Polymer-based Structures Research Articles

DESIGN A SINGLE SCREW EXTRUDER FOR POLYMER-BASED TISSUE ENGINEERING

In the area of tissue engineering, single screw extrusion (SSE) has gained attention due to its versatility and efficiency in fabricating polymer-based scaffolds. Furthermore, advancements such as the implementation of extrusion techniques and the integration of bioactive agents have significantly expanded the capabilities of SSE. This study aims to investigate the configuration of a custom-designed plastic extrusion for tissue engineering, highlighting its potential in fabricating suture technology for various regenerative biomedical applications. Furthermore, the challenges and future perspectives in SSE technology are discussed, with a focus on the need for additional research to optimize processing parameters, enhance structure bioactivity, and facilitate clinical usage. SSE provides precise regulation of structure morphology, mechanical properties, and porosity, which are critical factors that influence cell behavior and tissue regeneration. Overall, SSE holds great promise as a scalable and cost-effective manufacturing technique for producing polymer-based structures with tailored properties, advancing the field of tissue engineering towards effective clinical solutions. The paper provides a comprehensive overview of a filament extruder production machine that is capable of manufacturing high-quality filament sutures (FS) using thermoplastic materials, specifically bio-protein derived from human serum albumin. The main focus of the paper is to explain the design and operation principles of the filament extruder. The extruder is equipped with a die that can measure a range starting from 2.5 mm and going down to smaller scales. This allows for the extrusion of filaments with a diameter as small as 1.75 mm. Although the design of the extrusion apparatus closely resembles that of commercially available machines, the focus here is on its adaptability and cost-effectiveness for laboratory-scale production. Overall, the research contributes to advancing the understanding of extrusion processing technologies in the context of biomedical applications, with a specific focus on utilizing human serum albumin-derived thermoplastics for manufacturing FS.

Progress toward the Definition of X-ray Computed Tomography Accuracy in the Characterization of Polymer-Based Lattice Structures.

Lattice structures have become an innovative solution for the improvement of part design, as they are able to substitute solid regions, maintain mechanical capabilities, and reduce material usage; however, dimensional quality control of these geometries is challenging. X-ray computed tomography (XCT) is the most suitable non-destructive metrological technique as it is capable of characterizing internal features and hidden elements. Uncertainty estimation of XCT is still in development, and studies typically use high-resolution calibrated devices such as focal variation microscopes (FVMs) as a reference, focusing on certain parts of the lattice but not the whole structure. In this paper, an estimation of the accuracy of XCT evaluation of a complete lattice structure in comparison to a higher-resolution reference device (FVM) is presented. Experimental measurements are taken on ad hoc designed test objects manufactured in polyamide 12 (PA12) using selective laser sintering (SLS), optimized for the evaluation on both instruments using different cubic-based lattice typologies. The results confirm higher precision on XCT evaluation in both qualitative and quantitative analysis. Even with a lower resolution, XCT is able to characterize details of the surface such as re-entrant features; as well, standard deviations and uncertainties in strut diameter evaluation remain more stable in all cells in XCT, identifying on the other hand reconstruction problems on FVM measurements. Moreover, it is shown that, using XCT, no additional evaluation errors were found in inner cells, suggesting that the measurement of external elements could be representative of the whole structure for metrological purposes.

Low-velocity impact performance of 3D-printed PLA/Epoxy/Glass fibers of composite structures and latches

