Poster D6 - Confined Brownian Diffusion near PEG Lipid Bilayer

Thursday, October 24, 2024

2:45 PM - 3:45 PM EST

Location: Exhibit Hall E, F & G

Presenting Author(s)

Rachel Dorney

Undergraduate Student
Lehigh University
Schnecksville, Pennsylvania, United States

Co-Author(s)

Quinn Reed (he/him/his)

PhD Student
Lehigh University
Sellersville, Pennsylvania, United States
NF

Nicolas Fares

PhD Student
Laboratoire Ondes et Matière d'Aquitaine (LOMA), United States
ML

Maxime Lavaud

Post-Doc
Laboratoire Ondes et Matière d’Aquitaine (LOMA), United States
YA

Yacine Amarouchene

CNRS Researcher
Laboratoire Ondes et Matière d'Aquitaine (LOMA), United States

Primary Investigator(s)

TS

Thomas Salez

CNRS Researcher
Laboratoire Ondes et Matière d'Aquitaine (LOMA), United States

Last Author(s)

AH

Aurelia Honerkamp Smith, PhD (she/her/hers)

Associate Professor of Physics
Lehigh University
Bethlehem , Pennsylvania, United States

Introduction: Brownian motion, the random movement of microscopic particles suspended in a fluid, arises from collisions with the rapidly moving molecules within the fluid. This fundamental phenomenon underlies a range of processes at the micro and nanoscale. In confined environments, such as near surfaces or boundaries, Brownian motion is significantly influenced by the presence of these surfaces. Nothing in nature exists in isolation; all particles are subject to interactions with their surroundings. Near a wall, particles experience reduced mobility due to non-slip boundary conditions, which alter their movement through confinement-induced effects.

These effects are crucial in various biological and physical contexts, particularly in blood vessels where cells and particles move near vessel walls. In these confined environments, the interaction with soft membranes or interfaces alters their motion. Understanding these modifications in Brownian motion is essential for elucidating how cells navigate and interact within such environments.

Our research focuses on these confinement-induced effects by investigating the behavior of non-deformable microbeads near soft lipid bilayer membranes. By employing Mie holography and statistical inference, we explore how rigid particles interact with soft surfaces, revealing aspects of soft lubrication. Previous studies have explored similar interactions with soft particles near rigid surfaces. Our study extends this understanding by examining rigid particles near soft boundaries, thereby providing insights into the elastohydrodynamic forces at play.

Materials and

Methods: Polyethylene Glycol (polymer chain), Diphy – Normal disordered lipid, 0.5% Atto 488 – Lipid Dye (488 wavelength), 6 micron polystyrene beads

Prepare the lipid composition by adding 93 µL of Diphy, 6.5 µL of PEG, and 5.5 µL of Atto into a 5 mL vial. Dry the lipids with nitrogen and vacuum for 30 minutes. Then, add 1 mL of PBS to the dried lipids and sonicate for 20-30 minutes until clear. Dilute the vesicle solution by mixing 200 µL with 200 µL of PBS. Clean a glass coverslip with ethanol, plasma clean it, and assemble the chamber by layering parafilm sheets to create a channel. Inject the vesicle solution, wait 20-30 minutes for the bilayer to form, and rinse out excess vesicles with DI water.

Track individual rigid colloids in a dilute suspension using Mie holography, where a coherent plane wave illuminates the colloid and creates a hologram from scattered light. Holograms are recorded and analyzed with Lorenz-Mie theory to reconstruct the three-dimensional trajectories (x(t), y(t), z(t)). Correct for spatial defects by normalizing against a background image, and measure parameters affecting holograms separately. The liquid’s refractive index is determined with a refractometer. This method achieves a spatial tracking resolution of approximately 10 nm in the z-direction, as shown by the agreement between experimental and theoretical holograms.

Results, Conclusions, and Discussions:

Results: Our experiments focused on the interaction of rigid particles near a soft bilayer membrane, with reference to previous studies involving rigid particles near rigid surfaces. In those prior experiments, no hydrodynamic lift force was expected because rigid surfaces do not deform, resulting in identical equilibrium and total forces. This was confirmed by overlapping error margins, indicating no significant difference.

In contrast, our results with the soft bilayer membrane revealed significant differences. The deformability of the bilayer introduced hydrodynamic lift forces at short time scales due to surface deformation. This effect was evident from our force measurements, where the error bars for the total and equilibrium forces did not overlap, indicating a statistically significant difference. The bilayer's thickness, at most 25 nm, was sufficiently small to detect these softness effects, as indicated by the separation in error margins highlighting the additional lift forces associated with the soft bilayer.

Discussions: Our findings demonstrate that surface softness significantly influences hydrodynamic forces. The deformability of the bilayer membrane led to detectable lift forces, contrasting with the rigid surfaces where no such forces were observed. This underscores that even very thin soft surfaces, such as our 25 nm bilayer, can have a measurable impact on hydrodynamic interactions by altering flow dynamics through deformation. This aligns with existing literature, where soft boundaries are known to introduce additional forces due to their interaction with fluids.

Conclusions: This study highlights the critical role of surface softness in modulating hydrodynamic interactions. Our results show that a soft bilayer surface, with a thickness of up to 25 nm, significantly affects measured forces by introducing detectable lift forces due to surface deformation. These findings are particularly relevant for understanding fluid dynamics in biological systems, such as the behavior of particles near soft blood vessel walls. The ability to detect softness effects even at such small scales emphasizes the importance of considering surface properties in hydrodynamic studies.

Acknowledgements (Optional):