Theory of ultrathin films at metal-ceramic interfaces

A theoretical model for understanding the formation of interfacial thin films is presented, which combines density functional theory calculations for interface energies with thermodynamic modeling techniques for multicomponent bulk systems. The theory is applied to thin film formation in VC-doped WC-Co cemented carbides. It is predicted that ultrathin VC films may exist in WC/Co interfaces at the high temperature sintering conditions where most of the WC grain growth occurs, which provides an explanation of the grain growth inhibiting effect of VC additions in the WC-Co system

The Array Automated Assembly Task for the Low Cost Solar Array Project, Phase 2

During the program a process sequence was proposed and tested for the fabrication of dendritic welb silicon into solar modules. This sequence was analyzed as to yield and cost and these data suggest that the price goals of 1986 are attainable. Specifically, it was shown that a low cost POCL3 is a suitable replacement for the semiconductor grade, and that a suitable CVD oxide can be deposited from a silane/air mixture using a Silox reactor. A dip coating method was developed for depositing an antireflection coating from a metalorganic precursor. Application of photoresist to define contact grids was made cost effective through use of a dip coating technique. Electroplating of both Ag and Cu was shown feasible and cost effective for producing the conductive metal grids on the solar cells. Laser scribing was used to separate the cells from the dendrites without degradation. Ultrasonic welding methods were shown to be feasible for interconnecting the cells. A study of suitable low cost materials for encapsulation suggest that soda lime glass and phenolic filled board are preferred

Online oxygen monitoring using integrated inkjet-printed sensors in a liver-on-a-chip system

The demand for real-time monitoring of cell functions and cell conditions has dramatically increased with the emergence of organ-on-a-chip (OOC) systems. However, the incorporation of co-cultures and microfluidic channels in OOC systems increases their biological complexity and therefore makes the analysis and monitoring of analytical parameters inside the device more difficult. In this work, we present an approach to integrate multiple sensors in an extremely thin, porous and delicate membrane inside a liver-on-a-chip device. Specifically, three electrochemical dissolved oxygen (DO) sensors were inkjet-printed along the microfluidic channel allowing local online monitoring of oxygen concentrations. This approach demonstrates the existence of an oxygen gradient up to 17.5% for rat hepatocytes and 32.5% for human hepatocytes along the bottom channel. Such gradients are considered crucial for the appearance of zonation of the liver. Inkjet printing (IJP) was the selected technology as it allows drop on demand material deposition compatible with delicate substrates, as used in this study, which cannot withstand temperatures higher than 130 °C. For the deposition of uniform gold and silver conductive inks on the porous membrane, a primer layer using SU-8 dielectric material was used to seal the porosity of the membrane at defined areas, with the aim of building a uniform sensor device. As a proof-of-concept, experiments with cell cultures of primary human and rat hepatocytes were performed, and oxygen consumption rate was stimulated with carbonyl-cyanide-4-(trifluoromethoxy)phenylhydrazone (FCCP), accelerating the basal respiration of 0.23 ± 0.07 nmol s-1/106 cells up to 5.95 ± 0.67 nmol s-1/106 cells s for rat cells and the basal respiration of 0.17 ± 0.10 nmol s-1/106 cells by up to 10.62 ± 1.15 nmol s-1/106 cells for human cells, with higher oxygen consumption of the cells seeded at the outflow zone. These results demonstrate that the approach of printing sensors inside an OOC has tremendous potential because IJP is a feasible technique for the integration of different sensors for evaluating metabolic activity of cells, and overcomes one of the major challenges still remaining on how to tap the full potential of OOC systems.Peer ReviewedPostprint (author's final draft

The influence of the preparation method of NiOx photocathodes on the efficiency of p-type dye-sensitised solar cells

Improving the efficiency of p-type dye-sensitized solar cells (DSCs) is an important part of the development of high performance tandem DSCs. The optimization of the conversion efficiency of p-DSCs could make a considerable contribution in the improvement of solar cells at a molecular level. Nickel oxide is the most widely used material in p-DSCs, due to its ease of preparation, chemical and structural stability, and electrical properties. However, improvement of the quality and conductivity of NiO based photocathodes needs to be achieved to bring further improvements to the solar cell efficiency. The subject of this review is to consider the effect of the preparation of NiO surfaces on their efficiency as photocathodes. (C) 2015 Elsevier B.V. All rights reserved

Applications of 3D printing in the management of severe spinal conditions

The latest and fastest-growing innovation in the medical field has been the advent of three-dimensional printing technol- ogies, which have recently seen applications in the production of low-cost, patient-specific medical implants. While a wide range of three-dimensional printing systems has been explored in manufacturing anatomical models and devices for the medical setting, their applications are cutting-edge in the field of spinal surgery. This review aims to provide a com- prehensive overview and classification of the current applications of three-dimensional printing technologies in spine care. Although three-dimensional printing technology has been widely used for the construction of patient-specific ana- tomical models of the spine and intraoperative guide templates to provide personalized surgical planning and increase pedicle screw placement accuracy, only few studies have been focused on the manufacturing of spinal implants. Therefore, three-dimensional printed custom-designed intervertebral fusion devices, artificial vertebral bodies and disc substitutes for total disc replacement, along with tissue engineering strategies focused on scaffold constructs for bone and cartilage regeneration, represent a set of promising applications towards the trend of individualized patient care

Biomimetic modification of porous TiNbZr alloy scaffold for bone tissue engineering

