Synergistically biomimetic platform that enables droplets to be self-propelled

Droplet transport still faces numerous challenges, such as a limited transport distance, large volume loss, and liquid contamination. Inspired by the principle of ‘synergistic biomimetics’, we propose a design for a platform that enables droplets to be self-propelled. The orchid leaf-like three-dimensional driving structure provides driving forces for the liquid droplets, whereas the lotus leaf-like superhydrophobic surface prevents liquid adhesion, and the bamboo-like nodes enable long-distance transport. During droplet transport, no external energy input is required, no fluid adhesion or residue is induced, and no contamination or mass loss of the fluid is caused. We explore the influence of various types and parameters of wedge structures on droplet transportation, the deceleration of droplet speed at nodal points, and the distribution of internal pressure. The results indicate that the transport platform exhibits insensitivity to pH value and temperature. It allows droplets to be transported with varying curvatures in a spatial environment, making it applicable in tasks like target collection, as well as load, fused, anti-gravity, and long-distance transport. The maximum droplet transport speed reached (58 ± 5) mm·s−1, whereas the transport distance extended to (136 ± 4) mm. The developed platform holds significant application prospects in the fields of biomedicine and chemistry, such as high-throughput screening of drugs, genomic bioanalysis, microfluidic chip technology for drug delivery, and analysis of biological samples.


Introduction
In nature, droplets can be spontaneously and directionally transported on biological surfaces, such as nepenthes [1][2][3], rice leaves [4][5][6][7], and spider silk [8][9][10].Observations Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence.Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. of these surfaces have revealed the presence of homogeneously distributed macroscopic or microscopic structures.Leveraging homogeneously distributed surface structures for achieving directional droplet transport maintains the inherent characteristics of droplets without requiring external energy input.Hence, this approach has found extensive applications in microfluidic manipulation [11][12][13].The driving mode that does not require external energy input is commonly referred to as passive transport and primarily encompasses surface gradient [14][15][16] and asymmetric structure driving [17][18][19].For instance, Shen et al [20] prepared a gradient wettability membrane using electrostatic spinning, facilitating the spontaneous transport of droplets in a single direction.Cao et al [21], inspired by scallop shells, ingeniously designed a dual-asymmetric folded paper channel that, incorporating the principles of radiative cooling, enhances the condensation and transfer of droplets.Xie et al [22] used an asymmetric structure to drive the droplet and designed a periodic Janus gradient structure with terminal potential wells to address the problem of oriented long-distance droplet transport.Due to a wettability gradient or structural differences in passive transport, droplet transport can produce large volume loss.Moreover, achieving high-speed and longdistance droplet transport remains challenging owing to the resistance encountered at the solid-liquid interface [23].
In addition to the spontaneous passive actuation strategy, scientists have realized the active transport of droplets by applying energy fields such as light, heat, electricity, and magnetism [24][25][26][27][28][29][30][31][32][33][34].Wang et al [35] employed the concept of radiation pressure generated through light reflection, utilizing a laser beam in conjunction with a magnetic fluid.This approach induced thermo-capillarity, resulting in a surface depression in the fluid that initiated droplet actuation.Lagubeau et al [36] utilized a ratchet-like topology to deliver a high-temperature droplet.Sun et al [37] designed a surface with a charge gradient, utilizing electrostatic action to guide droplet motion.Jing et al [38] proposed a magnetic micropillar array surface to realize oriented droplet transport by changing the bending angle of the micropillar array by applying a rectangular magnetic field.However, when employing the principle of photo-induced deformation to drive droplets, achieving high-speed, multi-droplet transport proves challenging due to the constrained sensitivity of surface deformation governed by laser power and fluid characteristics.Similarly, in thermal response driving, temperature-induced volume reduction of the fluid leads to sluggish transport speeds.The droplet transport method based on the Leidenfrost effect improves the droplet transport rate.Nevertheless, the problem of large fluid loss owing to evaporation remains unavoidable.Utilizing electric fields to drive droplets necessitates intricate drive circuitry and a need for specialized electrode materials.Meanwhile, employing magnetic fields for directed droplet transport presents challenges such as costly surface preparation and potential fluid contamination [39].
In summary, commonly applied transport methods face several challenges, such as requiring external energy input, causing fluid adhesion or residue, fluid contamination, and mass loss.To minimize energy consumption, the droplet must be spontaneously transported, and no external energy field can be applied to the transport platform or droplet [40,41].Moreover, the droplet cannot be driven by a surface gradient or hydrophilic pattern to avoid contamination or mass loss of the fluid.
This work is based on the synergistic biomimetic concept, inspired by the hydrophobicity of the lotus leaf, the droplet self-driving effect of the orchid leaf, and the continuous bamboo structure, to invent a synergistically biomimetic platform for long-distance droplet transport.To achieve self-driven, loss-free droplet transport over long distances and at high rates, validation of the transport efficiency, observation of motion patterns, and exploration of various transport applications have been conducted.

