Hydrogel–hydrogel composites: The interfacial structure and interaction between water and polymer chains

Abstract

This work examines the interfacial structure and interaction between water and polymer chains in the hydrogel-hydrogel composites with the goal of establishing foundations for further investigation of drug diffusion from one hydrogel to another in the soft contact lens. This is based on the ability of the hydrogel-hydrogel composites to release ophthalmic drugs in a sustained manner. The hydrogel-hydrogel composites were synthesized by immersing the glycerol-swollen particles of crosslinked N-vinyl-2-pyrrolidone (NVP) into the monomer of hydroxyethylmethacrylate (HEMA) containing initiator benzoylperoxide (BPO) that polymerizes to form a matrix in the presence of the first networks. The hydrogel-hydrogel composites were characterized by UV/Vis spectrophotometer, scanning electronic micrography (SEM), and differential scanning calorimetry (DSC). The results showed that the samples of hydrogelhydrogel composites of the particles of crosslinked NVP and poly-HEMA were transparent and glassy and suitable for soft contact lens. Three types of the interfacial structure, no interpenetrating interface, partly interpenetrating interface, and fully interpenetrating interface, of the hydrogel-hydrogel composites existed, and the type of the interfacial structure was determined by the degree to which the monomer of HEMA penetrated into the first networks before formation of the matrix. Different from poly-HEMA hydrogels, the peaks near 08C on DSC curves of the hydrogel-hydrogel composites did not split while they were kept acute, and the amount of freezable-bound water was less. This shows that the water incorporated in the hydrogel-hydrogel composites does not strongly interact with polymer matrix, so the hydrogel-hydrogel composites cannot keep their shape during the phase transition of water.

Innovative Hydrogels Based on Semi-Interpenetrating p(HEMA)/PVP Networks for the Cleaning of Water-Sensitive Cultural Heritage Artifacts

“…Water inside swollen hydrogels can be classified into three different states: free, bound-freezable, and unfreezable water. This classification takes into account the extent of interactions of water molecules with the polar part of the polymer chains: free water is defined as the water with the same thermodynamic properties of bulk water; freeze-bound water interacts weakly with the polymer chains of the hydrogels so that its freezing point is lower than 0 °C; unfreezable water is strongly hydrogen bonded, and no phase transition is observed from −70 to 50 °C. , Because only free water is contributing to the cleaning process, the knowledge of the bound-freezable and free water fractions inside hydrogels is important to quantify the hydrogel capability to exchange the solvent at the surface and thus to prevent any excessive wetting. The distribution of “water states” inside hydrogels can be estimated through the calculation of freezable water, from the free water index (FWI) and freeze-bound water index (FBWI) parameters, both determined via DSC.…”

The effect of the glass transition temperature on the toughness of photopolymerizable (meth)acrylate networks under physiological conditions

“…[7] Conversely, the two linear monomers selected for the second network, BMA and 2HEMA, both have high T g 's in relation to body temperature (80°C and 110°C, respectively), but have side groups with opposing degrees of hydrophilicity (Figure 1). In addition, 2HEMA is a monomer that is extensively used in contact lenses and hydrogels [30, 31] while BMA has been shown to have enhanced toughness at its glass transition temperature. [32] From the results presented here, it can be suggested that network toughness under physiological conditions is dependent on T g , water absorption, and strain rate, in a manner related to network composition.…”

Systematic tailoring of water absorption in photopolymerizable (meth)acrylate networks and its effect on mechanical properties

“…The linear monomers, BZA and 2HEMA, were selected because they had side groups with opposing polarities allowing for a systematic change in PBS absorption (Table I). 2HEMA is extensively used in contact lenses and hydrogels30, 31 and contains highly polar hydroxyl side groups that readily form hydrogen bonds with water molecules 32. On the other hand, BZA contains a bulky benzyl side group which acts as a steric hindrance for water molecules to diffuse into the network 33, 34.…”