Materials

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13 pages, 3254 KiB

Open AccessArticle

3D Printed Cellulose-Based Filaments—Processing and Mechanical Properties

by Julia Utz, Jokin Zubizarreta, Nico Geis, Kirsi Immonen, Heli Kangas and Holger Ruckdäschel

Materials 2022, 15(19), 6582; https://doi.org/10.3390/ma15196582 - 22 Sep 2022

Cited by 4 | Viewed by 2053

Cellulose is an abundant and sustainable material that is receiving more and more attention in different industries. In the context of additive manufacturing, it would be even more valuable. However, there are some challenges to overcome in processing cellulose-based materials. Therefore, this study [...] Read more.

Cellulose is an abundant and sustainable material that is receiving more and more attention in different industries. In the context of additive manufacturing, it would be even more valuable. However, there are some challenges to overcome in processing cellulose-based materials. Therefore, this study used a new thermoplastic cellulose-based granulate to show its potential in filament extrusion and the fused filament fabrication printing process. Furthermore, the mechanical properties were investigated. It was shown that filaments with a suitable and uniform diameter could be produced. A parameter study for printing revealed that adhesion of the material on the bed and between layers was an issue but could be overcome with a suitable set of parameters. Tensile bars with different orientations of 0°, +/−45°, and 90° were printed and compared with injection-molded samples. It could be shown that different mechanisms (single strand breakage, shear failure) caused fracture for different printing orientations. In comparison with injection-molding, the printed parts showed lower mechanical properties (moduli of 74–95%, a tensile strength of 47–69%, and an elongation at break of 29–60%), but an improvement could be seen compared with earlier reported direct granule printing. The study showed that FFF is a suitable process for the new cellulose-based material to fabricate samples with good mechanical properties. Full article

(This article belongs to the Special Issue Additive Manufacturing (AM) of Biomaterials)

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21 pages, 6155 KiB

Open AccessArticle

A Parametric Study for Tensile Properties of Silicone Rubber Specimen Using the Bowden-Type Silicone Printer

by Jing Angelo Gonzaga Clet, Nai-Shang Liou, Chen-Hsun Weng and Yu-Sheng Lin

Materials 2022, 15(5), 1729; https://doi.org/10.3390/ma15051729 - 25 Feb 2022

Cited by 4 | Viewed by 1666

Abstract

Silicone printing can enable a lot more accessibility and customizability towards utilizing silicone in different applications, including medicine for its biocompatibility. However, challenges existed for printing in specific geometries due to the lack of guidelines and studies on the mechanical properties. To support [...] Read more.

Silicone printing can enable a lot more accessibility and customizability towards utilizing silicone in different applications, including medicine for its biocompatibility. However, challenges existed for printing in specific geometries due to the lack of guidelines and studies on the mechanical properties. To support the understanding of printing three-dimensional silicone structure having different infill patterns and gel-like material, this paper conducted a parametric study for the specimens printed using a Bowden-type silicone printer and measurements of the tensile properties. Four printing parameters of print speed, infill density, flow rate, and infill pattern, are categorized following the Taguchi L9 method, and arranged into the four-parameter-three-level orthogonal array. The signal-to-noise (S/N) ratio was calculated based on the principle of the-larger-the-better, and analysis of variance (ANOVA) was also obtained. Tensile performance was further discussed with the characterization of internal structure, using the cross-sections of the printed specimens. It was found that the change of flow rate is the most significant to the tensile stress; and for the tensile strain, infill pattern was found to be the most significant parameter. The Line infill pattern consistently presented the highest tensile stress. Agglomeration can be seen inside the printed structure, hence optimal printing parameters play an important role for complicated geometry, while ensuring the flow rate and infill density do not exceed a reasonable value. This study would serve as the guideline for printing three-dimensional silicone structures. Full article

(This article belongs to the Special Issue Additive Manufacturing (AM) of Biomaterials)

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17 pages, 8166 KiB

Open AccessArticle

An Enhanced Understanding of the Powder Bed Fusion–Laser Beam Processing of Mg-Y_3.9wt%-Nd_3wt%-Zr_0.5wt% (WE43) Alloy through Thermodynamic Modeling and Experimental Characterization

by Hanna Nilsson Åhman, Lena Thorsson, Pelle Mellin, Greta Lindwall and Cecilia Persson

Materials 2022, 15(2), 417; https://doi.org/10.3390/ma15020417 - 06 Jan 2022

Cited by 6 | Viewed by 2202

Abstract

Powder Bed Fusion–Laser Beam (PBF–LB) processing of magnesium (Mg) alloys is gaining increasing attention due to the possibility of producing complex biodegradable implants for improved healing of large bone defects. However, the understanding of the correlation between the PBF–LB process parameters and the [...] Read more.