Fabrication of the synergistically biomimetic platform
The parameters of the laser processing machine (SK-MARKER, Shanghai Sanke Laser Technology Co., Ltd) were set as follows.Line spacing is 0.025 mm, power is 18 W, frequency is 20 kHz, scanning speed is 900 mm s −1 (figure S1).The aluminum plate (Al, purity > 99%) was processed to obtain micro-/nanostructures by laser [42][43][44].The aluminum plate was then laser processed to obtain the wedgeangle structure.The patterned substrates were modified with fluoroalkylsilane [FAS, C 8 F 13 H 4 Si (OCH 2 CH 3 ) 3 , Degussa Co., Germany] to obtain superhydrophobic surface (figure S2).

Characterization
The 3D surface morphology and cross-sectional profile of the transport platform was observed using an ultra-depth 3D microscope (VHX-6000, Keenes, Japan).Scanning electron microscopy (SUPRA 55 SAPPHIRE, Germany) was used to observe the microscopic morphology.The elemental composition and distribution were observed using an energy dispersive x-ray spectrometer (SUPRA 55 SAPPHIRE, Germany).An optical contact angle meter (JC2000D4F, China) was used to characterize the contact angle.

Transport performance tests
The performance of droplet transport across node was investigated on a wedge-angle structure with a length of 55 mm with two layers (composition angles: 10  ), respectively.
To investigate the driving effect of a multi-layer wedgeangle structure, the instantaneous velocity of a 0.8 ml droplet on a six-layer wedge-angle structure (composition angles: 2 To investigate the effect of the wedge angle on the transport performance of droplets of different volumes, the maximum velocity of the movement of droplets ranging from 0.2 to 1 ml was tested on various wedge-angle structures (4 To investigate the effect of wedge-angle parameters on droplet transport performance, 0.8 ml droplets were tested on different wedge-angle lines (straight, concave, and convex) and wedge-angle cell (with equal lengths and widths).The first inner node wedge angle is 2 • -4 • , and the subsequent inner wedge angles is 2 • -14 • with a depth ranging from 0.2 to 0.4 mm, and a node length up to 3 mm.
In the analysis of the droplet transport mechanism, a threedimensional finite element simulation model of droplet transport was established.The simulation parameters were set in line with the experimental conditions.

Results and discussion
Long-distance, loss-free, self-driven droplet transport poses a significant challenge [45].Drawing inspiration from natural phenomena such as the hydrophobic properties of lotus leaves, the directional droplet transport observed in orchid leaves, and the continuous transport mechanism of bamboo nodes, we developed a synergistically biomimetic platform.This innovative design comprises two layers of continuous wedgeangle nested structures, following the concept of 'synergistic biomimetics' (figure 1(a)).Lotus leaf-like superhydrophobic surfaces enable loss-free droplet transport [46,47].Orchid leaf-like three-dimensional (3D) structures facilitate the selfdriving performance of the transport platform.Bamboo-like nodes realize the interconnection of the two-stage wedge unit, with the X 0 cross-section serving as the starting position of the node.The droplet has a water contact angle of (159 ± 2.3) • in the transportation zone and (160 ± 1.5) • in the non-transportation zone (figure S1(b) and S3).0.8 ml of droplet achieves long-distance, loss-free, and self-driven transport on the transport platform, with an average movement speed of approximately 27.4 mm s −1 within 5 s (figure 1(c), and movie S1).No liquid residue remains on the platform after droplets with fluorescence have been transported.Moreover, the transport platform contains no liquid residue after being immersed in red ink, demonstrating that the fully superhydrophobic transport platform successfully achieves the non-destructive transportation of liquids (figure S4).

