Study On Mechanics Behaviors Of Mosquito's Floating And Acupuncturing

Insect microsystems in biological world are actually natural micro-mechanical systems with a high reliability. The working mechanics principles of the insect's relevant organs often show perfect coordination and unification in the multi scale from macro to micro and even nano scale, which make the insects have many wonderful special skills. Study of the mechanics behaviors of biomaterials and micronano-stuctures related to these special skills has important significance to the design and fabrication of advanced micro-mechanical systems. Mosquito is a kind of common insect, but has many special skills. The first one is its superior "water floating" function. Mosquito can float, walk, lay eggs and take off or land freely on the water surface.The second is its "painless blood-sucking" skill. A mosquito uses a natural "microneedle" system with a large ratio of the length to the diameter and high flexibility and strength called fascicle to painlessly penetrate into human skin and suck blood. This natural "microneedle" system never has any strength problem in the penetrating process. The third one is its adhesion function. Mosquito can adhere to any solid surface freely, such as the wall, smooth glass and so on. The fourth one is its special flying skill. It can not only fly forward, but also stop immediately and even fly back in air. The fifth one is its spying and navigating skill. It can detect and aim exactly at a target that it wants to attack (bite) even at night. It also has too many other special functions to list here. In the present work, we study mainly the first two special skills. A series of researchs are carried out on the surface wettability and high water-supporting force of the mosquito leg, mechanical mechanism of the fascicle insertion into skin, and so on. Advanced micronano test and observation technique, appropriate theoretical model and trustworthy numerical technology are main research tools adopted.An experimental study is carried out to investigate the surface wettability of the mosquito leg. It has been found that the mosquito leg is a natural surface with excellent water repellent properties. The composition of the mosquito leg is studied by a FTIR spectrometer. The analytical result shows that the main composition of the mosquito leg is not enough to cause the superhydrophobicity, although it has some effects on the wettability. Scanning electron microscope (SEM) observations reveal that the uniquely three-level micronano-structure on the mosquito leg consists of numerous oriented ten-micron scales with uniform sub-micron longitudinal ridges and nanometer cross ribs. Based on the special micronano structures combined with the classical wetting theory, a "multi-level structure" model is proposed to analyze the superhydrophobicity of the mosquito leg. It has been theoretically demonstrated that the hierarchical micronano-structure on the leg surface results in such superior water repellency.The water supporting force of the mosquito leg is studied experimentally. It has been found that the mosquito leg has a surprising high water-supporting ability. The average water supporting force of a single leg reaches up to 600μN, about 23 times the total body weight of this insect. The process of the mosquito leg pressed into water is analyzed theoretically. The water supporting force of the mosquito leg is calculated. The theoretical solutions are compared with the experimental results. It has been found by using the theoretical model combined with experiments that to achieve a superior strong supporting ability on water a mosquito leg has several physical mechanisms, including the leg length, the hierarchical micronano-structure and the special cross-section shape.The micronano-structure of the mosquito fascicle and the biomechanics behavior of the fascicle inserting into human skin are studied experimentally. It has been shown that the two main piercing parts—the labrum and maxilla both have micronano-sharp tips. There are reinforced structures along the axis direction of the labrum and fine micronano saw-teeth along the bothsides of the maxilla. It is also found that the mosquito does not directly penetrate its feeding fascicle into a victim's skin, but instead firstly uses the labrum tip to puncture the skin surface and anchor it down into the top layer of the skin, and then use the micronano saw-toothed maxillae to saw their way into the tissue of skin with a special frequency. A quantitative analysis is carried out to study the rule of the oscillation inserting process of the mosquito fascicle. It has been found that the oscillation frequency is not a constant but decreases with the time (or the depth) of penetration, while the oscillation amplitude is about 40～80μm and increases with the time (or the depth) of penetration.Two different high precision micro-Newton force measurement devices are designed to measure the insertion force for mosquito fascicle to penetrate into human skin respectively. The measured results show that the mosquito uses a very low force (tens of micro-Newton in average) to penetrate into the skin. This force is at least three orders of magnitude smaller than the reported lowest insertion force for an artificial microneedle with an ultra sharp tip to insert into the human skin. In addition, it has also been found that after the mosquito fascicle tip penetrates into the surface of the skin, the force used by the mosquito to penetrate its fascicle deeper into the skin will not continuously increase, but firstly decreases with the increase in the insertion depth and then levels out at a surprisingly low mean force (even almost be zero). These characteristics differ from the insertion force variation observed using artificial microneedles. The study on the insertion mechanism of the mosquito fascicle shows that the mosquito's micronano-structured fascicle and its amazing oscillation inserting skill make it penetrate easily into human skin with a surprising low force. Based on the mechanical principle of the mosquito penetrating its fascicle into skin with a surprisingly low mean force, an oscillation micronano serrated scalpel has been designed and proved to have a good effect in reducing cutting force by experiment.Considering the mechanical properties of different skin layers and the failure of material, the processes of the insertion of artificial microneedle and natural "microneedle" (mosquito fascicle) into a skin are analyzed by using the non-liner finite element code ABAQUS. Firstly, through the finite element simulation analysis of the insertion process of an artificial microneedle into skin, the interaction mechanism between the microneedle and skin during the insertion process of the micro-needle is revealed. The skin deformation and failure and the general behavior of the microneedle force-displacement history are discussed. The insertion force can be got. A further study is given on the influences of the mechanical properties of the skin and microneedle geometry on the insertion force. A qualitative agreement occurs between computation and the experiment. The numerical results demonstrate the validity of this numerical model, laying a foundation for the numerical simulation of the insertion process of the natural "microneedle" (mosquito fascicle) into skin and giving a theory basis for the optimum design of the artificial microneedles. Then, the simulation model of the mosquito fascicle tip is built up by the three-dimensional modeling software CATIA. A numerical simulation is conducted to analyze the insertion process of the mosquito fascicle tip into human skin. The deformation and failure of the skin, the general behavior of the labrum force-displacement history and the insertion force are discussed. An ideal agreement is found between the numerical results and the experimental measurements.