Controlling the Internal Structure of Giant Unilamellar Vesicles by Means of Reversible Temperature Dependent Sol−Gel Transition of Internalized Poly(N-isopropyl acrylamide)

Abstract

In this work, we present preparation and basic applications of lipid-bilayer-enclosed picoliter volumes (microcontainers) of solutions of poly(N-isopropylacrylamide) (PNIPAAm). Giant unilamellar vesicles (GUVs) were prepared from phospholipids using a standard swelling procedure and subsequently surface immobilized. Clear, slightly viscous solutions of PNIPAAm of varying concentration in aqueous buffer were directly pressure-microinjected into the GUVs, using a submicrometer-sized, pointed capillary. The GUV was subjected to changing temperature over a 21-40 degrees C range. The typical phase transition of the polymeric material upon heating and cooling across the lower critical solution temperature was followed using optical microscopy and shown to be reversible over multiple sequential heating/cooling cycles without compromising the integrity of the GUV membrane. Fluorescent, carboxylic acid modified 200 nm latex beads, co-injected with the PNIPAAm solution, were temperature-reversibly immobilized during the phase transition, practically freezing the Brownian motion of the entrapped particles in the volume. Furthermore, a co-injected water soluble fluorescent polysaccharide-dye conjugate was shown not to migrate from the aqueous phase into the hydrophobic polymer part upon heating, whereas the fluorescent beads were completely but reversibly immobilized in the hydrophobic domains of dense polymer agglomerates. The system reported here provides a feasible method for the reversible stabilization and solidification of GUV interior volumes, e.g., as a micrometer-sized model system for controlled drug release.

Dynamic microcompartmentation in synthetic cells

“…Particularly notable is work in which pH-and ion-sensitive polymeric hydrogels coated with lipid bilayers were used to mimic secretory granules; these structures released drug molecules upon electroporation of the membrane (19). Thermoresponsive hydrogels have been microinjected into preformed GVs and GV networks, where they display characteristic sol-gel transitions (20). These hydrogel experiments were largely aimed at drug delivery but are also interesting in the present context in that their transitions are reversible, and the gel matrix mimics certain aspects of intracellular organization such as impeded diffusion.…”

Preparation of PVP hydrogel nanoparticles using lecithin vesicles

“…Larger nanogels (about 450 nm) are obtained from encapsulation of 20% dextran hydroyethylmethacrylate solution ( -Mn= 19000) inside vesicles obtained by phospholipids film hydration, followed by extru- sion. 37 Poly(ethylenedioxythiophene)/poly(styrenesulfonate) 13 and poly(N-isopropylacrylamide) 12,16 microgels, in conjunction with lipid bilayers, are obtained by injecting a polymer solution inside GUVs, followed by freeze-thaw cycles and electroporation. The vesicle diameters, in these latter cases, vary from 5 to 100 µm.…”

“…9 Alternatively, nanogels can be prepared by inclusion in reverse micelles of pre-formed polymers, followed by crosslinking. 10 Vesicles also can be used to obtain hydrogels nanoparticles, by monomer encapsulation followed by polymerization 11 or gelation of encapsulated polymers, generally induced by sol-gel temperature transitions 12 or ionic crosslinking, 13 typically without removal of the lipid bilayer. 14 These gel-like vesicles work as cell models, since they have elastic modulus comparable to that of cell cytoplasm 14 and are considered artificial cytoskeletons.…”

“…16 This temperature induced sol-gel transition within the vesicle mimics cell stiffening. 12 Hydrogel-liposome assemblies (lipobeads) can also be used as drug delivery systems. 17 The lipid bilayer is often left intact and the encapsulated polymer is not crosslinking.…”

Chemical Analysis in Nanoscale Surfactant Networks

“…The internal and external solution composition as well as different lipid compositions (which can also include membrane proteins) can be used to tailor a reactor. Furthermore, polymers can be included to create crowded environments (32,33). Network topology can be controlled, too, and it is possible to use either static-or dynamic-shell networks (where the network geometry is changed during the course of a reaction).…”