Exploring the structure and dynamics of soft and hard cuticle of Bombyx mori using solid-state NMR techniques

This study conducts a comprehensive analysis and comparison of Bombyx mori cuticles across different developmental stages, ranging from larval to adult, utilizing advanced solid-state NMR techniques. The primary objective is to elucidate the underlying reasons for the contrasting hardness of adult cuticles and softness of larval cuticles. Notably, PXRD analysis reveals a prominent broad peak at 19.34°, indicating the predominantly amorphous nature of both larval and adult cuticles. Analysis of ¹³C CP-MAS SSNMR spectra highlights an elevated proportion of phenoxy carbon in adult cuticles (6.77%) compared to larval cuticles (1.24%). Furthermore, a distinctive resonance line at 144 ppm is exclusively observed in adult cuticles, due to catechols, suggesting potential biochemical pathway variations during development. Significant variations in the primary components of ¹³C chemical shift anisotropy (CSA) tensors for aliphatic carbons of amino acids, catechols, and lipids between adult and larval cuticles indicate alterations in electronic environments. Additionally, the shorter spin-lattice relaxation time of carbon nuclei in larval cuticles compared to adult cuticles implies slower motional dynamics with enhanced degree of sclerotization in adults. By investigating the internal structure and dynamics of cuticles, this research not only contributes to biomimetic material development but also enhances our understanding of structural changes across different developmental stages of B. mori.