(172b) Understanding the Non-Fouling Mechanism by Paired Experiments and Simulations

While significant advances in biocompatible and environmentally sound materials have been made, one of the significant and still challenging issues is surface resistance to protein adsorption. The mechanisms for protein resistance are very poorly understood and the majority of new low and non-fouling material breakthroughs still come by chance. Some examples of fortuitously discovered non-fouling surfaces include ethylene glycol, phosophocholine, and some sugar aditols. Protein-surface interactions are difficult to study experimentally. The region of interest is often not directly addressable, and there are many complex components and interactions that frequently cannot be deconvoluted with generic laboratory techniques. Surface Plasmon Resonance Spectroscopy (SPR) is a powerful experimental technique that allows for real-time monitoring of adsorption phenomena. If the system chemistry is understood, SPR spectra can provide a wide range of adsorption data from kinetics to binding affinities. A second useful tool for studying buried interfaces and complex systems is molecular modeling which provides a method to separate the intermingling interactions and look directly at the buried interfaces. Thus, the purpose of this work is to study the non-fouling mechanism using SPR adsorption experiments paired with molecular simulations to achieve a level of understanding sufficient enough for rational design.

This work quantifies the relative importance and influence of two significant protein adsorption mechanisms: electrostatic attraction and surface-protein hydrogen bonding. Lysozyme and fibrinogen adsorption to self-assembled monolayers (SAMs) of hydroxyl (OH), carboxyl (COOH), and amine (NH2) terminated alkanethiols was tracked using SPR spectroscopy. The SAMs were chosen to provide an electrically positive (NH2), negative (COOH), and neutral surface (OH) which should significantly affect the adsorption behavior. The ionic strength and pH of the protein solutions were varied. By changing the solution ionic strength and pH it should be possible to selectively screen the electrostatic interactions and promote or inhibit hydrogen bonding between the protein and the SAM surface. By monitoring the amount of protein adsorption and the kinetics as a function of solution ionic strength and pH the protein-surface interaction mechanism and strength is more fully understood. In parallel to the SPR protein adsorption experiments, molecular dynamics simulations were used to model similar model systems of lysosyme and OH, COOH, NH2-SAMs in the presence of explicit water solutions that match experimental ionic strengths and pH of interest. The molecular simulations provide detailed information about surface hydration, and qualitative measures of the changing interaction forces as the solution chemistry changes.

Rational design of new non-fouling materials requires an explicit understanding of the mechanisms of protein adsorption. If we can quantify and prioritize protein adsorption pathways, it will allow future material designs and research efforts that directly address the key steps in protein adsorption. The combination of SPR spectroscopy and molecular simulations is a powerful tool for understanding protein adsorption mechanisms and provides a strong foundation to future advances in non-fouling chemistries and materials.