Optical dynamometry to study phase transitions in lipid membranes.

Area of Science:

• Biophysics
• Cell Biology
• Materials Science

Background:

• Cell membrane fluidity is essential for cellular functions, enabling the movement of embedded proteins.
• Lipid bilayers undergo phase transitions from fluid to gel states, significantly altering mechanical properties like viscosity and stiffness.
• Understanding these transitions is key to comprehending membrane dynamics and cellular processes.

Purpose of the Study:

• To investigate the changes in membrane mechanical properties during lipid bilayer phase transitions.
• To utilize optical trapping as a method for probing membrane fluidity and elasticity.
• To analyze the behavior of membrane inclusions during fluid-to-gel phase transitions.

Main Methods:

• Employing optical trapping and manipulation of microspheres attached to giant unilamellar vesicles (GUVs).
• Utilizing GUVs as model membranes for direct visualization of membrane responses.
• Monitoring the motion of attached particles under various forces (gravity, thermal noise, radiation pressure) to infer membrane properties.

Main Results:

• Observed divergence in shear surface viscosity as the lipid bilayer transitions to a gel phase, impeding particle motion.
• Measured a drop in membrane bending stiffness during the phase transition, followed by a significant increase upon further cooling.
• Demonstrated the correlation between particle mobility and the membrane's fluidity state.

Conclusions:

• Optical trapping of GUVs provides a powerful tool to study membrane mechanics across phase transitions.
• Lipid bilayer phase transitions profoundly impact membrane fluidity and elasticity, affecting the mobility of membrane inclusions.
• This technique allows for detailed characterization of model membranes and offers insights into biological membrane behavior.