Pore size in implanted polypropylene filters is critical for tissue organization

Abstract

Widely different implant materials induce surprisingly similar tissue reactions in vivo in contrast to their in vitro responses. Increasing attention has recently been given to the surface texture of the material. When both the material composition and the surface topography are varied, the surface topography seems to be the predominant factor for the induced tissue response. The present study addresses differences in the tissue response to commercially available Millipore mesh filters of polypropylene with pore sizes of 0.6, 10.0 or 30.0 microm. The Millipore filters with adjacent tissue were directly sectioned in a cryostat and evaluated via an immunofluorescence technique with double and triple staining, allowing simultaneous analysis of different antigens in tissue sections. These results show that macrophages, total cells, necrotic cells, nitric oxygen distribution, early angiogenesis, and capsule thickness were influenced by the surface structure. Implants with pore sizes of 0.6 microm, where entrance of inflammatory cells was inhibited, induce the most pronounced foreign body capsule formation. The 10- and 30-microm filters, in contrast, had large amounts of macrophages inside the filter structure, although very few inflammatory cells were found outside the filters. The inflammatory cells within the filters appeared not to influence the foreign body capsule induction. The critical factor for the formation of a foreign body capsule seems to be the localization of implant-close macrophages. Whether this is due to differences in cell activation or in signal transduction to collagen-synthesizing fibroblasts remains an open question.

The performance of a small-calibre graft for vascular reconstructions in a senescent sheep model

“…The progressive development of an avascular fibrous capsule can compromise the long-term performance of a graft [19,20]. Maintaining high vascularity around the implant is thought to be a means of reducing fibrosis.…”

Design concepts and strategies for tissue engineering scaffolds

“…In contrast, another study reported that unique biological activity including enhanced angiogenesis has been noted for implanted porous materials with tightly controlled pore size distributions around 35 μm [55]. The cellular responses of angiogenesis, inflammation, foreign body capsule formation, and tissue infiltration in vivo have all shown some dependence on average pore size and pore size distribution, but the specific range is still not conclusive [56], [57].…”

Esophageal epithelial cell interaction with synthetic and natural scaffolds for tissue engineering

“…While we have focused on the in vitro effects of pore size on epithelial cells, recent publications have indicated that pore size contributes to the in vivo response. Angiogenesis, inflammation, foreign body capsule formation, and tissue invasion have all shown a dependence on pore size [31][32][33][34][35][36]. Interestingly, unique biological reactivity, including enhanced angiogenesis, has recently been noted for implanted porous materials with tightly controlled pore-size distributions around 35 mm [36].…”