Design ideas of the synergistically biomimetic platform
On biological surfaces, the movement of droplets driven by capillary forces is a ubiquitous phenomenon.This occurrence is induced by the combined influence of surface tension and the curvature radius of the droplets.The driving force of Laplace pressure differential is a macroscopic manifestation of capillary action.It operates by creating disparate curvatures at the two ends of a droplet, thereby facilitating the movement of droplets on the surface of plant leaves.
As shown in figure 2(a), the orchid leaf was placed horizontally (figure 2(a-i)).When 1 ml of the droplet was applied to the tip of the leaf (figure 2(a-ii)), the droplet underwent automatic transport on the orchid leaf sheet.However, the average movement speed of the droplet was only 0.07 mm s −1 in 240 s (movie 2).Notably, the orchid leaf tip cross-section corresponds to a 3D wedge structure, producing asymmetric deformation on the droplet, thus driving the droplet to move spontaneously (figure 3(a-iii)).Inspired by the 3D wedge structure of the orchid leaf, a multilayer wedge structure was designed in the direction of the transport platform depth to enhance the asymmetry of the droplet deformation to achieve a more significant driving effect of the droplet (figures 2(b) and S5).Due to the adhesive effect of the liquid on the orchid leaf, the droplet spreads over the entire surface of the leaf during transportation, resulting in not only a greater resistance to movement of the droplet, but also a greater fluid loss [48].Therefore, the transport platform was fabricated to resemble a lotus leaf-like superhydrophobic surface to reduce droplet transport resistance and losses.Owing to the widening of the cross-sectional width of the driving platform at the location of the droplet, the asymmetry of droplet deformation degrades, resulting in decreased driving force of the droplet.Hence, a bamboo-like node was used to realize the connection of the multilayer wedge angle driving mechanism (figure 2(c)).Therefore, the conceptual design of the synergistically biomimetic platform can be summarized as follows: the driving force is generated through a 3D drive structure inspired by an orchid leaf, non-adhesive properties are achieved with a superhydrophobic surface resembling a lotus leaf, and long-distance transport is facilitated by bamboo-like nodes.
To optimize the orchid-leaf-like 3D driving mechanism, the two-stage multilayered wedge structure was connected in series to observe the maximum transport distance of the droplets (figure 2(d)).As the number of layers increases, the time for the droplet to reach the node decreases, i.e., the movement speed is accelerated.However, the droplet will stop at the node.As the number of layers decreases, the distance covered by the droplet front-end crossing the node increases.The results show that the two-layer wedge structure has the significant potential to realize the droplet's trans-node long-distance transportation (movie S3).
To analyze the influence of the number of layers of a multilayer wedge structure on droplet transport, the motion model of a droplet on a platform was established, and the droplet motion process was divided into three stages (figure 2

(e)). (I)
During the initial motion, the droplet is only in contact with the external wedge structure owing to the wedge width limitation and the repulsive effect of the superhydrophobic surface.In this case, only a small amount of droplet is trapped inside the structure, and the Laplace force on the droplet is small.(II) When the limiting effect of wedge width on droplet deformation decreases, the number of structural layers in contact with the droplet increases, and the driving force increases.As the wedge width continues to increase, the droplet contacts the internal wedge and disengages from the external wedge.Hence, gravity is involved in driving the droplet.(III) When the droplet is in full contact with the lowest wedge structure, the center of gravity no longer drops, and the droplet is only driven by the Laplace force generated by deformation.Compared with stage I, the droplet in stage III comes into contact with more layers of the wedge angle, resulting in increased volume deformation and, consequently, a stronger driving force.The Laplace driving force acting on a droplet within a multi-layer wedge structure originates not only from the planar wedge components but also from the wedge structures at varying angles in the depth direction.When these wedge units are linked in series, the presence of node walls constrains the lateral droplet transport between nodes, and this hindrance effect becomes more pronounced as the number of wedge angle layers increases.Consequently, within the multilayer wedge structure, reducing the number of wedge angle layers enhances the driving force applied to the droplet while minimizing the obstruction caused by contact with the wall.This observation is consistent with the findings depicted in figure 2(d).

