Ž . Carbohydrate Research 306 1998 19–26 A better understanding of the properties of alginate solutions and gels by quantitative magnetic ž / resonance imaging MRI Anna Degrassi a , Renato Toffanin b , Sergio Paoletti b,c , Laurance D. Hall a, ) a Herchel Smith Laboratory for Medicinal Chemistry, Cambridge UniÕersity School of Clinical Medicine, UniÕersity ForÕie Site, Robinson Way, Cambridge CB2 2PZ, UK b POLY-bios Research Centre, AREA Science Park, Padriciano 99, I-34012 Trieste, Italy ´ c Department of Biochemistry, Biophysics and Macromolecular Chemistry, UniÕersity of Trieste, Õia L. Giorgieri 1, I-34127 Trieste, Italy Received 12 June 1997; accepted 11 October 1997 Abstract Ž . A new, fully automated magnetic resonance imaging MRI procedure has been used to measure for the first time all the MRI parameters of water in both sodium alginate solutions Ž . Ž . and calcium alginate gels at concentrations of 1%, 2%, 3%, 4% wrw . Spin–spin T and 2 Ž . Ž . spin–lattice T relaxation times, magnetisation transfer processes MT and diffusion 1 Ž . coefficients D were measured to evaluate their potential use for studying gelling mecha- nisms and for determining gel characteristics. Four alginate samples, with different extents of O-acetylation were also studied and the use of MRI to discriminate between them was evaluated. q 1998 Elsevier Science Ltd. All rights reserved. Keywords: Alginate; Gels; MRI 1. Introduction Because of a total lack of toxicity and an ability to form viscous solutions and gels, alginate is becoming more widespread used in the food industry as a thickening agent, in biotechnology as an immobilisa- w x tion matrix for enzymes and living cells 1–4 and in medicine and agriculture for controlled release of drugs and pesticides. Gelation of alginates with cal- wx cium ions is understood in molecular terms 5;a ) Corresponding author. correlation between gel strength and alginate concen- tration has been established, and relevant properties of calcium alginate gels such as mechanical rigidity, volume stability, swelling and shrinking character- istics have been studied by a variety of techniques w x 6–8 . Much work has also been done in order to understand how differences in chemical structure in- w x fluence the functional properties 9,10 , which are important to the choice of which type of alginate and gelling methodology are most suitable for each spe- cific application. In particular, it has been observed that an increase in O-acetyl content results in a wx decrease in gel strength 9. Magnetic resonance 0008-6215r98r$19.00 q 1998 Elsevier Science Ltd All rights reserved.