Cross-linking properties of alginate gels determined by using advanced NMR imaging and Cu(2+) as contrast agent

• Published in: European biophysics journal 2004-02, Vol.33 (1), p.50-58
• Main Authors: Manz, B, Hillgärtner, M, Zimmermann, H, Zimmermann, D, Volke, F, Zimmermann, U
• Format: Article
• Language: English
• Subjects: Alginates - chemistry; Alginates - ultrastructure; Barium; Biophysical Phenomena; Biophysics; Capsules; Contrast Media; Copper; Cross-Linking Reagents; Gels; Glucuronic Acid - chemistry; Hexuronic Acids - chemistry; Magnetic Resonance Imaging
• ISSN: 0175-7571
• DOI: 10.1007/s00249-003-0341-8

The entrapment of enzymes, drugs, cells or tissue fragments in alginates cross-linked with Ca(2+) or Ba(2+) has great potential in basic research, biotechnology and medicine. The swelling properties and, in turn, the mechanical stability are key factors in designing an optimally cross-linked hydrogel matrix. These parameters depend critically on the cross-linking process and seemingly minor modifications in manufacture have a large impact. Thus, sensitive and non-invasive tools are required to determine the spatial homogeneity and efficacy of the cross-linking process. Here, we show for alginate microcapsules (between 400 microm and 600 microm in diameter) that advanced (1)H NMR imaging, along with paramagnetic Cu(2+) as contrast agent, can be used to validate the cross-linking process. Two- and three-dimensional images and maps of the spin-lattice relaxation time T(1) of Ba(2+) cross-linked microcapsules exposed to external Cu(2+) yielded qualitative as well as quantitative information about the accumulation of Cu(2+) within and removal from microcapsules upon washing with Cu(2+) free saline solution. The use of Cu(2+) (having a slightly higher affinity constant to alginate than Ba(2+)) for gelling gave a complementary insight into the spatial homogeneity of the cross-linking process together with information about the mechanical stability of the microcapsules. The potential of this technique was demonstrated for alginates extracted from two different algal sources and cross-linked either externally by the conventional air-jet dropping method or internally by the "crystal gun" method.