Device for Measuring Contact Reaction Forces during Animal Adhesion Landing/Takeoff from Leaf-like Compliant Substrates.

A precise measurement of animal behavior and reaction forces from their surroundings can help elucidate the fundamental principle of animal locomotion, such as landing and takeoff. Compared with stiff substrates, compliant substrates, like leaves, readily yield to loads, presenting grand challenges in measuring the reaction forces on the substrates involving compliance. To gain insight into the kinematic mechanisms and structural-functional evolution associated with arboreal animal locomotion, this study introduces an innovative device that facilitates the quantification of the reaction forces on compliant substrates, like leaves. By utilizing the stiffness-damping characteristics of servomotors and the adjustable length of a cantilever structure, the substrate compliance of the device can be accurately controlled. The substrate was further connected to a force sensor and an acceleration sensor. With the cooperation of these sensors, the measured interaction force between the animal and the compliant substrate prevented the effects of inertial force coupling. The device was calibrated under preset conditions, and its force measurement accuracy was validated, with the error between the actual measured and theoretical values being no greater than 10%. Force curves were measured, and frictional adhesion coefficients were calculated from comparative experiments on the landing/takeoff of adherent animals (tree frogs and geckos) on this device. Analysis revealed that the adhesion force limits were significantly lower than previously reported values (0.2~0.4 times those estimated in previous research). This apparatus provides mechanical evidence for elucidating structural-functional relationships exhibited by animals during locomotion and can serve as an experimental platform for optimizing the locomotion of bioinspired robots on compliant substrates.

Peking geckos (Gekko swinhonis) traversing upward steps: the effect of step height on the transition from horizontal to vertical locomotion.

The ability to transition between surfaces (e.g., from the ground to vertical barriers, such as walls, tree trunks, or rock surfaces) is important for the Peking gecko's (Gekko swinhonis Günther 1864) survival. However, quantitative research on gecko's kinematic performance and the effect of obstacle height during transitional locomotion remains scarce. In this study, the transitional locomotion of geckos facing different obstacle heights was assessed. Remarkably, geckos demonstrated a bimodal locomotion ability, as they could climb and jump. Climbing was more common on smaller obstacles and took longer than jumping. The jumping type depended on the obstacle height: when geckos could jump onto the obstacle, the vertical velocity increased with obstacle height; however, geckos jumped from a closer position when the obstacle height exceeded this range and would get attached to the vertical surface. A stability analysis of vertical surface landing using a collision model revealed that geckos can reduce their restraint impulse by increasing the landing angle through limb extension close to the body, consequently dissipating collision energy and reducing their horizontal and vertical velocities. The findings of this study reveal the adaptations evolved by geckos to move in their environments and may have applicability in the robotics field.

Incline-dependent adjustments of toes in geckos inspire functional strategies for biomimetic manipulators.

Geckos show versatility by rapidly maneuvering on diverse complex terrain because they benefit from their distributed, setae-covered toes and thus have the ability to generate reliable and adaptive attachment. Significant attention has been paid to their adhesive microstructures (setae), but the effectiveness of the gecko's adaptive attachment at the level of toes and feet remains unclear. In order to better understand the geckos' attachment, we first focused on the deployment of toes while challenging geckos to locomote on varying inclines. When the slope angle was less than 30°, their feet mainly interacted with the substrate using the bases of the toes and generated anisotropic frictional forces. As the slope angle increased to 90°, the participation of the toe bases was reduced. Instead, the setae contribution increased for the middle three toes of the front feet and for the first three toes of the hind feet. As the incline changed from vertical to inverted, the adhesive contribution of the toes of the front feet became more equal, whereas the effective adhesion contact of the hind feet gradually shifted to the toes oriented rearwards. Second, a mathematical model was established and then suggested the potential advantages of distributed control among the toes to regulate foot force. Finally, a physical foot model containing five compliant, adjustable toes was constructed and validated the discoveries with regard to the animals. Using the gecko toes' control strategies, the artificial foot demonstrated diverse behavior regulating attachment forces. The success of the foot prototype not only tested our understanding of the mechanism of biological attachment, but also provided a demonstration for the design and control of gecko-inspired attachment devices, grippers and other manipulators.

Size, shape and orientation of macro-sized substrate protrusions affect the toe and foot adhesion of geckos.

Geckos are excellent climbers using compliant, hierarchically arranged adhesive toes to negotiate diverse terrains varying in roughness at multiple size scales. Here, we complement advancements at smaller size scales with measurements at the macro scale. We studied the attachment of a single toe and whole foot of geckos on macroscale rough substrates by pulling them along, across and off smooth rods and spheres mimicking different geometric protrusions of substrates. When we pulled a single toe along rods, the force increased with the rod diameter, whereas the attachment force of dragging toes across rods increased from about 60% on small diameter rods relative to a flat surface to ∼100% on larger diameter rods, but showed no further increase as rod diameter doubled. Toe force also increased as the pulling changed from along-rod loading to across-rod loading. When toes were pulled off spheres, the force increased with increasing sphere diameter as observed for along-rod pulling. For feet with separated toes, attachment on spheres was stronger than that on rods with the same diameter. Attachment force of a foot decreased as rod and sphere size increased but remained sufficient to support the body weight of geckos. These results provide a bridge to the macroscale roughness seen in nature by revealing the importance of the dimension, shape and orientation of macroscale substrate features for compliant toe and foot function of geckos. Our data not only enhance our understanding of geckos' environmental adaptive adhesion but can also provide inspiration for novel robot feet in development.

