| 1. |
- Shah, Furqan A., et al.
(författare)
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3D printed Ti6Al4V implant surface promotes bone maturation and retains a higher density of less aged osteocytes at the bone-implant interface.
- 2016
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Ingår i: Acta Biomaterialia. - : Elsevier BV. - 1878-7568 .- 1742-7061. ; 30, s. 357-367
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Tidskriftsartikel (refereegranskat)abstract
- For load-bearing orthopaedic applications, metal implants having an interconnected pore structure exhibit the potential to facilitate bone ingrowth and the possibility for reducing the stiffness mismatch between the implant and bone, thus eliminating stress-shielding effects. 3D printed solid and macro-porous Ti6Al4V implants were evaluated after six-months healing in adult sheep femora. The ultrastructural composition of the bone-implant interface was investigated using Raman spectroscopy and electron microscopy, in a correlative manner. The mineral crystallinity and the mineral-to-matrix ratios of the interfacial tissue and the native bone were found to be similar. However, lower Ca/P ratios, lower carbonate content, but higher proline, phenylalanine and tyrosine levels indicated that the interfacial tissue remained less mature. Bone healing was more advanced at the porous implant surface (vs. the solid implant surface) based on the interfacial tissue ν1 CO3(2-)/ν2 PO4(3-) ratio, phenylalanine and tyrosine levels approaching those of the native bone. The mechanosensing infrastructure in bone, the osteocyte lacuno-canalicular network, retained ∼40% more canaliculi per osteocyte lacuna, i.e., a 'less aged' morphology at the interface. The osteocyte density per mineralised surface area was ∼36-71% higher at the interface after extended healing periods.
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| 2. |
- Shah, Furqan A., et al.
(författare)
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Long-term osseointegration of 3D printed CoCr constructs with an interconnected open-pore architecture prepared by electron beam melting.
- 2016
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Ingår i: Acta Biomaterialia. - : Elsevier BV. - 1878-7568 .- 1742-7061. ; 36:May, s. 296-309
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Tidskriftsartikel (refereegranskat)abstract
- In orthopaedic surgery, cobalt chromium (CoCr) based alloys are used extensively for their high strength and wear properties, but with concerns over stress shielding and bone resorption due to the high stiffness of CoCr. The structural stiffness, principally related to the bulk and the elastic modulus of the material, may be lowered by appropriate design modifications, to reduce the stiffness mismatch between metal/alloy implants and the adjacent bone. Here, 3D printed CoCr and Ti6Al4V implants of similar macro-geometry and interconnected open-pore architecture prepared by electron beam melting (EBM) were evaluated following 26week implantation in adult sheep femora. Despite higher total bone-implant contact for Ti6Al4V (39±4%) than CoCr (27±4%), bone formation patterns were similar, e.g., densification around the implant, and gradual ingrowth into the porous network, with more bone in the outer half (periphery) than the inner half (centre). Raman spectroscopy revealed no major differences in mineral crystallinity, the apatite-to-collagen ratio, or the carbonate-to-phosphate ratio. Energy dispersive X-ray spectroscopy showed similar Ca/P ratio of the interfacial tissue adjacent to both materials. Osteocytes made direct contact with CoCr and Ti6Al4V. While osteocyte density and distribution in the new-formed bone were largely similar for the two alloys, higher osteocyte density was observed at the periphery of the porous network for CoCr, attributable to slower remodelling and a different biomechanical environment. The results demonstrate the possibility to achieve bone ingrowth into open-pore CoCr constructs, and attest to the potential for fabricating customised osseointegrated CoCr implants for load-bearing applications.
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| 3. |
- Andrews, L, et al.
