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Improving the strength of -TCP scaffolds produced by Digital Light Processing using two-step sintering
(ELSEVIER SCI LTD, 2024-04-01) Paredes Sánchez, Claudia Isabel; Roleček, Jakub; Miranda, Pedro
Digital Light Processing is combined with two-step sintering to obtain bioactive scaffolds with improved strength and mechanical isotropy. Highly loaded photosensitive suspensions were prepared from beta-TCP powder to create scaffolds consisting of interpenetrating struts with two different designs. Two sintering methods were used: conventional sintering (CS) and two-step sintering (2SS). The latter resulted in a microstructure with uniformly shaped grains and reduced porosity. Their compressive strength was determined by uniaxial testing under two different load configurations, with the force applied parallel or perpendicular to the building plane of the scaffolds. Design optimisation and fine-tuning of the sintering process helped in reducing the presence of interlayer defects and minimise the shear-dominated fractures. Isotropic fracture behaviour was achieved, with similar central values of the Weibull distribution (49 +/- 1 MPa vs. 51 +/- 1 MPa) along both testing directions, showing a great potential for their use in load-bearing bone tissue engineering applications.
Evaluating the suitability of fast sintering techniques for the consolidation of calcium phosphate scaffolds produced by DLP
(ELSEVIER SCI LTD, 2023-11-01) Paredes Sánchez, Claudia Isabel; Roleček, Jakub; Pejchalová, Lucie; Spusta, Tomáš; Salamon, David; Miranda, Pedro
Porous scaffolds were fabricated via Digital Light Processing (DLP) from beta-TCP powder and sintered by conventional sintering in air (CSA), rapid sintering in air (RSA) and pressure-less spark plasma sintering in vacuum (pl-SPS), at four different temperatures: 1200, 1300, 1400 and 1500 degrees C. Each sintering strategy resulted in scaffolds with different phase composition, microstructure and mechanical properties. Long dwell times or high temperatures were required to achieve a complete beta ->alpha transformation, and rapid cooling rates avoided the reverse transformation. The presence of graphite in the sintering chamber played a crucial role in stabilising the alpha-TCP phase, phase prevailing in SPS-treated scaffolds, hindered their densification and avoided the generation of transformation-induced cracks. All scaffolds exhibited compressive strengths within the range of cancellous bone, with the highest average value of 22 +/- 4 MPa achieved by the RSA scaffolds sintered at 1300 degrees C, thanks to their greater densification and fine microstructure.
Dilatometric and microstructural study of particle and functionally graded composites based on hydroxyapatite and crystalline bioglass
(2023-10-23) Drdlík, Daniel; Drdlíková, Katarina; Maca, Karel
Hydroxyapatite (HA) and bioglass (BG) ceramics have become of prime importance in bone tissue engineering. Besides the appropriate composition, the microstructure of bone replacement plays a crucial role. In the present work, particle composites and functionally graded material (FGM) based on HA and BG prepared by electrophoretic deposition were thoroughly characterised in terms of the preparation method, sintering process, phase composition and microstructure. The sintering was monitored by high-temperature dilatometry in two directions, the sintering rates were calculated, and the overall sintering process was discussed. The SEM showed the continuous change in the microstructure of FGM with gradual interconnected porosity favourable for bio-applications. The fundamental fractographic analysis proved the crack development in FGM related to the sintering process, and the recommendations for the reduction of the crack development were given. The phase transformations during thermal treatment were analysed using X-ray diffraction analysis and deeply discussed.
Effect of powder milling on sintering behavior and monotonic and cyclic mechanical properties of Mo and Mo-Si lattices produced by direct ink writing
(Elsevier, 2023-10-05) Tkachenko, Serhii; Slámečka, Karel; Oliver Urrutia, Carolina; Ksenzova, Olha; Bednaříková, Vendula; Remešová, Michaela; Dvořák, Karel; Baláž, Matej; Deák, Andréa; Kachlík, Martin; Čelko, Ladislav; Montufar Jimenez, Edgar Benjamin
Molybdenum is a refractory metal regarded as a promising basis for producing high-temperature components. However, the potential of manufacturing molybdenum-based structures by direct ink writing (DIW) has not been explored. In this study, three-dimensional porous molybdenum (Mo) and molybdenum-silicon (Mo-Si) composite lattices were fabricated using DIW with non-milled and milled powders. The effects of Mo powder morphology (resulting from milling) and chemical composition (alloying Mo with 3 and 10 wt% of Si) on the microstructure, phase composition, and static and cyclic compression properties at room temperature were investigated. Lattices fabricated from commercial spherical Mo powder exhibited the highest intra-filament porosity. Conversely, lattices fabricated from milled Mo powder were denser and had higher compressive strength, offset stress, and quasi-elastic gradient. Alloying Mo with Si during sintering resulted in composite lattices with Mo thorn Mo3Si microstructure. A low content of Mo3Si slightly decreased monotonic compression properties but did not affect the cyclic compression response compared to Mo lattices made from milled powder. In contrast, a high content of Mo3Si produced quasi-brittle lattices with reduced compressive strength and increased damage accumulation during cyclic loading. The cyclic behavior of all lattices was characterized by a ratcheting-dominated stress-strain response. Lattices fabricated from milled Mo and milled Mo-3 wt.%Si powders demonstrated superior performance compared to those fabricated from commercial spherical Mo and milled Mo-10 wt%Si powders. The results suggest that using milled powders can enhance the mechanical reliability and promote the use of DIW as preferred additive manufacturing technology for the fabrication of Mo-Si composite lattices. (c) 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Co-extrusion of zirconia core-shell rods with controlled porosity in the core
(2018-10-01) Kaštyl, Jaroslav; Pouchlý, Václav; Trunec, Martin
A method for manufacturing bi-layered zirconia rods of core-shell geometry with a porous core and a dense shell has been developed. Core-shell rods were successfully prepared by thermoplastic co-extrusion of assembled feed rods composed of core and shell zirconia feedstocks. Rheological analysis and adjustment of the feedstock viscosities enabled co-extrusion of regular core-shell rods of uniform shell thickness. Tapioca starch was used as a pore-forming agent in the core feedstock. Binder removal and high temperature treatment had to be modified in order to safely remove the starch particles. Sintering analysis revealed constrained sintering of porous cores in the core-shell rods due to the rigid dense shell, which resulted in an increased porosity in the core. Defect-free core-shell rods with a core porosity of up to 40% and different thicknesses of the dense shell were prepared.

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