The integration of 3D printing into the synthesis process of polymeric composite structures can offer significant advantages in producing geometrically complex parts. Moreover, engineering components may be subjected to impact loads that can adversely affect their performance and, in some cases, lead to failure. Traditionally, fiber-reinforced composite structures have demonstrated improved responses to applied mechanical loads. In this study, we designed multi-material polymer-based composite structures to enhance structural responses to impact loads. Employing fused filament fabrication (FFF) and solution casting methods, we manufactured PLA lattice infilled with epoxy/Milled Glass Fibers (MGFs) of composite structures with varied MGFs content ranging from 0 to 7.5 vol%. The research provides a comprehensive analysis of the impact behavior of glass-fiber reinforced composite structures, specifically focusing on PLA lattice frames filled with epoxy resin and varying levels of MGFs. Through low-velocity impact tests, the study assesses key parameters such as peak force, peak absorbed energy, residual velocity, and displacement, providing insights into the materials' response to impact loading conditions. The findings highlight the effect of MGF reinforcement on enhancing the impact toughness and resistance to crack propagation, with higher MGF content leading to improved mechanical properties. The microstructural analysis demonstrates the morphology and interface bonding of the composite materials, elucidating the mechanisms. Finally, latches were designed, and their impact behavior was tested to examine the usability of the composite structure in real-life components. The results suggest that the incorporation of MGFs in 3D-printed composite latches significantly enhances their impact resistance, with potential implications for various engineering applications.

EVALUATING THE PLA AGING EFFECTS ON THE MECHANICAL PERFORMANCE OF 3D-PRINTED COMPONENTS

The aging influence on the mechanical performance of bio-degradable polymers holds significant importance in additive manufacturing, particularly in structural applications. Understanding the changes in mechanical properties over time is crucial for ensuring the long-term sustainability and reliability of polymer-based structures. Thus, this study aims to comprehensively evaluate the effects of aging on polylactic acid (PLA) by analyzing its failure mechanisms of 3D-printed samples subjected to compression load. To achieve this goal, specimens of PLA were exposed to natural environmental conditions for varying periods. Subsequently, the mechanical characteristics of the additively produced component were assessed after each exposure, providing valuable insights into its performance at different stages of aging. By quantifying the material’s ability to withstand applied forces, the study enables the prediction of its long-term structural integrity. In addition, the investigation of failure mechanisms aids in understanding the modes of failure that PLA may undergo as it ages. This knowledge is essential for developing strategies to prevent structural failures and enhance the overall reliability of PLA-based applications. The findings contribute to advancing the field of additive manufacturing, enabling PLA’s sustainable and reliable application in various industries.

EVALUATING THE PLA AGING EFFECTS ON THE MECHANICAL PERFORMANCE OF 3D-PRINTED COMPONENTS

The aging influence on the mechanical performance of bio-degradable polymers holds significant importance in additive manufacturing, particularly in structural applications. Understanding the changes in mechanical properties over time is crucial for ensuring the long-term sustainability and reliability of polymer-based structures. Thus, this study aims to comprehensively evaluate the effects of aging on polylactic acid (PLA) by analyzing its failure mechanisms of 3D-printed samples subjected to compression load. To achieve this goal, specimens of PLA were exposed to natural environmental conditions for varying periods. Subsequently, the mechanical characteristics of the additively produced component were assessed after each exposure, providing valuable insights into its performance at different stages of aging. By quantifying the material’s ability to withstand applied forces, the study enables the prediction of its long-term structural integrity. In addition, the investigation of failure mechanisms aids in understanding the modes of failure that PLA may undergo as it ages. This knowledge is essential for developing strategies to prevent structural failures and enhance the overall reliability of PLA-based applications. The findings contribute to advancing the field of additive manufacturing, enabling PLA’s sustainable and reliable application in various industries.

