Fig 2 - uploaded by Werner Baumgartner
Content may be subject to copyright.
Schematic illustration of a "fluidic diode" for passive unidirectional liquid transport bioinspired by the spermathecae of fleas. (a) The shape of the spermatheca is abstracted in order to form the unit cell of the fluidic diode for a liquid with a contact angle θ. For device design, several of these unit cells are connected to each other; (b) elementary components of one unit cell: (A) a straight capillary channel for bidirectional flow, (B) a conic capillary channel with a small angle of slope α for bidirectional flow and (C) a sideways junction to the conic capillary with an abrupt widening forming a singular transition point, which results in unidirectional flow.
Source publication
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...
Contexts in source publication
Context 1
... morphology of the rat flea spermatheca sug- gests a passive transport mechanism for storage and release of sperm ( Figs. 1 and 2). According to our hy- pothesis the shape of the spermatheca supports the re- lease of sperm and requires pressure for injection of sperm (Fig. 2a). The hilla resembles a straight (A) and the bulga a conic capillary (B), respectively. Both are assumed to allow for bidirectional transport of sperm. Following a biomimetic approach their shapes are ab- stracted correspondingly, taking into account their functionalities; both are assumed to allow bidirectional transport. According to ...
Context 2
... order to fabricate devices for passive, unidirec- tional liquid transport, we abstracted the shape of the spermatheca such that it forms the unit cell of the device. We then connected several of these unit cells to each other at the positions of the natural spermatheca's orifice and of the hilla tip ( Fig. 2a), respectively, yielding a capillary channel of serial connected unit cells. Two connected unit cells in Fig. 2a illustrate the flow in the forward direction and halting of the liquid front in the backward direction. We thus use the principle of facili- tated passive transport of sperm out of the spermatheca and hindered flow in the ...
Context 3
... we abstracted the shape of the spermatheca such that it forms the unit cell of the device. We then connected several of these unit cells to each other at the positions of the natural spermatheca's orifice and of the hilla tip ( Fig. 2a), respectively, yielding a capillary channel of serial connected unit cells. Two connected unit cells in Fig. 2a illustrate the flow in the forward direction and halting of the liquid front in the backward direction. We thus use the principle of facili- tated passive transport of sperm out of the spermatheca and hindered flow in the reverse direction to achieve unidirectional liquid transport in the forward direction of a microfluidic ...
Context 4
... by the natural model, we designed one unit cell of the structure (Fig. 2a) to consist of three func- tional unit cell components that are connected to each other ( Fig. 2b): (A) a rotationally symmetric straight capillary of approximately constant radius like the hilla, (B) a conic rotationally symmetric capillary like the bulga and (C) a junction of two rotationally symmetric capillaries with a sharp ...
Context 5
... by the natural model, we designed one unit cell of the structure (Fig. 2a) to consist of three func- tional unit cell components that are connected to each other ( Fig. 2b): (A) a rotationally symmetric straight capillary of approximately constant radius like the hilla, (B) a conic rotationally symmetric capillary like the bulga and (C) a junction of two rotationally symmetric capillaries with a sharp narrowing of the capillaries' radii (i.e., a sharp change in dimensions over a small distance) like the ...
Context 6
... scaled the structure up by a factor of about twelve, comparing the maximum diameter found in the natural structure to the maximum width in the artificial one. We designed the structure as shown in Fig. 2 with a unit cell length of 2.4 mm and an opening angle α of 26.6˚(6˚(video 1 provided as supplementary material). The width of the straight capillaries was chosen to be 0.3 mm. In our technical implementation, we ensured that inertia forces and gravitational forces are negligible by calcu- lating the Bond number, the Reynolds number ...
Context 7
... used a demonstrator with a single bioinspired capillary channel for accurate testing of distances cov- ered relative to time (Fig. 6, video 2 provided as sup- plementary material). This approach prevents excessive capillary channel overflow and possible crosstalk be- tween several capillary channels. We dispensed a droplet of 50 μL of the test liquid onto the single capillary channel and recorded five consecutive measurement cycles by means of a video camera. We evaluated ...
Context 8
... distances traveled by the fluid fronts in the forward direction and traveling time (Fig. 6a). Therefore fluid transport over large distances is faster than in standard straight capillaries, where the distance traveled by the meniscus is related to the square root of time [29] . This is due to the reservoir formed by the conic capillary (B) (Fig. 2) which is deeper than the connective straight capillary channel (Fig. 3). This reservoir acts as a liquid source for the following unit cell; the straight capillary (A) originates directly at the sideways junction (C) to this reservoir: At the initial point of each unit cell, i.e. at the starting point of the straight capillary, liquid ...
