Investigating the Effects of Biofilm Viscoelasticity on Immune Cell Phagocytosis

Biofilm infections affect 17 million Americans, cause half a million deaths, and cost the US healthcare system billions of dollars annually. Biofilms are communities of micro-organisms embedded in a polymer and protein matrix. Biofilms are inherently more resistant to antibiotics and immune cell clearance. The matrix gives the biofilm a mechanical response to shear that is characteristic of a viscoelastic solid. Our goal is to understand how distinct mechanical properties, including elastic modulus (G’) and yield strain, impact biofilm resistance to the immune system. We focus on neutrophils, the phagocytic first-responders to infection that are involved in the body’s attempts to clear biofilm infections. The best extant estimate for the stress exerted by neutrophils during phagocytosis is ~1 kPa. This is comparable to the ~1 kPa value we measure for G’ for some biofilms, but we find that biofilms can increase or decrease G’ by adjusting production of matrix polymers. We are developing two approaches to create “model biofilms” of known and tunable mechanics: gel macrobeads and photo-crosslinked micro-structures. We will challenge “model biofilms” with neutrophils and determine threshold mechanical values below which neutrophils can break off and engulf pieces of the “biofilm”.