A Lotus shaped acoustofluidic mixer: High throughput homogenisation of liquids in 2 ms using hydrodynamically coupled resonators

This paper presents an acoustically actuated microfluidic mixer that uses an array of hydrodynamically coupled resonators to rapidly homogenise liquid solutions and synthesise nanoparticles. The system relies on 8 identical oscillating cantilevers that are equally spaced on the perimeter of a circular well, through which the liquid solutions are introduced. When an oscillatory electrical signal is applied to a piezoelectric transducer attached to the device, the cantilevers start resonating. Due to the close proximity between the cantilevers, their circular arrangement and the liquid medium in which they are immersed, the vibration of each cantilever affects the response of its neighbours. The streaming fields and shearing rates resulting from the oscillating structures were characterised. It was shown that the system can be used to effectively mix fluids at flow rates up to 1400 µl.min⁻¹ in time scales as low as 2 ms. The rapid mixing time is especially advantageous for nanoparticle synthesis, which is demonstrated by synthesising Poly lactide-co-glycolic acid (PLGA) nanoparticles with 52.2 nm size and PDI of 0.44.