A ferric chloride pre-treatment to prevent calcification of Nafion membrane used for implantable biosensors

Since the perfluorosulfonated ionomer Nafion, commonly used for the protection of biosensors, experiences calcification in a biological environment, we evaluated the efficacy of preincubating Nafion membranes in a FeCl3 solution to reduce the number of nucleation sites responsible for the growth of the calcium phosphate crystals. Nafion membranes were prepared and divided into two groups. In the first group, the Nafion membranes were pre-incubated in 0.1 M FeCl3 for a 24 h period. In the second group, no pre-incubation took place. All membranes were placed in a culture medium for a period of up to 4 weeks. All membranes were then examined for changes in: (1) their surface topography (using scanning electron microscopy (SEM)); (2) their near surface chemical properties (using energy dispersive X-ray (EDX)); and (3) their permeability to glucose. The membranes that were not pre-incubated in FeCl3 showed significant cracking of the Nafion surface, extensive calcium phosphate deposits and a resulting decrease in permeability. In contrast, the membranes treated with FeCl3 showed almost no cracking, very little calcium phosphate deposits and no change in permeability to glucose. This study demonstrated that FeCl3 significantly reduces calcification of Nafion and thus should help in preserving the in vivo function of implantable biosensors that utilize Nafion in their design. (C) 1999 Published by Elsevier Science Ireland Ltd. All rights reserved.