Hexadecane-Nanoemulsion-Doped Polyacrylamide Hydrogels

Abstract

Hydrogels are promising supports for nanoemulsion drops since the skeleton provides a physical barrier to coalescence and possibly a thermodynamic barrier to Ostwald ripening. How these factors play a role in the encapsulation of oil drops in polymer networks for drug-delivery applications is largely unknown, owing to the challenge of measuring in situ drop size and understanding the drop–hydrogel interface. In this study, the electrokinetic sonic amplitude of sodium dodecyl sulfate (SDS)-stabilized hexadecane-in-water nanoemulsion drops in polyacrylamide hydrogels is harnessed to ascertain dynamic mobility spectra, which we interpret using a recently proposed model for highly charged nanodrops. The nanodrop radius in hydrogels was found to be close to their nanoemulsion counterparts (∼100–600 nm), with a frequency-independent shear viscosity (∼0.5 mPas at megahertz frequencies) and a frequency-independent shear modulus (∼1 kPa). From a macrorheological perspective, the low-frequency plateau modulus was concluded to increase systematically with the hexadecane volume fraction according to an Einstein intrinsic shear modulus having a quadratic correction for elastic interactions at finite volume fractions. The electroacoustic and micro- and macro-rheological analyses are complemented with swelling, confocal imaging, and electrical conductivity characterization. Together, these point to an “ideal behaving” microstructure that may be tailored for advanced drug-delivery systems. The electroacoustic testing platform developed in this work provides a beneficial tool for noninvasively characterizing the microstructure of nanoemulsion-doped hydrogels.

Ionic conductivity and hydrodynamic permeability of inhomogeneous (cavity doped) polyelectrolyte hydrogels

“…Such hydrogels readily transport small ions, as evidenced, for example, by the electrical conductivity of polyacrylic acid (anionic) hydrogels (Kuhn mesh sizes – nm) being comparable to those of the electrolyte ions within (Adibnia, Afuwape & Hill 2020). Similar conclusions have been drawn from the conductivity of uncharged polyacrylamide gels containing charged surfactant and added salt ions (Afuwape & Hill 2021). For the highly charged polyacrylic acid hydrogels of Adibnia et al.…”

“…Rehydrating the dried polymer would fill the cavities with water/electrolyte, creating a microstructure with an enhanced hydrodynamic permeability and modified electrical conductivity. Such an approach was recently demonstrated, in part, by Afuwape & Hill (2021), who immobilized surfactant-stabilized hexadecane drops in polyacrylamide hydrogels. However, the droplets in these composites did not evaporate when subjected to drying at relatively low temperatures.…”

Laponite-Doped Poly(acrylic acid-co-acrylamide) Hydrogels

“…According to Einstein's formula, rigid passive fillers (embedded in an incompressible, linear elastic continuum) are expected to increase the stiffness of the parent hydrogel by a factor 1 5 /2 + when the filler volume fraction ϕ ≪ 1. 45 Moreover, as highlighted in the Introduction, many studies have demonstrated Laponite actively increasing the stiffness of N-isopropylacrylamide and acrylamide-based hydrogels. Indeed, although sample-to-sample variations tend to increase with decreasing hydrogel charge, some values of G with f AAc = 0 (uncharged hydrogels) are ≈5 kPa greater than G of the parent hydrogel, qualitatively consistent with literature cited in the Introduction.…”

Natural polymer‐based adhesive hydrogel for biomedical applications

“…Certain synthetic polymers have impressive mechanical properties, such as poly(ethylene glycol) [90][91][92], poly(vinyl alcohol) [93,94] and polyacrylamide [95]. However, the poor biological activity of these materials is not conducive to the adhesion of cells and tissues, greatly limiting their applications in TE.…”