Drying and Rehydration of Calcium Alginate Gels

Abstract

In this paper, we study the rehydration properties of air-dried calcium alginate gel beads. Rehydration is shown to depend on alginate source (i.e. mannuronic to guluronic acid ratio) and the salt concentration in the rehydration medium. Rehydration curves are described adequately by the empirical Weibull equation. Wide-angle X-ray diffraction measurements are performed to obtain information on the microstructure of dried alginate gels. The X-ray diffraction patterns provide evidence for formation of ordered domains in which alginate polymers are laterally associated. Formation of ordered structures during drying is found to have a large impact on rehydration properties. Lateral association of alginate chains is reduced (and rehydration improved) by removing excess calcium ions from the gel beads in a washing step prior to air drying. In addition, rehydration properties of mixed alginate-carboxymethyl cellulose (CMC) gel beads are investigated. The presence of CMC in the gel matrix is found to reduce lateral association of alginate chains during drying and to improve rehydration properties.

Preparation and characterization of biodegradable paclitaxel loaded alginate microparticles for pulmonary delivery

“…As seen in Fig. 6A, B and 6D similar to previous studies pure paclitaxel [81][82][83], blank alginate microparticles [84,85] and physical mixture of blank alginate microparticles and paclitaxel indicates an amorphous pattern in X-ray diffractograms because there is no meaningful peak in the XRD patterns. However, XRD pattern of paclitaxel loaded microparticles, in Fig.…”

Rehydration of dried alginate gel beads: Effect of the presence of gelatin and gum arabic

“…When swelling in the presence of NaCl, Na + could diffuse into alginate gel beads and substitute Ca 2+ out of the network. This leads to the dismantling of the side-by-side aggregation, and the swelling of network (Vreeker et al, 2008). The increase in NaCl concentration accelerates the ion exchange between Na + and Ca 2+ , and speeds up the swelling process.…”

“…The controlled rehydratability of dried biopolymers either cross-linked or non-crosslinked is crucially important to many applications such as the preparation of instant foods and drug delivery (Vreeker, Li, Fang, Appelqvist, & Mendes, 2008). How to control and improve the rehydratability of dried biopolymer materials and understanding the physics behind it could add much value to the related applications.…”

“…The mechanism has been described as the 'egg-box' model (Grant, Morris, Rees, Smith, & Thom, 1973;Morris, Rees, Thom, & Boyd, 1978). If calcium alginate gel is dried in air, the gel network will collapse, and the egg-box junctions will form side-by-side aggregations under the mediation of free Ca 2+ , giving rise to poor swelling ability when rehydrated (Vreeker et al, 2008).…”

Kinetic analysis of metal uptake by dry and gel alginate particles

“…In a recent study on the rehydration of airdried calcium alginate beads, Vreeker et al observed a significant swelling of beads in salt solutions, but no rehydration in pure water [26]. Yet, if a washing step was applied to remove excess calcium ions from the gel beads prior to drying, rehydration was highly improved.…”