Ultrasound enhanced diffusion in hydrogels: An experimental and non-equilibrium molecular dynamics study

Area of Science:

• Biophysics
• Materials Science
• Acoustic Engineering

Background:

• Focused ultrasound is known to enhance nanoparticle diffusion.
• Understanding this phenomenon is crucial for targeted drug delivery and medical imaging.
• Previous studies showed enhanced diffusion, but the underlying mechanisms require further investigation.

Purpose of the Study:

• To investigate the effect of focused ultrasound on nanoparticle diffusion in hydrogels.
• To compare experimental findings with non-equilibrium molecular dynamics (NEMD) simulations.
• To determine the frequency and amplitude dependencies of ultrasound-enhanced diffusion.

Main Methods:

• Single particle tracking experiments with 40 nm and 100 nm polystyrene nanoparticles in agarose hydrogels.
• Development of a coarse-grained NEMD model with an oscillating external force field simulating focused ultrasound.
• Comparison of experimental results with simulation data and theoretical diffusion equations.

Main Results:

• Focused ultrasound significantly increased the mean square displacement (MSD) of nanoparticles in hydrogels.
• NEMD simulations reproduced experimental MSD trends, highlighting the role of particle velocity.
• The model showed frequency dependency matching the two-time continuous time random walk (CTRW) model.
• At high ultrasound intensities, the diffusion coefficient approached the non-hindered diffusion coefficient.

Conclusions:

• Focused ultrasound effectively enhances nanoparticle diffusion in hydrogels.
• Particle velocity is a significant factor in ultrasound-enhanced diffusion.
• The developed NEMD model accurately captures the observed diffusion behaviors.
• The non-hindered diffusion coefficient is applicable at high ultrasound intensities in hydrogels.