(författare)
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Infrared spectra of cis and trans-(NO)(2)(-) anions in solid argon
- 1998
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Ingår i: Journal of Chemical Physics. - 1089-7690 .- 0021-9606. ; 109:1, s. 177-185
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Tidskriftsartikel (refereegranskat)abstract
- Laser-ablation of over 20 different metal targets with concurrent 10 K codeposition of Ar/NO mixtures produces metal independent infrared bands at 1589.3 cm−1 due to (NO)2+, a new absorption at 1221.0 cm−1, and a band set at 1300.3, 1222.7, 884.4 cm−1. The latter bands decrease more on annealing than the 1221.0 cm−1 band. Isotopic substitution (14NO,15NO, 15N18O, and mixtures) shows that these new vibrations involve two equivalent N–O oscillators, which identifies two new (NO)2 species. The excellent agreement with frequencies, intensities, and isotopic frequency ratios from density functional theory calculations substantiates assignment of the 1221.0 cm−1 band to trans-(NO)2− and the three band set to cis-(NO)2−. The observation of a weak combination band at 2492.0 cm−1 further substantiates assignment of the two N–O stretching modes in cis-(NO)2−
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| 4. |
- Balachandramurthi, Arun Ramanathan, 1989-, et al.
(författare)
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Microstructure tailoring in Electron Beam Powder Bed Fusion Additive Manufacturing and its potential consequences
- 2019
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Ingår i: Results in Materials. - : Elsevier. - 2590-048X. ; 1
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Tidskriftsartikel (refereegranskat)abstract
- Electron Beam Powder Bed Fusion process for Alloy 718 was investigated, in the sense of microstructural evolution with varying process conditions. The existence of a geometric relationship between the melt front and the processing parameters was observed. By understanding and capitalizing on this relationship, it was possible to obtain columnar, equiaxed or bimodal microstructure.
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| 5. |
- Bauschlicher, C.W., et al.
(författare)
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A further study of the products of scandium and dioxygen reactions
- 1999
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Ingår i: Journal of Physical Chemistry A. - 1089-5639 .- 1520-5215. ; 103:28, s. 5463-5467
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Tidskriftsartikel (refereegranskat)abstract
- The products of the reaction of Sc and dioxygen have been reinvestigated. By adding the electron-trapping molecule CCl4 additional information about the IR spectra has been obtained, as well as the observation of new bands. New ab initio calculations are also performed on possible products of the Sc plus O-2 reaction. The previously observed band at 722.5 cm(-1) is assigned as the b(2) mode of ScO2-. Bands arising from ScO+, Sc(O-2)(+), and(O-2)ScO are also assigned. We are still unable to assign any bands to OScO. The problems associated with the computational study of ScO2 are discussed.
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| 6. |
- de Peppo, Giuseppe Maria, 1981, et al.
(författare)
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Free-form-fabricated commercially-pure Ti and Ti6Al4V porous scaffolds support the growth of human embryonic stem cell-derived medsodermal progenitors
- 2012
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Ingår i: The Scientific World Journal. - : Hindawi Limited. - 2356-6140 .- 1537-744X. ; 2012
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Tidskriftsartikel (refereegranskat)abstract
- Commercially-pure titanium (cp-Ti) and the titanium-aluminum-vanadium alloy (Ti6Al4V) are widely used as reconstructive implants for skeletal engineering applications, due to their good mechanical properties, biocompatibility and ability to integrate with the surrounding bone. Electron beam melting technology (EBM) allows the fabrication of customized implants with tailored mechanical properties and high potential in the clinical practice. In order to augment the interaction with the biological tissue, stem cells have recently been combined with metallic scaffolds for skeletal engineering applications. We previously demonstrated that human embryonic stem cell-derived mesodermal progenitors (hES-MPs) hold a great potential to provide a homogeneous and unlimited supply of cells for bone engineering applications. This study demonstrates the effect of EBM-fabricated cp-Ti and Ti6Al4V porous scaffolds on hES-MPs behavior, in terms of cell attachment, growth and osteogenic differentiation. Displaying different chemical composition but similar surface properties, EBM-fabricated cp-Ti and Ti6Al4V scaffolds supported cell attachment and growth, and did not seem to alter the expression of genes involved in osteogenic differentiation and affect the alkaline phosphatase activity. In conclusion, interfacing hES-MPs to EBM-fabricated scaffolds may represent an interesting strategy for design of third-generation biomaterials, with the potential to promote implant integration in clinical conditions characterized by poor bone quality. Copyright 2012 G. M. de Peppo et al.
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| 7. |
- Forslund, Robert, 1990, et al.
