| 1. |
- Amin Yavari, S., et al.
(författare)
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Layer by layer coating for bio-functionalization of additively manufactured meta-biomaterials
- 2020
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Ingår i: Additive Manufacturing. - : Elsevier BV. - 2214-8604 .- 2214-7810. ; 32
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Tidskriftsartikel (refereegranskat)abstract
- Additive manufacturing has facilitated fabrication of complex and patient-specific metallic meta-biomaterials that offer an unprecedented collection of mechanical, mass transport, and biological properties as well as a fully interconnected porous structure. However, applying meta-biomaterials for addressing unmet clinical needs in orthopedic surgery requires additional surface functionalities that should be induced through tailor-made coatings. Here, we developed multi-functional layer-by-layer coatings to simultaneously prevent implant-associated infections and stimulate bone tissue regeneration. We applied multiple layers of gelatin- and chitosan-based coatings containing either bone morphogenetic protein (BMP)-2 or vancomycin on the surface of selective laser melted porous structures made from commercial pure Titanium (CP Ti) and designed using a triply periodic minimal surface (i.e., sheet gyroid). The additive manufacturing process resulted in a porous structure and met the the design values comparatively. X-ray photoelectron spectroscopy spectra confirmed the presence and composition of the coating layers. The release profiles showed a continued release of both vancomycin and BMP-2 for 2–3 weeks. Furthermore, the developed meta-biomaterials exhibited a very strong antibacterial behavior with up to 8 orders of magnitude reduction in both planktonic and implant-adherent bacteria and no signs of biofilm formation. The osteogenic differentiation of mesenchymal stem cells was enhanced, as shown by two-fold increase in the alkaline phosphatase activity and up to four-fold increase in the mineralization of all experimental groups containing BMP-2. Eight-week subcutaneous implantation in vivo showed no signs of a foreign body response, while connective tissue ingrowth was promoted by the layer-by-layer coating. These results unequivocally confirm the superior multi-functional performance of the developed biomaterials.
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| 2. |
- Ananthanarayanan, Durga, et al.
(författare)
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Modelling columnar-to-equiaxed transition during fusion-based metal additive manufacturing
- 2023
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Ingår i: Additive Manufacturing. - : Elsevier BV. - 2214-8604 .- 2214-7810. ; 78
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Tidskriftsartikel (refereegranskat)abstract
- During fusion-based metal additive manufacturing, there is an inherent directionality in heat transfer, which leads to columnar grain growth. This may result in cracking and anisotropic mechanical properties in many alloy systems. Therefore, it is important to study the conditions under which columnar-to-equiaxed transition in grain structure occurs. The grain morphology is determined by several factors such as process conditions, local alloy composition, and number density of nucleating sites. In the present work, a model for simulating columnar-to-equiaxed transition is formulated, considering nucleating site size distribution, rapid solidification and constitutional undercooling in multicomponent alloys. Furthermore, the model is coupled with multicomponent Calphad-based thermodynamic and diffusion mobility descriptions. It is demonstrated that including the above aspects is important in accurately predicting the columnar-to-equiaxed transition by comparing with experimental data for an additively manufactured TiB2-reinforced AlSi10Mg alloy. The framework developed in this work may be used to predict columnar-to-equiaxed transition in additively manufactured technical alloys consisting of multiple elements.
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| 3. |
- Andersson, Henrik, Dr, 1975-, et al.
(författare)
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Variable low-density polylactic acid and microsphere composite material for additive manufacturing
- 2021
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Ingår i: Additive Manufacturing. - : Elsevier BV. - 2214-8604 .- 2214-7810. ; 40
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Tidskriftsartikel (refereegranskat)abstract
- Thermally expandable microspheres are extensively used in industry as a lightweight filler for many products. The spheres can expand up to 60 times the initial size and are used for different purposes, including material reduction and surface modification. In fused filament fabrication (FFF), a material is deposited in a layer-by-layer process. Typically, FFF objects need not be solid because such objects are typically used for applications with low mechanical stress. Low material infill percentages are commonly used inside a solid outer shell to reduce material usage, weight, and manufacturing time. This paper proposes a new composite filament for FFF consisting of polylactic acid (PLA) and thermally expandable Expancel microspheres in the form of masterbatch granules. These filaments contain unexpanded microspheres that can be expanded during printing by heating. Two types of filaments containing 2 wt% and 5 wt% of masterbatch granules were manufactured and tested. The filaments were successfully used with a commercial 3D printer to manufacture objects with a density of 45% compared to objects manufactured using standard PLA. The tensile strength of these objects changed linearly with density and was comparable to that of PLA objects of the same density prepared using infill patterns. The composite filaments are advantageous in that they can reduce the amount of material used, as is currently done by using different amounts of infill in a pattern. Further, by varying the nozzle temperature, their density can be adjusted directly during printing as well as during fabrication to produce layers of different densities in the same object.
