Executive Summary : | Hip fractures are more common in elderly people due to loss of balance or osteoporosis. Even after surgery, it may limit lifestyle, impose financial burdens and even lead to death. With growing elderly population, the number of hip fractures worldwide is estimated to be 4.5 to 6.5 million per year in 2050. To prevent hip fracture, hip protectors made of impact-resistant materials and even airbags are commercially available. Studies found that some of the hip protectors offer sufficient impact force attenuation to prevent a hip fracture during simple falls from standing height. However, the impact attenuation of these hip protectors made of polymers or polymer foams is not sufficient to prevent hip fracture during accidents involving higher impact velocity than simple falls. Airbags require a power source, and there is a possibility of failure in electronic triggering. Unlike developed countries, where hip fractures are generally due to simple falls, India record a significant fraction of hip fracture from road accidents. Some of the hip fractures, especially of elderly pedestrians, resulting from low-energy accidents may be prevented with an appropriate hip protector. In this proposal, alternative material is proposed, which performs better than the materials used in existing hip protectors. Microlattice structures, a type of 3D-printed metamaterials, have periodic porosity with strut or rod size in the sub-millimetre range and studies have proved that microlattices can have superior energy absorption ability than porous stochastic foams. Shear thickening fluids(STFs) are non-Newtonian fluids that show an increase in viscosity with applied shear rate and display impact resistance through viscous dissipation. The proposed hip protector will be designed by combining both microlattice and STF to attain higher impact attenuation so that the protector can prevent pedestrian hip fractures resulted from low-energy road accidents apart from simple falls. This composite material is inspired from impact-resistant biological structures that possess both soft and hard phases. A few studies by other researchers and a preliminary study by the PIs have proved that STF can enhance the energy absorption ability of lattices. In fact, STF-filled foam has been studied for hip protectors. The primary objective is to design and develop a hip protector for elderly people made of composite STF-filled metamaterial. The STF with desired shear thickening parameters, i.e. critical shear rate and shear thickening ratio, will be filled in a microlattice made of highly ductile polymer with rationally designed lattice topology. The STF will enhance the impact force attenuation and prevent plastic deformation of the lattice. The performance of the prototype will be tested using pendulum impact test custom-made for simulation of sideway hip impact. This proposed hip protector is expected to prevent hip fractures from simple falls as well as low-energy impact pedestrian accidents. |