Tunable Adsorption of Soft Colloids on Model Biomembranes

A simple procedure is developed to probe <i>in situ</i> the association between lipid bilayers and colloidal particles. Here, a one-step method is applied to generate giant unilamellar 1,2-dioleoyl-<i>sn</i>-glycero-3-phosphocholine (DOPC) vesicles (GUVs) by application of an alternating electric field directly in the presence of thermo­responsive poly(<i>N</i>-isopropyl­acrylamide) (PNIPAM) microgels. We demonstrate that the soft PNIPAM microgel particles act as switchable stabilizers for lipid membranes. The change of the particle conformation from the swollen to the collapsed state enables the reversible control of the microgel adsorption as a function of temperature. At 20 °C, the swollen and hydrophilic soft microgel particles adsorb evenly and densely pack in 2D hexagonal arrays at the DOPC GUV surfaces. In contrast, at 40 °C, that is, above the volume phase transition temperature (<i>T</i>_VPT = 32 °C) of the PNIPAM microgels, the collapsed and more hydrophobic particles partially desorb and self-organize into domains at the GUV/GUV interfaces. This study shows that thermo­responsive PNIPAM microgels can be used to increase and control the stability of lipid vesicles where the softness and deformability of these types of particles play a major role. The observed self-assembly, where the organization and position of the particles on the GUV surface can be controlled “on demand”, opens new routes for the design of nanostructured materials

Tunable Adsorption of Soft Colloids on Model Biomembranes

A simple procedure is developed to probe <i>in situ</i> the association between lipid bilayers and colloidal particles. Here, a one-step method is applied to generate giant unilamellar 1,2-dioleoyl-<i>sn</i>-glycero-3-phosphocholine (DOPC) vesicles (GUVs) by application of an alternating electric field directly in the presence of thermo­responsive poly(<i>N</i>-isopropyl­acrylamide) (PNIPAM) microgels. We demonstrate that the soft PNIPAM microgel particles act as switchable stabilizers for lipid membranes. The change of the particle conformation from the swollen to the collapsed state enables the reversible control of the microgel adsorption as a function of temperature. At 20 °C, the swollen and hydrophilic soft microgel particles adsorb evenly and densely pack in 2D hexagonal arrays at the DOPC GUV surfaces. In contrast, at 40 °C, that is, above the volume phase transition temperature (<i>T</i>_VPT = 32 °C) of the PNIPAM microgels, the collapsed and more hydrophobic particles partially desorb and self-organize into domains at the GUV/GUV interfaces. This study shows that thermo­responsive PNIPAM microgels can be used to increase and control the stability of lipid vesicles where the softness and deformability of these types of particles play a major role. The observed self-assembly, where the organization and position of the particles on the GUV surface can be controlled “on demand”, opens new routes for the design of nanostructured materials

Properties of the donor formulations and the gels comprised between the membranes, followed by resulting steady state flux (J_ss).

<p>Properties of the donor formulations and the gels comprised between the membranes, followed by resulting steady state flux (J_ss).</p

Representative FCS measurements on a mucin solution and a highly concentrated mucin film.

<p>Autocorrelation functions for measurements in (A) 0.1 wt% (B) 1.0 wt% (C) 10.0 wt% mucin solution and (D) concentrated mucin film with water activity of 0.97 are shown, together with fits with a model for pure diffusion.</p

Fluorescence recovery after photobleaching of fluorescein in mucin gels.

<p>(A) Representative images before and after bleaching for mucin gels with water activities as indicated to the left and (B) representative normalized recovery curves obtained for gels with water activity of 0.97 (blue), 0.94 (green), 0.85 (red), 0.81 (cyan) and 0.12 (black) are shown. Scale bars in (A) are 10 μm. </p

Penetration of metronidazole through polymer gels with different water activities.

<p>Accumulated amount of metronidazole penetrated through combined silicone and Millipore GV membranes alone (A) separated by PEG gels (B) or mucin gels (C) is shown vs water activity. Water activity of donor formulations, which also regulated the water activity of the gels enclosed between the membranes, was 0.996 (blue open triangles), 0.981 (green open squares), 0.930 (yellow open circles) and 0.867 (red open diamonds). Steady state flux, calculated over 6–24 h from data provided in Fig 1A to CC, versus water activity for membranes only (green filled triangles), PEG gels (blue filled circles) and mucin gels (red filled squares) are shown in D. </p

Diffusion in concentrated mucin gels.

<p>Diffusion of metronidazole through mucin gels shown in a lin-lin scaling and a log-lin scaling (insert). The diffusion was measured by penetration (blue diamonds) experiments and diffusion coefficient of fluorescein in mucin gels measured by FRAP (red triangles) and FCS (green square) experiments. The triangles and inverted triangles shows the fast and slow diffusion process, respectively, measured in FRAP experiment. Below water activity of 0.94, the diffusion of sodium fluorescein is not measurable under the current experimental conditions and the markers (open symbols) are only added to visualize the qualitative trend.</p

Approximate diffusion coeficients of flourescein in mucin gels obtained by FCS measurements.

<p>Approximate diffusion coeficients of flourescein in mucin gels obtained by FCS measurements.</p