Fig 7 - uploaded by Mehrshad Mehrpouya
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Schematic overview of the 4D printing process of an origami pyramid; First, a conventional 3D printer fabricates a flat (origami) structure using SMP. Then an exposure to an external stimulus (like light or temperature) activates the smart materials and modifies the shape or function (in this case a pyramid shape).
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Additive manufacturing has attracted much attention in the last decade as a principal growing sector of complex manufacturing. Precise layer-by-layer patterning of materials gives rise to novel designs and fabrication strategies that were previously not possible to realize with conventional techniques. Using suitable materials and organized variati...
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... materials must have unique characteristics that make them responsive to external stimuli. Such responsiveness can enable printed devices to be activated with specialized functions after the fabrication process. As 3D printing has been applied to SMPs, these materials can now be fabricated in complicated 2D and 3D shapes, as exemplified in Fig. 7, supporting novel transformations -and associated applications -upon being exposed to external impulses. 3D printers with multiple extruders support even more unique applications by fabricating parts that interlace SMPs with other ...
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... bending. The future success of 4D printing will depend critically on the continued development of tools for precisely modeling responses of printed objects to external stimuli [160]. Besides, creativity in designs will help to develop a new generation of smart products with a diverse range of applications in various fields and industrial domains. Fig. 17 represents the potential and future applications of the 4D printing technology of PLA ...
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Additive manufacturing has been of increasing interest to the construction industry for the last ten years. The subject of the research is the printing of concrete, metals, and plastics. In their analysis and research, authors have focused on printing plastics. 3D printing of reinforcement of concrete elements made of plastics can significantly imp...
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... T g is considered an important parameter along with T d and T r , as it governs the shape memory properties [16][17][18], and it has been observed that the presence of color pigments can affect the mechanical properties and dimensional accuracy of 3D prints by altering T g [19]. Therefore, it was of interest to investigate the impact of this factor on 4D-printed parts' forms and dimensional properties, as no such study has been conducted so far. ...
This study investigates the impact of material and process parameters-specifically, filament color, infill density, and pattern-on the dimensional accuracy of 4D-printed polylactic acid (PLA) objects featuring holes of varying diameters (6, 8, and 10 mm) that undergo a heat-induced recovery process. The objective was to understand how these factors affect shape retention and the dimensional accuracy of holes through a comparative analysis of the diameters before and after recovery. Increased variability in the hole diameters was noted after recovery, regardless of the values of the independent variables. The objects did not fully return to their original planar shape, and the holes did not completely return to their circular form, resulting in smaller diameters for each sample. No significant differences in the hole diameters could be determined. Additionally, there was no consistent trend in identifying the most influential parameter affecting the accuracy of the recovered holes. However, it was observed that higher infill densities improved shape retention. A quasi-static finite elements analysis model was developed to capture the mechanical behavior of the 4D-printed parts. This model incorporated temperature-dependent material characteristics to predict the strain occurring near the holes. Nodal displacements were defined according to the deformed shape. A correlation was established between the observed strains and the post-recovery dimensional accuracy of the specimens. The importance of this work was demonstrated through a case study involving a two-sieve filtering device for small objects.
... This semi-crystalline thermoplastic polyester is derived from biodegradable and renewable energy sources [12]. Notably, PLA exhibits a shape memory property, coupled with outstanding mechanical strength, including high strength and modulus [13]. Nevertheless, PLA has a characteristic brittleness attributed to its slow crystallization and relatively high Young's modulus. ...
... PLA was one of the most studied thermoplastics in the TPV systems, which is due to the fact that it is biodegradable and bioresorbable with a high elastic modulus [19,20]. However, its brittle nature limits its application in large scale [21] while numerous strategies were devised to improve its toughness [22]. Rubbers are used as impact modifiers for the rigid PLA matrix; however, these two polymers lack phase compatibility, which directly affect their final properties [23,24]. ...
