Spin locking in liquid entrapped in nanocavities: Application to study connective tissues

Area of Science:

• Biophysics
• Materials Science
• Biomolecular Physics

Background:

• Spin-lattice relaxation in the spin-locking state provides unique insights into atomic and molecular dynamics.
• This contrasts with information gained from spin-lattice relaxation in strong external magnetic fields.
• Investigating biological samples with fibril structures using this technique reveals relaxation time anisotropy under spin locking (T1ρ).

Purpose of the Study:

• To explain the anisotropy of spin-lattice relaxation under spin-locking in connective tissues.
• To develop a model representing connective tissue as nanocavities containing water.
• To estimate water molecular motion correlation times and nanocavity volumes in biological samples.

Main Methods:

• Utilized spin-locking technique to study spin-lattice relaxation in biological samples.
• Developed a model of connective tissue as a set of water-filled nanocavities.
• Applied Gaussian distributions to nanocavity directions for anisotropy calculations.

Main Results:

• Estimated water molecular motion correlation time (τc=30μs) and average nanocavity volume (V≃5400nm³) in articular cartilage.
• Demonstrated good agreement between the nanocavity model and experimental data from articular cartilage and tendon.
• Obtained fitting parameters for each layer of articular cartilage, showing variation with anatomical microstructure.

Conclusions:

• The developed nanocavity model successfully explains the anisotropy of spin-lattice relaxation under spin-locking in connective tissues.
• The model's fitting parameters correlate with the known microstructures of articular cartilage and tendons.
• These parameters can be utilized for future characterization of fine fibril structures in biological samples.