Biomechanics of vascular plant as template for engineering design

Plants are biocomposites with a hierarchical organization and multifunctionality with several unique characteristics different from animals (lack of motion and neurological control). Consequently, a stronger correlation is expected between plant structure, function, and mechanical response. Insights into these changes can have broad implications in bioinspired design, biobased material development, and precision agriculture. We use nanomechanical methods to investigate structural and compositional changes in sunflower plants at longitudinal stages of growth. Specifically, we use Scanning Electron Microscopy for microstructural analysis and Raman Spectroscopy and Optical Microscopy for compositional analysis. These studies together revealed several aspects of longitudinal growth. Specifically, the rapid plant growth during the vegetative stage (28% from week 4 to week 6) significantly slows (8%) during the transition to the reproductive stage (week 6 to week 8) and beyond. During the transition period, the thickness of the vascular zone increases significantly (28%), accompanied by modest thickening of cell walls (8%) and increases in cell diameter (4%), all of which impacting fluid flow dynamics. The increase in the vascular zone comes with a corresponding decrease internal flexible hydraulic chamber (17%), indicating the underlying mechanics of loss of flexibility. Raman spectroscopy revealed a high concentration of metabolites (molybdenum sulfide and crocetin), which are responsible for stress signaling and plant defense in the early stages of growth. Together, the study is first of its kind to quantify structure-composition changes of stem growth, Several engineering implications of the insight is discussed for applications varying from bioinspired design, biocomposites, and devices for precision agriculture.