Experimental investigation of pressure drop and heat transfer in porous media based on 3D printed triple periodic minimum surfaces

ABSTRACT Porous media are widely preferred for heat transfer applications because of complex structure and high porosity. It is relatively easy to produce complex structures with the additive manufacturing method. In this study, Gyroid-based triple periodic minimal surface is produced ABS (Acrylonitrile butadiene styrene) and PLA (polylactic acid) materials using 3D printers. The pressure drops and heat transfer in the porous structure with the gyroid model are investigated experimentally. Permeability and Forchheimer coefficients are determined for each gyroid porous channel. While the permeability and Forchheimer coefficient of the porous medium of PLA were calculated as 2.97 × 10−8 m2 and 0.07, respectively, the permeability and Forchheimer coefficient of the porous medium of ABS were calculated as 5.52 × 10−8 m2 and 0.09. The correlation between the Reynolds number and pressure drop per length is given. The gyroid structure-filled channel is heated by an asymmetric heat flux on the bottom side. The convection heat transfer in polymer-based porous media was investigated. Also, the correlation between the Nusselt number and the Reynolds number based on permeability is presented. While the Nusselt correlation of the PLA porous medium was obtained as N u K = 0.08 R e K 0.57 , the Nusselt correlation of the ABS porous medium was found to be N u K = 0.09 R e K 0.61 . There are improvements in heat transfer due to the flow mixing effect of the porous medium. The study aims to broaden the current knowledge of heat transfer in polymer porous structures. Especially, this study investigates heat transfer and flow in polymer-based porous structures with a low thermal conductivity coefficient produced by 3D printers.

Cyclodextrin-based nanosponges as promising carriers for active pharmaceutical ingredient.

Effective drug distribution at the intended or particular location is a critical issue that researchers are now dealing. Nanosponges have significantly increased in importance in medication delivery using nanotechnology in recent years. An important step toward solving these problems has been the development of nanosponges. Recently created and proposed for use in drug delivery, nanosponge is a unique type of hyper-crosslinked polymer-based colloidal structures made up of solid nanoparticles with colloidal carriers. Nanosponges are solid porous particles that may hold pharmaceuticals and other actives in their nanocavities. They can be made into dosage forms for oral, parenteral, topical, or inhalation use. The targeted distribution of drugs in a regulated manner is greatly aided by nanosponge. The utilization of nanosponges, their benefits, their production processes, the polymers they are made of, and their characterization have all been covered in this review article.

Polymer-Based Self-Assembled Drug Delivery Systems for Glaucoma Treatment: Design Strategies and Recent Advances.

Glaucoma has become the world's leading cause of irreversible blindness, and one of its main characteristics is high intraocular pressure. Currently, the non-surgical drug treatment scheme to reduce intraocular pressure is a priority method for glaucoma treatment. However, the complex and special structure of the eye poses significant challenges to the treatment effect and safety adherence of this drug treatment approach. To address these challenges, the application of polymer-based self-assembled drug delivery systems in glaucoma treatment has emerged. This review focuses on the utilization of polymer-based self-assembled structures or materials as important functional and intelligent carriers for drug delivery in glaucoma treatment. Various drug delivery systems, such as eye drops, hydrogels, and contact lenses, are discussed. Additionally, the review primarily summarizes the design strategies and methods used to enhance the treatment effect and safety compliance of these polymer-based drug delivery systems. Finally, the discussion delves into the new challenges and prospects of employing polymer-based self-assembled drug delivery systems for the treatment of glaucoma.

Mechanical characterisation and crashworthiness performance of additively manufactured polymer-based honeycomb structures under in-plane quasi-static loading

ABSTRACT Additive manufacturing technology is suitable for producing energy-absorbing devices with tunable mechanical properties and improved crashworthiness performance. In this study, the mechanical properties and macrostructural crushing behaviour of five additively manufactured polymer-based honeycomb structures (HS) are investigated. Subjected to in-plane loading, the experimental results of the HS are compared with numerical findings and theoretical predictions. Results indicate that deformation modes and overall crushing performance are influenced by utilising different parent materials. The polymer HS made from polyethylene terephthalate glycol gives the best overall crushing performance over the other polymers and polymer-fibre reinforcement HS. However, the crush force efficiency of HS made from polylactic acid is the least promising. The polymer-fibre reinforced HS outperforms some of the pure polymer-based ones in terms of specific energy absorption and shows a characteristic lightweight advantage. Hence, spotting it as a promising energy absorber utilised for crashworthiness application especially where ultra-lightweight property is highly desired.

