Hydration studies in polymer hydrogels

Abstract

Polymer hydrogels have attracted much interest in recent years based on numerous applications mainly in biotechnology and medicine. For the knowledge-based design and development of new materials for these and similar applications, it is essential to understand better the hydration properties of hydrogels and of polymers in general. With this term, we mean the particular organization of water in the hydrogel, which determines the properties of the water component, typically different than those of bulk water, and the impact of water on the properties of the polymer matrix itself. In this review, we focus on recent work with hydrogels based on poly(hydroxyethyl acrylate), mostly copolymers with a second hydrophobic polymer and silica nanocomposites. The combination of water sorption/diffusion, thermal and dielectric studies, by fully exploiting the capabilities of each individual technique, proves essential in providing significant information on particular aspects of hydration, such as water uptake, water organization, and diffusion coefficients; glass transition and plasticization; water and polymer dynamics; protonic conductivity, and in revealing interesting correlations between these particular aspects. In the outlook similarities and differences to other related systems, such as proteinwater and polymer solutions in non-polar solvents, are stressed in the perspective of a broader study. V C 2012 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 159-175 KEYWORDS: copolymers; nanocomposites; plasticization; polymer dynamics; polymer hydrogels; protonic conductivity; relaxation; uncrystallized water; water clusters INTRODUCTION Polymer hydrogels are hydrophilic macromolecular networks which are able to absorb large amounts of water, because of being hydrophilic, but swell rather than dissolve in water, because of being cross-linked.1,2 Their hydrophilicity is the consequence of the existence of both polar groups included in their chemical structure, which form hydrogen bonds with water molecules, and network expansion. Good biocompatibility and water permeation properties, in addition to several other good properties arising from their polymeric nature, form the basis for several applications of polymer hydrogels, in particular biomedical applications, 1-7 however also applications in other diverse fields, such as ion-conducting membranes, 8 water retention in agriculture, 9 and sensors and actuators. [10][11][12] The scientific and technological interest in hydrogels is reflected also in the large number of recent reviews on various aspects of hydrogels and related topics, next to those on applications mentioned above. [13][14][15][16][17][18] For designing new materials with superior properties for these and similar applications, it is essential, among others, to investigate in detail and understand better their hydration properties. With this term, we mean the particular organization of water in the hydrogel, which determines the properties of the water component, typically di...

Hydrophilic nanocomposites based on polyurethane/poly(2‐hydroxyethyl methacrylate) semi‐IPNs and modified/unmodified nanosilica for biomedical applications

“…In addition, dielectric measurements were performed at various levels of water content, providing information about effects of water on polymer dynamics, which can be correlated with water uptake. 44 …”

Glass Transition and Water Dynamics in Hyaluronic Acid Hydrogels

“…In addition, correlations were observed between results on the organization of water in the hydrogels and on water effects on polymer dynamics. In particular, distinct changes in the dielectric response at the water content of the completion of the first hydration layer indicated that water molecules themselves contribute to the dielectric response at higher water contents [20]. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 Despite the extended use of HA hydrogels in biological applications, the dielectric behavior of such materials at low water concentrations and subzero temperatures has not been studied so far in detail.…”

“…In the case of globular proteins the observed dielectric relaxation associated to the calorimetric glass transition has been attributed in literature to a combined motion of uncrystallized water molecules in the protein hydration shell and segments of the protein surface [19,24,25,30]. Measurements in synthetic hydrogels based on poly(hydroxyl ethyl acrylate) (PHEA) by dielectric and other experimental techniques showed that the segmental α relaxation (dynamic glass transition) is significantly plasticized by water [20]. In addition, correlations were observed between results on the organization of water in the hydrogels and on water effects on polymer dynamics.…”

“…Glass transition and water dynamics in hyaluronic acid hydrogels. Food Dielectric measurements contribute to the study of the molecular dynamics of water at biological interfaces, in the case of several biomolecules, such as polysaccharides [14] and hydrated proteins [15][16][17][18][19] and also in the case of synthetic hydrogels [20]. In the case of hydrated proteins, it has been shown that the observed dynamics depends strongly on the hydration level and a minimum amount of water is necessary for the onset of enzymatic activity in globular proteins [21].…”

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, J.; A. Kyritsis; Monleón Pradas, M.; Vallés Lluch, A.; Gallego Ferrer, G.; P. Pissis (2013). Glass transition and water dynamics in hyaluronic acid hydrogels.

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