Droplet motion performance on the synergistically biomimetic platform
To optimize droplet transport on the synergistically biomimetic platform, several factors were considered for analysis: the external wedge angle, the coupling relationship between internal and external wedge structures, the internal wedge angle, and the length of the nodes.
As shown in figure 3(a), on a single-layer wedge structure with a length of 30 mm, the maximum speed of different droplet volumes is affected by the wedge angle.On the wedge structure, the maximum degree of asymmetric deformation that the droplet can generate does not change significantly with increasing droplet volume [49].Moreover, the various angles of the wedge structure result in different positions where the droplet loses contact with the wedge edge due to the varying widths of the wedges.The results suggest that with a wedge angle of 8 • , the variation in maximum speed among different droplet volumes is minimal, and a droplet volume of 0.8 ml can achieve a maximum transport speed of 48.6 mm s −1 .
When the internal and external wedge structures are combined in various configurations, five transportation structures are assessed to enhance the driving performance (figure 3  of droplet subsidence, and the droplet retains a velocity of 37.4 mm s −1 after passing through the second-stage node.Therefore, the coupling method in which the internal wedge extends to the midpoint of the secondary external wedge was chosen for subsequent studies. Within the described coupling relationship between internal and external structures, variations in the length of the initial wedge unit of the outer layer compared to subsequent units result in differing wedge angles for the first segment of the internal layer and subsequent wedge angles.Herein, the internal wedge angle ranges from 0 • to 5 • for the first section and 0 • -14 • for the subsequent sections.The internal wedge angle was varied to determine the movement speed of the droplet after crossing the wedge end (figures 3(c) and (d)).The results show that the droplet speed reaches a maximum value of 41.6 mm s −1 when the first section internal wedge angle is 2 • and the subsequent angle is 4 • .Moreover, the depth of the driving mechanism affects droplet transportation.A smaller depth cannot sufficiently deform the droplet, while a larger depth increases the resistance of the droplet as it traverses the node.As shown in figure 3(e), when the total depth of the wedge structure is 0.3 mm, the movement speed of the droplet across the node is higher.
The resistance encountered by the droplet during its motion primarily originates from the node, necessitating the droplet to elevate its center of gravity while traversing the node.Furthermore, narrowing the cross-section of the node induces a reverse Laplace force.Once the node depth is established, the reverse Laplace force experienced by the droplet at the node can be controlled by adjusting the node length.Under different node length conditions, the movement speed of the droplet across the internal wedge end first increases and then decreases (figure 3(f)).At a node length of 2 mm, the droplet can maintain a high movement speed.After optimizing the parameters of the transport platform, the droplet achieves a maximum movement speed of 58.8 mm s −1 at the end of the first wedge unit.The length of the platform between the two nodes is uniquely determined by the aforementioned parameters (figure S6).
For a droplet with a volume of 0.8 ml, the optimized parameters for the biomimetic transport platform are as follows: an external wedge angle (α) of 8 • , an internal wedge angle (β) of 2 • for the first section, a subsequent internal wedge angle (γ) of 4 • , a depth of 0.3 mm, and a node length of 2 mm.The maximum transport speed of the optimized transport platform for a 0.8 ml of droplet is 58.8 mm s −1 .Despite the need for optimal parameters of the Synergistically Biomimetic Platform to be compatible with the volume of liquid droplets, the approach of achieving longdistance self-propulsion through nested wedge-like structures is of universal significance (figure S7).Furthermore, the platform maintains excellent wetting properties and droplet driving performance even after 8 months of placement (figure S7).
It is observed that smaller-volume droplets lose contact with the wedge angle tips and edges, resulting in the disappearance of Laplace driving forces, while larger-volume droplets, experiencing equal driving forces, encounter increased motion resistance.Hence, the optimal parameters of the transport platform need to match the volume of the droplets to ensure the maximum difference between the driving force and resistance exerted on the droplets on the platform.As illustrated in figure 4(a), upon completion of parameter optimization, the platform is capable of transporting droplets with a minimum volume of 0.3 ml, albeit limited to traversing a single node.
In more refined application scenarios, where the transportation of smaller-volume droplets is imperative, guided by the strategy of enhancing driving forces through coupled wedge structures, we have engineered a downsized Synergistically Biomimetic Platform.This innovative design successfully facilitates the transport of droplets with a volume as small as 0.1 ml, as exemplified in figure 4(b).
In our investigation into the intrinsic properties of droplets, we have found that transport performance is primarily influenced by the surface tension of the droplets.As depicted in figures (c) and (d), the platform exhibits excellent transport efficiency for droplets with surface tensions greater than 60 mN m −1 .When the surface tension is significantly lower than that of water, such as in the case of oil drops (lubricating oil, with a surface tension of 28.2 mN m −1 ), the droplets cannot maintain a spherical shape after being placed.Due to the hindered process of surface energy conversion to potential energy, the droplets remain stationary at their initial positions.

