Acoustic Propulsion of Micron-Sized Solids for Small Scale Mixing and Drug Delivery
Acoustic propulsion is a rapidly growing field with great potential in medical and environmental applications that require guiding of small scale objects (e.g. cells, drug micro-carriers, etc).
However experimental observations of acoustic propulsion (acoustophoresis) still need a robust theoretical interpretation, which would help for the design of optimised drug micro-carriers.
The transport of synthetic micro-scale particles has recently seen a revival of activity, due to the possible biomedical and environmental use of these objects. Indeed, small active solid bodies could be employed in the near future to achieve targeted drug delivery in biological media and small-scale mixing. In this project, we aim at providing a rational method for the design and propulsion of optimised acoustically actuated micro-swimmers. We focus here on non-homogeneous (non-deformable swimmers), for which inertia and position of the centre of mass both depend on the mass repartition. Swimming efficiency in biofluids such as lymph, blood plasma and synovia, and the ability to go through phospholipid membranes will be assessed. In this context, the possible hemolysis effects of the acoustic radiation on red blood cells will also be appraised.
We use a comprehensive analytical approach to derive the propulsion speed of asymmetric micro-objects ‘illuminated’ by an acoustic incident field. In principle, the non linear (rectified) acoustic streaming flow, which triggers the propulsion should be calculated and the corresponding stress integrated over the particle surface. In order to circumvent the problem and avoid a cumbersome calculation, we derive an integral expression of the propulsion speed by means of Lorentz’ reciprocal theorem. For some simple geometries (bottom heavy spheres etc) the latter integral can be actually integrated to provide a full analytical (integrated) form of the acoustic propulsion speed.
Acoustic propulsion is of central interest for drug delivery in bio-fluids, essentially because of its biocompatibility (unlike most chemical actuation methods such as Janus electrochemical propulsion). UK bioengineering industry could benefit in the short to mid term from our optimisation methods so that technological transfer to the field of medical application could occur in the near future. More generally, the present project will contribute to the progress of acoustic micro-propulsion for diseased cell targeting and small-scale mixing, a topic of growing interest worldwide.
Dr Francois Nadal - Senior Lecturer in Fluid Engineering
“With the emergence of micro- and nano-carriers as drug delivery platforms, acoustic propulsion has received growing attention in recent years. In collaboration with the University of Cambridge (DAMTP), the Ecole Polytechnique (Paris, France) and Penn State University (Philadelphia, USA), here we aim at developing advanced numerical models to inform the optimisation of such carriers.”