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Issue 20, 2017
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Dynamic studies of the interaction of a pH responsive, amphiphilic polymer with a DOPC lipid membrane

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Abstract

Deeper understanding of the molecular interactions between polymeric materials and the lipid membrane is important across a range of applications from permeation for drug delivery to encapsulation for immuno-evasion. Using highly fluidic microcavity supported lipid bilayers, we studied the interactions between amphiphilic polymer PP50 and a DOPC lipid bilayer. As the PP50 polymer is pH responsive the studies were carried out at pH 6.5, 7.05 and 7.5, corresponding to fully, partly protonated (pH = pKa = 7.05) and fully ionized states of the polymer, respectively. Fluorescence correlation spectroscopy (FCS) using both labelled lipid and polymer revealed the PP50 associates with the bilayer interface across all pHs where its diffusion along the interface is impeded. Both FCS and electrochemical impedance spectroscopy (EIS) data indicate that the PP50 does not penetrate fully into the bilayer core but rather forms a layer at the bilayer aqueous interface reflected in increased resistance and decreased capacitance of the bilayer on PP50 binding. The extent of these effects and the dynamics of binding are influenced by pH, increasing with decreasing pH. These experimental trends concurred with coarse grained Monte Carlo simulations of polymer–bilayer interactions wherein a model hydrophilic polymer backbone grafted with side chains of varying hydrophobicity, to mimic the effect of varying pH, was simulated based on the bond fluctuation model with explicit solvent. Simulation results showed that with increasing hydrophobicity, the polymer penetrated deeper into the contacting bilayer leaflet of the membrane suppressing, consistent with EIS data, solvent permeation and that a full insertion of the polymer into the bilayer core is not necessary for suppression of permeability.

Graphical abstract: Dynamic studies of the interaction of a pH responsive, amphiphilic polymer with a DOPC lipid membrane

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Publication details

The article was received on 23 Nov 2016, accepted on 27 Feb 2017 and first published on 28 Feb 2017


Article type: Paper
DOI: 10.1039/C6SM02645A
Citation: Soft Matter, 2017,13, 3690-3700
  • Open access: Creative Commons BY-NC license
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    Dynamic studies of the interaction of a pH responsive, amphiphilic polymer with a DOPC lipid membrane

    S. Ramadurai, M. Werner, N. K. H. Slater, A. Martin, V. A. Baulin and T. E. Keyes, Soft Matter, 2017, 13, 3690
    DOI: 10.1039/C6SM02645A

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