Development of high-reflectivity polymer/air-Bragg micromirror structures for nanophotonic applications

We report the design, nanofabrication, and characterization of high-quality polymer-based micromirror structures employing the 3D two-photon polymerization lithography technique. Compared to conventional microcavity approaches, our innovative concept provides microstructures, which allow fast prototyping. Moreover, our polymer-based mirrors are cost effective and environmentally sensitive, as well as compatible with a wide range of wavelengths from near-infrared to the telecom C-band. We demonstrate polymer/air distributed Bragg reflectors and full microcavity structures with up to 14 mirror pairs with a target wavelength of 1550 nm and a reflectivity close to 99%. Additionally, our 3D printed micromirrors are reproducible and mechanically stable, and enable hybrid nanophotonic devices based on quantum dots, molecules, or 2D quantum materials as the active medium.

Influence of wall thickness on mechanical properties and porosity of additive manufactured polymer-based porous structures for fibula bone regeneration

In the recent past, Bone tissue engineering (BTE) has become a potentially effective solution for repairing bone defects. In the meantime, various fields, such as material science, additive manufacturing, and clinical medicine, are interlinked in the fast-emerging field of bone tissue engineering. Additive Manufacturing (AM) is a unique technology that accumulates content rather than waste materials in the form of chips. AM techniques like selective laser sintering (SLS), commonly used to create complex polymer structures, allow for the direct fabrication of complex structural implant components for use in BTE. However, the wall thickness of the product limits the SLS systems. In detail, research into the influence of wall thickness on mechanical properties and scaffold porosity is required to develop such lightweight and complex structures. In this study, Polyamide12-based bone Scaffolds were fabricated using the SLS technique by varying the wall thickness ranging from 0.9 mm to 1.10 mm in steps of 0.05 mm. Compression tests, porosity, scanning electron microscopy, and differential scanning calorimetry were conducted on the fabricated specimens. The studies demonstrated that the higher wall thickness benefits in reduction of porosity. The sample fabricated with a wall thickness of 1.1 mm has about 76% less porosity than the sample fabricated with a wall thickness of 0.9 mm. In addition, the study also found that compression strength decreases as porosity increases. The compressive strength of the scaffolds has been measured to be between 45.62 and 90.67 MPa for a wall thickness between 0.90 and 1.10 mm. The maximum compressive strength of a porous polyamide specimen is 90.67 MPa at a wall thickness of 1.10 mm. The fabricated samples with wall thicknesses of 0.9 and 0.95 mm were not mechanically stable, as their compressive strength values were lower than the compressive strength of human fibula bone (68 N/mm2).

A nonlinear and rate-dependent fracture phase field framework for multiple cracking of polymer

Designing durable polymer-based materials and structures requires understanding how the physical processes and failure mechanisms associated with moisture intrusion and loading rate combine to produce the complex damage modes observed in their applications. While numerous experiments have assisted us in gaining general insight into the above issues, in-situ characterization is still lacking, and rational prediction on the failure procedure of polymer in the moisture–mechanical​ coupling environment remains challenging. Here we present a thermodynamically consistent theoretical framework and its computational implementation to reveal how the dependence of epoxy’s mechanical behavior on rate- and moisture dictates the initiation and evolution of highly localized deformation zones and cracks. A multi-physical hydrothermal-viscoelastic–viscoplastic-damage model is first proposed to fully couple the effects of strain rate, moisture degradation, strain softening, and adiabatic heating of the bulk epoxy in a highly humid environment. The constitutive models are augmented by a phase field that enables spontaneous tracing of the nucleation and growth of cracks under a wide range of strain rates (from 4.60 × 10−5/s to 3.80 × 103/s). The theoretical model is implemented into an efficient computational procedure that is used to calculate illustrative examples to demonstrate the influence of the intimate coupling between the multi-physical phenomena. The results highlight significant mechanisms underlying the coupled damage process, including: heat accumulation along the crack propagation path; identification of the energies associated with moisture-induced toughening; prediction of crack deflection in the presence of moisture absorption; and illustration that a portion of the plastic work plays a dominant role in the nucleation of cracks at a wide scale of strain rates.

