식물의 동적 거동 매커니즘 규명 및 생체 모사 기술 개발

Abstract

Most previous studies have investigated the motile mechanism of plants from a biochemical perspective. However, to explain the underlying principles of movements, an interdisciplinary study on the structural characteristics of motile plants should be accompanied. Firstly, I studied about Mimosa pudica that rapidly shrinks its body in response to external stimuli. M. pudica does not perform merely simple movements, but exhibits a variety of movements that quickly change depending on the type of stimuli. In this study, structural characteristics and seismonastic reactions of M. pudica were experimentally investigated using advanced bio-imaging techniques. The results show that the key factors for the flexible movements by the pulvinus are bendable xylem bundle, expandable/shrinkable epidermis, tiny wrinkles for surface modification, and a xylem vessel network for efficient water transport. I also studied about pine cones. Pine cones fold their scales when it rains to prevent seeds from short-distance dispersal. Given that the scales of pine cones consist of nothing but dead cells, this folding motion is evidently related to structural changes. In this study, the structural characteristics of pine cones were experimentally investigated using various advanced bio-imaging techniques. The results shows that raindrops fall along the outer scales to the three layers (bract scales, fibers and innermost lignified structure) of the inner pine cones. However, not all the layers but only the bract scales get wet and then, most raindrops move to the inner scales. These morphological structures reduce the amount of water used and minimize the time spent on structural changes. Pine cones were found to have structural advantages that could influence on the efficient motion of pine cones. In addition, pine cones open and release their embedded seeds on dry and windy days for long-distance dispersal. In this study, how the pine seed attach to and detach from the pine cone scale for efficient seed dispersal were experimentally investigated by using X-ray micro-imaging technique. The cone and seeds adhere to one another in the presence of water, which could be explained by the surface tension and contact angle hysteresis. Otherwise, without water, the waterproof seed wing surface permits rapid drying for detach and wind dispersion. On the other hand, during wildfires, pine cones open their seed racks and detach the pine seeds from pine cones for rapid seed dispersal. Due to these structural advantages, pine seeds are released safely and efficiently depending on surrounding environment. Inspired by the structure of pine cone scales, a system was designed using temperature-sensitive hydrogel with embedded fishing lines. Stimuli-responsive hydrogels have been intensively studied, because of their potential applications in drug delivery, cell culture, and actuators. The layers composed of same hydrogel PNIPAAm always shrinks in response to heat. To design the bending hydrogel, I exploited the coupled responses of the hydrogel. The intercalating fishing line changes the dynamic behaviour of the hydrogel. Lastly, I designed a pine cone scale-inspired movable temperature-sensitive symmetric hydrogel containing Fe3O4. Alignment of Fe3O4 along the magnetic force is key in the motion control in which Fe3O4 acts like fibers in a pine cone scale. Although a homogeneous temperature-sensitive hydrogel cannot respond to temperature gradient, the Fe3O4-containing hydrogel demonstrates considerable bending motion. Varying degrees and directions of motion are easily facilitated by controlling the amount and alignment angle of the Fe3O4. The shape of the hydrogel layer also has influence on the morphological structure. In this study, introduced facile and low-cost methods are proposed to control various bending motions. The present results can be applied to many fields of engineering, especially dynamic actuators.