Calcium Phosphate Bone Cements

Biomaterials utilized in biomedical applications are of various characteristics and cements are unique in their in situ, biomimetic formation ability. They present the most topographically complex surfaces that usually elicit a favorable cellular response for tissue regeneration. In addition their composition may provide an effective chemical gradient around the resorbing implant to induce desired cellular activity that leads to rapid wound healing and regeneration. These are the main reasons for many cement systems to function well in the body, especially as hard tissue replacements. The properties and the setting mechanisms of the clinically most relevant cement system, calcium phosphate cements have been elucidated in this chapter

Preparation and Evaluation of Methytrifluoropropyl-Containing Vinyl-Functionalized Terpolysiloxanes for “All-in-One” Pastes for Additive Manufacturing

In this work, the effects of the degree of polymerization (DP) and incorporation (mol %) of methytrifluoropropylsiloxy (MeTfpS) repeat units into vinyl-functionalized terpolysiloxanes in crosslinked elastomers from “All-in-One” pastes (A/1Ps) for additive manufacturing were investigated. It was found that the DP and mol % of MeTfpS-containing repeat units do not contribute to the rheological properties of non-crosslinkable pastes, which can be mostly attributed to the thixotropic additive and both the type and relative amount of filler added. Crosslinkable A-1/Ps with higher DP polymers exhibited faster curing (crosslinking) while the mol % of MeTfpS had little to no effect on the curing times. A/1Ps underwent a year-long shelf-life stability study indicating only a slight loss in storage modulus for pastes using MeTfpS-containing terpolymers with targeted DPs of 160 and 240 after six months. The crosslinked elastomers exhibited strain-induced crystallization (via DMA) only in elastomer samples containing 5 mol % of MeTfpS and with a DP of 240 or higher in the temperature range of -80 to -30 °C, characteristic for pure polydimethylsiloxane (PDMS) melting transition

Protocol for determining porosity and mechanical properties of ZrO2 obtained throug 3D-printing

New technologies, such as robocasting, arrive in the 20thcentury fordoing the competence to traditional manufacturing techniques. These techniquesenablethe possibility to produce more versatile ceramic pieces,where biomedical implants are the best example. In this Master’s thesis, Zirconia is going to be investigated due to its high biocompatibility and proper mechanical properties. ZrO2presents a toughening mechanism (i.e. phase transformation in the crack tip accompanied with a volume grain expansion) which increases the resistance of the material to crack propagation. Nevertheless, ZrO2presents a low temperature degradation mechanism in which mechanical properties become dropped off in humid environments. In that context, three commercialgradesofZrO2powders (CY3Z-RA, GY3Z-R60and TZ-3YS-E) are going to be examinedin order to compare them.First of all, it will be characterized the powder. To complete this purpose it will be determined the powder particle size through laser diffraction and the linear intercept method. After on, microstructure will be analysed with x-ray diffraction, and specific surface are by means of BET analysis. Finally, the powder density is going to be determined through He pycnometry, and the amount of binder in GY3Z-R60using a thermo-balance. The second step is to characterize the paste that is going to be printed. In that case, a plate-plate rheometer will analyse the rheology parameters. Afterwards, for the printed specimens, the microstructural (e.g., density,porosity,etc.) and micromechanical properties (e.g. hardness, elastic modulus, etc.) will be determined by using advanced characterization techniques, such asfield emission scanning electron microscopyornanoindentation, among others.The results obtainedfor the powdersare in accordance with the data sheet provided by the suppliers. The pastes present a clear Herschel-Bulkleyfluid with a shear thinning behaviour, indispensable for printing ZrO2parts. After that, four pieces are going to be fabricated through the robocasting technique at 100% and 50% filling spacewith the two first aforementioned feedstocks. Finally it will be characterized the porosity and the mechanical properties of them. Regarding porosity, it will be characterized through 2D and 3D imaging, micro-CT and BET/BJH. It is concluded that 3D imaging is the most suitable characterization technique. However, it is not the most efficientway.With regard to mechanical properties, hardness, indentation fracture toughness and Young’smodulus are going to be determined. The results obtained are an averageof 12.5 GPa for hardness, 5.2 MPa m-1/2for indentation fracture toughness and 230 GPa for the elastic modulusfor both materials. These resultsare in accordance with the reported for ZrO2parts obtained through traditional manufacturing techniques. Hence, the robocasting technique is suitable for manufacturingZrO2parts. To sum up, it is concluded that i) the binder facilitates the rheology of paste,ii) the mixing must be optimized,iii)3D-printing must be performed in a humidity chamber to avoid drying of the pasteand using a metallic nozzle,iv) more efficient or new characterization techniques must be investigated in order to ease porosity measurements, and v) the 3D-printed parts fulfilthe mechanical requirements

