High-Performance Polarization Microscopy Reveals Structural Remodeling in Rat Calcaneal Tendons Cultivated In Vitro.

Area of Science:

• Biomaterials Science
• Tissue Engineering
• Cell Biology

Background:

• Collagenous tissues possess anisotropic optical properties like birefringence and linear dichroism (LD) due to their ordered structure.
• Polarization microscopy can assess macromolecular order and aggregation in tendon collagen bundles.
• Limited data exists on macromolecular organization changes in tendon explants cultured in vitro.

Purpose of the Study:

• To evaluate birefringence and LD in rat calcaneal tendon explants cultured on substrates of varying mechanical stiffness (plastic vs. glass).
• To investigate the relationship between collagen bundle organization and cell migration from explants.
• To understand the impact of substrate stiffness on tendon explant remodeling in vitro.

Main Methods:

• Rat calcaneal tendon explants were cultured for 8 and 12 days on glass or plastic substrates.
• Birefringence was measured using high-performance polarization microscopy on unstained sections.
• Linear dichroism (LD) was assessed on sections stained with Ponceau SS (proteins) and toluidine blue (GAGs) under polarized light.

Main Results:

• Significant structural remodeling, including reduced macromolecular orientation and collagen bundle alignment, was observed in explants cultured on plastic substrates.
• Decreased birefringence intensity and LD values correlated with structural remodeling on plastic.
• Cell migration from explants to the substrate was earlier and more intense on plastic, with cells aligning axially over time.

Conclusions:

• Plastic substrates induce structural remodeling in tendon explants, characterized by decreased collagen organization.
• This remodeling may facilitate cell migration, suggesting substrate stiffness influences tenocyte behavior.
• The axial alignment of migrating cells indicates mechanosensitivity, with collagen fibers potentially acting as signaling cues.