Unidirectional passive liquid transport bio-inspired by the spermathecae of fleas
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Bionik Kongress Bremen "Bionik: Patente aus der Natur"
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We designed, fabricated and tested microfluidic devices for unidirectional passive liquid transport bio-inspired by the spermathecae of fleas. To this end, we studied the shape of the spermathecae (receptaculum seminis) of rabbit fleas (Spilopsyllus cuniculi) and rat fleas (Xenopsylla cheopis). The spermatheca is an organ of female fleas to store sperm until the fleas find suitable conditions to lay eggs. According to our hypothesis, the shape of this organ facilitates the ejection of sperm, while the injection of sperm requires pressure. For device design, we abstracted the shape of the spermatheca and used it as a unit cell of a continuous capillary channel. Based on the physics of capillary fluid transport, we described the function of the different components of the bio-inspired unit cell. As a result of the underlying theory we found the physical principles responsible for the halting of the liquid front in backward direction and for transport in forward direction. For model-guided device fabrication, we arranged several unit cells in series in order to form a continuous capillary channel. We then positioned several of these capillary channels in parallel and engraved them in a poly(methyl methacrylate) (PMMA) plate using CO2 laser ablation. We tested the demonstrators and found that they transported soapy water with velocities of about 1 mm/s in forward direction, while halting the liquid completely in backward direction. Most interestingly, the transport velocity is constant with time, while the velocity decreases rapidly in other passive microfluidic devices. Furthermore, the fabricated demonstrator transports liquid unidirectionally even against gravity. Since PMMA is a standard material in microfluidics, possible fields of application range from lab-on-a-chip and biomedical microfluidics to micro-analysis devices. Transferring the principle to other materials, might make it useful for lubrication, wear reduction and cooling of electronics.