Microparticle Patterning inside Capillary Tubes on Bendable Thin Film SAW Devices

Capillary tubes can potentially substitute conventional microchannels and become integrated with SAW devices either without fluid flow or in a continuous flow application for manipulating microparticles and cells. They have been used to manipulate, deform, trap, enrich, align, arrange, focus, pattern and separate microparticles and biological cells, for applications such as cell studies [1, 2] to immobilise cells in a cured gel to form a fibre and continuous flow applications to trap [3-6] and to focus [7] microparticles. There have also been a few studies on modelling of acoustofluidics platforms integrated with capillary tubes to investigate the fundamentals of particle manipulation inside capillary tubes [4, 8-10]. However, various patterns generated by using different cross-sections of capillary tubes and positioning the tubes at different directions compared with the electrode directions have not been systematically studied. Moreover, the published work is focused only on rigid and brittle lithium niobate (LiNbO3) SAW devices [1, 11, 12] without addressing flexible thin film SAW devices, which have advantages such as better mechanical qualities and potential applications in flexible microfluidic platforms, body conforming wearable devices, flexible sensors and electronics as well as soft robotics. This study aims to systematically investigate the patterning and alignment of microparticles inside glass capillary tubes using a zinc oxide (ZnO) thin film based flexible SAW device and capillary tubes with rectangular and circular cross-sections and at different tube positioning relative to the direction of the IDTs. The effects of positioning the tubes on the SAW device at different angles in relation to the IDTs were also studied. Additionally, both the rectangular and circular capillary tubes were used in a continuous flow setup to understand the effects of different flow rates on the particle patterning and alignment inside the tube.