Elucidating the Molecular Mechanisms for the Interaction of Water with Polyethylene Glycol-Based Hydrogels: Influence of Ionic Strength and Gel Network Structure

Abstract

The interaction of water within synthetic and natural hydrogel systems is of fundamental importance in biomaterial science. A systematic study is presented on the swelling behavior and states of water for a polyethylene glycol-diacrylate (PEGDA)-based model neutral hydrogel system that goes beyond previous studies reported in the literature. Hydrogels with different network structures are crosslinked and swollen in different combinations of water and phosphate-buffered saline (PBS). Network variables, polyethylene glycol (PEG) molecular weight (MW), and weight fraction are positively correlated with swelling ratio, while “non-freezable bound water” content decreases with PEG MW. The presence of ions has the greatest influence on equilibrium water and “freezable” and “non-freezable” water, with all hydrogel formulations showing a decreased swelling ratio and increased bound water as ionic strength increases. Similarly, the number of “non-freezable bound water” molecules, calculated from DSC data, is greatest—up to six molecules per PEG repeat unit—for gels swollen in PBS. Fundamentally, the balance of osmotic pressure and non-covalent bonding is a major factor within the molecular structure of the hydrogel system. The proposed model explains the dynamic interaction of water within hydrogels in an osmotic environment. This study will point toward a better understanding of the molecular nature of the water interface in hydrogels.

Deciphering the Molecular Mechanism of Water Interaction with Gelatin Methacryloyl Hydrogels: Role of Ionic Strength, pH, Drug Loading and Hydrogel Network Characteristics

“…The gradual increase in ion concentration in the swelling media favors the recruitment of Wnfb ion-dipole bonds between the ions and water molecules and/or GelMA functional groups. This section's results confirmed the hypothesis elaborated in Section 3.1 and also reported by Yang et al [71]. Higher mesh size may be expected to correlate with lower mechanical stiffness due to the higher swelling ratio of these samples.…”

“…The gradual increase in ion concentration in the swelling media favors the recruitment of Wnfb ion-dipole bonds between the ions and water molecules and/or GelMA functional groups. This section's results confirmed the hypothesis elaborated in Section 3.1 and also reported by Yang et al [71]. The water content of hydrogels, particularly at the polymer interface, plays an essential role in hemocompatibility [8], as well as protein adsorption and folding [2].…”

“…The gradual increase in ion concentration in the swelling media favors the recruitment of W nfb ion-dipole bonds between the ions and water molecules and/or GelMA functional groups. This section's results confirmed the hypothesis elaborated in Section 3.1 and also reported by Yang et al [71]. The hydrogel mesh size is derived from the equilibrium swelling ratio (See Materials and Methods section and Figure 5 and S6) and was most significantly impacted by the ionic strength of the swelling media at low GelMA concentrations of 5%, compared to 10% and 15%, but overall followed a decreasing trend with increasing ionic strength (Figure 5).…”

“…For GelMA h drogels swelled in water, the absence of ions or the minimal level of ions in hydrog crosslinked in PBS, the ion-dipole bonds are essentially absent, and hydrogen bonds a the primary interaction between water and the hydrogel. This hypothesis also seems to valid for neutral hydrogels, particularly poly (ethylene glycol) diacrylate hydrogels, which water state distributions were affected similarly by ionic strength [71]. Wnfb molecules in dark blue have two bonds (hydrogen bond or ion-dipole bond), have the lowest mobility, and are not crystallizable.…”

Comparison of the effect of polyethylene glycol 40% and fig syrups on the treatment of chronic functional constipation in children: A randomized clinical trial

“…Polyethylene glycol (PEG) is a water-soluble polymer with a high molecular weight that can form hydrogen bonds with 100 molecules of water per molecule of PEG. When PEG is orally consumed, it hydrates the contents of the colon and facilitates intestinal passage and painless defecation as a linear curve in a dose-dependent manner (10,11). Therefore, PEG-based laxatives can be more useful for complete feces excretion compared to rectal prescriptions (12).…”