Similar publications
Vortex generators are devices that modify the wind behavior near the surface of wind turbine blades. Their use allows the boundary layer shedding transition zone to be varied. Bio-inspired design has been used to improve the efficiency of aerodynamic and hydrodynamic systems by creating devices that use shapes present in animals and plants. In this...
Citations
... It should be noted that even if the spreading behavior shows an approximate linear relationship, it may not fully imply a classical convective flow. Actually, the liquid spreading behavior entails a step-wise structural "filling" process [53]. The process of breaking the pinning of each row of pillars requires additional time, resulting in a non-linear speed for the overall spreading process. ...
Through the utilization of smart materials and well-designed structures, functional surfaces have been developed to enable small-scale liquid/solid manipulation tasks, thereby facilitating crucial applications in the fields of microfluidics, soft robotics, and biomedical engineering. However, the design of functional systems with flexible, tunable, and multimodal liquid/solid manipulation capabilities remains a challenging endeavor. Here, inspired by asymmetric structural features in natural plants and metachrony in cross-scale biological systems, I report a magnetic-responsive functional surface that can achieve rich liquid operations under static magnetic fields, while also enabling the transportation of solids with multiple degrees of freedom (DOFs) under dynamic magnetic fields. The presence of curvature pillars on the surface, combined with their magnetic-driven tilt/gradient arrangement, imparts liquids with multi-directional spreading modes based on the asymmetry of Laplace pressure. I elucidate the mechanisms governing these liquid spreading modes and subsequently develop compelling liquid operations, such as adjustable anti-gravity climbing, spontaneous modal shifts in liquid transport, and liquid mixing. Furthermore, the dynamic metachronal motion of the magnetic pillars can be harnessed for solid object transportation. I illustrate the synchronous/asynchronous transport modes of the surface and propose a novel strategy for achieving 3-DOF solid transportation by coordinating the arrangement of objects and employing magnetic actuation strategies. This study presents a new design concept for application-oriented manipulation surfaces, which hold significant potential for extensive engineering applications.
... These studies have inspired novel research of biomimicry and applied fluid dynamics engineering inspired not only drawing from reptiles (e.g. Buchberger et al., 2015Buchberger et al., , 2018Comanns, 2016;Comanns et al., 2015Comanns et al., , 2017 but also from other animals as natural models (e.g. Hischen et al., 2018;Lifka et al., 2021;Plamadeala et al., 2017). ...
Rain‐harvesting behaviour represents an adaptation for water collection that has evolved in some species of iguanian reptiles inhabiting arid environments. To date, such behaviour has been observed only in members of the families Agamidae and Phrynosomatidae. A common set of integumentary features characterizes these rain‐harvesting species, including scale surface microstructures (SSMs), capillary channels and hinge joints. The influence of variations in these features on rain‐harvesting has been a subject of discussion for many decades. Nevertheless, a comprehensive comparative study of similarities and differences between harvesting and non‐harvesting species on a broader scale remains lacking. In this study, we classify scale surface microstructures into three categories: large hexagons (SSM1), smaller nested hexagons (SSM2) and hinge pits (SSM2H). As the first two SSM types are widespread, they do not appear to be directly linked to the adaptation for rain‐harvesting. Conversely, the presence or absence of hinge pits distinguishes harvesters from non‐harvesters. Additionally, channel hierarchy, width and structure determine the effectiveness of the rain‐harvesting architecture. Only Moloch horridus exhibits distinct integumentary features in comparison to other agamids and rain‐harvesting species. Ancestral character state reconstruction suggests that rain‐harvesting behaviour was likely absent in the ancestor of Iguanians, even though overlapping scales and SSM1 were present. Our findings illustrate that rain‐harvesting species have independently converged upon similar structural solutions to address their water acquisition challenges, building upon shared pre‐existing features.
... Imbibition (intrusion and extrusion) of liquid in microscale and nanoscale capillaries is one of the most fundamental problems of thermodynamics of liquid in confined space not only in various field of natural science [1][2][3][4][5][6] but also in various engineering problems in micro-and nano-scale [7][8][9][10][11][12][13] . Recently, there have been growing interests in addressing the problem of imbibition in asymmetric capillaries with geometrical gradient 5 because it is relevant to the engineering [14][15][16] of various micro-and nano-fluidics functional devices. ...
