Improvements in the resolution of the foreign body reaction by the modulation of macrophage polarization towards an M2 phenotype at the tissue-implant interface by local release of IL-4 from layer by layer coated polypropylene meshes

Abstract

Event Abstract Back to Event Improvements in the resolution of the foreign body reaction by the modulation of macrophage polarization towards an M2 phenotype at the tissue-implant interface by local release of IL-4 from layer by layer coated polypropylene meshes Daniel Hachim1, 2, Sam T. Lopresti1, 2, Deepa Mani1 and Bryan N. Brown1, 2, 3 1 University of Pittsburgh, Bioengineering, United States 2 University of Pittsburgh, McGowan Institute for Regenerative Medicine, United States 3 University of Pittsburgh, Department of Obstetrics, Gynecology and Reproductive Sciences, United States Introduction: Surgical mesh implantation is a common option for hernia repair and pelvic organ prolapse; however, associated with severe complications such as pain, organ perforation and mesh exposure[1]. Mesh complications are mostly due to host chronic foreign body reaction, performed by pro-inflammatory (M1) macrophages at the tissue implant interface[2]. On the other hand, pro-remodeling (M2) macrophages have been found to be important players in tissue remodeling[3]. Also, the M2:M1 ratio has been described to be a predictor of success of a biomaterial in-vivo[4]. It has been hypothesized that transient polarization of macrophages at the tissue-implant interface to an M2 phenotype will mitigate the foreign body reaction. Therefore, a nanometer thickness coating with the ability to provide local delivery of IL-4 (an in-vitro M2 polarizing cytokine) has been developed. Materials and Methods: Gynemesh® Polypropylene (PP) meshes were treated with radio frequency glow discharge (RFGD) to produce a negatively charged surface. To construct the coating, a layer-by-layer (LbL) procedure was performed using chitosan as polycation and dermatan sulfate as polyanion. Cycles were repeated with intermediate washing steps until desired number of layers. Loading of IL-4 was performed by prior incubation with dermatan sulfate. X-ray photoelectron spectroscopy (XPS), ATR-FTIR and alcian blue staining were used to characterize the coating. ELISA assays were used to evaluate the release of IL-4 at different time points. Also, a murine macrophage culture was used to corroborate the bioactivity of the released IL-4 by means of an arginase-1 immunolabeling and quantitative analysis. Finally, 1 cm2 pieces of mesh were implanted subcutaneously on the abdomen of female C57BL/6J mice and then sections of mesh-surrounding tissue were harvested at 7, 14 and 90 days for histology. Results and Discussion: Appearance of new peaks on the XPS and ATR-FTIR spectra but also stained meshes by alcian blue consistently confirmed the presence of a uniform, conformal coating made of both chitosan and dermatan sulfate. Similarly, confocal microscopy images of immunolabeled meshes showed a uniform loading of IL-4 through all the mesh surface (Figure 1A). ELISA assays showed that the amount and release time of IL-4 from coated meshes were dependent on the number of coating bilayers, but the power law dependence profile of release remained constant (Figure 1B). Additionally, higher expression of arginase-1 from macrophages exposed to IL-4 loaded meshes demonstrated M2 polarization and maintenance of IL4 bioactivity (Figure 1C). Interestingly, histological studies of mice implanted with IL-4 loaded meshes revealed less dense cellular inflammatory infiltrates around mesh fibers and a higher percentage of M2 macrophages compared to control meshes at 7 (Figure 2) and 14 days. Finally, mice implanted with IL-4 loaded meshes resulted in a diminished capsule formation at 90 days, as shown by Masson’s Trichrome (Figure 2) and Picro Sirius Red staining, compared to control meshes. Conclusions: Local release of IL-4 from coated polypropylene meshes is tunable and capable to polarize macrophages to an M2 phenotype both in-vitro and in-vivo, but also have shown to decrease inflammation and capsule formation in-vivo, suggesting improvements in the resolution the foreign body reaction against implanted mesh. This work was supported by the NIH grants K12HD043441 and R21GM107882. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.