Micron-scale topographies affect phagocytosis of bacterial cells on polydimethylsiloxane surfaces

Many medical devices implanted in patients to mitigate diseases and medical conditions have different types of topographic features. While appropriate textures can promote the integration of host cells and reduce scar tissue formation, some textured implants with inappropriate topographies have been associated with inflammation, bacterial colonization, or even malignant complications. To better understand how surface topography affects host immune response to colonizing bacteria, a protocol was developed to investigate phagocytosis of bacterial cells attached on polydimethylsiloxane (PDMS) surfaces with different square-shaped recessive patterns. The interaction between activated RAW 264.7 macrophages and Escherichia coli in recessive wells was visualized in 3D using multiple fluorescent markers. The results revealed that there is a threshold dimension of topography, below which phagocytosis of attached bacterial cells is significantly impeded. Specifically, under our experimental condition, up to 100-fold reduction in phagocytosis was observed in square-shaped patterns with 5 µm side length and 10 µm depth compared to the flat control and patterns with 10 µm or longer side length. The spacing between wells also showed significant effects; e.g., phagocytosis in the wells further decreased when spacing increased to 50 µm. These results are helpful for understanding how undesired topographies may contribute to bacterial colonization and thus infection and other associated complications. STATEMENT OF SIGNIFICANCE: Surface topography plays an important role in bacteria-material infections and thus the safety of implantable medical devices. Undesired topographic features can cause biofilm formation and related complications. However, how surface topography affects the capability of host immune cells to clear colonizing bacteria is not well understood. In this study, the interaction between macrophage RAW264.7 and colonizing E. coli cells on polydimethylsiloxane (PDMS) with recessive features is investigated. It was discovered that the size of recessive features and the spacing between these features have significant effects on phagocytosis of bacteria by macrophages. These new results are helpful for understanding the complex interaction among host cells, bacteria, and implanted biomaterials, which will help guide the rational design of safer medical devices.