... In particular, truncated conical capillaries have been extensively studied as the simplest model to study the effect of geometrical gradient and, in particular, as the model of imbibition into porous substrates 5 . Also, they have been studied for their potential applications as micro-and nano-fluidic devices 12,16,[18][19][20][21][22][23] such as liquid diode 12,16,20,21 , ionic current rectifier 18 , pump 19 , Janus paper 22 , and water harvesting 23 . Carbon nanocone seems the most promising candidate of conical nano capillaries 23,24 . ...
... In particular, truncated conical capillaries have been extensively studied as the simplest model to study the effect of geometrical gradient and, in particular, as the model of imbibition into porous substrates 5 . Also, they have been studied for their potential applications as micro-and nano-fluidic devices 12,16,[18][19][20][21][22][23] such as liquid diode 12,16,20,21 , ionic current rectifier 18 , pump 19 , Janus paper 22 , and water harvesting 23 . Carbon nanocone seems the most promising candidate of conical nano capillaries 23,24 . ...
Thermodynamics of imbibition (intrusion and extrusion) in capillaries of double conical structures is theoretically studied using the classical capillary model. By extending the knowledge of the thermodynamics of a single conical capillary, not only the nature of spontaneous imbibition but that of forced imbibition under applied external pressure are clarified. Spontaneous imbibition in capillaries of double conical structure can be predicted from the Laplace pressure in a single conical capillary. To understand the forced imbibition process, the free energy landscape along the imbibition pathway is calculated. This landscape shows either a maximum or a minimum. The former acts as the energy barrier, and the latter acts as the trap for the liquid–vapor meniscus so that the imbibition process can be either abrupt with a pressure hysteresis or gradual and continuous. The landscape also predicts a completely filled, a half-filled, and a completely empty state as the thermodynamically stable state. Furthermore, it also predicts a completely filled and a half-filled state of metastable liquid, which can be prepared by the combination of the intrusion and the extrusion process. Our study could be useful for understanding various natural fluidic systems and for designing functional fluidic devices such as a diode and a switch.
... and 31.23). To this end, inspiration from nature [11,196,202,[208][209][210][211][212] was beneficial, namely, mimicking the liquid transport capability of spermathecae of fleas [212] (Fig. 31.19), of the integument of lizards [11,211,213,214] (Fig. 31.20), and of bugs' cuticle [196,202,208,215] (Fig. 31. ...
... and 31.23). To this end, inspiration from nature [11,196,202,[208][209][210][211][212] was beneficial, namely, mimicking the liquid transport capability of spermathecae of fleas [212] (Fig. 31.19), of the integument of lizards [11,211,213,214] (Fig. 31.20), and of bugs' cuticle [196,202,208,215] (Fig. 31. ...
... Buchberger et al. [211][212][213] applied a commercial laser engraver with a CO 2 laser source to render surfaces of some square centimeters able to transport microliters of liquid unidirectionally in asymmetric capillary channels (Figs. 31.19 and 31.20). ...
Laser structuring enables modification of sample topography, surface chemistry, and/or physical properties of materials. Examples of these processes are ripple, nap or wall formation, surface oxidation, induction of polymerization reactions, or changes in crystallinity or contact angle. These – most of the time – interrelated modifications are exploited widely for biomedical applications. They range from cell-repellent surfaces for easy-to-replace cardiac pacemakers, control of cell proliferation required in regenerative medicine, to increased cell adhesion for cell arrays. Furthermore, ns-laser-induced nanoripples were used for formation of gold nanowires for future surface plasmon resonance sensors directly integrated into biotechnological devices. Additive nano- and microscale manufacturing by two-photon polymerization allows for considerable progress in cell scaffold formation, paving the path for in vitro–grown organs, bones, and cartilages. The very same fs-laser-based technique was also used for biomimetic microneedles with enhanced liquid spreading on their surface. Microneedles are promising candidates for low-cost, high-throughput drug delivery and vaccination applicable even by nonmedically trained personnel. Microfluidic systems fabricated by fs-lasers have enabled progress in 3D microscopy of single cells and in studies on thrombocyte activation with the help of nanoanchors. Explicating the abovementioned and further biomedical applications, the authors put special focus on the achieved limits pointing out what scientists have accomplished so far in their pursuit of extreme scales.
