Collagen chirality and three-dimensional orientation studied with polarimetric second-harmonic generation microscopy

Area of Science:

• Biophysics
• Materials Science
• Optical Microscopy

Background:

• Collagen is a key structural protein in connective tissues.
• Understanding collagen's 3D organization is crucial for tissue engineering and disease research.
• Nonlinear optical microscopy offers unique insights into molecular properties.

Purpose of the Study:

• To characterize the nonlinear optical properties of collagen using P-SHG microscopy.
• To determine a 3D orientation map of collagen fibers in pig tendon.
• To extract molecular susceptibility ratios and assess collagen's chiral structure.

Main Methods:

• Polarization-dependent second-harmonic generation (P-SHG) microscopy.
• Linear polarization-in polarization-out (PIPO) imaging technique.
• Analysis of thin pig tendon sections at varying angles.

Main Results:

• Established C6 symmetry for nonlinear susceptibility tensor component ratios.
• Introduced a new parameter related to collagen's chiral structure.
• Observed and quantified collagen fiber polarity based on out-of-plane tilt.

Conclusions:

• P-SHG microscopy effectively maps 3D collagen organization.
• Nonlinear chiral properties provide insights into collagen's molecular frame.
• This technique enables orientation-independent characterization of collagen fibers.