Prevention of hip fractures in elderly patients using a protective garment incorporating a shear thickening fluid

Barlaz, David
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University of Delaware
Fall induced hip fractures are a common form of injury among the elderly. On average, people over 65 years of age suffer at least one fall each year. Possible results include permanent loss of mobility and quality of life if the bone heals or death if complications ensue. Hip fractures are expected to become increasingly common as the current baby boomer generation reaches their later years. Current garments intended to prevent hip fractures, often made of foam, are largely ineffective and are often accompanied by low patient compliance due to comfort and aesthetic issues. Incorporation of a shear thickening fluid (STF) into a protective garment may improve performance because of the large amount of energy dissipated by viscous effects during flow, while providing a solution to some of the comfort issues surrounding patient compliance. A number of STFs were impact tested using an Instron drop tower to determine their viability in a garment designed for hip fracture prevention. Discontinuously thickening STFs, notably a dispersion of 45 volume % low polydispersity silica nanoparticles in MW=200 polyethylene glycol, were found to be the best candidates. This specific suspension was chosen over similar candidates due to lower cost of materials. This was due to the peak force experienced by the suspension during impact exhibiting low sensitivity to changes in energy. For a four fold increase in energy, peak force increased less than two fold in this suspension, while it increased as much as six fold for other fluids. All samples exhibited similar sensitivity to variation in sample height.Squeeze flow simulations of Newtonian fluids were developed in parallel with the drop tower experiments. The inertial effect of the fluid was found to be minimal, thus simplifying future simulations. The effect of the foam casing used was also found to be negligible provided its Young’s modulus was less than 1 MPa. The STF/foam composites were fabricated by loading STF in columns at a variety of area fractions by varying column diameter and holding column spacing constant. Good performance at lower area fractions aids significantly in garment design making the pad more flexible, more lightweight, and cheaper. Performance was found to peak at an area fraction of approximately 0.50. This result was found on both the linear motion impact of the drop tower, as well as the rotational motion of the pendulum impact device. The rotational motion impact decreased peak forces up to an order of magnitude from the linear experiment, the best performing samples had peak forces of about 1.5 kN. Although increased area fraction did not significantly reduce peak force, it did reduce variability in the peak force.