Title

Modulating bacterial-macrophage interactions at a biomaterial surface

Date of Completion

January 2001

Keywords

Engineering, Biomedical|Engineering, Chemical

Degree

Ph.D.

Abstract

Biomaterials are widely used in medical devices, such as prosthetic joints and cardiovascular devices. Biomaterials engineered to evoke true “healing” may circumvent current problems, such as infection and inflammation, that lead to the device performing under its expectations. The macrophage is a central cell type involved in the wound healing process, including directing host inflammatory and immune responses. Conceptually, biomaterials may be designed to promote a desired cellular behavior (e.g. adhesion, production of cytokines) that is implicated in successful integration of a medical device. ^ PEG-g-PA co-polymers were fabricated that inhibited non-specific protein and cellular adhesion. Fouling studies indicated an average 86% reduction in the maximum amount of adsorbed protein for studies using 3 different blood plasma proteins. PEG-g-PA co-polymers were covalently modified with peptides and monoclonal antibody fragments known to promote monocyte/macrophage integrin-mediated adhesion. Specific covalent immobilization methods were used to orient the peptide or antibody fragments, which allowed a controlled study of the influence of a specific biological signal on the corresponding cellular response. Modified materials were characterized in terms of (a) degree of random protein adsorption and bacterial adhesion, (b) monocyte/macrophage adhesion and response (cytokine secretion, oxidative burst) and (c) bacterial-monocyte/macrophage interactions, particularly monocyte/macrophage phagocytic response. ^ Overall, this work demonstrated the following: (1) PEG-g-PA as a non-fouling substratum significantly diminished random protein adsorption and bacterial adhesion. (2) P. aeruginosa and S. epidermidis adhesion to PEG-g-PA materials modified with peptides was statistically the same as non-modified PEG-g-PA base material. A slight increase in adherence was observed to materials modified with monoclonal fragments. (3) Monoclonal antibody fragments were more effective than peptides directed toward integrin receptors in promoting adhesion of monocyte/macrophage cells. (4) The specific presentation of peptides and monoclonal antibody fragments via PEO tethering molecules (a) further diminished non-specific random protein adsorption and bacterial adhesion and (b) modulated monocyte/macrophage responses as quantified by adhesion, cytokine secretion, and oxidative burst. (5) Adhesion of monocyte/macrophages to certain peptides or monoclonal antibody fragments bound to a biomaterial surface enhanced phagocytic response and bacterial killing of both opsonized P. aeruginosa and S. epidermidis. ^