APPLICATION OF POLYANION/Fe³⁺ MULTILAYERED MEMBRANES IN PREVENTION OF BIOSENSOR MINERALIZATION

ABSTRACT

Controlled analyte permeability, calcification resistance and biocompatibility are among the many prerequisites necessary for the fabrication of outer membranes for implantable biosensors. In this study, multilayered films of polyelectrolytes (i.e., Nafion^TM, a perfluorinated ionomer, and Humic Acids (HAs), naturally occurring biopolymers) were investigated as potential semi-permeable membranes for implantable glucose sensors. These films were fabricated using the layer-by-layer self-assembly of polyanions (either Nafion or HAs) with oppositely charged ferric ions. Spectroscopic and quartz crystal microbalance (QCM) studies point towards a stepwise film growth pattern, with growth rates as high as 47 and 24.3 nm per layer for Nafion and HAs, respectively. These assemblies were characterized by growth rates that are strongly dependent on the pH and ionic strength of the polyanion solution. Nafion/Fe³⁺ assembled films exhibit an order of magnitude lower calcification level as compared to dip-coated and annealed Nafion films. Additionally, these self-assembled films do not require annealing to impart insolubility. Sig nificantly, after four-week immersion in DMEM cell culture media, HAs/Fe³⁺ assembled films were devoid of calcium phosphate. Moreover, their hydrolytic stability was found to be dependent on film growth condi tions and optimum stability was obtained when the films were assembled at pH and ionic strengths comparable to those of the in vitro testing media.

Keywords:

• Self-assembly
• Semi-permeable membranes
• Calcification
• Nafion
• Humic acids

ACKNOWLEDGMENTS

The authors wish to thank our collaborators: Drs. D. J. Burgess, S. Huang, J. T. Koberstein, D. Kreutzer, and F. Moussy for stimulating discussions. This work was supported by the NIH-R01RR14171, NSF-Career DMR-970220, ONR N00014-00-1-0333 and AFOSR F49620-01-0545 grants.