of PLA than the beech wood. Contact angle values of the 3D printed wood/PLA specimens having wood flour content up to 30?wt% were less than 90°.     

All‐in‐One Cellulose Nanocrystals for 3D Printing of Nanocomposite Hydrogels

Cellulose nanocrystals (CNCs) with >2000 photoactive groups on each can act as highly efficient initiators for radical polymerizations, cross‐linkers, as well as covalently embedded nanofillers for nanocomposite hydrogels. This is achieved by a simple and reliable method for surface modification of CNCs with a photoactive bis(acyl)phosphane oxide derivative. Shape‐persistent and free‐standing 3D structured objects were printed with a mono‐functional methacrylate, showing a superior swelling capacity and improved mechanical properties.     

3D printed polylactic acid nanocomposite scaffolds for tissue engineering applications

In this study, biodegradable polylactic acid (PLA) and PLA nanocomposite scaffolds reinforced with magnetic and conductive fillers, were processed via fused filament fabrication additive manufacturing and their bioactivity and biodegradation characteristics were examined. Porous 3D architectures with 50% bulk porosity were 3D printed, and their physicochemical properties were evaluated. Thermal analysis confirmed the presence of ~18 wt% of carbon nanostructures (CNF and GNP; nowonwards CNF) and ~37 wt% of magnetic iron oxide (Fe₂O₃) particles in the filaments. The in vitro degradation tests of scaffolds showed porous and fractured struts after 2 and 4 weeks of immersion in DMEM respectively, although a negligible weight loss is observed. Greater extent of degradation is observed in PLA with magnetic fillers followed by PLA with conductive fillers and neat PLA. In vitro bioactivity study of scaffolds indicate enhancement from ~2.9% (PLA) to ~5.32% (PLA/CNF) and ~ 3.12% (PLA/Fe₂O₃). Stiffness calculated from the compression tests showed decrease from ~680 MPa (PLA) to 533 MPa and 425 MPa for PLA/CNF and PLA/Fe₂O₃ respectively. Enhanced bioactivity and faster biodegradation response of PLA nanocomposites with conductive fillers make them a potential candidate for tissue engineering applications such as scaffold bone replacement and regeneration.     

How to Obtain the Maximum Properties Flexibility of 3D Printed Ketoprofen Tablets Using Only One Drug-Loaded Filament?

The flexibility of dose and dosage forms makes 3D printing a very interesting tool for personalized medicine, with fused deposition modeling being the most promising and intensively developed method. In our research, we analyzed how various types of disintegrants and drug loading in poly(vinyl alcohol)-based filaments affect their mechanical properties and printability. We also assessed the effect of drug dosage and tablet spatial structure on the dissolution profiles. Given that the development of a method that allows the production of dosage forms with different properties from a single drug-loaded filament is desirable, we developed a method of printing ketoprofen tablets with different dose and dissolution profiles from a single feedstock filament. We optimized the filament preparation by hot-melt extrusion and characterized them. Then, we printed single, bi-, and tri-layer tablets varying with dose, infill density, internal structure, and composition. We analyzed the reproducibility of a spatial structure, phase, and degree of molecular order of ketoprofen in the tablets, and the dissolution profiles. We have printed tablets with immediate- and sustained-release characteristics using one drug-loaded filament, which demonstrates that a single filament can serve as a versatile source for the manufacturing of tablets exhibiting various release characteristics.     

On‐Demand Production of Flow‐Reactor Cartridges by 3D Printing of Thermostable Enzymes

The compartmentalization of chemical reactions is an essential principle of life that provides a major source of innovation for the development of novel approaches in biocatalysis. To implement spatially controlled biotransformations, rapid manufacturing methods are needed for the production of biocatalysts that can be applied in flow systems. Whereas three‐dimensional (3D) printing techniques offer high‐throughput manufacturing capability, they are usually not compatible with the delicate nature of enzymes, which call for physiological processing parameters. We herein demonstrate the utility of thermostable enzymes in the generation of biocatalytic agarose‐based inks for a simple temperature‐controlled 3D printing process. As examples we utilized an esterase and an alcohol dehydrogenase from thermophilic organisms as well as a decarboxylase that was thermostabilized by directed protein evolution. We used the resulting 3D‐printed parts for a continuous, two‐step sequential biotransformation in a fluidic setup.     