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| 4. |
- Brandau, Benedikt, et al.
(författare)
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Proof-of-concept of an absorbance determination of a powder bed by high resolution coaxial multispectral imaging in laser material processing
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Ingår i: Additive Manufacturing. - 2214-8604 .- 2214-7810.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Imaging techniques are very popular for process monitoring in laser material processing due to their high information content. At the same time, coaxial systems focused by passive laser optics still present a major challenge, because most laser optics cause imaging errors for the monitoring channel. In this paper, the design, methodology and procedure are shown to be able to acquire coaxial image data by standard laser components, which is demonstrated by components for a laser powder bed fusion system and their use on a powder bed. The focus is on the correction of the image data to produce a high-resolution, geometrically accurate and gap-free overview image of the entire processing area. For this purpose, optical simulations of the system are performed to detect aberrations, distortions and chromatic errors and to correct them by hardware elements or in software post-processing. Over the entire 114 mm by 114 mm working area, objects can be captured geometrically accurate with a maximum deviation of 22 μm - 49 μm, depending on the detection wavelength. By capturing images atPaper C: Coaxial multispectral imaging Benedikt Brandau148wavelengths of 405 nm, 450 nm, 520 nm, 580 nm, 625 nm and 850 nm, multispectral information is gained over the entire working area. In addition, an absorbance of the powder bed is derived from the images. To qualify this methodology, tests are performed on 20 different powders. These include different particle sizes, aged and oxidized powders of different metals. The ability to determine absorbance is simulated by ray tracing powder surfaces. This allows the determination of in-line absorbances from the powder bed with a maximum deviation of 2.5 % compared to absorbance spectra of established methods. The origins of component defects such as foreign particles, powder oxidation, spatter and uncoated areas were able to be identified down to a diameter of 20 μm.
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| 5. |
- Cantoni, Federico, et al.
(författare)
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Round-robin testing of commercial two-photon polymerization 3D printers
- 2023
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Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 76
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Tidskriftsartikel (refereegranskat)abstract
- Since its introduction in the 1980s, 3D printing has advanced as a versatile and reliable tool with applications in different fields. Among the available 3D printing techniques, two-photon polymerization is regarded as one of the most promising technologies for microscale printing due to its ability to combine a high printing fidelity down to submicron scale with free-form structure design. Recently, the technology has been enhanced through the implementation of faster laser scanning strategies, as well as the development of new photoresists. This paves the way for a wide range of applications, which has resulted in an increasing number of available commercial systems. This work aims to provide an overview of the technology capability by comparing three commercial systems in a round-robin test. To cover a wide range of applications, six test structures with distinct features were designed, covering various aspects of interest, from single material objects with sub-micron feature sizes up to multi-material millimeter-sized objects. Application-specific structures were printed to evaluate surface roughness and the stitching capability of the printers. Moreover, the ability to generate free-hanging structures and complex surfaces required for cell scaffolds and microfluidic platform fabrication was quantitatively investigated. Finally, the influence of the numerical aperture of the fabrication objective on the printing quality was assessed. All three printers successfully fabricated samples comprising various three-dimensional features and achieved submicron resolution and feature sizes, demonstrating the versatility and precision of two-photon polymerization direct laser writing. Our study will facilitate the understanding of the technology maturity level, while highlighting specific aspects that characterize each of the investigated systems.
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| 6. |
- Cederberg, Emil, et al.
(författare)
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Physical simulation of additively manufactured super duplex stainless steels : microstructure and properties
- 2020
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Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 34
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Tidskriftsartikel (refereegranskat)abstract
- The behavior of high performance super duplex stainless steel (SDSS) during additive manufacturing (AM) has been investigated using a novel arc heat treatment technique. Tungsten inert gas (TIG) arc pulses were applied on a disc shaped sample mounted on a water-cooled chamber to physically simulate AM thermal cycles. SDSS base metal and a duplicated additively manufactured structure (DAMS) were used as initial microstructures. Samples were melted one, five, or 15 times by arc heat treatment. Samples were also produced with a controlled slope down of the current to create slower cooling compared to pulsing. Microstructure characterization and modelling were performed to study the evolution of microstructure and properties with successive AM cycles. Microstructural changes were dependent on the number of reheating cycles, cooling rate, and peak temperature. In particular, the DAMS austenite morphology and fraction changed after reheating to peak temperatures above 700 °C. Nitrides and sigma were observed in the high and low temperature heat affected zones, respectively. Sensitization to corrosion was more pronounced in reheated DAMS than in the base metal. Hardness was increased more by multiple remelting/reheating than by slow cooling. It was found that AM thermal cycles significantly affect SDSS properties especially for an initial microstructure similar to that produced by AM. © 2020 Elsevier B.V.