High-fidelity simulation model for moisture-induced deformation of CFRP structure considering anisotropic nonlinear moisture absorption-desorption characteristics

This study developed a high-fidelity simulation model for predicting moisture-induced deformation of polymer-based composite structures. First, to identify the anisotropic moisture diffusion in unidirectional carbon fiber/epoxy composites, coupon-level tests were conducted for each principal material direction (i.e., fiber-parallel, in-plane transverse, and out-of-plane transverse directions). In addition, the moisture-induced strain in the fiber and the transverse directions of unidirectional composites was evaluated using an optical fiber sensor. Nonlinear strain against moisture content was identified in each direction. Next, the strain history in the tube element for the metering truss structure was monitored using an optical fiber sensor during the moisture absorption-desorption cycle. Finally, a prediction of the strain behavior was provided using a finite element analysis (FEA) model. The model accurately reflected the complex moisture absorption-desorption characteristics (e.g., directional dependence, nonlinearity, and irreversibility) obtained from the coupon tests. The prediction was compared with the monitoring data and agreed with the experiment.

Hierarchically Structured Hybrid Membranes for Continuous Wastewater Treatment via the Integration of Adsorption and Membrane Ultrafiltration Mechanisms

Growing environmental concerns are stimulating researchers to develop more and more efficient materials for environmental remediation. Among them, polymer-based hierarchical structures, attained by properly combining certain starting components and processing techniques, represent an emerging trend in materials science and technology. In this work, graphene oxide (GO) and/or carbon nanotubes (CNTs) were integrated at different loading levels into poly (vinyl fluoride-co-hexafluoropropylene) (PVDF-co-HFP) and then electrospun to construct mats capable of treating water that is contaminated by methylene blue (MB). The materials, fully characterized from a morphological, physicochemical, and mechanical point of view, were proved to serve as membranes for vacuum-assisted dead-end membrane processes, relying on the synergy of two mechanisms, namely, pore sieving and adsorption. In particular, the nanocomposites containing 2 wt % of GO and CNTs gave the best performance, showing high flux (800 L × m-2 h-1) and excellent rejection (99%) and flux recovery ratios (93.3%), along with antifouling properties (irreversible and reversible fouling below 6% and 25%, respectively), and reusability. These outstanding outcomes were ascribed to the particular microstructure employed, which endowed polymeric membranes with high roughness, wettability, and mechanical robustness, these capabilities being imparted by the peculiar self-assembled network of GO and CNTs.

Effect of lattice design on mechanical response of PolyJet additively manufactured cellular structures

Additively manufactured complex lattice geometries incorporated in structural materials is a relatively new concept and gaining popularity. In this approach solid bodies are replaced by repeating tailored design cellular structures enabling significantly light-weighted components. However, as a building block of the entire part, these cellular structures' design has crucial role on the overall mechanical properties. The purpose of this work is to reveal how different design parameters (3 different cell types representative of stiff, just stiff and under stiff cases, and cell size) affect the modulus of elasticity and the maximum stress of the compression test samples additively manufactured in cellular fashion. A comprehensive methodology is presented for the design, fabrication, and prediction of mechanical properties of polymer-based lattice structures. A commercial material jetting based 3D printer (i.e., the Objet 30 Prime by Stratasys) was used to manufacture the rigid translucent photosensitive polymer samples with porosity ranging from 54 to 70% and different unit cell structures. Uniquely designed or existing unit cells were used to obtain stretch and bending dominated mechanical behaviors. The failure mechanisms and the performance of the custom design unit cell specimens are investigated via numerical simulation and compression tests. The elastic modulus of cellular structures was calculated and compared using both Gibson-Ashby and Hooke equations. The effect of the unit cell structure and size on mechanical properties is discussed. The results show that while stretch dominated diagonal model shows better strength properties (up to 250%), bending dominated centered model has better elongation (up to 120%). As a general conclusion, it is seen that mechanical properties are enhanced with downsizing of the cell scales. Fine tuning of the unit cells gives a new perspective on tailored lattice structures, enabling structures with stiff or rubber-like behavior to be obtained using the same material.