Polylactic acid (PLA) is the main candidate among the synthetic polymers for food packaging application. However, its poor processing and mechanical performance have limited its practical application. Here, we prepared a supertough thermoplastic vulcanizate (TPV) using PLA and ethylene vinyl acetate (EVA) copolymer with optimized EVA composition. The dynamic curing agent, dicumyl peroxide (DCP), was used as EVA-DCP masterbatch to improve its curing efficiency. Cellulose nanocrystals (CNCs) were further used as the biocompatible and renewable nanofiller, used in the form of PLA-CNC masterbatch, leading to improved mechanical strength and shape memory performance (SMP). Dynamically curing the thermoplastic elastomer (TPE) precursors diminished the temperature-dependency of elastic modulus (E′\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$E^{\prime}$$\end{document}) prior to PLA’s glass transition. Thus, improving the shape fixity (FR) of the TPVs compared to their TPEs as the TPVs showed FR>98%\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$FR>98\%$$\end{document} while the TPV60 (60% PLA) showed the highest FR of 100%. The TPVs showed higher recovery ratio (RR) with RR>87.25%\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$RR>87.25\%$$\end{document} with the TPV60 containing 1.5% CNC, which showed the highest RR of 94.1%. The mechanical performance analyses showed that the optimized TPV: CNC possesses a supertough nature, achieved by tuning the rheological behavior and morphology of the final TPVs. The results were quite promising for smart food packaging applications.
... Smart materials in 4D printing adapt their properties or shapes in response to external stimuli. These materials can also harness energy, typically thermal, to perform mechanical tasks [17]. 4D printing technologies have facilitated scientific exploration into material research, stimulus responsiveness, mathematical modeling, and the subsequent development of intelligent structures. ...
In this paper thermo-mechanical behavior of 4D printed Polylactic Acid (PLA) was investigated, focusing on its response to varying strain rates and temperatures below the glass transition temperature. Dynamic mechanical analysis and uniaxial tensile tests confirmed PLA's dependency on strain rate, showcasing its sensitivity to external stimuli. Stress-strain curves exhibited typical thermoplastic behavior, with yield stresses varying with strain rates, underscoring PLA's responsiveness to different deformation speeds. Clear strain rate dependence was observed, particularly at quasi-static rates, with temperature and strain rate fluctuations significantly influencing PLA's mechanical properties, including yield stress and deformation behavior. Isothermal compression tests demonstrated predictable stress-strain curves with distinct yield points, while adiabatic tests reveal additional complexities such as heat accumulation leading to further softening. Thermal imaging revealed temperature increase during deformation, highlighting the material's thermo-sensitive nature. These findings provide the basis for future research with the focus on advanced modeling techniques and mitigation strategies for self-heating effects, aiming to enhance PLA-based product reliability and performance in applications with deformations at higher strain rates, while also developing models to simulate shape recovery in 4D printed PLA structures at both cold and hot programming temperatures.
... There are various methods to enhance the properties of PLA, including mixing it with different materials [71]. It has been found that in PLA/poly(εcaprolactone) (PCL) blends, the homogeneous distribution of components in the composite indicates the microphase separation phenomena, indicating that PLA and PCL are immiscible [72]. ...
Four-dimensional (4D) printing has recently received much attention in the field of smart materials. It concerns using additive manufacturing to obtain geometries that can change shape under the effect of different stimuli. Such a technique enables the fabrication of 3D printed parts with the additional functionality of scalable, programmable, and controllable part shapes over time.
This review provides a comprehensive examination of advances in the field of 4D printing, emphasizing the integration of fiber reinforcement and auxetic structures as crucial building blocks.
The incorporation of fibers enhances structural integrity, while auxetic design principles contribute unique mechanical properties, such as negative Poisson's ratio and great potential for energy absorption due to their specific deformation mechanisms. Therefore, they present potential applications in aerospace, drones, and robotics.
The objective of this review article is first to describe the distinctive properties of shape memory polymers (SMPs), auxetic structures, and composite (fiber-reinforced) materials. A review of applications that use combinations of such materials is also presented when appropriate. The goal is to get a grip on the delicate balance between the different properties achievable in each case. The paper concludes by describing recent advances in 4D printing of fiber-reinforced auxetic structures.
... Lactic acid is an organic acid found in nature. Lactic acid can be produced through either chemical synthesis or fermentation of carbohydrates such as sugars such as sugar beets, corn, rice, wheat, sugar cane and sweet corn (Mehta et al. 2005;Zhou et al. 2021;Mehrpouya et al. 2021) (Rajan et al. 2014). The synthesis of lactic acid-based polymers can occur through two main pathways, polycondensation or ring-opening polymerization (ROP) (Södergård and Stolt 2002;Rajan et al. 2014). ...
... PLA and poly(lactide) are bio-based and biodegradable polymers that belong to the aliphatic polyester group. Polycondensation of lactic acid yields a low molecular weight polymer (PLA), with relatively poor mechanical properties (Södergård and Stolt 2002;Mehrpouya et al. 2021). Additionally, polycondensation requires relatively long polymerization times (more than 30 h) and requires that the water formed as a by-product be removed to avoid the reduction in the polymer molecular weight (Mehrpouya et al. 2021). ...
