This study involves the development of novel methods to enhance structural efficiency in the development of high performance lightweight stiff metal mechanical components. Optimised designs are created from biologically-inspired templates, taking advantage of new additive manufacturing techniques which enable the realisation of more complex shapes. The study focuses on the numerical side of design development and evaluation. Two case studies of aerospace components are considered: first, of an aircraft engine nacelle and second, of turbine blisks. In the first study, rib stiffeners, based on fibre arrangement in plant stem cells, are introduced and their geometric features are optimised for mass minimisation with mechanical response constraints done via genetic algorithms coupled with finite element analysis. The displacements of the optimised nacelle are lower compared to the original. Mass has lower optimisation emphasis, thus final values approach the mass limit. Optimised designs from different loading cases and magnitudes thereof have similar physical features. In the second study, turbine blisks are redesigned with an internal foam structure based on cancellous bones. Optimised 3D foam blisks are developed evaluated against the original solid design and with a different foam type. A study undertaken on 2D foam discs under inertial load demonstrates that foam configuration and densification methods influence the mechanical responses. The thesis shows that viable biologically-inspired designs can be developed using optimisation techniques. In both cases remarkable mass reduction is achieved while remaining within mechanical constraints. The Pareto front is traced on the design space from optimisation results, representing the set of optimal designs rather than a single unique solution. In the nacelle the displacement contour heavily influences the rib layout, which prefers intersections at boundary condition sites. The weight-to-displacement ratios of bio-inspired designs are lower than in equivalent topologically-optimised ones. In the turbine blisk, foam stiffness under inertial load is found to increase with node connectivity. Increasing relative density increases stresses but decreases displacement, and the specific behaviour is influenced by the method in varying density. In 3D the resulting foam blisks have higher stresses and displacement than the solid one, but their weight-to-displacement ratio can be improved using high-connectivity foams.