A novel synthetic strategy for bioinspired functionally graded nanocomposites employing magnetic field gradients

In order to mimic the complex architecture of many bio-materials and synthesize composites characterized by continuously graded composition and mechanical properties, an innovative synthetic strategy making use of magnetic field gradients and based on the motion of superparamagnetic Fe sub(3)O sub(4)iO sub(2 ) core-shell nanoparticles is adopted. It is demonstrated that by lowering the viscosity of the system through particle functionalization, and increasing the magnetic force acting on the nanoparticles upon optimization of a simple set-up composed of two permanent magnets in repulsion configuration, the magnephoretic process can be considerably accelerated. Thus, owing to the magnetic responsiveness of the Fe sub(3)O sub(4) core and the remarkable mechanical properties of the SiO sub(2) shell, approximately 150 mu m thick polymeric films with continuous gradients in composition and characterized by considerable increments in elastic modulus (up to approximately 70%) and hardness (up to approximately 150%) when going from particle-depleted to particle-enriched regions can be synthesized, even in times as short as 1 hour. The present methods are highly promising for a more efficient magnetic force-based synthesis of inhomogeneous soft materials whose composition is required to be locally tuned to meet the specific mechanical demands arising from non-uniform external loads.