Mechanics, additive manufacture, and characterisation of novel lattice biostructures

With an increasingly ageing population, challenges within healthcare in the coming decades are expected to be in the area of repair and replacement of tissues and organs. The advent of Additive Manufacturing has afforded new opportunities for the fabrication of biomedical scaffolds and structured materials. This work addresses manufacturing and mechanics of 3D printed structures for biomedical applications, with an aim to promote their mechanical performance. Here we present a novel idea to create micro-patterned 3D printed scaffolds by developing new 3D printer nozzles, as well as introducing hierarchical porosity by printing polymer-porogen blends. The fabricated parts and filaments were characterised microscopically and mechanically. The structure-property relationship of woodpile lattice fabricated using fused deposition modeling under compressive loading along stacking direction is studied analytically, computationally and experimentally. Lattices with a variety of cross-sectional shape of the struts are successfully fabricated and characterised. Novel 3D printing dies capable of printing such lattices are manufactured and the effectiveness of this strategy is assessed experimentally as well as numerically and theoretically. Lattices with aligned and staggered arrangements are investigated. While the compression of the staggered arrangement is bending-dominated, the response of lattices in the aligned configuration is primarily due to diametrical compression of the struts. Novel scaling laws are reported. Analytical expressions for the apparent stiffness are derived accounting for filament flexure, diametrical compression, and response of tube under diametrically pinched load. Excellent agreement with numerical and experimental results is obtained.