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

Abstract

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 Fe₃O₄@SiO₂ 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 Fe₃O₄ core and the remarkable mechanical properties of the SiO₂ shell, approximately 150 μm thick polymeric films with continuous gradients in composition and characterized by considerable increments in elastic modulus (up to ≈70%) and hardness (up to ≈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.