Mechanism of droplet motion on the synergistically biomimetic platform
As shown in figures 5(a) and S8, the droplet's motion on the transport platform can be described as follows: the center of gravity decreases, whereas the speed increases when the droplet moves over the wedge unit.Conversely, the center of gravity increases, and the speed decreases when the droplet crosses the node.Three types of Laplace forces drive droplets: (1) the external wedge driving force F L-out , (2) the internal wedge driving force F L-in , (3) and the internal and external layers coupling angle difference driving force F L-c .Owing to the three driving forces, the droplet achieves a large movement speed when moving to the end of the unit.When crossing the node, the droplet is subjected to a reverse Laplace force F L-re generated by the external wedge, and the internal wedge structure provides pulling force to the droplet.Additionally, resistance is encountered by the droplet at the internal wedge end, even as the external wedge structure continues to exert a forward driving force on the droplet.
According to the Laplace pressure difference formula, the external wedge angle driving force acting on the droplets on the horizontal plane can be expressed as: The equation above incorporates γ as the surface tension of the droplet, with R o1 and R o2 representing the curvature radii of the droplet's rear and front ends in the direction of motion.Similarly, F L-in and F L-c can also be correspondingly expressed.As the droplet is subjected to volumetric forces, and each driving force contributes differently to the droplet's acceleration, the expression is modified as follows: In the equation, S represents the cross-sectional area of contact between the droplet and various surfaces, while V denotes the volume of the droplet.
Numerical simulations of the liquid droplet transport process were conducted (figures S9(a) and (b)), and the transport profiles are depicted in figure 5(b).The internal pressure within the droplet at the node reaches its maximum value.As the droplet reaches the node position, the front end experiences a reverse Laplace force, leading to deceleration.Meanwhile, the back end of the droplet continues to accelerate due to the influence of the external wedge structure.As a result, the droplet is squeezed and contracted, and the internal pressure increases.When the droplet is in motion within the wedge unit, two primary forces come into play.(1) When the droplet is not in contact with the internal wedge end, the force is more pronounced.Owing to the influence of the wedge structure, the curvature radius of the deformation at the back end of the droplet aligns with the direction of motion.In contrast, the curvature radius of the deformation at the front end aligns in the opposite direction of motion.Consequently, the front and back ends of the droplet generate Laplace forces in opposing directions, resulting in compression of the droplet.(2) When the droplet crosses the internal wedge end, the force is relatively small.The internal wedge structure does not exert a driving force on the droplets, and the wedge end is a weak barrier to the droplets.
Figures 5(c) and (d) illustrate the interaction between the droplet and the transport platform at the nodes and the internal wedge end, respectively.The center of gravity of the droplet lifts at the nodes, and the droplet disengages from the bottom surface of the internal wedge structure.Throughout the whole process of crossing the node, the droplet is always in contact with the vertical wall of the internal wedge structure, suggesting that the internal wedge structure has a continuous driving effect on the droplet.At the internal wedge end, the droplet remains in contact with both platform surfaces (movie S5, figure S9(c)).
The simulated and experimental values shown in figure 5(e) confirm that the simulation model is highly accurate.The movement speed curve of the droplet illustrates that when crossing the node, the droplet starts to decelerate under the effect of larger resistance, and the driving force provided by the internal wedge structure acts as an auxiliary traction effect.When crossing the internal wedge end, the movement speed of the droplet increases, suggesting that the external wedge structure determines the movement speed of the droplet (figure S10).
To study the droplet speed loss at the nodes, the starting and end speeds of different volumes of droplets at the same node, as well as the speed loss, were examined (figure 5(f)).As indicated, small droplets have a large movement speed at the node.The reduction in droplet speed after passing through various nodes sequentially remains approximately constant and is inversely proportional to the droplet's volume.The droplet's trans-node speed loss is less than the speed gained by accelerating in the subsequent wedge unit, indicating the presence of an ultimate droplet transport distance.For instance, the 0.8 ml droplet loses approximately 7.4 mm s −1 of speed while crossing the node but gains approximately 6.5 mm s −1 of speed after crossing the node.
In summary, a multi-stage wedge unit connected in series with a node facilitates long-distance droplet transport.As the droplet moves within the wedge unit, it acquires significant momentum through the combined action of the external wedge driving force, internal wedge driving force, and the differential driving force arising from the angle disparity between the internal and external layers.At the node, due to the droplet's large kinetic energy and the forward traction provided by the internal wedge structure, the droplet overcomes the resistance generated by the height of the node wall and realizes trans-node transport.At the internal wedge end, the wall resistance of the droplet is smaller than the driving force, and the movement speed increases.

