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FIGURE 3.4

FIGURE 3.5 Quantitative comparison of foreign body reactions around long-term implants (means with standard deviations in n cats) showing capsule thickness in A (corrected for collapse after removal of the implants) and inflammatory cell scores in B using a method modified from Black.17 Implant code: NC MS = non-coated BION1 implant, C MS = BION1

FIGURE 3.5 Quantitative comparison of foreign body reactions around long-term implants (means with standard deviations in n cats) showing capsule thickness in A (corrected for collapse after removal of the implants) and inflammatory cell scores in B using a method modified from Black.17 Implant code: NC MS = non-coated BION1 implant, C MS = BION1

Previous literature has suggested that the form factor of devices may contribute significantly to the nature and thickness of the tissue response around implanted materials.18,19 In this study, however, the invaginated profiles of the devices did not seem to stimulate the production of thicker capsules than those around the smoothly contoured silicone rods. With time, the devices with invaginated surfaces around the electrodes appeared to integrate quite securely into the muscle tissue. At the histo-logical level, streams of thickened perimysial tissue appeared to emanate from the ends of the capsules around the devices into the interstices of surrounding muscle fascicles (Figure 3.4B). We hypothesize that this web of connective tissue helps to reduce the mechanical shear between the rigid device and the surrounding muscle during muscle contractions and serves to improve the tolerance of the implanted foreign body by the muscle. In three instances, silicone or polyethylene rods were found to have migrated from their sites of implant. The thin, rather sharp ends of the polyethylene rods may have encouraged the penetration of the rod through the muscle tissue. The propensity of the glass capsules to migrate was evaluated in a separate study in cats implanted with BION-sized, smooth glass capsules. The initial implantation sites were permanently stained with a fluorescent marker that remained colocalized with the connective tissue capsules surrounding the glass capsules at the end of three months of normal physical activity.20

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