Insights into the micromechanics and patterning of growing plant cell wall as a multifunctional composite

• Reveals new engineering principles behind the growing plant cell wall. • Integrates multiscale and multimodal tools (Raman Spectroscopy, Scanning Electron Microscopy, and Nanoindentation). • Links cell wall layering and patterning as design strategies for flexible materials such as robotic skins or electron packaging. • Proposes design features for an easier translation to engineered systems than typically reported in biomimetic space. • Demonstrates sustainable composite innovation guiding principles using biopolymers (cellulose, pectin, and lignin). The plant cell wall (CW) is a fiber-reinforced composite present as an interconnected unit providing plants with structural form and multifunctionality, from flexibility at the growing stage to stiffness and strength at the mature stage. This study investigates the xylem CW of sunflower stems to identify structural and compositional transitions underlying its growth demands. The study was conducted using Raman spectroscopy, scanning electron microscopy, and instrumented nanoindentation techniques on samples from four-week-old and eight-week-old. At these two growth points, both longitudinal and transverse sections are analyzed for as-cut healthy growth and after selective enzymatic treatment to target cellulose and pectin removal, the key components of growing CW. The results revealed an increase in cellulose content and crystallinity with age, indicating increased organization in CW. Single and double helical coiling, changes in wall thickness, and the presence of pitted walls, as observed via SEM, revealed the geometrical strategies adopted by CW for supporting longitudinal growth while optimizing stiffness and water transportation. Greater disruption of its structure and strength post-enzymatic treatment, especially pectin removal, was observed via the opening of helical coiling, the impact on cellulose organization, and the loss of modulus and hardness, highlighting the important role of pectin in maintaining the structure and the interdependence of pectin and cellulose components of CW. These results are presented in the context of design strategies such as directional reinforcements, spatial optimization, polymer composition balance and their interactions, which can be translated for biomimicking composite design and manufacturing for targeted performance achievement.