Application scenarios for droplet on the synergistically biomimetic platform
In practical transportation scenarios, platforms are often constrained by the characteristics of liquid droplets and lack the flexibility to control the motion paths of the droplets [50].The design of the synergistically biomimetic platform offers a novel solution to address the aforementioned challenges.
In the high-throughput screening of drugs and genomic bioanalysis, ensuring the stability and reliability of reactions necessitates the precise control of droplet temperature and pH during transport.To verify that the transport platform can drive droplets of different properties, a comparison of droplet transport at different temperatures and pH values was performed (figures 6(a) and (b)).Under temperatures of 20 • C, 50 • C, and 100 • C, and pH values of 6, 7, and 8, respectively, droplets move approximately the same distance within 1.5 s, suggesting that variations in temperature and pH have minimal influence on droplet transport (movie S6).This insensitivity can provide an optimal liquid environment for active pharmaceuticals, which is crucial for the accuracy of test results.
Microfluidic chips and ex vivo drug delivery, among others, impose elevated demands on droplet transport pathways to facilitate operations such as mixing, separation, and reaction.Traditional delivery platforms are limited to driving droplets in a single direction.To realize curved droplet transport within the horizontal plane and to accommodate scenarios involving obstacle-bypassing during transport, the transport platform depicted in figure 6(c) has been designed.Fabricating the substrate of the transport platform into a wavy shape changes the movement curvature of the droplet in the vertical direction, and the results show that the transport platform can be applied to pitted substrates (figure 6(d), movie S7).
As illustrated in figure 6(e), the collection of the target was accomplished by positioning polystyrene spheres along the trajectory of droplet transport, greatly enhancing the efficiency of sample surface microbial and chemical contaminant collection and detection.Moreover, the transportation of small-mass objects by droplets within a plane can also be employed for the fabrication and assembly of microdevices, such as microsensors and microfluidic devices.Figure 6(f) shows the load transport capability of the transport platform, consisting of polystyrene beads and aluminum foil.
In the analysis and diagnosis of biological samples, droplets are frequently utilized in clinical settings for the collection of patient specimens.By merging sample droplets with reagents along the transport pathway, rapid testing and analysis can be conducted.Figure 6(g) illustrates the fused transport of small droplets on a platform.Droplets with a volume of 0.2 ml are released sequentially from the narrow end of the platform, and the first released droplet stagnates in the second stage of the wedge unit.Subsequently, the released droplet fuses with the stalled droplet and continues to move across the node.After the fusion of droplets, continued transport facilitates the clearance of samples within the pathway, offering a strategy to ensure rapid and reproducible testing.The panel depicted in figure 6(h) illustrates the transport of biological blood droplets with a volume fraction of 40% on the platform, enabling determination of blood concentration (figure S11).As depicted in figure 6(i), the droplet achieves longdistance transport across seven nodes, covering a distance of (136 ± 4) mm, significantly broadening the application scope for medical and chemical testing reliant on droplet transport.(movie S8).
In summary, the synergistically biomimetic platform had no sensitivity to the pH value and temperature, enabling spatial curvature variation, droplet fusion, and anti-gravity transport.Hence, it can be used for target collection and load transport.Finally, long-distance transport with a distance of (136 ± 4) mm was achieved across seven nodes.

