Polarimetric second harmonic generation microscopy of partially oriented fibers II: Imaging study

Area of Science:

• Biophysics
• Microscopy
• Materials Science

Background:

• Biological and biomimetic fibrillar structures possess complex ultrastructural organization.
• Understanding this organization is crucial for various scientific and medical applications.
• Existing imaging techniques may have limitations in resolving fine structural details.

Purpose of the Study:

• To investigate the ultrastructural organization of partially oriented fibrillar structures using polarimetric second harmonic generation (SHG) microscopy.
• To analyze how different configurations of fibrils (2D and 3D) influence SHG imaging.
• To establish a basis for interpreting SHG microscopy images in terms of 3D fibril organization.

Main Methods:

• Utilized linear polarization-in polarization-out SHG microscopy.
• Examined biological samples (rat tail tendon, rabbit cornea, pig cartilage) and biomimetic meso-tetra(4-sulfonatophenyl)porphine (TPPS4) cylindrical aggregates.
• Measured SHG intensity and susceptibility component ratios (R and C) under varying fiber orientations and crossings.

Main Results:

• SHG intensity and susceptibility ratios are sensitive to fiber arrangements, including parallel/antiparallel orientations, tilting, and 2D/3D crossings.
• Observed distinct differences in the dependence of the R ratio on fiber configuration in collagen and TPPS4 aggregates.
• Experimental results showed good agreement with analytical expressions and computational modeling of fibril configurations.

Conclusions:

• Polarimetric SHG microscopy is effective for elucidating the 3D ultrastructural organization of fibrillar materials.
• The study provides a framework for interpreting SHG microscopy data based on fibril configuration.
• This technique offers a powerful tool for analyzing the micro- and nanostructure of diverse materials.