Biomechanical Investigation of Plant Vascular Tissue for Bio-Inspired Design and Flexible Composites

Since the inception of evolution, nature has continuously optimized all the natural materials. These optimizations are so efficient that scientists and engineers have started taking inspiration from nature. Such inspiration-based solutions provide sustainable development of new materials with enhanced structural properties and functionalities (such as stiffness, stability, toughness, self-healing etc.). This variety of properties and functionalities is mainly due to the hierarchical organization of such components. Abstraction of the hidden cues of the hierarchical organization, principles and underlying structure-function relations are some of the critical approaches of bioinspired materials design. Inspiration from animals and plants has helped develop the design concept of aerodynamics, robotics, tissue scaffolding, composites materials and construction. However, while studying both systems (animal and plant), significant effort has been focused on rigid natural composites such as bone, wood, and bamboo for designing structures optimized for strength, toughness, and density. So, in this study, the effort has been given to explore the soft vascular tissue of plants for flexible biocomposite design. Plants stem exhibit mechanical design principles, and their multi-functionality and hierarchical structures allow them to grow. So, we investigated the structure and composition changes of sunflower and soybean stem and their cell wall at different time points of normal growth using microscopy and spectroscopy techniques. To study morphology and cellular microstructure, we have used Scanning Electron Microscopy (SEM). Also, SEM images were used to quantify the area contribution of different regions of sunflowers and soybean stem (e.g., cortex, pith, xylem and phloem), and linear measurements such as vessels diameter and wall thickness. To study the compositional changes, we have used Raman Spectroscopy. Optical Microscopy and Electrical Impedance Spectroscopy is used to study the difference in the electrical response within the stem due to abiotic stress. These biomechanical observations can provide the ultra-structural hidden cues of plants growth, and later it can lead to early indications of plant health. The first set of studies on a sunflower is carried out to understand healthy longitudinal growth. However, the second set of studies on soybean is carried out to observe the ultrastructural changes in a healthy and stressed condition. Together, the study is the first of its kind to quantify structurecomposition changes of stem growth. Several engineering implications of the insight is discussed for applications varying from bioinspired design, biocomposites, and devices for precision agriculture