... It is also worth noting that several of the works conducted on liquid diodes are inspired by nature, 13 exhibiting passive unidirectional transport of liquids with remarkable efficiency and precision. These include fleas, 14 insects, 15 lizards, 16 butterflies, 17 spider silk, 18 cacti, 19 pitcher plants, 20 and the beak of shorebirds. 21 Despite the continuous growth of this field, further developments are needed to improve the performance of these passive devices in terms of flow rate and directionality, and to provide general design guidelines that are adaptable to multiple use cases. 2 To this end, we present 3D-printed spreading-mode liquid diodes with a highly modifiable design. ...
... 22 Here, the use of 3D-printing allows us to easily adjust key structural features in the diode design. This economic and accessible choice may replace other frequently used fabrication techniques such as laser cutting, 14 self-assembled monolayers, 23,24 lithography, 25 etching, 26 or additional delicate post-treatments. 27 These methods are often expensive and laborious, with potential for irregularities and durability problems in the long term. ...
Directional and self-propelled flow in open channels has a variety of applications, including microfluidic and medical devices, industrial filtration processes, fog-harvesting, and condensing apparatuses. Here, we present versatile three-dimensional-printed liquid diodes that enable spontaneous unidirectional flow over long distances for a wide range of liquid contact angles (CAs). Typically, we can achieve average flow velocities of several millimeters per second over a distance of tens to hundreds millimeters. The diodes have two key design principles. First, a sudden widening in the channels' width, in combination with a small bump, the pitch, ensure pinning of the liquid in the backward direction. Second, an adjustable reservoir with differing expansion angles, the bulga, is introduced to manipulate the liquid velocity. Using a combination of experiments and lattice Boltzmann simulations, we provide a comprehensive analysis of the flow behavior and speed within the channels depending on CAs, pitch heights, and bulga angles. This provides guidelines for the fabrication of bespoke liquid diodes with optimal design for their potential applications. As a feasibility investigation, we test our design for condensation of water from fog and subsequent transport uphill.
... It is also worth noting that several of the works conducted on liquid diodes are inspired by nature, 13 exhibiting passive unidirectional transport of liquids with remarkable efficiency and precision. These include fleas, 14 insects, 15 lizards, 16 butterflies, 17 spider silk, 18 cacti, 19 pitcher plants, 20 and the beak of shorebirds. 21 Despite the continuous growth of this field, further developments are needed to improve the performance of these passive devices in terms of flow rate and directionality, and to provide general design guidelines that are adaptable to multiple use cases. 2 To this end, we present 3D-printed spreading-mode liquid diodes with a highly modifiable design. ...
... 22 Here, the use of 3D-printing allows us to easily adjust key structural features in the diode design. This economic and accessible choice may replace other frequently used fabrication techniques such as laser cutting, 14 self-assembled monolayers, 23,24 lithography, 25 etching, 26 or additional delicate post-treatments. 27 These methods are often expensive and laborious, with potential for irregularities and durability problems in the long term. ...
Directional and self-propelled flow in open channels has a variety of applications, including microfluidic and medical devices, industrial filtration processes, fog-harvesting and condensing apparatuses. Here, we present versatile three-dimensional (3D)-printed liquid diodes that enable spontaneous unidirectional flow over long distances for a wide range of liquid contact angles. Typically, we can achieve average flow velocities of several millimeters per second over a distance of tens to hundreds of millimeters. The diodes have two key design principles. First, a sudden widening in the channels' width, in combination with a small bump, the pitch, ensure pinning of the liquid in the backward direction. Second, an adjustable reservoir, the bulga, is introduced to manipulate the liquid velocity with differing expansion angles. Using a combination of experiments and lattice Boltzmann simulations, we provide a comprehensive analysis of the flow behavior and speed within the channels with varying contact angles (CA), pitch heights and bulga angles. This provides guidelines for the fabrication of bespoke liquid diodes with optimal design for their potential applications. As a feasibility investigation, we test our design for condensation of water from fog and subsequent transport uphill.
... Capillary imbibition and capillary rise have been studied for centuries and their theoretical foundation was established approximately a century ago [1][2][3][4][5][6] . Recently, capillary imbibition [7][8][9][10][11][12][13] and droplet transport [14][15][16] into capillaries, grooves and tracs of micro-and nano-scales with geometrical gradients have been attracting much attention, in particular, to investigate the feasibility of the one-way transport devices called the liquid diode. ...
