Chemotactic droplets for multifunctional fluidic systems
Florea, Larisa and Francis, Wayne and Delaney, Colm and Diamond, Dermot (2017) Chemotactic droplets for multifunctional fluidic systems. In: FLOW17, 3-5 July 2017, Paris, France.
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The controlled transport of chemical species in fluids is essential to the function of living systems. This, together with the ability to selectively transport chemical species in a controlled way, against chemical or electrochemical gradients, has been at the core of complex natural systems development. While transport over short distances (e.g. intracellular) is typically achieved by cargo-carrying vesicles or motor proteins acting like a conveyor belt, many single cell and multicellular organisms move in response to chemical stimuli present in their environment, through chemotaxis. Emulating such structures and processes in the synthetic world herein we present micro-vehicle droplets, based on ionic liquids (ILs), that show chemotactic behaviour. The movement is generated through asymmetric release of an IL surfactant, which results in an imbalance in the local surface tension causing the droplet to move spontaneously towards regions of lower surface tension. This interesting behaviour is of great interest, as it provides a simple mechanism for programmed movement to a specific location, without the need to pump the bulk fluid or externally stimulate the system. This points the way towards futuristic fluidic systems that can, to an extent, monitor their own condition using the chemistry of the local environment to provide a driving force and propel the droplet. The mechanism is illustrated in Fig. 1A.
These trihexyl(tetradecyl)phosphonium chloride ([P6,6,6,14]Cl) IL droplets can be moved spontaneously and guided to specific destinations in fluidic channels in the presence of ionic strength gradients . In addition, signalling and seeking IL droplets, which chemotactically find each other in open fluidic networks, were also developed. In this study the signal droplet, which is stationary, releases a chemical signal that creates a chemical gradient inside the fluidic channel. In response to this signal, the seeker droplet is enabled to chemotactically find the signaller droplet and merge with it at its location, in a manner similar to the triggered cell migration seen in chemokine proteins. The chemotactic IL droplets were also demonstrated for a range of additional functionalities including cargo transport to specific destinations, chemical reactions (Fig 1B-D), dynamic sensing and reporting, damage detection (i.e. a leak in the fluidic channel) and repair, among others.
Such autonomous, self-directed movement of micro “vehicles” offers many intriguing and beneficial opportunities in the microfluidics field and could perhaps revolutionize the area of open droplet microfluidic devices, where the driving force for movement is dictated by the chemistry of the fluidic system itself rather than externally controlled by the user. This could enable the realization of multifunctional biomimetic fluidic systems with advanced functionality, such as autonomic detection and repair of damage, self-management and healing.
1. Van Haastert et al., Chemotaxis: signalling the way forward. Nature reviews, 2004. 5(8): p. 626-634.
2. Florea L., et al., Electrotactic ionic liquid droplets. Sensors and Actuators B: Chemical, 2017. 239: p. 1069-1075.
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