Histologic evaluation of the inflammatory response around implanted hollow fiber membranes

Hollow fiber membranes are enjoying widespread use as barrier materials in many implanted applications. In order to predict in vivo device behavior, it is important to understand and quantify the changes to the membrane and to the tissue immediately surrounding it that occur following implantation. We have considered a range of commercially available hollow fiber membranes for their suitability as candidates for subcutaneously implanted applications. Through analysis of excised tissue sections by light microscopy, membranes were screened at 3, 6, and 12 weeks post-implantation for the ability to maintain integrity, foreign-body reaction, and thickness of the external fibrotic capsule layer. The polysulfone microfiltration membranes and cellulose diacetate membranes investigated were found to be unsuitable owing to extensive degradation. All membranes exhibited typical foreign body reaction with fibrotic capsule formation. The thinnest capsules were observed on the regenerated cellulose microdialysis membranes and the polysulfone ultrafiltration membranes. Extensive cellular penetration into the membrane matrix of the latter was observed, but did not appear to affect the foreign body reaction. A heat-sealing method was also considered for thermoplastic membranes and found to effectively prevent cellular penetration into the lumen of the hollow fiber for the duration of the 12-week implantation.