Visualizing molecular polar order in tissues via electromechanical coupling.

Area of Science:

• Biophysics
• Materials Science
• Connective Tissue Biology

Background:

• Electron microscopy (EM) and atomic force microscopy (AFM) are standard for collagen fibril analysis.
• These methods cannot determine collagen fibril polarity (amine to carboxyl termini orientation).

Purpose of the Study:

• To introduce and validate piezoresponse force microscopy (PFM) for visualizing collagen fibril polarity and alignment.
• To assess the applicability of PFM on biological tissues with minimal sample preparation.

Main Methods:

• Utilized a voltage-modulated AFM technique, PFM, to probe collagen fibril polarity.
• Applied PFM to rat tail tendon and porcine eye tissues under ambient conditions.

Main Results:

• PFM successfully visualized both collagen fibril alignment and polar orientation in tissues.
• Observed domain-like arrangements of fibrils with opposite polarizations, extending to individual fibrils.
• Found evidence of anti-parallel ordering of polarity in fibril bundles and individual fibrils; uniform polarity was not observed.

Conclusions:

• PFM is a viable technique for mapping collagen fibril polarity and alignment in biological tissues.
• The observed anti-parallel ordering has implications for understanding mechanical properties, biofunctionality, and connective tissue development.
• PFM can be applied to diverse biological materials with piezoelectric properties.