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      Critical review: impacts of macromolecular coatings on critical physicochemical processes controlling environmental fate of nanomaterials

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          Abstract

          Challenges in predicting effects of macromolecules on nanoparticle behavior.

          Abstract

          Attachment of engineered and naturally occurring macromolecules greatly affects the environmental fate and toxicity of engineered nanomaterials (ENMs). A better understanding of macromolecule–ENM interactions at the nanoscale will improve the ability to predict the effects of macromolecular coatings, e.g. natural organic matter (NOM), on ENM fate, reactivity, and toxicity. This review briefly discusses relevant theory from colloid and polymer science for highly idealized polymers on surfaces that can be used to describe ENM environmental behaviors and introduces classes of macromolecules of interest in the field of environmental nanotechnology. Methods to characterize adsorbed macromolecules on ENMs are presented along with their limitations for ENMs in natural systems. Finally, the current state of knowledge regarding the effects of attached organic macromolecules, both engineered and incidental, on the environmental fate and reactivity of ENMs is critically reviewed. These concepts in whole are synthesized to identify the fundamental gaps in understanding and metrology that must be addressed to improve our mechanistic understanding of the effects of organic macromolecules on ENM environmental fate, and approaches to correlate the properties of coated ENMs to their environmental fate are discussed. We postulate that a first principles approach to modeling ENM–macromolecule interactions is not warranted, particularly for complex and heterogeneous natural macromolecules. On the other hand, a mechanistic understanding is needed to inform parameter selection for empirical correlations, which may offer tractable alternatives to predicting the behavior of macromolecule–coated ENMs. Development of these empirical correlations and prediction of the long-term fate of ENMs is currently hampered by incomplete characterization of the adsorbed macromolecule layer properties and their evolution over time in natural systems.

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          Most cited references214

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          The Fluid Mosaic Model of the Structure of Cell Membranes

          A fluid mosaic model is presented for the gross organization and structure of the proteins and lipids of biological membranes. The model is consistent with the restrictions imposed by thermodynamics. In this model, the proteins that are integral to the membrane are a heterogeneous set of globular molecules, each arranged in an amphipathic structure, that is, with the ionic and highly polar groups protruding from the membrane into the aqueous phase, and the nonpolar groups largely buried in the hydrophobic interior of the membrane. These globular molecules are partially embedded in a matrix of phospholipid. The bulk of the phospholipid is organized as a discontinuous, fluid bilayer, although a small fraction of the lipid may interact specifically with the membrane proteins. The fluid mosaic structure is therefore formally analogous to a two-dimensional oriented solution of integral proteins (or lipoproteins) in the viscous phospholipid bilayer solvent. Recent experiments with a wide variety of techniqes and several different membrane systems are described, all of which abet consistent with, and add much detail to, the fluid mosaic model. It therefore seems appropriate to suggest possible mechanisms for various membrane functions and membrane-mediated phenomena in the light of the model. As examples, experimentally testable mechanisms are suggested for cell surface changes in malignant transformation, and for cooperative effects exhibited in the interactions of membranes with some specific ligands. Note added in proof: Since this article was written, we have obtained electron microscopic evidence (69) that the concanavalin A binding sites on the membranes of SV40 virus-transformed mouse fibroblasts (3T3 cells) are more clustered than the sites on the membranes of normal cells, as predicted by the hypothesis represented in Fig. 7B. T-here has also appeared a study by Taylor et al. (70) showing the remarkable effects produced on lymphocytes by the addition of antibodies directed to their surface immunoglobulin molecules. The antibodies induce a redistribution and pinocytosis of these surface immunoglobulins, so that within about 30 minutes at 37 degrees C the surface immunoglobulins are completely swept out of the membrane. These effects do not occur, however, if the bivalent antibodies are replaced by their univalent Fab fragments or if the antibody experiments are carried out at 0 degrees C instead of 37 degrees C. These and related results strongly indicate that the bivalent antibodies produce an aggregation of the surface immunoglobulin molecules in the plane of the membrane, which can occur only if the immunoglobulin molecules are free to diffuse in the membrane. This aggregation then appears to trigger off the pinocytosis of the membrane components by some unknown mechanism. Such membrane transformations may be of crucial importance in the induction of an antibody response to an antigen, as well as iv other processes of cell differentiation.
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            Physical-chemical aspects of protein corona: relevance to in vitro and in vivo biological impacts of nanoparticles.

            It is now clearly emerging that besides size and shape, the other primary defining element of nanoscale objects in biological media is their long-lived protein ("hard") corona. This corona may be expressed as a durable, stabilizing coating of the bare surface of nanoparticle (NP) monomers, or it may be reflected in different subpopulations of particle assemblies, each presenting a durable protein coating. Using the approach and concepts of physical chemistry, we relate studies on the composition of the protein corona at different plasma concentrations with structural data on the complexes both in situ and free from excess plasma. This enables a high degree of confidence in the meaning of the hard protein corona in a biological context. Here, we present the protein adsorption for two compositionally different NPs, namely sulfonated polystyrene and silica NPs. NP-protein complexes are characterized by differential centrifugal sedimentation, dynamic light scattering, and zeta-potential both in situ and once isolated from plasma as a function of the protein/NP surface area ratio. We then introduce a semiquantitative determination of their hard corona composition using one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis and electrospray liquid chromatography mass spectrometry, which allows us to follow the total binding isotherms for the particles, identifying simultaneously the nature and amount of the most relevant proteins as a function of the plasma concentration. We find that the hard corona can evolve quite significantly as one passes from protein concentrations appropriate to in vitro cell studies to those present in in vivo studies, which has deep implications for in vitro-in vivo extrapolations and will require some consideration in the future.
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              Understanding and controlling the interaction of nanomaterials with proteins in a physiological environment.

              Nanomaterials hold promise as multifunctional diagnostic and therapeutic agents. However, the effective application of nanomaterials is hampered by limited understanding and control over their interactions with complex biological systems. When a nanomaterial enters a physiological environment, it rapidly adsorbs proteins forming what is known as the protein 'corona'. The protein corona alters the size and interfacial composition of a nanomaterial, giving it a biological identity that is distinct from its synthetic identity. The biological identity determines the physiological response including signalling, kinetics, transport, accumulation, and toxicity. The structure and composition of the protein corona depends on the synthetic identity of the nanomaterial (size, shape, and composition), the nature of the physiological environment (blood, interstitial fluid, cell cytoplasm, etc.), and the duration of exposure. In this critical review, we discuss the formation of the protein corona, its structure and composition, and its influence on the physiological response. We also present an 'adsorbome' of 125 plasma proteins that are known to associate with nanomaterials. We further describe how the protein corona is related to the synthetic identity of a nanomaterial, and highlight efforts to control protein-nanomaterial interactions. We conclude by discussing gaps in the understanding of protein-nanomaterial interactions along with strategies to fill them (167 references).
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                Author and article information

                Journal
                ESNNA4
                Environmental Science: Nano
                Environ. Sci.: Nano
                Royal Society of Chemistry (RSC)
                2051-8153
                2051-8161
                2016
                2016
                : 3
                : 2
                : 283-310
                Affiliations
                [1 ]Center for the Environmental Implications of NanoTechnology (CEINT)
                [2 ]Carnegie Mellon University
                [3 ]Pittsburgh
                [4 ]USA
                [5 ]Department of Civil and Environmental Engineering
                [6 ]Department of Chemical Engineering
                Article
                10.1039/C5EN00104H
                d98e689e-7e4a-42f0-ae66-905b84824fec
                © 2016
                History

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