Protein adsorption behavior has been a topic of intense research and great debate in the field of biomaterials surface science for decades. Experimentalists have studied the adsorption behavior of hundreds of different proteins on varying surfaces including metals, ceramics, glasses, synthetic polymers, natural polymers[5,6], and atop other proteins. Despite this extensive library of research, a fundamental understanding of protein adsorption remains uncertain. In this work, we approach the problem with the tools of molecular simulations. We utilize the mesoscale simulation method of dissipative particle dynamics (DPD) to explore the adsorption behavior of model proteins in solution in the presence of surfaces of varying hydrophilicity. Moreover a quantitative explanation of adsorption and desorption kinetics is included.
In DPD multiple atoms or molecules are considered to be grouped into beads characterized by a center of mass, position, and momentum. The technique has been extended to biomolelcular system including vesicles, lipid bilayers, microtubules, and, in a very limited number of studies, model proteins[9,10]. Studies which have included model proteins have mostly focused on their behavior when embedded within lipid bilayers and the effect of hydrophobic mismatch. Recently, we used the DPD method to compare the adsorption behavior of large and small elongated proteins in solution in the presence of a hydrophobic surface. To the best of our knowledge, this was the first time DPD had been used to study protein adsorption.
Here , we compare the adsorption kinetics of systems containing multiple proteins in solution in the presence of a solid surface. In the first phase of the study, we compare systems containing homogeneous model proteins of two different sizes (small and large elongated) near surfaces ranging from lightly hydrophobic to highly hydrophobic. We find distinct differences in adsorption and desorption behavior between the small and large elongated proteins which arise from the difference in total available protein-surface bead-bead interaction. In addition, we note an inability for the large elongated proteins to desorb from the surface once adsorbed, irrespective of the degree of hydrophobicity. We also note a striking difference in the diffusion and adsorption kinetics between the two types of proteins: the small elongated proteins exhibit rapid diffusion as well as adsorption kinetics, while their larger counterparts were much slower. In the second phase, we explore the effect of initial configuration (protein position within the simulation box) on the time-to-adsorption as well as steady-state behavior.
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