Powder Bed Fusion–Laser Beam (PBF–LB) processing of magnesium (Mg) alloys is gaining increasing attention due to the possibility of producing complex biodegradable implants for improved healing of large bone defects. However, the understanding of the correlation between the PBF–LB process parameters and the microstructure formed in Mg alloys remains limited. Thus, the purpose of this study was to enhance the understanding of the effect of the PBF–LB process parameters on the microstructure of Mg alloys by investigating the applicability of computational thermodynamic modelling and verifying the results experimentally. Thus, PBF–LB process parameters were optimized for a Mg WE43 alloy (Mg-Y_3._9wt%-Nd_3wt%-Zr_0.5wt%) on a commercially available machine. Two sets of process parameters successfully produced sample densities >99.4%. Thermodynamic computations based on the Calphad method were employed to predict the phases present in the processed material. Phases experimentally established for both processing parameters included α-Mg, Y₂O₃, Mg₃Nd, Mg₂₄Y₅ and hcp-Zr. Phases α-Mg, Mg₂₄Y₅ and hcp-Zr were also predicted by the calculations. In conclusion, the extent of the applicability of thermodynamic modeling was shown, and the understanding of the correlation between the PBF–LB process parameters and the formed microstructure was enhanced, thus increasing the viability of the PBF–LB process for Mg alloys. Full article

(This article belongs to the Special Issue Additive Manufacturing (AM) of Biomaterials)

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25 pages, 8527 KiB

Open AccessArticle

Localized Corrosion Resistance on Additively Manufactured Ti Alloys by Means of Electrochemical Critical Localized Corrosion Potential in Biomedical Solution Environments

by Dong-Il Seo and Jae-Bong Lee

Materials 2021, 14(23), 7481; https://doi.org/10.3390/ma14237481 - 06 Dec 2021

Cited by 7 | Viewed by 1849

Abstract

This study proposes a new method, electrochemical critical localized corrosion potential (E-CLCP), in order to evaluate localized corrosion resistance of biomedical additive manufacturing (AM) titanium (Ti) alloys. The procedures for determining E-CLCP are completely different from that of the electrochemical critically localized corrosion [...] Read more.

This study proposes a new method, electrochemical critical localized corrosion potential (E-CLCP), in order to evaluate localized corrosion resistance of biomedical additive manufacturing (AM) titanium (Ti) alloys. The procedures for determining E-CLCP are completely different from that of the electrochemical critically localized corrosion temperature (E-CLCT) method (ISO 22910:2020). However, its application should be limited to pH and temperature of the human body because of the temperature scan. E-CLCP displays the localized corrosion resistance of AM Ti alloys based on the human body’s repassivation kinetics, whereas E-CLCT displays the localized corrosion resistance of the alloys based on passive film breakdown in much harsher corrosive environments. Full article

(This article belongs to the Special Issue Additive Manufacturing (AM) of Biomaterials)

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17 pages, 2599 KiB

Open AccessArticle

The Potential of Stereolithography for 3D Printing of Synthetic Trabecular Bone Structures

by Ana Grzeszczak, Susanne Lewin, Olle Eriksson, Johan Kreuger and Cecilia Persson

Materials 2021, 14(13), 3712; https://doi.org/10.3390/ma14133712 - 02 Jul 2021

Cited by 9 | Viewed by 2799

Abstract

Synthetic bone models are used to train surgeons as well as to test new medical devices. However, currently available models do not accurately mimic the complex structure of trabecular bone, which can provide erroneous results. This study aimed to investigate the suitability of [...] Read more.

Synthetic bone models are used to train surgeons as well as to test new medical devices. However, currently available models do not accurately mimic the complex structure of trabecular bone, which can provide erroneous results. This study aimed to investigate the suitability of stereolithography (SLA) to produce synthetic trabecular bone. Samples were printed based on synchrotron micro-computed tomography (micro-CT) images of human bone, with scaling factors from 1 to 4.3. Structure replicability was assessed with micro-CT, and mechanical properties were evaluated by compression and screw pull-out tests. The overall geometry was well-replicated at scale 1.8, with a volume difference to the original model of <10%. However, scaling factors below 1.8 gave major print artefacts, and a low accuracy in trabecular thickness distribution. A comparison of the model–print overlap showed printing inaccuracies of ~20% for the 1.8 scale, visible as a loss of smaller details. SLA-printed parts exhibited a higher pull-out strength compared to existing synthetic models (Sawbones ™), and a lower strength compared to cadaveric specimens and fused deposition modelling (FDM)-printed parts in poly (lactic acid). In conclusion, for the same 3D model, SLA enabled higher resolution and printing of smaller scales compared to results reported by FDM. Full article

