A Comparative Immunological Assessment of the Capsules From Silicone Implants With 0-µm and 4-µm Surfaces

BACKGROUND: The immune system drives the foreign body response (FBR) to breast implants, triggering cellular and molecular events that lead to the formation of an implant capsule. Implant surface topography may influence this immunological process. OBJECTIVES: Assess the immune response to silicone implants with smooth or 4-μm surface roughness. METHODS: Custom-made, miniaturized implants or coupons of commercially available breast implant shells with smooth (0-μm) or 4-μm surfaces were implanted subcutaneously in the dorsolumbar region of mice. Capsule samples were harvested after 3, 6, or 9 weeks. Immune cells were characterized via histology scoring based on the International Organization for Standardization (ISO) 10993-6:2016 guidelines (biological evaluation of medical devices), flow cytometry, immunohistochemistry, and gene expression analysis. RESULTS: Histological total sum scores, indicating overall inflammation, were similar between smooth and 4-µm implants at 3, 6, and 9 weeks postimplantation. Macrophages, key regulators of the FBR, were comparable between smooth and 4-µm implants, as demonstrated by flow cytometry analysis and CD11b+ histology staining. Further analysis of proinflammatory and anti-inflammatory macrophages showed similar phenotypes between smooth and 4-µm implants. Regulatory T cell populations, which are responsible for suppressing excessive immune responses and maintaining immune balance, were similar in capsule tissues from smooth and 4-µm implants, as determined by flow cytometry and Foxp3 gene expression analysis. Gene expression of markers for cell populations and mechanotransduction were comparable at all timepoints. CONCLUSIONS: Host immune responses were similar for breast implants with surface roughness of 0 µm or 4 µm up to 9 weeks postimplantation in mice.