[Simultaneous determination of polycyclic aromatic hydrocarbons and phthalate esters in surface water by dispersive liquid-liquid microextraction based on solidification of floating organic drop followed by high performance liquid chromatography].

Polycyclic aromatic hydrocarbons (PAHs) and phthalate esters (PAEs) are internationally recognized as priority pollutants; hence, it is important to monitor their concentrations in the environment. However, the low concentrations of PAHs and PAEs in surface water make the direct and sensitive determination of these compounds by instrumental methods difficult. Therefore, the development of an accurate and rapid sample pretreating method for the determination of PAHs and PAEs in water has always been the goal of environmental scientists. Dispersive liquid-liquid microextraction based on solidification of floating organic droplet (DLLME-SFO) is a simple, rapid, low-cost, sensitive, and environmentally friendly method. Methods based on DLLME-SFO for the simultaneous determination of PAHs and PAEs in surface water have rarely been reported. In this study, a novel DLLME-SFO method was developed for the simultaneous determination of 16 PAHs and 6 PAEs in surface water samples. To optimize the extraction efficiency for the target compounds, various parameters, including the types and volumes of extractants and dispersants, ionic strength, and extraction time, were investigated. First, 1-undecanol (melting point:19℃) and 1-dodecanol (melting point:24℃) were selected as extractive solvents, and their extraction efficiency was investigated. The results showed that 1-dodecanol had better extraction efficiency. The melting point of 1-undecanol was relatively low, and the droplets that solidified during the experiment were easy to melt and break, which led to the low recovery rate of extraction. Then, the effect of the volume (10, 20, 30, 40, 50 µL) of 1-dodecanol was investigated, and the extraction efficiency of the target compounds was found to decrease with increasing volume of 1-dodecanol. Second, the effect of four dispersive solvents (methanol, ethanol, acetonitrile, and acetone) on the extraction efficiencies was studied. The extraction efficiencies of the target compounds were the highest when methanol was used as the dispersant; hence, the effect of different volumes of methanol on the extraction efficiency was further examined. When the volume of methanol was less than 500 µL, the contact area between the extraction solvent and the water phase increased with increasing methanol volume, and the extraction efficiency increased. However, when the volume of methanol was more than 500 µL, the excessive dispersant increased the solubility of the target compound in the water phase, which led to a decrease in the extraction efficiency. Finally, the effects of salt addition and vortex oscillation time on the extraction efficiency were probed. The experimental results indicated that the extraction efficiency increased with an increase in the quantity of NaCl. When the NaCl quantity was greater than 0.2 g, there was no notable change in the extraction efficiency. Vortex oscillation could accelerate the establishment of the extraction equilibrium, and the extraction efficiency reached a stable state when the vortex oscillation time was more than 2 min. According to the abovementioned results, the optimized DLLME-SFO conditions were established as follows:for 5.0 mL water samples, 10 µL of 1-dodecanol was chosen as the extraction solvent, 500 µL of methanol was used as the dispersive solvent, the vortex oscillation extraction time was 2 min, and the NaCl quantity was 0.2 g. The target compounds were analyzed by high-performance liquid chromatography. Separation of the PAHs and PAEs was achieved on a SUPELCOSILTM LC-PAH column (150 mm×4.6 mm, 5 µm) with acetonitrile-water as the mobile phase using a gradient elution program. Fifteen PAHs were detected using a fluorescence detector, and six PAEs and acenaphthylene were detected by an ultraviolet detector. Quantitative determination was achieved by the external standard method. This method was successfully validated for the analyses of the 16 PAHs and 6 PAEs in two types of water samples (tap water and river water). The average recoveries of the target compounds were 60.2%-113.5%, and the corresponding relative standard deviations (RSDs, n=3) were 1.9%-14.3%. The limits of detection (LODs, S/N=3) ranged from 0.002 µg/L to 0.07 µg/L for the PAHs and from 0.2 µg/L to 2.2 µg/L for the PAEs. The limits of quantification (LOQs, S/N=10) ranged from 0.006 µg/L to 0.23 µg/L for the PAHs and from 0.8 µg/L to 7.4 µg/L for PAEs. The proposed method is simple, fast, low-cost, and environmentally friendly, and it is suitable for the rapid determination of trace PAHs and PAEs in surface water samples.

Copper-catalyzed double N-alkenylation of amides: an efficient synthesis of di- or trisubstituted N-acylpyrroles.

An efficient copper-catalyzed double alkenylation of amides with (1Z,3Z)-1,4-diiodo-1,3-dienes is reported for the first time. The reactions proceed to afford di- or trisubstituted N-acylpyrroles in good to excellent yields using CuI as the catalyst, Cs2CO3 as the base, and rac-trans-N,N'-dimethylcyclohexane-1,2-diamine as the ligand.