Thermodynamics and hydrodynamics of spontaneous and forced imbibition of liquid into conical capillaries are studied to assess the feasibility of a conical liquid diode. The analytical formulas for the Laplace pressure and the critical Young's contact angle of the capillary for the onset of spontaneous imbibition are derived using the classical capillary model of thermodynamics. The critical contact angle below which the spontaneous imbibition can occur belongs to the hydrophilic region for the capillary with a diverging radius while it belongs to the hydrophobic region for the capillary with a converging radius. Thus, by choosing Young's contact angle between these two critical contact angles, only the spontaneous imbibition toward the converging radius occurs. Therefore, the capillary with a converging radius acts as the forward direction and that with a diverging radius as the reverse direction of diode. Even under the external applied pressure, the free-energy landscape implies that the forced imbibition occurs only to the forward direction by tuning the applied pressure. Furthermore, the scaling rule of the time scale of imbibition is derived by assuming Hagen-Poiseuille steady flow. Again, the time scale of the forward direction is advantageous compared to the reverse direction when the imbibition to both direction is possible. Therefore, our theoretical analysis shows that a conical capillary acts as a liquid diode.
... Capillary imbibition and capillary rise have been studied for centuries and their theoretical foundation was established approximately a century ago [1][2][3][4][5][6] . Recently, capillary imbibition [7][8][9][10][11][12][13] and droplet transport [14][15][16] into capillaries, grooves and tracs of micro-and nano-scales with geometrical gradients have been attracting much attention, in particular, to investigate the feasibility of the one-way transport devices called the liquid diode. ...
Thermodynamics and hydrodynamics of spontaneous and forced imbibition of liquid into conical capillaries are studied to assess the feasibility of a conical liquid diode. The analytical formulas for the Laplace pressure and the critical Young's contact angle of the capillary for the onset of spontaneous imbibition are derived using the classical capillary model of thermodynamics. The critical contact angle below which the spontaneous imbibition can occur belongs to the hydrophilic region for the capillary with a diverging radius while it belongs to the hydrophobic region for the capillary with a converging radius. Thus, by choosing Young's contact angle between these two critical contact angles, only the spontaneous imbibition towards the converging radius occurs. Therefore, the capillary with a converging radius acts as the forward direction and that with a diverging radius as the reverse direction of diode. Even under the external applied pressure, the free-energy landscape implies that the forced imbibition occurs only to the forward direction by tuning the applied pressure. Furthermore, the scaling rule of the time scale of imbibition is derived by assuming Hagen-Poiseuille steady flow. Again, the time scale of forward direction is advantageous compared to the reverse direction when the imbibition to both direction is possible. Therefore, our theoretical analysis shows that a conical capillary acts as a liquid diode.
... In the spermathecae, female flea store sperm until suitable conditions to lay eggs are found. The spermathecae is a capillary system which is shaped in such a way to allow passive, unidirectional transportation of the stored sperm [13] . Some true bug species (Pentatomidae, Cydnidae and Dysodius) show droplet-shaped surface structures, which are part of their External Scent Efferent System (ESES). ...
... On the other hand, it has been proven, that these kinds of structures also work with pure water and not only with soapy water or oil, as it was used in the experimental of Refs. [13][14][15]. ...
... In the course of evolution, nature has developed a broad range of nanostructured surfaces with many different purposes: to optimize friction behavior (e.g., [1][2][3]) or the behavior of liquids (e.g., [4,5]), to achieve antimicrobial (e.g., [6,7]) or antireflective effects (e.g., [8][9][10]) and to achieve decorative effects (e.g., [11][12][13][14]), just to name a few. Many of these nanostructures are also of high interest for technical applications and have been investigated accordingly (e.g., [1,[15][16][17]). ...
The nanoimprint replication of biomimetic nanostructures can be interesting for a wide range of applications. We demonstrate the process chain for Morpho-blue-inspired nanostructures, which are especially challenging for the nanoimprint process, since they consist of multilayer undercut structures, which typically cannot be replicated using nanoimprint lithography. To achieve this, we used a specially made, proprietary imprint material to firstly allow successful stamp fabrication from an undercut master structure, and secondly to enable UV-based nanoimprinting using the same material. Nanoimprinting was performed on polymer substrates with stamps on polymer backplanes to be compatible with roller-based imprinting processes. We started with single layer undercut structures to finally show that it is possible to successfully replicate a multilayer undercut stamp from a multilayer undercut master and use this stamp to obtain multilayer undercut nanoimprinted samples.