Curcumin‐loaded biodegradable polyurethane scaffolds modified with gelatin using 3D printing technology for cartilage tissue engineering

We described the curcumin‐loaded biodegradable polyurethane (PU) scaffolds modified with gelatin based on three‐dimensional (3D) printing technology for potential application of cartilage regeneration. The printing solution of poly(ε‐caprolactone) (PCL) triol (polyol) and hexamethylene diisocyanate (HMDI) in 2,2,2‐trifluoroethanol was printed through a nozzle in dimethyl sulfoxide phase with or without gelatin. The weight ratio of HMDI against PCL triol was varied as 3, 5, and 7 in order to evaluate its effect on the mechanical properties and biodegradation rate. A higher ratio of HMDI resulted in higher mechanical properties and a lower biodegradation rate. The use of gelatin increased the mechanical properties, biodegradation rate, and curcumin release due to the surface cross‐linking, nanoporous structure, and surface hydrophilicity of the scaffolds. In vitro study revealed that the released curcumin enhanced the proliferation and differentiation of chondrocyte. The 3D‐printed biodegradable PU scaffold modified with gelatin should thus be considered as a potential candidate for cartilage regeneration.     

Three‐Dimensional Printing with Biomass‐Derived PEF for Carbon‐Neutral Manufacturing

Biomass‐derived poly(ethylene‐2,5‐furandicarboxylate) (PEF) has been used for fused deposition modeling (FDM) 3D printing. A complete cycle from cellulose to the printed object has been performed. The printed PEF objects created in the present study show higher chemical resistance than objects printed with commonly available materials (acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), glycol‐modified poly(ethylene terephthalate) (PETG)). The studied PEF polymer has shown key advantages for 3D printing: optimal adhesion, thermoplasticity, lack of delamination and low heat shrinkage. The high thermal stability of PEF and relatively low temperature that is necessary for extrusion are optimal for recycling printed objects and minimizing waste. Several successive cycles of 3D printing and recycling were successfully shown. The suggested approach for extending additive manufacturing to carbon‐neutral materials opens a new direction in the field of sustainable development.     

A Stereolithography‐Based 3D Printed Hybrid Scaffold for In Situ Cartilage Defect Repair

Damage to articular cartilage can over time cause degeneration to the tissue surrounding the injury. To address this problem, scaffolds that prevent degeneration and promote neotissue growth are needed. A new hybrid scaffold that combines a stereolithography‐based 3D printed support structure with an injectable and photopolymerizable hydrogel for delivering cells to treat focal chondral defects is introduced. In this proof of concept study, the ability to a) infill the support structure with an injectable hydrogel precursor solution, b) incorporate cartilage cells during infilling using a degradable hydrogel that promotes neotissue deposition, and c) minimize damage to the surrounding cartilage when the hybrid scaffold is placed in situ in a focal chondral defect in an osteochondral plug that is cultured under mechanical loading is demonstrated. With the ability to independently control the properties of the structure and the injectable hydrogel, this hybrid scaffold approach holds promise for treating chondral defects.     

Study on the Influence of Melt Processing on Segmented Polyurethanes Morphology

A study on thermoplastic polyurethanes (TPU) is described. The investigation focuses on morphology of TPU parts depending on processing conditions and its relation with mechanical and thermal properties. It was found that TPU materials present different crystalline structures depending on chemical composition and melt processing conditions during part manufacturing. Due to that fact, strong variations in mechanical and tribological properties are expected.     

Scanning Electrochemical Microscopy (SECM) Investigation of 3D Printed Parts Produced by CMT Welding Technology

In the field of manufacturing technology an exciting revolution is in progress today. The different methods of the so called additive manufacturing (AM) technologies are under fast developments. Several versions of them are called 3D printing. Less interest has been given to study the corrosion resistance character of the differently made 3D printed metal alloy items. In this work corrosion behaviour of 3D printed AlMg4.5Mn0.7 alloy samples were investigated. Conventional methods like open circuit potential measurements, Tafel plots taking and scanning electrochemical microscopy (SECM) – with pH measuring tungsten micro‐tip and micro‐disc type Pt electrode were used. The metal samples were embedded in epoxy resin. 2D SECM images and line scans were made to see the local changes of oxygen concentration. Flame atomic absorption spectroscopy was used for measuring the metal composition of manufacturing wire and printed sample. The local activity of the surface spots were measured using approach curves recorded in case of ferrocene methanol mediator.