Characterization of the foreign body response to common surgical biomaterials in a murine model

Background Implanted biomaterials are subject to a significant reaction from the host, known as the foreign body response (FBR). We quantified the FBR to five materials following subcutaneous implantation in mice. Methods Polyvinyl alcohol (PVA) and silicone sheets are considered highly biocompatible biomaterials and were cut into 8-mm-diameter disks. Expanded PTFE (ePTFE) and polypropylene are also widely used biocompatible biomaterials and were cut into 2 cm-long cylinders. Cotton was selected as a negative control material that would invoke an intense FBR, was cut into disks, and implanted. The implants were inserted subcutaneously into female C57BL/6 mice. On post-implantation days 14, 30, 60, 90, and 180, implants were retrieved. Cellularity was assessed with DAPI stain, collagen with Masson's trichrome stain, mast cells with toluidine blue, macrophages with F4/80 immunohistochemical stain, and capsular thickness and foreign body giant cells with hematoxylin and eosin. Results DAPI revealed a significantly increased cellularity in both PVA and silicone, and ePTFE had the lowest cell density. Silicone showed the lowest cellularity at day 14 and day 90, whereas ePTFE showed the lowest cellularity at days 30, 60, and 180. Masson's trichrome staining demonstrated no apparent difference in collagen. Toluidine blue showed no differences in mast cells. There were, however, fewer macrophages associated with ePTFE. On day 14, PVA had highest number of macrophages, whereas polypropylene had the highest number at all time points after d14. Giant cells increased earlier and gradually decreased later. On day 90, PVA exhibited a significantly increased number of giant cells compared to polypropylene and silicone. Silicone consistently formed the thinnest capsule throughout all time points. On day 14, cotton had formed the thickest capsule. On day 30, polypropylene gas formed the thickest capsule, and on days 60, 90, and 180, PVA had formed the thickest capsule. Conclusions These data reveal differences in capsule thickness and cellular response in an implant-related manor, indicating that fibrotic reactions to biomaterials are implant-specific and should be carefully considered when performing studies on fibrosis when biomaterials are being used.