(This article belongs to the Special Issue Additive Manufacturing (AM) of Biomaterials)

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20 pages, 1442 KiB

Open AccessArticle

Cartilage Tissue Engineering by Extrusion Bioprinting: Process Analysis, Risk Evaluation, and Mitigation Strategies

by Mauro Petretta, Giovanna Desando, Brunella Grigolo and Livia Roseti

Materials 2021, 14(13), 3528; https://doi.org/10.3390/ma14133528 - 24 Jun 2021

Cited by 8 | Viewed by 1855

Abstract

Extrusion bioprinting is considered promising in cartilage tissue engineering since it allows the fabrication of complex, customized, and living constructs potentially suitable for clinical applications. However, clinical translation is often complicated by the variability and unknown/unsolved issues related to this technology. The aim [...] Read more.

Extrusion bioprinting is considered promising in cartilage tissue engineering since it allows the fabrication of complex, customized, and living constructs potentially suitable for clinical applications. However, clinical translation is often complicated by the variability and unknown/unsolved issues related to this technology. The aim of this study was to perform a risk analysis on a research process, consisting in the bioprinting of a stem cell-laden collagen bioink to fabricate constructs with cartilage-like properties. The method utilized was the Failure Mode and Effect Analysis/Failure Mode and Effect Criticality Analysis (FMEA/FMECA) which foresees a mapping of the process to proactively identify related risks and the mitigation actions. This proactive risk analysis allowed the identification of forty-seven possible failure modes, deriving from seventy-one potential causes. Twenty-four failure modes displayed a high-risk level according to the selected evaluation criteria and threshold (RPN > 100). The results highlighted that the main process risks are a relatively low fidelity of the fabricated structures, unsuitable parameters/material properties, the death of encapsulated cells due to the shear stress generated along the nozzle by mechanical extrusion, and possible biological contamination phenomena. The main mitigation actions involved personnel training and the implementation of dedicated procedures, system calibration, printing conditions check, and, most importantly, a thorough knowledge of selected biomaterial and cell properties that could be built either through the provided data/scientific literature or their preliminary assessment through dedicated experimental optimization phase. To conclude, highlighting issues in the early research phase and putting in place all the required actions to mitigate risks will make easier to develop a standardized process to be quickly translated to clinical use. Full article

(This article belongs to the Special Issue Additive Manufacturing (AM) of Biomaterials)

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12 pages, 3837 KiB

Open AccessArticle

Analysis and Optimization of Mechanical Properties of Laser-Sintered Cellulose/PLA Mixture

by Hui Zhang, David L. Bourell and Yanling Guo

Materials 2021, 14(4), 750; https://doi.org/10.3390/ma14040750 - 05 Feb 2021

Cited by 2 | Viewed by 1725

Abstract

This studied aimed at improving the mechanical properties for a new biopolymer feedstock using laser-sintering technology, especially when its laser-sintered parts are intended to be applied in the industrial and medical fields. Process parameter optimization and thermal post-processing are two approaches proposed in [...] Read more.

This studied aimed at improving the mechanical properties for a new biopolymer feedstock using laser-sintering technology, especially when its laser-sintered parts are intended to be applied in the industrial and medical fields. Process parameter optimization and thermal post-processing are two approaches proposed in this work to improve the mechanical properties of laser-sintered 10 wt % cellulose-polylactic acid (10%-CPLA) parts. Laser-sintering experiments using 2³ full factorial design method were conducted to assess the effects of process parameters on parts’ mechanical properties. A simulation of laser-energy distribution was carried out using Matlab to evaluate the experimental results. The characterization of mechanical properties, crystallinity, microstructure, and porosity of laser-sintered 10%-CPLA parts after thermal post-processing of different annealing temperatures was performed to analyze the influence of thermal post-processing on part properties. Image analysis of fracture surfaces was used to obtain the porosity of laser-sintered 10%-CPLA parts. Results showed that the optimized process parameters for mechanical properties of laser-sintered 10%-CPLA parts were laser power 27 W, scan speed 1600 mm/s, and scan spacing 0.1 mm. Thermal post-processing at 110 °C produced best properties for laser-sintered 10%-CPLA parts. Full article

(This article belongs to the Special Issue Additive Manufacturing (AM) of Biomaterials)

