Controlled actuation of a floating liquid marble, a liquid droplet coated with hydrophobic particles floating on another liquid surface, is a potential digital microfluidics platform for the transport of aqueous solution with minimal volume loss. This paper reports our recent investigation on the magnetic actuation of floating liquid marbles filled with magnetic particles. The magnetic force and frictional force acting on the floating liquid marble determine the horizontal movement of the marble. We varied the magnetic flux density, flux density gradient, concentration of magnetic particles and speed of the marble to elucidate the relationship between the acting forces. We subsequently determined the suitable operating conditions for the actuation and derived the scaling laws for the actuation parameters.
This paper reports a wirelessly powered ionic polymer-metal composite (IPMC) soft actuator operated by external radio frequency (RF) magnetic fields for targeted drug delivery. A 183 μm thick IPMC cantilever valve was fitted with an embedded LC resonant circuit to wirelessly control the actuator when the field frequency is tuned to its resonant frequency of approximately 25 MHz. Experimental characterization of the fabricated actuator showed a cumulative cantilever deflection of 160 μm for three repeated RF ON-OFF cycles at 0.6 W input power. The device was loaded with a dye solution and immersed in DI water to demonstrate wireless drug release. The qualitative result shows the successful release of the dye solution from the device reservoir. The release rate can be controlled by tuning the RF input power. We achieved a maximum average release rate of ∼0.1 μl s-1. We further conducted an in vitro study with human tumor cells (HeLa) to demonstrate the proof of concept of the developed device. The experiments show promising results towards the intended drug delivery application.
This review paper first discusses the design considerations that are being applied in the development of a highly sensitive, miniaturised and high throughput assay microcalorimeter. Major factors include reaction chamber, thermal insulation, fluid handling, mixing techniques and temperature sensing. Miniaturisation is the key to handle smaller sample volume within the nanoliter to picoliter regions, which is made possible by advancement in materials and fabrication technologies. Materials under review include silicon, silicon nitride, parylene-C, PMMA, PDMS, SU-8 and polymide. The materials are compared in terms of size, cost, biocompatibility, chemical resistance and thermal properties. Finally, we compile the list of works across the globe and their contributions that demonstrated microcalorimeter prototypes with high thermal insulation, precise microfluidic handling capabilities, rapid mixing of fluids and high throughputs. This review offers broad perspectives and insights for those working on microcalorimeter, enthalpy arrays, microfluidic biosensor, thermal sensor and micromixer.
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