Lipid vesicle pools studied by passive X-ray microrheology

Area of Science:

• Biophysics
• Soft Matter Physics
• Materials Science

Background:

• Vesicle pools, also known as vesicle clusters, form via liquid-liquid phase separation (LLPS) driven by attractive interactions.
• These clusters exhibit liquid-like order and can be considered condensates, necessitating study of their structure and dynamics.
• Understanding vesicle diffusion within these arrested states is crucial for comprehending heterogeneous biomolecular fluids.

Purpose of the Study:

• To evaluate passive microrheology using X-ray photon correlation spectroscopy (XPCS) as a tool for studying artificial lipid vesicle systems undergoing LLPS.
• To investigate the dynamics of single and collective vesicle movement within these phase-separated systems.
• To explore the utility of XPCS for analyzing other heterogeneous biomolecular fluids.

Main Methods:

• Utilized X-ray photon correlation spectroscopy (XPCS) for passive microrheology.
• Incorporated highly scattering tracer particles into model systems of artificial lipid vesicles.
• Varied calcium chloride (CaCl2) concentrations to induce and study liquid-liquid phase separation (LLPS).

Main Results:

• XPCS successfully inferred both single vesicle and collective dynamics through tracer particle analysis.
• At low CaCl2 concentrations, tracer particles exhibited free diffusion.
• At higher CaCl2 concentrations (around 8 mM), the relaxation rate showed a nonlinear dependence, indicating arrested diffusion in percolating vesicle clusters.

Conclusions:

• Passive microrheology with XPCS is effective for studying dynamics in vesicle clusters formed by LLPS.
• The observed nonlinear relaxation rate signifies a transition to arrested diffusion within percolating vesicle clusters.
• This approach provides valuable insights into the dynamics of heterogeneous biomolecular fluids.