Brain tissue reaction to permselective polymer capsules.

The brain tissue reaction to permselective polymer capsules implanted in rats was evaluated for 1 to 54 weeks. The polymer capsules were well tolerated in all animals and no recognizable neurological or behavioral deficits were associated with the implants. Necrosis at the brain/polymer interface, as assessed with Nissl stain, was not observed. Foreign body giant cells were consistently absent. Immunocytochemically identified reactive neuroglial cells showed a remarkably low-grade tissue response to the synthetic material beyond the first 2 weeks of observation. Immunolabeled cortical neurons revealed conserved columnar arrays around the implants. Transmission electron microscopy showed a minimal degree of collagen deposition compared to implants in peripheral sites, and normal synapses within a few micrometers from the brain/polymer interface, supporting the prospect of biocompatible, immunoisolated xenografts in the central nervous system.