Some aspects of the injection moulding of alumina and other engineering ceramics

The literature concerning the injection moulding of engineering ceramics has been reviewed. This indicated that a number of claims had been made for the successful use of different organic binders during moulding and their removal prior to sintering. However, many of the claims were not supported by detailed/exact eScperimental evidence as to powder-binder compositions, moulding conditions, moulded properties, debinding times/cycles, or details of the structure and properties of the solid ceramic bodies produced. From the available information it was clear that there were few systematic and scientific investigations concerning the understanding of each stage of the injection moulding process. The present research programme has been carried out in two phases as follows. The first phase was concerned with the reinvestigation and re-evaluation of binder systems claimed to be successful for the injection moulding of alumina ceramics. The binders re-investigated included the thermoplastic-based binders such as polystyrene, polyacetal and atactic polypropylene and the water-based methylcellulose (Rivers) binder system. Alumina was chosen as the main powder to be investigated due to its simple handling and, highest applications amongst ceramic materials and on the basis that there is incomplete published work for almost every step of the injection moulding process. During the first stage of this work the optimum properties such as powder-binder compositions, mixing and moulding conditions, debinding properties, green and sintered densities provided by each binder system were determined. The results of these investigations showed that all the previous (re-evaluated) binder systems had major limitations and disadvantages. These included low volume loading (64 % maximum) of the alumina powder resulting in rather low sintered densities (96 % maximum-of theoretical density) and very long debinding times in the case of the thermoplastic-based binders. it ry low alumina volume loading (55 % maximum resulting in a 94 % . sintered theoretical density) and long moulding cycle time (- 5 min) along with adhesion and distortion problems during demoulding occurred in the case of the water-based methylcellulose binder system. Further work did not appear worthwhile. The newly developed binder systems have been used with a number of other powders such as zirconia, silicon nitride, silicon carbide, tungsten carbide-6 weight % cobalt and iron-2 weight % nickel, to establish- whether injection moulding is feasible. Optimum properties such as powder volume loadings, mixing, moulding, demoulding, moulded densities, debinding and some sintered density results showed that these new binder systems can also be used successfully for the injection moulding of other ceramic and metallic powders, although a fuller evaluation of the properties such as optimum sintered densities and mechanical properties is required

Measurement and mapping of cell traction forces on liquid crystal based force transducer

A novel cell traction force transducer based on shear sensitive cholesteryl ester liquid crystals (LCTFT) has been developed. This transducer incorporated with a custom-built cell traction force measurement and mapping (CTFM) software showed improved sensitivity and spatial resolution in sensing traction forces of human keratinocytes. The sensing output of the LCTFT was displayed as linear deformation lines in the liquid crystal surface that were induced by contraction of actin filaments via the focal adhesions of cells. In this context, the traction forces that were exerted locally by two clusters of focal adhesions induced strains in bi-axial directions in the liquid crystal surface. By using cell relaxation technique, these strains were determined and they were correlated by Poisson's ratio. With the displacement information, traction forces of single cells were calculated based on Hooke's theorem and the force-deformation relationships were derived. In this study, the transducer detected a wide range of cell traction forces (~10 - 140 nN) indicating the sensitivity of the system. The cell traction force maps generated by our CTFM software at a spatial resolution of ~ 5μm showed good representations of localised cell traction force fields and might be useful for time-based study of dynamic cells tractions.</p

Effects of an enzyme, depolymerization and polymerization drugs to cells adhesion and contraction on lyotropic liquid crystals

A novel cell force transducing assay based on liquid crystals has been developed. Human keratinocytes (HaCaTs) attached to and formed localized deformation on the surface of highly flexible cholesteryl ester liquid crystals. Cells have shown affinity to the lyotropic phase of the cholesteric liquid crystals which was immersed in culture media. In studying the nature of the attachment, 30μM cytochalasin-B and 0.25 Trypsin-EDTA were applied in independent experiments to qualitatively evaluate the force transmitted from the cytoskeletons and adhesion proteins to the liquid crystals substrate. 2 formaldehyde was used to fix the cells and to interrogate the mechanical creep effects in the liquid crystals. Cytochalasin-B reduced the forces exerted by the cells on the liquid crystals indicating that the liquid crystal surface could be used to sense forces generated internally by actin filaments. This study was supported by an additional experiment in which cells attachment was inhibited by the trypsin indicating the forces induced on the liquid crystals by the actin filaments were transmitted to the surface via protein couplings, i.e., focal contacts. Cells morphologies were also distinctly different in both treatments. The study on the creep effects at micro scale showed that a constant stress on the material imposed a regular strain on the material. Liquid crystals has shown stability in response to a constant and long term stress over a period of three days. The experiments demonstrated that the cholesteric liquid crystals could provide a flexible substrate to which cells readily attached, whilst enabling stable transduction of forces generated internally and transmitted to the liquid crystals film via cell surface receptors over a period of several days.</p

Interactions of cells with elastic cholesteryl liquid crystals

Exploitation of elastic property of the liquid crystal to sense cells mechanics is a novel application. Both quantitative and qualitative analysis of cholesteryl liquid crystal has shown flexibility and elasticity of the material to sense cell contraction and relaxation over a period of time. Importantly, cells adhesion was precluded with the use of extracellular matrix proteins in this technique. The optimum operating range with linear elasticity of the cholesteryl liquid crystal is � 0.1s -1 which has a good correlation with the shear rate of the cells originated from the focal adhesions. Localized contraction was observed with a good resolution. In addition, clear definition of deformation lines between two cells has shown their interacting path through active mechano-sensing. © 2009 Springer-Verlag.</p