... Polycondensation of lactic acid yields a low molecular weight polymer (PLA), with relatively poor mechanical properties (Södergård and Stolt 2002;Mehrpouya et al. 2021). Additionally, polycondensation requires relatively long polymerization times (more than 30 h) and requires that the water formed as a by-product be removed to avoid the reduction in the polymer molecular weight (Mehrpouya et al. 2021). ...
Global environmental concerns have recently accelerated interest in the usage of biodegradable polymers to replace petroleum-based conventional plastics. Lactic acid-based polymers are some of the most promising and widely studied biobased materials, which are suitable for packaging and biomedical applications. This is mainly due to their appealing characteristics such as relatively good mechanical properties, biocompatibility, and multiple end-of-life options such as recyclability and biodegradability in industrial composting conditions. However, the use of lactic acid-based polymers in advanced applications is constrained by their inherent brittleness, poor melt strength, and relatively high cost. These disadvantages can be remedied by reinforcement with cellulose nanomaterials which can enhance their mechanical properties while maintaining their biodegradability. This review provides an overview of recent studies on the development of biodegradable lactic acid-based polymer composites and nanocomposites reinforced with cellulose nanofibrils (CNFs), cellulose nanocrystals (CNCs) and microcrystalline cellulose (MCC). The different processing methods and chemical modification techniques utilised on modification and functionalisation of cellulosic nanomaterials for improving the properties of lactic acid-based polymer nanocomposites are also discussed.
... Another common point of PLA and PEG polymers is that they exhibit shape memory polymer properties. Shape memory polymers (SMPs) can deform from an initial shape to a temporarily retained shape until shape recovery is triggered by an external stimulus, these external stimuli vary according to the polymer type (external stimuli can be pressure, temperature, pH) (Julich-Gruner et al. 2013;Liang et al. 2021;Mehrpouya et al. 2021;Pandey et al. 2022;Pilate et al. 2016). The shape memory effect in polymers was first discovered in 1953 (Senatov et al. 2016). ...
Composite films with Ag nanoparticles, which are active in biological applications such as biosensors, wound healing and cancer treatment, have been obtained in recent years on a blend consisting of polylactic acid and polyethylene glycol, which has the feature of working shape recovery. The characteristic signals of PLA and PEG were determined by making functional group analyses with attenuated total reflection infrared spectroscopy (ATR-IR) of polymer composite films obtained by the solution casting method. From the results of thermal analysis with thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), it can be interpreted that Ag nanoparticle increases the initial decomposition temperature (Ti) of the polymer blend, that is, increases its thermal stability. The use of a high PEG ratio showed that the droplets in the scanning electron microscopy (SEM) images of the blend were large, while it was observed that these droplets were almost filled with the increasing Ag nanoparticle ratio. The characteristic XRD diffraction angles of Ag nanoparticles were determined more clearly in the composite containing 20% Ag at 2θ = 38.1°, 44.5°, 64.6° and 77.3°. Finally, when the antimicrobial activities of the composites on L. Monocytogenes, C. perfringens, P. aeruginosa and E. coli O: 157 bacteria are examined, the antimicrobial activity with the highest Ag percentage proves the antimicrobial property of Ag.
... This can pose difficulties at the interface between cells and the material. 19 Nevertheless, to their distinctive characteristics, biopolymers and bio-based polymers are utilized in various industries (Fig. 3), including biomedical uses such as tissue science, drug release systems, and bioprinting to create living tissues and organs. Customized medical devices, sustainable products, food and nutrition solutions, drug delivery systems, and environmental applications are among the many other areas where bio-based polymers and 3D printing intersect. ...
... Customized medical devices, sustainable products, food and nutrition solutions, drug delivery systems, and environmental applications are among the many other areas where bio-based polymers and 3D printing intersect. 19 Therefore, a variety of biopolymers and bio-based polymeric materials has been employed in 3D printing machines to manufacture a wide range of products for various applications. However, priority should be given to designing 3D-printed products that are biodegradable and recyclable and converting plant-based polymers to replace current materials, supporting the establishment of a cyclic plastic ecosystem that produces no waste. ...
