Dynamics of long-term protein aggregation on low-fouling surfaces

Abstract

Understanding the mechanisms of protein interactions with solid surfaces is critical to predict how proteins affect the performance of materials in biological environments. Low-fouling and ultra-low fouling surfaces are often evaluated in short-term protein adsorption experiments, where ‘short-term’ is defined as the time required to reach an initial apparent or pseudo-equilibrium, which is usually less than 600 s. However, it has long been recognized that these short-term observations fail to predict protein adsorption behavior in the long-term, characterized by irreversible accumulation of protein on the surface. This important long-term behavior is frequently ignored or attributed to slow changes in surface chemistry over time—such as oxidation—often with little or no experimental evidence. Here, we report experiments measuring protein adsorption on “low-fouling” and “ultralow-fouling” surfaces using single-molecule localization microscopy to directly probe protein adsorption and desorption. The experiments detect protein adsorption for thousands of seconds, enabling direct observation of both short-term (reversible adsorption) and long-term (irreversible adsorption leading to accumulation) protein-surface interactions. By bridging the gap between these two time scales in a single experiment, this work enables us to develop a single mathematical model that predicts behavior in both temporal regimes. The experimental data in combination with the resulting model provide several important insights: (1) short-term measurements of protein adsorption using ensemble-averaging methods may not be sufficient for designing antifouling materials; (2) all investigated surfaces eventually foul when in long-term contact with protein solutions; (3) fouling can occur through surface-induced oligomerization of proteins which may be a distinct step from irreversible adsorption; and (4) surfaces can be designed to reduce oligomerization or the adsorption of oligomers, to prevent or delay fouling.