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22 pages, 41297 KiB

Open AccessArticle

Processing of Polyester-Urethane Filament and Characterization of FFF 3D Printed Elastic Porous Structures with Potential in Cancellous Bone Tissue Engineering

by Agnieszka Haryńska, Iga Carayon, Paulina Kosmela, Anna Brillowska-Dąbrowska, Marcin Łapiński, Justyna Kucińska-Lipka and Helena Janik

Materials 2020, 13(19), 4457; https://doi.org/10.3390/ma13194457 - 08 Oct 2020

Cited by 22 | Viewed by 3521

Abstract

This paper addresses the potential of self-made polyester-urethane filament as a candidate for Fused Filament Fabrication (FFF)-based 3D printing (3DP) in medical applications. Since the industry does not provide many ready-made solutions of medical-grade polyurethane filaments, we undertook research aimed at presenting the [...] Read more.

This paper addresses the potential of self-made polyester-urethane filament as a candidate for Fused Filament Fabrication (FFF)-based 3D printing (3DP) in medical applications. Since the industry does not provide many ready-made solutions of medical-grade polyurethane filaments, we undertook research aimed at presenting the process of thermoplastic polyurethane (TPU) filament formation, detailed characteristics, and 3DP of specially designed elastic porous structures as candidates in cancellous tissue engineering. Additionally, we examined whether 3D printing affects the structure and thermal stability of the filament. According to the obtained results, the processing parameters leading to the formation of high-quality TPU filament (TPU_F) were captured. The results showed that TPU_F remains stable under the FFF 3DP conditions. The series of in vitro studies involving long- and short-term degradation (0.1 M phosphate-buffered saline (PBS); 5 M sodium hydroxide (NaOH)), cytotoxicity (ISO 10993:5) and bioactivity (simulated body fluid (SBF) incubation), showed that TPU printouts possessing degradability of long-term degradable tissue constructs, are biocompatible and susceptible to mineralization in terms of hydroxyapatite (HAp) formation during SBF exposure. The formation of HAp on the surface of the specially designed porous tissue structures (PTS) was confirmed by scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS) studies. The compression test of PTS showed that the samples were strengthened due to SBF exposure and deposited HAp on their surface. Moreover, the determined values of the tensile strength (~30 MPa), Young’s modulus (~0.2 GPa), and compression strength (~1.1 MPa) allowed pre-consideration of TPU_F for FFF 3DP of cancellous bone tissue structures. Full article

(This article belongs to the Special Issue Additive Manufacturing (AM) of Biomaterials)

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17 pages, 4540 KiB

Open AccessArticle

Influence of Controlled Cooling on Crystallinity of Poly(L-Lactic Acid) Scaffolds after Hydrolytic Degradation

by Javier Vazquez-Armendariz, Raquel Tejeda-Alejandre, Aida Rodriguez-Garcia, Yadira I. Vega-Cantu, Christian Mendoza-Buenrostro and Ciro A. Rodriguez

Materials 2020, 13(13), 2943; https://doi.org/10.3390/ma13132943 - 30 Jun 2020

Cited by 4 | Viewed by 2355

Abstract

The use of hybrid manufacturing to produce bimodal scaffolds has represented a great advancement in tissue engineering. These scaffolds provide a favorable environment in which cells can adhere and produce new tissue. However, there are several areas of opportunity to manufacture structures that [...] Read more.

The use of hybrid manufacturing to produce bimodal scaffolds has represented a great advancement in tissue engineering. These scaffolds provide a favorable environment in which cells can adhere and produce new tissue. However, there are several areas of opportunity to manufacture structures that provide enough strength and rigidity, while also improving chemical integrity. As an advancement in the manufacturing process of scaffolds, a cooling system was introduced in a fused deposition modeling (FDM) machine to vary the temperature on the printing bed. Two groups of polylactic acid (PLA) scaffolds were then printed at two different bed temperatures. The rate of degradation was evaluated during eight weeks in Hank’s Balanced Salt Solution (HBSS) in a controlled environment (37 °C–120 rpm) to assess crystallinity. Results showed the influence of the cooling system on the degradation rate of printed scaffolds after the immersion period. This phenomenon was attributable to the mechanism associated with alkaline hydrolysis, where a higher degree of crystallinity obtained in one group induced greater rates of mass loss. The overall crystallinity was observed, through differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA), and Fourier transformed infrared spectroscopy (FTIR) analysis, to increase with time because of the erosion of some amorphous parts after immersion. Full article

(This article belongs to the Special Issue Additive Manufacturing (AM) of Biomaterials)

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