Phase separation in calcium alginate gels

Abstract

Alginates are polysaccharides consisting of beta-D-mannuronate and alpha-L-guluronate units. In the presence of bivalent cations like calcium the guluronate blocks form physically cross-linked gels. The gelation properties of alginates play an important role in the stability of extracellular polymer substances and in the food industry. When stock solutions of Ca2+ ions and alginate are mixed, the gelation starts before the Ca2+ ions are evenly distributed, which leads to non-uniform gels. In this contribution, Ca alginate gels were prepared by in situ gelation using glucono-delta-lactone and CaCO3. In this way, uniform gels could be prepared directly in the measuring cell. Below a critical concentration, highly viscous solutions were obtained, which were below the critical point of gel formation. In these solutions at low rotational speeds a Schlieren peak arose, which became smaller and steeper with increasing time until a new meniscus could be detected. This behaviour is in contrast to the peak broadening due to diffusion after a synthetic boundary was formed. Evaluation of the data leads to negative diffusion coefficients. It has been shown by others that the mutual diffusion coefficient must be negative in the spinodal region. This phenomena is known as uphill diffusion and leads to phase separation of a binary system. The formation of the gel phase in this case is therefore discussed as uphill diffusion.

Rheological investigation of alginate chain interactions induced by concentrating calcium cations

“…Currently, dialysis/diffusion (Bellich, Borgogna, Cok, & Cesaro, 2011;Iijima, Hatakeyama, Nakamura, & Hatakeyama, 2002;Li et al, 2011;Rayment et al, 2009;Tu et al, 2005) and internal setting (Funami et al, 2009;Josef et al, 2010;Liu et al, 2003;Lu, Liu, Tong, & Gao, 2006;Straatmann & Borchard, 2003) are commonly used methods for gelling alginate. However, these gelling processes are not easy to control to produce desirable outcomes in terms of the gel properties.…”

Evaluation of the stimulus response of hydroxyapatite/ calcium alginate composite gels

“…8,9 Alginates are polysaccharides extracted from seaweed and electrolytes that have carboxyl groups. They are composed of two monomers, b-D-mannuronate and a-L-guluronate, 10,11 which are known to form gels in the presence of bivalent cations such as Ca 2+ . [10][11][12] Hydroxyapatite is generated from calcium chloride (CaCl 2 ) and diammonium hydrogenphosphate ((NH 4 ) 2 HPO 4 ).…”

“…They are composed of two monomers, b-D-mannuronate and a-L-guluronate, 10,11 which are known to form gels in the presence of bivalent cations such as Ca 2+ . [10][11][12] Hydroxyapatite is generated from calcium chloride (CaCl 2 ) and diammonium hydrogenphosphate ((NH 4 ) 2 HPO 4 ). 13 Hydroxyapatite, which has a good biocompatibility and a high biological affinity, is used as bone-filling material for treating bone defects caused by disease or injury.…”

Transport properties of aqueous solutions of sodium alginate at 298.15K

“…2) and its derivatives in alginate gels are used in anti cellulite cosmetics, due to their lipolytic activity on fatty cells. In addition, their gelation properties play an important role in the stability of extracellular polymer substances (Straatmann & Borchard, 2003) and they have been widely used to encapsulate cells for artificial organ applications (Rebecca, Li, & Altreuter, 1996), as well as, drug delivery systems for realising proteins, anti-inflammatory compounds, or gentle preparation of nanoparticles (Paradies, Wagner, & Fischer, 1996).…”

“…A few diffusion coefficients for the binary aqueous systems containing sodium alginate (Paradies et al, 1996;Straatmann & Borchard, 2003), have been reported, but as far as the authors know, after careful literature search, no data are available in the literature for systems involving sodium alginate with caffeine for the same concentrations at 298.15 K. We have been particularly interested in the characterization of diffusion and viscosity of sodium alginate in aqueous dilute solutions, beneath 0.5%, alone and in combination with caffeine at 298.15 K. In the present work, the interdiffusion coefficients were measured using an open-ended conductimetric capillary cell in aqueous solutions (Ribeiro, Lobo, Azevedo, Miguel, & Burrows, 2001;Ribeiro, Lobo, & Natividade, 2002;Ribeiro et al, 2005;Ribeiro et al, 2006;Ribeiro et al, 2007) and in aqueous solutions in presence of caffeine, at 0.005 mol dm À3 , 0.010 mol dm À3 , 0.025 mol dm À3 and 0.050 mol dm À3 concentrations. Densities and viscosities were also measured.…”