Sol–Gel transition of alginate solution by the addition of various divalent cations: A rheological study

Wang, Zheng‐Yu ‐Y; Zhang, Qing‐Zhi ‐Z; Konno, Mikio; Saito, Shozaburo

doi:10.1002/bip.360340606

Cited by 39 publications

(25 citation statements)

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“…Sodium alginate gels ionotropically at constant temperature upon addition of divalent cations, such as Ca 2+ , Sr 2+ , and Cu 2+ [6][7][8][9]. Ionotropic gelation follows the egg-box modelinterchain associations of G-block sequences of 20 or more residues with arrays of site bound ions sandwiched between the participating chains [10,11].…”

Section: Introductionmentioning

confidence: 99%

Rheology and Thermotropic Gelation of Aqueous Sodium Alginate Solutions

Florián‐Algarín

Acevedo

2010

J Pharm Innov

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In this work, we present the evaluation of the thermotropic gelling ability and steady-state rheology of aqueous sodium alginate (NaAlg) solutions. NaAlg is been considered due to its gelling capabilities and to determine its suitability as a film-forming agent with the potential capacity for immobilization of very potent, solid, and hydrophobic drugs. The existence of a thermally induced gelation of 1.0 to 2.5 wt.% sodium alginate solutions between 13°C to 22°C was demonstrated through three independent rheological tests: the constant-stress temperature-ramp viscosity, dynamic viscoelastic moduli, and thixotropy tests. Oscillatory dynamic tests also showed the thermoreversible nature of the NaAlg gels, but a large hysteresis between the gel formation and the gel melting was observed. The steady-state viscosity was experimentally determined as a function of shear rate for NaAlg concentrations between 1.0 to 2.5 wt.% and for temperatures from 20°C (or above T gel ) to 90°C. A viscosity master curve was constructed by applying time-temperature superposition and a semi-empirical shift factor for concentration. A power-law fluid modeladjusted to the data from 20°C to 60°C and found to provide good agreement with fitting parameters k=4.81 and n=−0.449±0.003.

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Section: Introductionmentioning

confidence: 99%

Rheology and Thermotropic Gelation of Aqueous Sodium Alginate Solutions

Florián‐Algarín

Acevedo

2010

J Pharm Innov

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“…9,10 By viscometry, † To whom correspondence should be addressed. Wang et al 11,12 and Zheng et al 13 investigated the critical phenomena of sol-gel transition in aqueous alginate solutions induced by divalent cations.…”

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confidence: 99%

Sol–Gel Transition in Aqueous Alginate Solutions Induced by Cupric Cations Observed with Viscoelasticity

Liu

Qian

et al. 2003

Polym J

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ABSTRACT:Sol-Gel transition was occurred in 2 wt% aqueous solutions of four alginate samples with different molecular weight M w and the ratio M/G of repeat unit mannuronate (M) to guluronate (G) induced by adding cupric ions. The transition was monitored with dynamic moduli G and G in the linear region of viscoelasticity and the gel point was determined according to the Winter's criterion where the loss angle tan δ became independent of frequency ω. The mole ratio of Cu 2+ to the carboxyl group in alginate at gel point, f gel , was higher for the samples with lower molecular weight than those with higher molecular weight without obvious M/G dependence. This suggested there was no M/G selection of Cu 2+ complex formation with alginate. The relaxation critical exponent n for alginate samples with higher G content was lower than 0.5, meaning G > G for the critical gels with a denser network. The cupric ion number relevant to one alginate chain at the gel point, N gel , was estimated from f gel M n /M 0 and reflected the gel elasticity.KEY WORDS Alginate / Cupric Cations / Sol-Gel Transition / Critical Exponent / Dynamic Viscoelasticity / Alginate is a natural polysaccharide consisting of β-D-mannuronate (M) and its C-5 epimer α-L-guluronate (G) residues (Figure 1) (1→4) linked in a nonregular blockwise pattern along the linear chain and is mainly used as a gelling agent in numerous food and pharmaceutical applications. [1][2][3][4] There are three types of dyad sequential blocks as MM, GG, and MG. These residue sequences endow with the alginate chain different stiffness, e.g., that the mean square end-to-end distance per uronate residue for G component is 2.2 times larger than that for the M component. 5 The chemical composition and sequence of the M and G residues depend on the biological source and growth and seasonal conditions. 1,2 The most attractive ability of alginate is the gel formation induced by adding various divalent cations, except Mg 2+ . 6 The gelation behavior and gel strength of aqueous alginate solutions strongly depend on the content of guluronate residues and also on the molecular weight and molecular weight distribution of alginates. [6][7][8] Matsumoto and Mashiko investigated the influence of added salts on the viscoelastic properties of aqueous alginate solution and argued that the interaction between alginate and metal cations did not work as the cross-linking point. 8 Matsumoto et al. also followed the gelation process in sodium alginate solutions induced by increasing polymer concentration without any divalent cations and found the promoting effect to the gelation of chain stiffness, i.e., the alginate with higher G residue content formed gel at lower concentration with more perfect structure. 9, 10 By viscometry, † To whom correspondence should be addressed.

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“…2 [12,14]. Its aqueous solution with different lower concentrated additional salt may be regarded in accordance with Manning's polyelectrolyte theory model.…”

Section: Resultsmentioning

confidence: 97%

“…In order to remove low molecular weight material that could permeate through the membrane, the sample was carefully purified by a previously reported technique [12][13][14]. Its solution was first dialyzed in distilled water using cellulose tubular membranes, and then further dialyzed in deionized water.…”

Section: Experimental Materials Purificationmentioning

confidence: 99%