The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Frank A Muller - One of the best experts on this subject based on the ideXlab platform.
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Cellular Ti-6Al-4V structures with interconnected Macro Porosity for bone implants fabricated by selective electron beam melting
Acta Biomaterialia, 2008Co-Authors: Peter Heinl, Lenka Muller, Carolin Körner, Robert Friedrich Singer, Frank A MullerAbstract:Selective electron beam melting (SEBM) was successfully used to fabricate novel cellular Ti-6Al-4V structures for orthopaedic applications. Micro computer tomography (μCT) analysis demonstrated the capability to fabricate three-dimensional structures with an interconnected Porosity and pore sizes suitable for tissue ingrowth and vascularization. Mechanical properties, such as compressive strength and elastic modulus, of the tested structures were similar to those of human bone. Thus, stress-shielding effects after implantation might be avoided due to a reduced stiffness mismatch between implant and bone. A chemical surface modification using HCl and NaOH induced apatite formation during in vitro bioactivity tests in simulated body fluid under dynamic conditions. The modified bioactive surface is expected to enhance the fixation of the implant in the surrounding bone as well as to improve its long-term stability. © 2008 Acta Materialia Inc.
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fabrication of hydroxyapatite ceramics with interconnected Macro Porosity
Key Engineering Materials, 2005Co-Authors: Lenka Muller, Frank A Muller, Jurgen Zeschky, Tobias Fey, Peter GreilAbstract:Calcium phosphate bioceramics with an interconnective pore structure were produced by foaming of hydroxyapatite and methyl phenyl poly(silsequioxane) melts in the temperature range between 250 °C and 310 °C. The cellular structure of the resulting porous bodies were controlled by foaming parameters and filler load. A Porosity of up to 92 % was achieved by decreasing the HAfiller amount and increasing the foaming temperature. Subsequent pyrolysis in air at temperatures of 900 °C and 1100 °C resulted in Macroporous foams composed of HA and HA/b-TCP, respectively. The porous bodies with tailorable structure and composition are of interest for bone tissue engineering scaffolds and orthopedic implants.
Paolo Colombo - One of the best experts on this subject based on the ideXlab platform.
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additive manufacturing of ceramic components by digital light processing a comparison between the bottom up and the top down approaches
Journal of The European Ceramic Society, 2019Co-Authors: Oscar Santoliquido, Paolo Colombo, Alberto OrtonaAbstract:Abstract A systematic study of the additive manufacturing of complex ceramic objects was carried out using two different Digital Light Processing (DLP) approaches, the "bottom-up" and "top-down" ones, employing the same projector as light source and a photosensitive Al2O3-based ceramic slurry. Cylindrical periodic architectures having different Macro-Porosity, as well a bulk (dense) component in the form of a disk, were designed and additively manufactured with the two printers employing similar printing conditions. In the "bottom-up" approach, the periodic detachment of the part being manufactured from the bottom surface of the vat, to enable the insertion of a fresh layer of slurry, introduced stresses and deformations in the component, leading to several problems. In the "top-down" approach, the main issue is that the thickness of the printed slices is not precise and constant, due to the difficulty of the viscous slurry to uniformly wet and coat the already printed layers.
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Additive Manufacturing of ceramic components by Digital Light Processing: A comparison between the “bottom-up” and the “top-down” approaches
Journal of the European Ceramic Society, 2019Co-Authors: Oscar Santoliquido, Paolo Colombo, Alberto OrtonaAbstract:A systematic study of the additive manufacturing of complex ceramic objects was carried out using two different Digital Light Processing (DLP) approaches, the “bottom-up” and “top-down” ones, employing the same projector as light source and a photosensitive Al2O3-based ceramic slurry. Cylindrical periodic architectures having different Macro-Porosity, as well a bulk (dense) component in the form of a disk, were designed and additively manufactured with the two printers employing similar printing conditions. In the “bottom-up” approach, the periodic detachment of the part being manufactured from the bottom surface of the vat, to enable the insertion of a fresh layer of slurry, introduced stresses and deformations in the component, leading to several problems. In the “top-down” approach, the main issue is that the thickness of the printed slices is not precise and constant, due to the difficulty of the viscous slurry to uniformly wet and coat the already printed layers.
