Anisotropy Analysis of Bamboo and Tooth Using 4‐Angle Polarization Micro‐Spectroscopy

ABSTRACT To investigate the anisotropic properties of biomaterials, two distinct classes are considered as follows: polymer‐based (cellulose in plants) and crystalline‐based (enamel in teeth), each demonstrating distinct structural and functional characteristics. Four‐angle polarization spectral mapping of sub‐1‐ bamboo slices was carried out in the mid‐IR spectral range (2.5–20 ) to reveal the 3D organization of the chemical bonding of cellulose using the key characteristic absorption bands associated with C–O–C and C–N vibrational modes. The longitudinal and transverse microtome slices revealed a switch between the presence and absence of dichroism in parenchyma cell walls and vascular bundles. The cell wall showed continuous alignment of the C–O–C stretching vibrational mode (8.6 /1163 ) down to the pixel resolution of in the transverse slice; the cell wall thickness is . Thin microtomed slices of a tooth were measured in transmission and reflection modes. The single‐point reflection measurements, performed using two perpendicular orientations, revealed orientational anisotropy in the enamel, which was absent in the dentin region. High subdiffraction lateral resolution was numerically validated using a simplified toy model of a Gaussian beam. The model showed that the orientation of small absorbers can be revealed using a focal spot of .