Quantitative chemical mapping of sodium acrylate and N-vinylpyrrolidone-enhanced alginate microcapsules

TOHRU ARAKI (1), ADAM P. HITCHCOCK (1), FENG SHEN (2), PATRICIA L. CHANG(2), MAGGIE WANG(1) and RONALD F. CHILDS (1)

1 Department of Chemistry, McMaster University, Hamilton, Ontario, Canada L8S 4M1
2 Department of Pediatrics, McMaster University, McMaster University, Hamilton, Ontario, Canada L8N 3Z5

Received 10 May 2004; accepted 10 September 2004

ABSTRACT: Alginate microcapsules enclosing recombinant cells secreting therapeutic products have been used successfully to treat several murine models of human diseases. The mechanical and chemical properties of these alginate capsules can be improved by the addition and in situ photopolymerization of sodium acrylate and N-vinylpyrrolidone in the alginate capsule. The purpose of this modification was to form additional covalent cross-links. In this work we have used scanning transmission X-ray microscopy (STXM) to probe the nature and location of the chemical modifications in the modified capsules by comparison with unmodified capsules. Analysis of X-ray image sequences and selected area spectra has been used to map the calcium gradient in capsules, to identify the presence of polyacrylate throughout the capsules and the localization of poly-N-vinylpyrrolidone in the outer regions of the alginate capsules. The differences in the spatial distributions of these species have led to better understanding of the chemical modifications that provide a mechanically more stable capsule structure.

Key words: Molecular imaging; co-polymer; hydrogel; image analysis; photopolymerization.

© VSP 2005.