title: NMR properties of alginate microbeads.
abstract: Alginates are a family of unbranched polysaccharides with properties that vary widely depending on their composition. In the presence of multivalent cations (frequently Ca2+), alginates form a gel. Consequently, alginates have been used to encapsulate a variety of biological materials, including cells. In this study, we present NMR relaxation and diffusion data from alginate microbeads with similar size and properties to those used in the development of a bioartificial pancreas. Our data demonstrate that the transverse relaxation time (T2) of water within the gel depends on the guluronic acid content of the alginate, whereas the longitudinal relaxation time (T1) and the apparent diffusion coefficient of water do not. Our data further suggest that the diffusion of Ca2+ ions is hindered by the presence of a poly-L-lysine layer, a layer commonly added to provide mechanical support to the beads and immunoprotection to the encapsulated cells in the event of implantation. The impact of these data on our understanding of the role of alginate gels in the development of a bioartificial pancreas is discussed.
authors.affiliation: Department of Medicine, Division of Endocrinology, University of Florida, Gainesville, FL 32610, USA.
authors.forename: Nicholas E
authors.initials: NE
authors.lastname: Simpson
authors.forename: Samuel C
authors.initials: SC
authors.lastname: Grant
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Blackband
authors.forename: Ioannis
authors.initials: I
authors.lastname: Constantinidis
mesh_terms: D000464:Alginates / Q000737:chemistry*; D000818:Animals; D018929:Cell Culture Techniques / Q000379:methods*; D020099:Coated Materials, Biocompatible / Q000737:chemistry*; D005947:Glucose / Q000378:metabolism; D020723:Glucuronic Acid / Q000737:chemistry*; D006603:Hexuronic Acids / Q000737:chemistry*; D007515:Islets of Langerhans / Q000254:growth & development* / Q000378:metabolism*; D016381:Islets of Langerhans Transplantation / Q000295:instrumentation* / Q000379:methods; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D051379:Mice; D008863:Microspheres; D008968:Molecular Conformation; D019397:Pancreas, Artificial
chemical_list: D000464:Alginates; D020099:Coated Materials, Biocompatible; D006603:Hexuronic Acids; D020723:Glucuronic Acid; D005947:Glucose