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high strength metakaolin based geopolymer foams with variable Macroporous structure
Journal of The European Ceramic Society, 2016Co-Authors: Giorgia Franchin, Hamada Elsayed, Paolo Colombo, Alberto ConteAbstract:Abstract Metakaolin-based geopolymer foams were synthesized by mechanical frothing, using hydrogen peroxide as additional foaming agent; three vegetable oils were added in order for the saponification reaction to occur. The combined use of the two foaming techniques (mechanical frothing and H 2 O 2 decomposition) led to interconnected Porosity: the in-situ formation of the soap molecules generated by the saponification reaction was exploited to generate Macro-Porosity. This combined route enabled the production of geopolymer foams with a range of total Porosity and strength values, with an optimal sample possessing a total Porosity of to ∼81 vol%, an open Porosity of ∼79 vol%, and a compressive strength of ∼3.1 MPa. Moreover, factors that influence the compressive strength, the Porosity, and the pore size distribution were investigated. The results showed that the cell size and cell window size can be controlled by adding different oils and different contents of peroxide.
Zvi Schwartz - One of the best experts on this subject based on the ideXlab platform.
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Additively manufactured 3D porous Ti-6Al-4V constructs mimic trabecular bone structure and regulate osteoblast proliferation, differentiation and local factor production in a Porosity and surface roughness dependent manner
Biofabrication, 2014Co-Authors: Alice Cheng, Aiza Humayun, David J. Cohen, Barbara D Boyan, Zvi SchwartzAbstract:Additive manufacturing by laser sintering is able to produce high resolution metal constructs for orthopedic and dental implants. In this study, we used a human trabecular bone template to design and manufacture Ti-6Al-4V constructs with varying Porosity via laser sintering. Characterization of constructs revealed interconnected porosities ranging from 15-70% with compressive moduli of 2579-3693 MPa. These constructs with Macro Porosity were further surface-treated to create a desirable multi-scale micro-/nano-roughness, which has been shown to enhance the osseointegration process. Osteoblasts (MG63 cells) exhibited high viability when grown on the constructs. Proliferation (DNA) and alkaline phosphatase specific activity, an early differentiation marker, decreased as Porosity increased, while osteocalcin, a late differentiation marker, as well as osteoprotegerin, vascular endothelial growth factor and bone morphogenetic proteins 2 and 4 increased with increasing Porosity. Three-dimensional (3D) constructs with the highest Porosity and surface modification supported the greatest osteoblast differentiation and local factor production. These results indicate that additively manufactured 3D porous constructs mimicking human trabecular bone and produced with additional surface treatment can be customized for increased osteoblast response. Increased factors for osteoblast maturation and differentiation on high Porosity constructs suggest the enhanced performance of these surfaces for increasing osseointegration in vivo.
Nilanjan Mitra - One of the best experts on this subject based on the ideXlab platform.
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thermal conductivity of cement paste influence of Macro Porosity
Cement and Concrete Research, 2021Co-Authors: Prodip Kumar Sarkar, Nilanjan MitraAbstract:Abstract Thermal conductivity of cement paste is significantly influenced by the presence of Macro-pores within it. These pores (pores with size greater than 6 μm, measured using microCT) which may be filled with air and/or water significantly alters the thermal conductivity of the resulting material. A combination of experiments, molecular dynamic investigations of major constituents of the cement paste, multiscale homogenization techniques, and inclusion of thermal conductivity of the pores containing either air or water has been utilized in this study to reveal the influence of pores in the calculation of thermal conductivity of the composite material.
Peter Heinl - One of the best experts on this subject based on the ideXlab platform.
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Cellular Ti-6Al-4V structures with interconnected Macro Porosity for bone implants fabricated by selective electron beam melting
Acta Biomaterialia, 2008Co-Authors: Peter Heinl, Lenka Muller, Carolin Körner, Robert Friedrich Singer, Frank A MullerAbstract:Selective electron beam melting (SEBM) was successfully used to fabricate novel cellular Ti-6Al-4V structures for orthopaedic applications. Micro computer tomography (μCT) analysis demonstrated the capability to fabricate three-dimensional structures with an interconnected Porosity and pore sizes suitable for tissue ingrowth and vascularization. Mechanical properties, such as compressive strength and elastic modulus, of the tested structures were similar to those of human bone. Thus, stress-shielding effects after implantation might be avoided due to a reduced stiffness mismatch between implant and bone. A chemical surface modification using HCl and NaOH induced apatite formation during in vitro bioactivity tests in simulated body fluid under dynamic conditions. The modified bioactive surface is expected to enhance the fixation of the implant in the surrounding bone as well as to improve its long-term stability. © 2008 Acta Materialia Inc.