Additive manufacturing of ceramics and ceramic composites via robocasting

In the last two decades additive manufacturing (AM) has emerged as a highly important and influential technology. A large range of approaches to AM have been developed which give rise to hundreds of distinct techniques. Many of these are specific to one material system, and only a handful have been successful at producing ceramic parts. Robocasting is one such technique, having been used to produce complex ceramic parts with reasonable mechanical properties. In this thesis robocasting is investigated further, firstly by characterising the rheology of the robocasting paste, and then by measuring the strength and reliability of ceramic parts produced by robocasting. The critical defects associated with the process are identified, and efforts have been made to eliminate them. Furthermore, it was possible to produce a new class of ceramic composites consisting of alumina platelets aligned by the shear forces that arise during printing. These platelets themselves and the composites were extensively characterised. A new in-situ double cantilever test was developed in order to study the fracture behaviour of the composites. Lastly, the principle of using the printing process to align platelets was applied to fibres in order to create printed fibre reinforced ceramic matrix composites, and printed carbon fibre reinforced epoxy.Open Acces

Additive manufacturing of advanced ceramics for demanding applications

Interest and investment in additive manufacturing (AM) has been growing exponentially in recent years. Many AM processes for polymers and metals are nearing maturity, however for ceramics there are fewer processes available and they are in their early stages of development, with a significantly narrower material selection. AM offers benefits of light-weighting and increased efficiency through complex functional designs not possible by conventional manufacturing techniques whilst reducing material waste and tooling costs for different components. Ceramic heaters that exhibit positive temperature coefficient of resistance (PTCR) could be fabricated by AM for improved use in automotive and aerospace applications. This project demonstrates the feasibility of using AM to fabricate PTCR heating elements in various shapes and sizes including honeycomb lattice structures with the same material extrusion equipment – thus signifying the flexibility and suitability of AM to manufacture complex heater geometries. The project work traverse through an entire power-to-product processing excursion to achieve a functional prototype PTCR ceramic heater. Barium titanate (BT) and lanthanum/manganese doped barium titanate (BT) based PTCR functional heater elements/structures were fabricated with desirable electrical properties for the first time using additive manufacturing by material-extrusion (robocasting). 3D printed components of varying size and shape, and prototype honeycomb lattices with high density were achieved with comparable and in some cases superior electrical properties. Aqueous, less organic containing (2.5 wt% additives versus 10-30 wt% added typically), eco-friendly ink formulations were developed with suitable rheological properties for 3D printing. For BT prints, the sintered densities of the 3D ceramic parts were found to be >99% TD, this is the highest reported value so far. The rheology of pastes required for robocasting was investigated in detail to understand the effect of dispersant, solids loading and viscofier contents. The rheological characteristics studied included yield stress, viscosity, shear stress, storage modulus and loss modulus. Different BT based PTCR mixtures were investigated through 3D printing, calcination, sintering along with conventional pressing & sintering for comparison. Effect of printing parameters on print quality and print microstructure were investigated. Drying of the prints was investigated as a parameter to allow printing of a wider range of pastes with different viscosity and yield stress. Yield stress of paste formulations and controlled drying were identified as key contributors to the successful 3D fabrication via robocasting. The microstructure, electrical properties and heating characteristics of the printed PTCR components were studied in detail and their thermal stability evaluated using infrared imaging and benchmarked against commercial PTCR heating element. The heating behaviour of the solid and porous 3D printed components was demonstrated to be similar, paving the way for light weight ( ̴47% reduction in weight) heaters suitable for automotive, aeronautical and even astronautical applications and the technique can also lead to significant materials savings during device fabrication. The general applicability of the robocasting-based AM technique augers well for its use to manufacture complex shaped advanced ceramics for demanding applications, for example, in automotive (heaters as described here), healthcare (biomedical implants - personalised dental and hip/knee implants), defence (high frequency, high temperature conformal antenna structures) and energy (battery components) sectors.</div