Visualization of alginate–poly-L-lysine–alginate microcapsules by confocal laser scanning microscopy

Authors

  • Berit L. Strand,

    Corresponding author
    1. Department of Biotechnology, Norwegian University of Science and Technology, Trondheim, Norway; telephone: +47 7359-0662; fax: +47 7359-1283
    • Department of Biotechnology, Sem Saelandsvei 6/8, 7491 Trondheim, Norway
    Search for more papers by this author
    • These authors contributed equally to this paper.

  • Yrr A. Mørch,

    1. Department of Biotechnology, Norwegian University of Science and Technology, Trondheim, Norway; telephone: +47 7359-0662; fax: +47 7359-1283
    Search for more papers by this author
    • These authors contributed equally to this paper.

  • Terje Espevik,

    1. Department of Cancer Research and Molecular Biology, Norwegian University of Science and Technology, Trondheim, Norway
    Search for more papers by this author
  • Gudmund Skjåk-Bræk

    1. Department of Biotechnology, Norwegian University of Science and Technology, Trondheim, Norway; telephone: +47 7359-0662; fax: +47 7359-1283
    Search for more papers by this author

Abstract

Confocal laser scanning microscopy (CLSM) was used to study the distribution of polymers and cross-linking ions in alginate–poly-L-lysine (PLL) –alginate microcapsules made by fluorescent-labeled polymers. CLSM studies of Ca-alginate gel beads made in the presence and absence of non-gelling sodium ions revealed a more inhomogeneous distribution of alginate in beads formed in the absence of non-gelling ions. In the formation of alginate-PLL capsules, the polymer gradients in the preformed gel core were destabilized by the presence of non-gelling ions in the washing step and in the PLL solution. Ca-alginate gels preserved the inhomogeneous structure by exposure to ion-free solution in contrast to exposure to non-gelling ions (Na+). By exchanging Ca2+ with Ba2+ (10 mM), extremely inhomogeneous gel beads were formed that preserved their structure during the washing and exposure to PLL in saline. PLL was shown to bind at the very surface of the alginate core, forming a shell-like membrane. The thickness of the PLL-layer increased about 100% after 2 weeks of storage, but no further increase was seen after 2 years of storage. The coating alginate was shown to overlap the PLL layer. No difference in binding could be observed among coating alginates of different composition. This paper shows an easy and novel method to study the distribution of alginate and PLL in intact microcapsules. As the labeling procedures are easy to perform, the method can also be used for a variety of other polymers in other microencapsulation systems. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 82: 386–394, 2003.

Ancillary