Hydrogel-colloid interfacial interactions: a study of tailored adhesion using optical tweezers

Area of Science:

• Soft matter physics
• Colloid science
• Biomaterials science

Background:

• Colloidal particle dynamics on soft substrates are crucial for biological and biomimetic applications.
• Factors influencing these dynamics include fluid environment, inter-molecular interactions (DLVO theory), and substrate viscoelasticity.

Purpose of the Study:

• To investigate colloidal particle dynamics at soft interfaces.
• To understand how substrate elasticity and particle surface modifications affect adhesion and diffusion.

Main Methods:

• Utilized optical tweezers back-focal-plane interferometry to track Brownian motion of silica microspheres near polyacrylamide hydrogels.
• Varied hydrogel crosslinking density to control elasticity.
• Modified microsphere surfaces with zwitterionic and PEG-grafted lipid bilayers to tune inter-molecular interactions.

Main Results:

• Time-dependent mean-squared displacements followed single exponential relaxation, yielding diffusion coefficients and binding stiffness.
• Increased hydrogel stiffness reduced microsphere diffusion and position variance.
• Zwitterionic lipid bilayers eliminated adhesion, while PEG-grafted bilayers enhanced it, suggesting polymer-hydrogel interactions.

Conclusions:

• Substrate elasticity and particle surface chemistry significantly control colloidal dynamics at soft interfaces.
• Tunable adhesion can be achieved by modifying particle coatings and substrate properties.
• Findings offer insights for designing advanced nanoparticles and substrates for targeted delivery and sorting applications.