In the past ten years, there has been significant growth in the global 3D printing market, particularly in the development of natural and bio-based polymers. However, a major challenge is the limited availability of sustainable 3D printable resins capable of matching the performance of synthetic materials. This underscores the urgent need for the development of innovative and environmentally friendly resin materials. Herein, we introduce bio-based polymers, highlighting their recent advancements and offering a comprehensive overview of their diverse applications across various fields, including 3D printing. An area that has received less attention in this domain is polymers derived from vegetable oil (VO) or plant-based oil. Specifically, we thoroughly investigate the acrylation of epoxidized VOs and the subsequent formation of resins from these acrylates, which are essential materials for digital light processing (DLP), stereolithography (SLA), and extrusion-based 3D printing. The chemical modification of VOs, such as epoxidation and acrylation, is extensively explored, together with their respective types and applications. Furthermore, we delve deeply into the suitability of acrylate resins for 3D printing purposes. In conclusion, this review offers insights into the potential applications of 3D printed products utilizing materials derived from VOs.
... The hard segment is responsible for fixing the shape, while the soft segment is responsible for restoring it to its original state. There are various types of SMPs, such as segmented polyurethane [13], PLA [14], polystyrene-blockpoly(ethylene-co-butylene)-block-polystyrene (SEBS) [15], and ethylene-vinyl acetate (EVA) [16]. Combining thermoplastic polymers can result in the development of a customized SMP with tailored shape fixity and recovery ratios. ...
... [17]. PLA had better shape fixity and recovery in general [14,18]. Multilayer PCL (polycaprolactone)/ TPU was co-extruded. ...
Shape memory polymers (SMPs) are a new class of materials that have the ability to change their shape over time. The use of SMP in three-dimensional (3D) printing has resulted in the development of a new concept called four-dimensional (4D) printing. It is important to identify the main parameters affecting shape memory behavior in order to be utilized in new applications of SMP. In this study, polylactic acid (PLA) and thermoplastic polyurethane (TPU) were used as the main materials. A number of 3D printing parameters as well as the recovery temperature of the printed object have been investigated to explore how these factors affect shape memory behavior. For design of experiments (DOEs), the Box–Behnken method from response surface methodology (RSM) was used. RSM can be applied to model the effect of different parameters on the shape memory behavior to apply in the appropriate conditions. As part of the evaluation of the mechanical properties of the material, tensile tests were also performed. At higher layer heights, there was generally a decrease in the tensile modulus and strength of the material. Testing equipment was manufactured in order to conduct the testing. It was found that when the whole SMP was made of PLA, the fixity ratio increased. There was a significant correlation between the shape recovery ratio and the recovery temperature. Both shape fixity and recovery ratios were not significantly affected by layer height or infill angle, according to the analysis of variance (ANOVA). To determine the highest fixity and recovery ratios, an optimization was conducted. Using the optimized values, a sample was manufactured and compared with the values obtained from the RSM model.
... While 3D-printing produces static structures by adjusting the geometry and printing parameters, 4D-printing allows to control the final shape of an adaptable structure with programmable configuration, with the ability of materials to respond to external stimuli, such as light, humidity, heat, pH, or magnetic field, over time [4][5][6][7]. Various materials can be employed in 3D-printing; however, most of them cannot be applied to 4D-printing as these materials do not respond to external stimuli [5,8,9]. Shape memory polymers (SMP) were presented as a promising class of materials to reach the fourth dimension, as these materials exhibit an ability to recover from a temporary programmed shape to a permanent shape in response to an external stimulus [3,10]. ...
Morphing effect control is still a major challenge in 4D-printing of polylactic acid (PLA). In this work, the influence of extrusion-based 3D-printing parameters on PLA-based material morphing was studied. A design of experiments was performed, where 5 factors (printing temperature, bed temperature, printing speed, fan speed, and flow) were explored at 2 levels. Crystallinity and morphing properties of each 3D-printed structure were determined and discussed. The crystallinity rates of the PLA-based specimens ranged from ca. 14% up to ca. 71%. The interaction between bed temperature and printing speed showed a significant impact on PLA-based samples crystallinity, where using these two parameters at their higher levels contributed to producing PLA-based specimens with higher crystallinity. When exposed to an external thermal stimulus of 60 °C, all settings were capable of acquiring a temporary shape and recover between ca. 71% and ca. 99% of the original shape, depending on the configurations the recovery times ranged from 8 to 50 s. The configuration that resulted in the highest recovery rate was: printing temperature at 220 °C, bed temperature at 40 °C, printing speed at 80 mm/s, fan speed at 0%, and flow at 100%. Regarding recovery time, the configuration of 180 °C for printing temperature, 80 °C for bed temperature, 10 mm/s for printing speed, 100% for fan speed and 150% for flow resulted in the longest recovery time. Overall, the experimental results clearly showed that the parameters of extrusion-based 3D-printing influence the crystallinity and transformability of PLA-based materials.