Conclusion
A novel synergistically biomimetic platform was proposed for droplet transport.This platform leverages a 3D driving mechanism inspired by orchid leaves as the driving force, a superhydrophobic surface resembling lotus leaves to prevent adhesion, and bamboo-like nodes for extended transport distance.Operating without the need for energy input, this platform prevents fluid adhesion or residue, safeguarding against contamination or loss of fluid.The platform is a superhydrophobic surface featuring two layers of wedge structures fabricated through a combination of laser processing and low surface energy treatment involving FAS.Experiments revealed the following optimized structural parameters: external wedge angle (α) = 8 • , first internal wedge angle (β) = 2 • , subsequent internal wedge angle (γ) = 4 • , depth = 0.3 mm, and node length = 2 mm.The droplet obtains large kinetic energy under the synergistic action of the external and internal wedge driving forces and the driving force of the coupling angle difference between the internal and external layers, overcoming the wall resistance at the nodes and internal wedge end, thus realizing long-distance, loss-free transport.In the realms of biomedical and chemical sciences, it demonstrates pivotal application prospects.

Figure 1 .
Figure 1.The design concept and characterization of the synergistically biomimetic platform.(a) Principle of the synergistically biomimetic.(b) Characterization of the platform.(c) Droplet transport effect.
(b), movie S4).(1) Absence of internal wedge structure.Driven solely by a single-layer wedge structure, the droplet's speed on the wedge end reaches only 30.9 mm•s −1 , insufficient for trans-node transport.(2) Internal and external wedge structures are of equal length.The movement speed of the droplet at the wedge end increases to 42.4 mm s −1 .However, the end wall surface of the two-layer wedge structure hinders the simultaneous movement of droplets, failing to realize trans-node transport.(3) The internal wedge extends to the end of the peer node.Here, the droplet is driven by the internal wedge structure as it crosses the node.However, the increased crosssection width at the end of the node strengthens the obstruction to the droplet, and the droplet fails to realize the trans-node transport.(4) The internal wedge extends to the midpoint of the secondary external wedge.The internal wedge structure provides a driving force for the droplet during the droplet's crossing of the node, facilitating trans-node transport.The droplet finally stalls in front of the second-stage node with an end speed of 28.2 mm s −1 .(5) Taking the end of the node as the starting point of the wedge unit, the internal wedge extends to the midpoint of the secondary external wedge.When the droplet crosses the second-stage node, the section width of the internal wedge structure is smaller, reducing the degree

Figure 2 .
Figure 2. The principle of synergistic bio-inspiration and the optimization of multi-layer wedge angle structures.(a) Orchid leaves.(b) Multi-layer wedge angle structure.(c) Design ideas.(d) Images of droplet transport on two-, three-, and six-layer wedge-angle structures.(e) Schematic diagram of droplet transport on a six-layer wedge-angle structure.

Figure 3 .
Figure 3. Structural optimization of the synergistically biomimetic platform.(a) Angle of wedge angle.(b) Relative position of inner and outer wedge angle structures.(c) Angle of the first nodal wedge angle in the inner layer.(d) Angle of subsequent wedge angles in the inner layer.(e) Depth of the wedge angle.(f) Length of the node.

Figure 5 .
Figure 5. Mechanistic and simulation analysis of droplet transport.(a) Schematic diagram of droplet center of gravity changes and force situation.(b) Simulation diagram of droplet transport pressure distribution.(c) and (d) Contact between droplet and transport platform when crossing the outer and inner nodes.(e) Droplet motion velocity profile.(f) Velocity and velocity loss of droplets before and after crossing the node.

Figure 6 .
Figure 6.Transport scenarios.(a) and (b) Images of droplet motion at different temperatures and pH values.(c) Droplet transport around the barrier.(d) Droplet transport on a wavy substrate.(e) Target collection.(f) Load transport.(g) Fusion transport.Where the numbers in the figure are droplet designations.(h) Biological droplet transport (Blood volume fraction: 40%).(i) Long-distance transport.Scale bars:10 mm.