Study On The Adhesion Force And Characterization Methods Of Drosophila Melanogaster On Substrate With Different Roughness

People have been always in the way exploring the reason for living things with superior attaching and detaching ability. Geckos can easily climb on a variety of substrates. It can also quickly climb at the speed of76cm/s on a very smooth ceiling; even flies can climb on glass, it also can hang on the ceiling. It was discovered that this amazing phenomenon was determined by the special multi-fibrous structure of insects’foot, so we can design similar fiber foot by bionic to accomplish bio-mimic adhesion foot and structure.This paper analyzed insects’feet, and divided it into three adhesion forms:hairy adhesive pads, smooth adhesive pads and claw. We took drosophila melanogaster as our object of study, which was commonly used for biology experiment. It was found by SEM (Scanning Electron Microscope) that each foot of it included a pair of hom-like claw and hairy pulvillus. The tip diameter of the claw was about1.40μm. The pulvilli were tree-branch in shape and its main trunk was approximate15-20μm. The length of each seta was about6-7μm, and the diameter was about0.5μm. The top of the seta was spatula-like in shape,1.6μm in length.1.2μm in width, and100nm in thickness. The area of the top was about1.50μm2.Besides the own structure of drosophila melanogasters’feet, the particle number and surface area their feet contacted also played an important role in adhesion.10friction plates with different particle sizes were observed and analyzed by SEM and AFM (Atom Force Microscope). It was shown that with the increase of particle size, the surface was becoming rougher, and the height difference became even larger. The surface of silica and glass could be seen as smooth. The particle was conical in shape when the diameter of the particle was from0.02to5μm, while it was smisphere when the diameter of the particle was over15μm. And correspondingly we could calculate the surface area of the particle. At the same time we could calculate the root mean square roughness (RMS), namely surface roughness, which was used to characterize the roughness of the friction plate. According to correlation analysis between RMS and surface particle diameter d, it was well proved that the two parameters had good correlation. That was to see, surface roughness was determined by particle diameter.Using self-designed adhesion probability measuring device, the adhesion performance of insects contacting substrate was tested, and it was found that the surface roughness, adhesion angle, swing frequency, and vibration frequency of the substrate certainly affected the adhesion probability p of drosophila melanogaster. With the increase of particle diameter d, the adhesion probability p weakened at first and enhanced then. It achieved the minimum value when the particle diameter d reached0.3μm. The adhesion probability p was negatively correlated with the adhesion angle, swing frequency and vibration frequency. And mechanical models were established to give analysis. Moreover, the movement adaptation of drosophila melanogaster contacting different roughness surfaces were tested by using special plates made of different frication plates. It was found that drosophila melanogaster would respond quickly and transfer to the side with better performance when stimulated by the external environment.The adhesion testing equipment was used to measure the adhesion force value F of drosophila melanogaster contacting6substrates owning different particle diameter d. The result showed that the F value firstly decreased and then rose with particle diameter d increasing. When particle diameter d was0.3μm, it got the minimum value. That was0.0085mN. Synchronously we established Van der Waals model, divided the situation that drosophila melanogaster contacted substrate into five states, calculated the theoretical adhesion force in each state, and the results achieved a better fit with the actual value. When the surface roughness reached the situation that the gap between the surfaces of the particles was larger than3μm, the extrusion friction griping function of seta and griping friction of claw had worked. It led to the adhesion force larger than theoretical value. It was concluded that adhesion force was a compound function of van der Waals force by hairy adhesive pads and gripping function. Although in relatively smooth surface, the Van der Waals forces played a leading role, while in rough surface the mechanical gripping force played a leading role.