Responsive Giant Vesicles Filled with Poly(N-isopropylacrylamide) Sols or Gels

Abstract

We prepared giant unilamellar vesicles (GUVs) enclosing solutions or covalent gels of Poly(Nisopropylacrylamide) (PolyNipam). Concentrated suspensions of GUVs were prepared by applying an alternative field on a lipid film hydrated by a monomer solution containing N-isopropylacrylamide, crosslinker (N,N'-methylene-bis-acrylamide), initiator and sucrose. Vesicle inner medium was polymerised and cross-linked by U.V.irradiation of the suspension, yielding viscous vesicles enclosing a solution of linear PolyNipam chains (when no bisacrylamide was used) or elastic vesicles filled with a covalent PolyNipam gel. We show that gel-filled vesicles are responsive systems triggered by the temperature: they shrink, reducing by a factor eight their volume below the critical temperature (32°C in water, lower in presence of sucrose) and re-swell in a reversible and reproducible way upon decreasing temperature. In both cases, we show that the vesicle lipid membrane interacts with the internal polymer, resulting in an strong resistance of the vesicles to external mechanical stresses (enhanced tension of lysis).

Volume transition in composite poly(NIPAM)–giant unilamellar vesicles

“…In previous studies, 9,12 GUVs filled with a poly(NIPAM) gel were shown to also undergo a significant volume change around 32.5 C. The deswelling ratio a ¼ V/V 0 , where V 0 is the gel volume at room temperature and V the volume after collapse, was in good agreement with experiments on comparable macroscopic gels. 11 Furthermore, a was found to be independant of the vesicle size, revealing no effect of the confinement inside the vesicles.…”

“…3 row (b), we observe local demixing of the poly(NIPAM) chains for the GUVs prepared with F NIPAM ¼ 0.03 and 0.06, as has been already reported. 9,12,16 As expected, the internal medium of the vesicle flickers because of the concentration heterogeneities associated with the frustrated phase transition, but the radius of the vesicle remains constant. The behaviour observed in the case of the vesicle prepared with a volume fraction F NIPAM ¼ 0.07 is dramatically different.…”

“…The preparation of the gel and sol-filled giant unilamellar vesicles (gel-GUVs and sol-GUVs) follows closely the preparation method previously described. 9,10,12 All the steps leading to the gel (or sol) formation are performed under a controlled argon atmosphere inside a glove box. Irradiation with a UV-B irradiation lamp (Sunlight-Erythemal, Harvard Apparatus) is performed through a band pass filter (320 nm-400 nm) that prevents the fluorescent phospholipids becoming damaged.…”

“…1 In an effort to develop mechanico-mimetic systems of the whole cell, a number of biopolymers and other species have been added to the membrane [2][3][4][5] or encapsulated within the vesicle. [6][7][8][9] We have recently shown that GUVs filled with a gel of crosslinked poly(NIPAM) exhibit an elastic modulus comparable to that of living cells. 10 The elastic properties of these composite systems can be tuned by controlling the gel crosslinker content but also by exploiting the phase behaviour of poly(NIPAM).…”

Multicompartmentalized polymeric systems: towards biomimetic cellular structure and function

“…The most developed approach using polymers, especially by Viallat and coworkers, consists in encapsulating a poly(N-isopropylacrylamide) (PNIPAAm)-based solution in liposomes, which will in situ polymerize upon photoactivation into covalently crosslinked gels. [48][49][50][51][52][53][54] Jesorka, Orwar and coworkers reported other important contributions to the field using viscous solutions of non-crosslinked PNIPAAm that were microinjected in liposomes. Reversible sol-gel transitions were observed by heating above LCST, 55 and by doing so in the presence of poly-(acrylic acid) PAA, poly(sodium 4-styrene sulfonate) PSS and 2 000 000 g mol À1 dextran.…”