Porous titanium (Ti) and Ti alloys are important scaffold materials for bone tissue engineering. In the present study, a new type of porous Ti alloy scaffold with biocompatible alloying elements, that is, niobium (Nb) and zirconium (Zr), was prepared by a space-holder sintering method. This porous TiNbZr scaffold with a porosity of 69% exhibits a mechanical strength of 67MPa and an elastic modulus of 3.9GPa, resembling the mechanical properties of cortical bone. To improve the osteoconductivity, a calcium phosphate (Ca/P) coating was applied to the surface of the scaffold using a biomimetic method. The biocompatibility of the porous TiNbZr alloy scaffold before and after the biomimetic modification was assessed using the SaOS2 osteoblast&ndash;like cells. Cell culture results indicated that the porous TiNbZr scaffold is more favorable for cell adhesion and proliferation than its solid counterpart. By applying a Ca/P coating, the cell proliferation rate on the Ca/P-coated scaffold was significantly improved. The results suggest that high-strength porous TiNbZr scaffolds with an appropriate osteoconductive coating could be potentially used for bone tissue engineering application.<br /

Simulation-Based Identification of Operating Point Range for a Novel Laser-Sintering Machine for Additive Manufacturing of Continuous Carbon-Fibre-Reinforced Polymer Parts

Additive manufacturing using continuous carbon-fibre-reinforced polymer (CCFRP) presents an opportunity to create high-strength parts suitable for aerospace, engineering, and other industries. Continuous fibres reinforce the load-bearing path, enhancing the mechanical properties of these parts. However, the existing additive manufacturing processes for CCFRP parts have numerous disadvantages. Resin- and extrusion-based processes require time-consuming and costly post-processing to remove the support structures, severely restricting the design flexibility. Additionally, the production of small batches demands considerable effort. In contrast, laser sintering has emerged as a promising alternative in industry. It enables the creation of robust parts without needing support structures, offering efficiency and cost-effectiveness in producing single units or small batches. Utilising an innovative laser-sintering machine equipped with automated continuous fibre integration, this study aims to merge the benefits of laser-sintering technology with the advantages of continuous fibres. The paper provides an outline, using a finite element model in COMSOL Multiphysics, for simulating and identifying an optimised operating point range for the automated integration of continuous fibres. The results demonstrate a remarkable reduction in processing time of 233% for the fibre integration and a reduction of 56% for the width and 44% for the depth of the heat-affected zone compared to the initial setup

Selective laser sintering of bioactive glass scaffolds and their biological assessment for bone repair

Bone scaffold fabrication using powder-bed based additive manufacturing techniques, like the selective laser sintering (SLS) process, provides control over pore interconnectivity, pore geometry, and the overall shape of the scaffold, which aids in repairing different regions of the bone. The main objectives of this dissertation were to develop bioactive glass (BG) scaffolds using the SLS process and evaluate the scaffolds for their effectiveness in bone repair both in vitro and in vivo. 13-93 glass, a silicate based BG, and 13-93B3 glass, a borate based BG, are designed to accelerate the body\u27s natural ability to heal itself and are used in this research. After the initial feasibility study, the material and process parameters were optimized to improve the compressive strength from ~20 MPa to ~41 MPa, for a 13-93 BG scaffold with a porosity of ~50%. Pore geometry of the scaffold plays a crucial role as it not only affects the mechanical properties and subsequent degradation but also the bone cell proliferation. Scaffolds with a porosity of ~50% and five different pore geometries, namely, cubic, spherical, X, diamond, and gyroid, were fabricated and assessed in vitro for a possible preferential cell proliferation. The MTT labeling experiments indicated that the scaffolds with diamond and gyroid pore geometries have higher curvature-driven MLO-A5 cell proliferation. Finally, scaffolds with diamond and cubic pore geometries were evaluated in vivo using a rat calvarial defect model for 6 weeks. Though the results indicated no significant difference in the amount of new bone formation with respect to the defect region, the maturation of the fibrous tissue to bone appeared to be quicker in the scaffolds with diamond architecture --Abstract, page iv

Unravelling densification during sintering by multiscale modelling of grain motion

The resulting microstructure after the sintering process determines many materials properties of interest. In order to understand the microstructural evolution, simulations are often employed. One such simulation method is the phase-field method, which has garnered much interest in recent decades. However, the method lacks a complete model for sintering, as previous works could show unphysical effects and the inability to reach representative volume elements. Thus the present paper aims to close this gap by employing molecular dynamics and determining rules of motion which can be translated to a phase-field model. The key realization is that vacancy absorption induced motion of grains travels through a grain structure without resistance. Hence the total displacement field of a green body is simply the superposition of all grains reacting in isolation to local vacancy absorption events. The resulting phase-field model is shown to be representative starting from particle counts between 97 and 262 and contains the qualitative correct dependence of sintering rate on particle size

A novel pathway for efficient characterisation of additively manufactured thermoplastic elastomers

Thermoplastic elastomers (TPE) are commonly used to fabricate structures for application in repeatable, energy absorption environments. The emergence of additive manufacturing (AM) means scope now exists to design and build complex TPE components that can mechanically outperform traditionally manufactured equivalents. The ability to efficiently characterize these new TPE AM materials is, however, a barrier preventing wider industrial uptake. This study aims to establish a novel pathway for efficiently characterizing materials used in transient, dynamic applications, to ultimately enable accurate finite element (FE) simulation. A laser sintered TPE powder was characterised by performing low, intermediate and high rate uniaxial tension tests, plus planar and equibiaxial loading states. These data demonstrated significantly different behaviour across strain rates and deformation modes, necessitating fit of an augmented hyperelastic and linear viscoelastic model. FE software was then used to calibrate material model coefficients, with their validity evaluated by comparing the simulated and experimental behaviour of the material in isolated (uniaxial tensile) and mixed modal (lattice-based impact) deformation states. Close correlation demonstrated this novel approach efficiently generated valid material model coefficients, removing a barrier to industry adopting these materials. This creates opportunity to exploit these new technologies for the design optimization and fabrication of high-performance component