Abstract:One of the most common complications from long-term wheelchair use or bed rest is pressure ulcers. Pressure ulcers have significant morbidity and are associated with high mortality. Prolonged sitting can cause high pressures in the skin and subcutaneous tissue which can lead to local ischemia and breakdown of skin. Rapid relief of pressure prevents ulcer formation. One prevention strategy is to change the temporal distribution of pressure at the interface between user and surface so that no one area is subjected to high pressures for long periods of time. While there are several dynamic interfaces in use currently, there is no definitive evidence of enhanced pressure ulcer prevention with their use. The purpose of this research was to parametrically evaluate interface array sizes, shapes and patterns for dynamic support surfaces to optimize pressure redistribution to prevent pressure ulcers. Finite element analyses, anatomical phantom deep tissue pressure measurements and interface pressure mapping were used to test various support geometries and sizes and different array spacing and patterns. Results indicate that modulating pressure in an array of supports that are equally spaced is not effective. Only interrupted pattern arrays resulted in sufficient pressure reduction. These data suggest that dynamic surface supports can be optimized based on the geometry and size of the individual supports and the pattern of the array to further reduce the likelihood of pressure ulcer formation.
An investigation into the solvent and thermal debinding behaviour of a typical paraffin wax-polymer binder system for titanium alloy Ti-6Al-4V powder injection moulding (PIM) feedstock was conducted. Details of the mixing parameters, powder loading, temperature and mixing speed were evaluated for optimal compounding of the feedstock. The feedstock was injection moulded into 22 mm diameter by 3 mm thick disks. Debinding is conducted in two stages, an initial solvent debinding step to remove the waxes, followed by a thermal debinding step to remove the polymers. Solvent debinding was conducted by immersing the injection moulded specimens in n-heptane heated to 50 °C for a period of 5 hours. The mass loss rate was logged during solvent debinding in order to determine the efficiency of the solvent debinding step. From these measurements, it was determined that 94 wt% of the wax (paraffin wax and stearic acid) components of the binder were removed during solvent debinding. A thermo-gravimetric analysis (TGA) was conducted in air on the Ti-6Al-4V powder, as well as the green and solvent debound feedstock. These results show the effect of debinding the feedstock in air and were used to design a thermal debinding cycle for the system.
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