Dielectric properties of alginate beads and bound water relaxation studied by electrorotation

Abstract

The electrical and dielectric properties of Ba 2ϩ and Ca 2ϩ cross-linked alginate hydrogel beads were studied by means of single-particle electrorotation. The use of microstructured electrodes allowed the measurements to be performed over a wide range of medium conductivity from about 5 mS/m to 1 S/m. Within a conductivity range, the beads exhibited measurable electrorotation response at frequencies above 0.2 MHz with two well-resolved co-and antifield peaks. With increasing medium conductivity, both peaks shifted toward higher frequency and their magnitudes decreased greatly. The results were analyzed using various dielectric models that consider the beads as homogeneous spheres with conductive loss and allow the complex rotational behavior of beads to be explained in terms of conductivity and permittivity of the hydrogel. The rotation spectra could be fitted very accurately by assuming (a) a linear relationship between the internal hydrogel conductivity and the medium conductivity, and (b) a broad internal dispersion of the hydrogel centered between 20 and 40 MHz. We attribute this dispersion to the relaxation of water bound to the polysaccharide matrix of the beads. The dielectric characterization of alginate hydrogels is of enormous interest for biotechnology and medicine, where alginate beads are widely used for immobilization of cells and enzymes, for drug delivery, and as microcarriers for cell cultivation.

A Novel Class of Amitogenic Alginate Microcapsules for Long‐Term Immunoisolated Transplantation

“…Electrorotation studies have revealed that the aqueous environment within the capsules is completely different to that of the bulk solution. 25,26 As shown in FIGURE 7 the dispersion of water centered around 20 GHz for free water is shifted to about FIGURE 5. (A) Typical growth curves of the adherent cell line C3H10T1/2 transfected permanently with a gene encoding for bone morphogentic protein BMP-2 (similar curves were obtained for cells transfected with BMP-4).…”

“…Incorporation of proteins into the alginate capsules shifts the dispersion back to higher frequencies (about 106 MHz), whereas perfluorocarbons (Fluosol®) reduce the concentration of bound water as indicated by a decrease in the relative permittivity of the capsules (alginate : Fluosol ® = 1 : 1). For further details, see Esch et al 25 sules retrieved after a four-week implantation in the peritoneum of a rat show no significant changes in the topography of their surfaces ( see FIGURE 8 A). In contrast, AFM images of perfluorocarbon-alginate capsules implanted for 15 months show deposition of fibrils on their surfaces (FIG.…”

The apoplast and its significance for plant mineral nutrition

“…A factor of little consideration is the property of water bound to gels such as pectins. Recent studies determining water relaxation in a model system however, suggest highly structured properties, quite different from those of free water (Esch et al , 1999). Implications for the activity of enzymes and dyes frequently used in studies on ion relations in cell walls are far from being understood.…”

Distribution and function of epistomatal mucilage plugs

“…In the light of the above results we can conclude that epistomatal mucilage plugs (and layers) are a widespread phenomenon. Water uptake and binding of acid mucopolysaccharides are extremely high, in particular in the presence of di-(multi-)valent cations (Morse 1990;McCully and Boyer 1977;Esch et al 1999;Zimmermann et al 2007b). This suggests that epistomatal mucilage plugs (and layers) are involved in moisture uptake and particularly in buffering the leaves against rapid and excessive turgor pressure loss at low relative humidity.…”