\u201cFluidic diode\u201d for passive unidirectional liquid transport bioinspired by the spermathecae of fleas

Gerda Buchberger,Agnes Weth,Philipp Comanns,Alexander Kogler,Siegfried Bauer,Werner Baumgartner,Richard Baumgartner

doi:10.1007/s42235-017-0003-7

Gerda Buchberger, Agnes Weth + Show 5 more

Open Access

https://doi.org/10.1007/s42235-017-0003-7

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Abstract

We present a device for passive unidirectional liquid transport. The capillary channels used are bioinspired by 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 that stores sperm until suitable conditions to lay eggs are found. We translated and multiplied the natural form and function of a spermatheca to create a continuous capillary system from which we designed our microfluidic device based directly on the model from nature. Applying the Young-Laplace equation, we derived a theoretical description of local liquid transport, which enables model-guided design. We arranged the bioinspired capillaries in parallel and engraved them in poly(methyl methacrylate) (PMMA) plates by CO2 laser ablation. The fabricated structures transport soapy water passively (i.e., without external energy input) in the forward direction at velocities of about 1 mm·s−1 while halting the liquid fronts completely in the backward direction. The bioinspired capillary channels are capable of unidirectional liquid transport against gravity. Distance and velocity measurements prove the feasibility of the concept. Unidirectional passive liquid transport might be advantageous in technical surfaces for liquid management, for instance, in biomedical microfluidics, lab-on-chip, lubrication, electronics cooling and in micro-analysis devices.

Highlights

Existing approaches to unidirectional liquid transport on technical surfaces usually require an external energy source of vibration, electrical energy, radiation or similar[1,2,3]
Our video analysis revealed that all eight capillary channels on the device transported the test fluid in the forward direction at a velocity in the range of 1 mm·s−1 while stopping the liquid fronts in the backward direction for test distances of about 26 mm in both directions
We used a demonstrator with a single bioinspired capillary channel for accurate testing of distances covered relative to time (Fig. 6, video 2 provided as supplementary material)

Summary

Introduction

Existing approaches to unidirectional liquid transport on technical surfaces usually require an external energy source of vibration, electrical energy, radiation or similar[1,2,3]. Our “liquid diodes”, in contrast, allow liquids to be transported passively (i.e., without external energy input) in a preferential direction while halting the liquid front in the reverse direction. The spermatheca is a flaskshaped organ with a globular base (bulga) that is connected via a diaphragm to a longer, bended narrow neck (hilla)[4,5] (Fig. 1). In this organ, sperm can only enter and be released through the orifice (a sideways junction with sharp change in diameter) of the spermathecal duct (ductus spermathecae[6] or ductus receptaculi seminis[7]). All parts have diameters in the range of 35 μm to 90 μm (Fig. 1)

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