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

Abstract

Dynamics of colloidal particles adhering to soft, deformable substrates, such as tissues, biofilms, and hydrogels play a key role in many biological and biomimetic processes. These processes, including, but not limited to colloid-based delivery, stitching, and sorting, involve microspheres exploring the vicinity of soft, sticky materials in which the colloidal dynamics are affected by the fluid environment (e.g., viscous coupling), inter-molecular interactions between the colloids and substrates (e.g., Derjaguin-Landau-Verwey-Overbeek (DLVO) theory), and the viscoelastic properties of contact region. To better understand colloidal dynamics at soft interfaces, an optical tweezers back-focal-plane interferometry apparatus was developed to register the transverse Brownian motion of a silica microsphere in the vicinity of polyacrylamide (PA) hydrogel films. The time-dependent mean-squared displacements are well described by a single exponential relaxation, furnishing measures of the transverse interfacial diffusion coefficient and binding stiffness. Substrates with different elasticities were prepared by changing the PA crosslinking density, and the inter-molecular interactions were adjusted by coating the microspheres with fluid membranes. Stiffer PA hydrogels (with bulk Young's moduli ≈1-10 kPa) immobilize the microspheres more firmly (lower diffusion coefficient and position variance), and coating the particles with zwitterionic lipid bilayers (DOPC) completely eliminates adhesion, possibly by repulsive dispersion forces. Remarkably, embedding polyethylene glycol-grafted lipid bilayers (DSPE-PEG2k-Amine) in the zwitterionic fluid membranes produces stronger adhesion, possibly because of polymer-hydrogel attraction and entanglement. This study provides new insights to guide the design of nanoparticles and substrates with tunable adhesion, leading to smarter delivery, sorting, and screening of micro- and nano-systems.

Engineering Hydrogel Adhesion for Biomedical Applications via Chemical Design of the Junction

“…80 On the basis of the scale of these forces, the DLVO theory is commonly applied to describe colloidal stability or adhesion and fouling of colloidal objects (e.g., nanoparticles, bacteria, polymers) at the interfaces. 81 In this Review, we focus on designed hydrogels interfaces with engineered chemical bonding, which can include van der Waals forces, covalent bonds, strong electrostatic interactions, and chain entanglements of polymers. While many of the underlying physics are similar to features of the DLVO theory, junction engineering enables adhesion forces that are suitable for joining macroscale hydrogel interfaces, which is generally not observed in the absence of a designed interface.…”

“…For example, the DLVO theory (Derjaguin–Landau–Verwey–Overbeek) describes how adhesion can occur through an interplay between attractive van der Waals forces and the generally repulsive forces from electric double-layer interactions . On the basis of the scale of these forces, the DLVO theory is commonly applied to describe colloidal stability or adhesion and fouling of colloidal objects (e.g., nanoparticles, bacteria, polymers) at the interfaces . In this Review, we focus on designed hydrogels interfaces with engineered chemical bonding, which can include van der Waals forces, covalent bonds, strong electrostatic interactions, and chain entanglements of polymers.…”

Instant Strong Adhesive Behavior of Nanocomposite Gels toward Hydrophilic Porous Materials

“…The adhesiveness of a hydrogel is also an important property that is widely useful in industrial, architectural, civil engineering, and biomedical applications. Several reports to date have described improving hydrogel adhesion from the perspectives of tissue adhesion, , polymer-network control, , and 3D bioprinting . In addition, basic studies on creating tough adhesion between a hydrogel and various substrates or tissues, using different strategies, have been conducted. − In particular, additives such as nanoparticles (NPs) (e.g., silica NPs), bridging polymers (e.g., polymers with positively charged primary amine groups, polyelectrolyte complexes, or chitosan), − specific monomers (e.g., cyanoacrylate-based dispersions), and hydrogels (e.g., polyampholyte hydrogels) have been used as adhesives that form tough bonds between hydrogels or hydrogels and substrates.…”

Nanoparticle Coupling to Hydrogel Networks: New Insights from Electroacoustic Spectroscopy

“…Microscale interactions of hydrogels and NPs have been studied using dynamic light scattering, microrheology, and electroacoustic spectroscopy. , However, a detailed study of the effect of hydrogel composition and polymer adsorption on these interactions has not been undertaken. Generally, hydrogel composition can be varied to form hydrogels with elasticities similar to those of biological tissues.…”

“…6 Incapsulating drugs in nanoparticles or nanogels (as secondary drug release vehicles) embedded in hydrogels (as the primary drug delivery vehicle) is effective in controlling drug release. 2 Several other studies, which have exploited NP adsorption to hydrogels to achieve useful properties, are reviewed by Haraguchi, 7 Schexnailder and Schmidt, 8 and Thoniyot et al 4 Microscale interactions of hydrogels and NPs have been studied using dynamic light scattering, 9 microrheology, 10 and electroacoustic spectroscopy. 11,12 However, a detailed study of the effect of hydrogel composition and polymer adsorption on these interactions has not been undertaken.…”