Anatomical maturity grading and fiber cell wall properties of small-diameter bamboo

The mechanical performance of bamboo is largely determined by the properties of its fiber cell walls, which develop progressively during culm maturation. Conventional maturity assessments based on age or visual inspection are often unreliable for small-diameter species, where external indicators are indistinct. In this study, an anatomical grading method was applied to evaluate the maturity of Bambusa multiplex culms, and fiber cell wall properties were examined across different maturity types. Culms were categorized into three maturity classes according to fiber wall thickness and lumen size. A combination of atomic force microscopy (AFM), X-ray diffraction (XRD), Raman spectroscopy, and nanoindentation was used to characterize cell wall ultrastructure, chemical composition, and micromechanics. The results showed that mature culms contained fibers with thickened secondary walls (S), lower microfibril angle (MFA), and higher cellulose crystallinity. Nanoindentation confirmed significantly greater modulus of elasticity and hardness in mature fibers compared with immature ones. Raman spectra further indicated increased deposition of lignin and hemicellulose and a relative decrease in cellulose concentration with increasing maturity. These findings demonstrate that anatomical maturity grading provides a reliable and practical approach to assess developmental status in small-diameter bamboo. Linking anatomical features to structural and mechanical properties offers a scientific basis for the selective utilization of small-diameter bamboo in fiber-based products and sustainable material applications. • Established an anatomical grading of Bambusa multiplex maturity. • Characterized fiber wall properties across maturity levels. • Mature fibers showed thicker walls, lower MFA, higher crystallinity, and strength. • Raman imaging mapped chemical components distribution across maturity levels. • Findings support targeted utilization of small-diameter bamboo culms.