(författare)
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Analytical solution for heat conduction due to a moving Gaussian heat flux with piecewise constant parameters
- 2019
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Ingår i: Applied Mathematical Modelling. - : Elsevier BV. - 0307-904X. ; 66, s. 227-240
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Tidskriftsartikel (refereegranskat)abstract
- We provide an analytical solution of the heat equation in the half-space subject to a moving Gaussian heat flux with piecewise constant parameters. The solution is of interest in powder bed fusion applications where these parameters can be used to control the conduction of heat due to a scanning beam of concentrated energy. The analytical solution is written in a dimensionless form as a sum of integrals over (dimensionless) time. For the numerical computation of these integrals we suggest a quadrature scheme that utilizes pre-calculated look-up tables for the required quadrature orders. Such a scheme is efficient because the required quadrature orders are strongly dependent on the parameters in the heat flux. The possibilities of using the obtained computational technique for the control and optimization of powder bed fusion processes are discussed.
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| 8. |
- Karlsson, Joakim, et al.
(författare)
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Characterization and comparison of materials produced by Electron Beam Melting (EBM) of two different Ti-6Al-4V powder fractions
- 2013
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Ingår i: Journal of Materials Processing Technology. - : Elsevier BV. - 0924-0136 .- 1873-4774. ; 213:12, s. 2109-2118
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Tidskriftsartikel (refereegranskat)abstract
- Electron Beam Melting (EBM) has been recognized as a revolutionary technique to produce mass-customized parts to near-net-shape from various metallic materials. The technique produces parts with unique geometries from a powder stock material and uses an electron beam to melt the powder layer-by-layer to fully solid structures. In this study we have investigated the use of two different Ti-6Al-4V powders of different size fractions in the EBM process; a larger 45-100 mu m powder, and a smaller 25-45 mu m powder. We have also investigated the effects of two build layer thicknesses, 70 mu m and 50 mu m. respectively. We hypothesize that the smaller powder has the potential to improve surface resolution of parts produced in the EBM process. The EBM as-built parts were investigated regarding surface and bulk chemistry, surface oxide thickness, macro- and microstructure, surface appearance and mechanical properties. We conclude from the results that both powders and both build layer thicknesses are feasible to use in the EBM process. The investigated material properties were not significantly affected by powder size or layer thickness within the studied range of process parameters. However, the surface appearance was found to be different for the samples made with the different powder sizes.
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| 9. |
- Karlsson, Joakim, 1984-, et al.
(författare)
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Digital image correlation analysis of local strain fields on Ti6Al4V manufactured by electron beam melting
- 2014
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Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 618, s. 456-461
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Tidskriftsartikel (refereegranskat)abstract
- Additive manufacturing, or 3D-printing as it is often called, build parts in a layer-by-layer fashion. A common concern, regardless of the specific additive manufacturing technique used, is the risk of inadequate fusion between the adjacent layers which in turn may cause inferior mechanical properties. In this work, the local strain properties of titanium parts produced by Electron Beam Melting (EBM®) were studied in order to gain information about the quality of fusion of the stock powder material used in the process. By using Digital Image Correlation (DIC) the strain fields in the individual layers were analyzed, as well as the global strain behavior of the bulk material. The results show that fully solid titanium parts manufactured by EBM are homogenous and do not experience local deformation behavior, neither on local nor on a global level.
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| 10. |
- Karlsson, Joakim, 1984-, et al.
(författare)
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Thickness dependency of mechanical properties for thin-walled titanium parts manufactured by Electron Beam Melting (EBM®)
- 2024
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Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810.
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Tidskriftsartikel (refereegranskat)abstract
- Metal powder bed additive manufacturing technologies, such as the Electron Beam Melting process, facilitate a high degree of geometric flexibility and have been demonstrated as useful production techniques for metallic parts. However, the EBM process is typically associated with lower resolutions and higher surface roughness compared to similar laser-based powder bed metal processes. In part, this difference is related to the larger powder size distribution and thicker layers normally use As part of an effort to improve the resolution and surface roughness of EBM fabricated components, this study investigates the feasibility of fabricating components with a smaller powder size fraction and layer thickness (similar to laser based processes). The surface morphology, microstructure and tensile properties of the produced samples were evaluated. The findings indicate that microstructure is dependent on wall-thickness and that, for thin walled structures, tensile properties can become dominated by variations in surface roughness.
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