Microscopic Observations of the Lotus Leaf for Explaining the Outstanding Mechanical Properties

The leaf of lotus （Nelumbo nucifera） exhibits exceptional ability to maintain the opening status even under adverse weather conditions, but the mechanism behind this phenomenon is less investigated. In this paper, lotus leaves were investigated using environmental scanning electron microscopy in order to illustrate this mechanism. The macro-observations show that the primary veins are oriented symmetrically from leaf center and then develop into fractal distribution, with net-shaped arrangement of the side veins. Further micro-observations show that all the veins are composed of honeycomb micro-tubes viewed from cross section, the inner of micro-tubes are patterned with extended closed-hexagons from vertical section. Different positions of leaf possess diverse mechanical properties by size variation of diameter and inner hexagons of veins, which is theoretically analyzed by building a regular honeycomb model. Specifically, the central area of lotus tends to be stiffer while its margin be softer. These special distribution and composition of the veins mainly account for the distinct behavior of lotus.