Macrophage interactions with biomaterial surfaces and their effects on endothelial cell activation

Abstract

This research project focused on the development of in vitro models to study cell reactions with material surfaces and how materials exert their influence on cell-cell interactions. Macrophage inflammatory cytokine release was shown to be affected by surface chemistry, topography and extracellular matrix (ECM) coating. Material characteristics could affect endothelial cell (EC) activation through material-induced macrophage cytokine signaling. The degree of EC activation depended upon the material the macrophages contacted.Surface chemistry affected the number of human monocytes that initially adhered to the different polymers. The materials studied were mixed esters of cellulose (MEC), and the fluoropolymers polytetrafluoroethylene (PTFE) and expanded PTFE (ePTFE). Materials varied in porosity, but not surface chemistry. The fluoropolymers had significantly lower monocyte adhesion compared to the MEC, but adhesion could be improved with fibronectin (FN) pre-coating.Monocytes seeded on the different polymer surfaces were activated to varying degrees, determined by measuring inflammatory cytokine release. Macrophages contacting MEG showed low levels of interleukin-1$\beta$ (IL-1$\beta )$ and tumor necrosis factor-$\alpha$ (TNF$\alpha )$ secretion. The fluoropolymers showed significantly higher levels of secretion of IL-1$\beta$ and TNF$\alpha .$ Cytokine release increased with increasing fibril length in the fluoropolymer series. All cytokine data was normalized to cell number.FN pre-coating had varied effects, depending on the surface chemistry and fibril length of the ePTFE materials. FN did not significantly influence cytokine production on the MECs, whereas significant decreases in IL-1$\beta$ and TNF$\alpha$ release from macrophages contacting 10$\mu$ and 30$\mu$ ePTFE were seen. Pre-coating 60$\mu$ ePTFE did not lower IL-1$\beta$ or TNF$\alpha$ secretion.EC activation by macrophage-derived products was determined by monitoring neutrophil adherence to EC after being incubated in macrophage conditioned medium. There was a direct correlation between EC activation and material-induced macrophage cytokine production.These results support the hypothesis that macrophage activation can be influenced by surface properties, such as surface chemistry, porosity or fibril length, and ECM coatings. Also, material-induced macrophage activation can cause activation of ECs, having profound implications for macrophage interactions with materials in vivo. Several material characteristics were identified that could aid in the development of more biocompatible medical implants.