Experimental study on the blood-sucking mechanism of a female mosquito and development of a bio-inspired mosquito-pump

Abstract

Female mosquitoes are known to have a magnificent micro-scale pumping system that can transport small quantities of blood very effectively. If one could bio-mimic the blood-sucking mechanism of a mosquito, it could contribute to the development of a high-efficiency micro-pump that can be utilized in various bio-chips as a liquid-phase sample supplying system. Therefore, an experimental study on the fluid mechanical characteristics of a blood-sucking female mosquito is essential to analyze its inherent feeding mechanism in more detail.They are equipped with two pumping organs located inside their heads: the cibarial (CP) and the pharyngeal (PP) pumps. To analyze the functional relationship of these pumps during the blood-sucking process, synchrotron X-ray micro imaging method were employed. The two pumps are well coordinated with a phase shift (α) and time shift (β) to have their own function in the liquid-sucking process. The second pump (PP) starts to expand in advance with a time shift (β) before the first pump (CP) begin to contract, playing a key role to improve pumping performance. The systaltic motion of the two pumps works systematically in a well-coordinated manner. The pumping performance of blood-sucking female mosquitoes is demonstrated to be superior to that of nectar-eating male mosquitoes. Intake flow rate is maximized by reducing relaxation time of CP and increasing the pumping frequency.The 3D three-dimensional morphological structure of the pump system of a female mosquito was visualized using synchrotron X-ray microscopic computed tomography (SR-μCT). To verify the cross-sectional images acquired by SR-μCT, complementary paraffin-sectioning data were compared. Expandable volume capacities of two pump chambers were measured for several mosquito samples of similar size. Time-resolved information of volumetric variations was deduced by comparing the 3D images of the pump system obtained from two entities which represent the contraction and the expansion states, respectively. Based on these results, we suggest a dynamic operation model for the blood-sucking process of a female mosquito.The intake rate of female mosquitoes feeding various sucrose solutions was estimated using a micro particle image velocimetry technique. As the sucrose concentration increases from 1% to 50%, the intake rate decreases from 17.3 nl/s to 5.8 nl/s. Furthermore, the temporal volume variations of the two-pump chambers were estimated based on the velocity and acceleration information of the flow at the center of food canal of the proboscis. One pumping period is divided into four elementary phases, which are related to the different operational modes of the two pumps. According to the hypothetical model established in this study, the phase shift (α) between the two-pump chambers increases from 14 ms to 28 ms and the percentage of reversal flow to forward flow in a pumping period decreases 7.6% to 1.7% with increasing viscosity. Based on the flow characteristics of liquid-feeding mosquitoes, two different micropumps consisting of serial-connected two-pump chambers and three diffuser elements were fabricated using the conventional MEMS fabrication process. The two-pump chambers of the type 1 pump (TP I) have the same size, whereas those of the type 2 pump (TP II) have a different size. The volume flow rate was measured with varying the operating frequency and the phase shift by using a specially designed control system. The pumping performance of the serial-connected two micropumps is heavily dependent on the phase shift. The optimum phase shifts of both micropumps are 180° out-of-phase at high operating frequencies. As the operating frequency is decreased below 500 Hz, they approach to in-phase (θ = 0°) condition. The pumping performance, including the linear relationship between the operating frequency and phase shift, of the TP II micropump is similar to that of liquid-feeding female mosquitoes. The results obtained in this study would be helpful for understanding the blood-sucking mechanism of a female mosquito and developing a high-efficiency micro-pump which bio-inspire the two-pump system of mosquitoes.