Volumetric interpretation of protein adsorption: Interfacial packing of protein adsorbed to hydrophobic surfaces from surface-saturating solution concentrations

Department of Electrical Engineering, The Pennsylvania State University, University Park, PA 16802, USA.
Biomaterials (Impact Factor: 8.56). 10/2010; 32(4):969-78. DOI: 10.1016/j.biomaterials.2010.09.075
Source: PubMed


The maximum capacity of a hydrophobic adsorbent is interpreted in terms of square or hexagonal (cubic and face-centered-cubic, FCC) interfacial packing models of adsorbed blood proteins in a way that accommodates experimental measurements by the solution-depletion method and quartz-crystal-microbalance (QCM) for the human proteins serum albumin (HSA, 66 kDa), immunoglobulin G (IgG, 160 kDa), fibrinogen (Fib, 341 kDa), and immunoglobulin M (IgM, 1000 kDa). A simple analysis shows that adsorbent capacity is capped by a fixed mass/volume (e.g. mg/mL) surface-region (interphase) concentration and not molar concentration. Nearly analytical agreement between the packing models and experiment suggests that, at surface saturation, above-mentioned proteins assemble within the interphase in a manner that approximates a well-ordered array. HSA saturates a hydrophobic adsorbent with the equivalent of a single square or hexagonally-packed layer of hydrated molecules whereas the larger proteins occupy two-or-more layers, depending on the specific protein under consideration and analytical method used to measure adsorbate mass (solution depletion or QCM). Square or hexagonal (cubic and FCC) packing models cannot be clearly distinguished by comparison to experimental data. QCM measurement of adsorbent capacity is shown to be significantly different than that measured by solution depletion for similar hydrophobic adsorbents. The underlying reason is traced to the fact that QCM measures contribution of both core protein, water of hydration, and interphase water whereas solution depletion measures only the contribution of core protein. It is further shown that thickness of the interphase directly measured by QCM systematically exceeds that inferred from solution-depletion measurements, presumably because the static model used to interpret solution depletion does not accurately capture the complexities of the viscoelastic interfacial environment probed by QCM.

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    • "Results obtained are consistent with that obtained by tensiometry [22] [23] [24] [25] [26] [27] and quartz-crystal microbalance (QCM) [21]. These adsorption isotherms approximate a Henry isotherm wherein adsorbed amount is in direct proportion to solution concentration W 0 "
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    ABSTRACT: Comparison of protein mass-adsorption-rates to rates-of-change in interfacial tensions reveals that mass adsorption is decoupled from interfacial energetics. This implies that energy-barrier theories describing protein-adsorption kinetics do not accurately capture the physics of the process. An alternative paradigm in which protein molecules rapidly diffuse into an inflating interphase which subsequently slowly shrinks in volume, concentrating adsorbed protein and causing slow concomitant decrease in interfacial tensions, is shown to be consistent with adsorption kinetics measured by solution depletion and tensiometry. Mass adsorption kinetics observed from binary-protein solution is compared to adsorption kinetics from single-protein solution, revealing that organization of two different-sized proteins within the interphase can require significantly longer than that adsorbed from single-protein solution and may require expulsion of initially adsorbed protein which is not observed in the single-protein case.
    Applied Surface Science 12/2012; 262:19–23. DOI:10.1016/j.apsusc.2011.12.014 · 2.71 Impact Factor
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    • "In general, the interfacial water surrounding a protein can be categorized as (i) buried internally (ii) ordered on the protein surface, and (iii) disordered and thereby contributing to the bulk water [49]. To estimate the contribution of the associated water content in an adsorbed layer, previous researchers have compared their QCM-D measurements to values determined from optical techniques such as surface plasmon resonance and ellipsometry [45, 46], as well as to XPS data [50] or to solution depletion measurements [51]. To obtain a general approximation of the hydration contribution to the ELP coatings, the current QCM-D surface coverage values (from an ELP bulk concentration of 5.8 mg/mL) were compared to the previously reported surface coverage values obtained under similar coating conditions but using an elastin specific assay (Fastin™ Elastin Assay, FEA) [17], as illustrated in Fig. 10. "
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    ABSTRACT: The surface properties of a family of elastin-like polypeptides (ELPs), differing in molecular weight and sequence length, were investigated to understand how the nature of the polypeptide film might contribute to their thrombogenic profile. Physical adsorption of the ELPs onto Mylar increased surface wettability as the sequence length decreased while X-ray spectroscopy analysis showed an increasing amide content with sequence length. Chemical force microscopy analysis revealed that the ELP-coated surfaces displayed purely hydrophilic adhesion forces that increased as the ELP sequence length decreased. Adsorption isotherms performed using the quartz crystal microbalance with dissipation, showed that the surface coverage increased with ELP sequence length. The longer polypeptides (ELP2 and ELP4) also displayed higher specific dissipation values indicating that they established films with greater structural flexibility and associated water content than the shorter polypeptide, ELP1. Additionally, the stability of the ELP coating was lower with the shorter polypeptides. This study highlights the different surface properties of the ELP coatings as well as the dynamic nature of the ELP adsorbed layer wherein the conformational state may be an important factor contributing to their blood response.
    Journal of Materials Science Materials in Medicine 09/2012; 24(1). DOI:10.1007/s10856-012-4772-6 · 2.59 Impact Factor
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    Journal of the American College of Cardiology 04/2011; 57(14). DOI:10.1016/S0735-1097(11)60065-X · 16.50 Impact Factor
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