BEDYN: development of a methodology to characterize the behaviour of composite structures under dynamic loading

The methodology of design of polymer-based composite structures under static loadings, and even fatigue loads, is quite mature and well stablished. However, for intermediate and high dynamic loading conditions, the methods are still under development and often limited to academic research levels, without any type of standardization. It is crucial to understand how the materials used in the aerospace sector behave under dynamic loadings. Composite materials may exhibit strain rate effects and the analysis tools based on static formulations could be far away from the actual material and structural response, therefore robust and industrial dedicated dynamic tests, analysis and modelling methods are then necessary to design and certify composite airframe structures. This is what the proposed project will deal with. The aim of BEDYN project is to address a methodology to properly characterize the dynamic behaviour up to rupture of thermoset polymer-based composite structures submitted to dynamic loading. BEDYN is a European granted Clean Sky 2 Joint Undertaking (JU). 

Guided fractures in graphene mechanical diode-like structures.

The concept of a diode is usually applied to electronic and thermal devices but very rarely for mechanical ones. A recently proposed fracture rectification effect in polymer-based structures with triangular void defects has motivated us to test these ideas at the nanoscale using graphene membranes. Using fully-atomistic reactive molecular dynamics simulations we showed that robust rectification-like effects exist. The fracture can be 'guided' to more easily propagate along one specific direction than its opposite. We also observed that there is an optimal value for the spacing between each void for the rectification effect.

Correction to: HVOF-Sprayed AlSi50 Alloy Coatings as a Novel Electrothermal Anti-icing/De-icing System for Polymer-based Composite Structures

Correction to: HVOF-Sprayed AlSi50 Alloy Coatings as a Novel Electrothermal Anti-icing/De-icing System for Polymer-based Composite Structures

Tunable Omnidirectional Antireflection Coatings Inspired by Inclined Irregular Nanostructures on Transparent Blue-Tailed Forest Hawk Dragonfly Wings.

Randomly arranged inclined irregular nanostructure-covered blue-tailed forest hawk dragonfly wings are highly transparent for wide viewing angles. Inspired by the dragonfly wings, monolayer silica colloids are self-assembled on shape memory polymer-coated substrates and utilized as plasma etching masks to pattern disorderly arranged inclined irregular conical structures. The structures build gradual refractive index transitions at various angles of incidences, resulting in omnidirectional antireflection performance over the whole visible wavelength region. In comparison with a bare substrate, the optimized structure-covered substrate presents 10% higher optical transmission at 0° and even 41% higher optical transmission at an angle of incidence of 75°. Importantly, by manipulating the structural configuration of the shape memory polymer-based structures, the corresponding antireflection characteristics can be instantaneously and reversibly eliminated and recovered after drying out of common household liquids or applying contact pressures in ambient environments. The tunable omnidirectional antireflection coatings are prospective candidates for realizing optical modulation, which exhibits an enormous application value in smart windows, intelligent display screens, optical components, and novel optoelectronic devices.

HVOF-Sprayed AlSi50 Alloy Coatings as a Novel Electrothermal Anti-icing/De-icing System for Polymer-based Composite Structures

HVOF-Sprayed AlSi50 Alloy Coatings as a Novel Electrothermal Anti-icing/De-icing System for Polymer-based Composite Structures