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| 7. |
- Chinga-Carrasco, Gary, et al.
(författare)
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Bagasse—A major agro-industrial residue as potential resource for nanocellulose inks for 3D printing of wound dressing devices
- 2019
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Ingår i: Additive Manufacturing. - : Elsevier B.V.. - 2214-8604 .- 2214-7810. ; 28, s. 267-274
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Tidskriftsartikel (refereegranskat)abstract
- Sugarcane bagasse, an abundant residue, is usually burned as an energy source. However, provided that appropriate and sustainable pulping and fractionation processes are applied, bagasse can be utilized as a main source of cellulose nanofibrils (CNF). We explored in this study the production of CNF inks for 3D printing by direct-ink-writing technology. The CNF were tested against L929 fibroblasts cell line and we confirmed that the CNF from soda bagasse fibers were found not to have a cytotoxic potential. Additionally, we demonstrated that the alginate and Ca 2+ caused significant dimensional changes to the 3D printed constructs. The CNF-alginate grids exhibited a lateral expansion after printing and then shrank due to the cross-linking with the Ca 2+ . The release of Ca 2+ from the CNF and CNF-alginate constructs was quantified thus providing more insight about the CNF as carrier for Ca 2+ . This, combined with 3D printing, offers potential for personalized wound dressing devices, i.e. tailor-made constructs that can be adapted to a specific shape, depending on the characteristics of the wound healing treatment.
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| 8. |
- Da Silva, Adrien, et al.
(författare)
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The effects of laser irradiation on an aluminium powder stream in Directed Energy Deposition
- 2021
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Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 41
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Tidskriftsartikel (refereegranskat)abstract
- Additive Manufacturing with aluminium alloys is a subject of increasing industrial interest. Directed Energy Deposition using high power lasers and a powder feed is a useful option but the interactions between the powder stream and the laser beam are not completely understood. It is well known that the powder particles heat up in the laser beam and some theoretical models predict that they can reach their vaporisation temperature and have their flight path altered by the associated recoil pressure. In order to learn more about these phenomena, powder streams were observed with a high-speed camera at different laser powers (up to 6 kW) and with three batches of powder (AlSi10Mg) of different particle sizes. The results showed an increase of powder focussing with increased laser power. In addition, some particles were found to disintegrate in the laser beam. It is demonstrated that particle disintegration is most likely to be caused by the momentum induced by the recoil pressure.
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| 9. |
- Dadbakhsh, Sasan, et al.
(författare)
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Heat treatment possibilities for an in situ βTi-TiC composite made by laser powder bed fusion
- 2020
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Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 36
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Tidskriftsartikel (refereegranskat)abstract
- After laser powder bed fusion (LPBF) of an ultra-strong in situ TiC whisker reinforced β-Ti composite, this paper investigates the evolution of microstructure and mechanical properties in response to heat treatment at different temperatures. Using in depth nano-SEM and TEM analyses, it is shown that ageing at 400 °C rounds the whiskers, annihilates the strain fields and grows Mo segregated nano-cells, but without improving the ductility. In contrast, ageing at 600 °C enables the transformation of metastable β to a lamellar β + α, leading to a dual phase matrix embedding TiC particles. This is in such a manner that extra ageing at 600 °C coalesces the nano-lamellar α + β microstructure to form a coarser micro-lamellar α + β matrix. This microstructure achieves 66 % of the compressive deformation of Cp-Ti, and over 1400 MPa compressive strength after 1 h of ageing at 600 °C. Despite this success under compression, hard and stiff TiC particles may still cause large spherical fractured voids, severely limiting the plastic deformation under tension.
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| 10. |
- Fedina, Tatiana, et al.
(författare)
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A comparative study of water and gas atomized low alloy steel powders for additive manufacturing
- 2020
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Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 36
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Tidskriftsartikel (refereegranskat)abstract
- This work reports a study of the differences between laser processing of water and gas atomized low alloy steel powders with a focus on powder behavior and performance in additive manufacturing. Material packing densities were measured to establish a relationship between powder packing and track formation. The results showed that the track height when using water atomized powder was 15% lower than the value achieved for the gas atomized powder. High-speed imaging was utilized to observe the material behavior and analyze the powder particle movement under laser irradiation. It was found that water atomized powder has less particle entrainment due to its tendency towards mechanical interlocking. The occurrence of powder spattering and melt pool instabilities was also studied. More frequent spatter ejection is believed to be due to the higher amount of oxygen in the water atomized powder.
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