Polymersomes in polymersomes: multiple loading and permeability control.

Polymer vesicles polymersomes are vesicles obtained from the self-assembly of amphiphilic block copolymers in aqueous solution as a result of free-energy minimization. Their potential use as drug delivery systems, sensors, and/or nanoreactors has recently attracted a great deal of interest. Polymersomes exhibit larger mechanical stability and lower permeability than liposomes, their structural analogues that often suffer from premature drug leakage. To circumvent this limitation, Zasadzinski and co-workers developed liposomes in liposomes structures, also referred as “vesosomes”. With such a compartmentalized structure, a molecule encapsulated in the inner liposome, would have to permeate through two successive membranes, instead of a single one before leaking into the outside environment. This double-membrane effect was demonstrated by observing the serum half-life of ciprofloxacin drug increasing from 10 min in single liposomes to 6 h in vesosomes. Other reports evidenced the biomedical impact of such vesosomes for transcutaneous, and oral administration, important areas in drug delivery and cancer therapy. More complex or compartmentalized structures in general, have started to appear because they enable an unprecedented level of control, in particular in the fields of drug delivery and confined reactors. However, it is still very challenging to encapsulate multiple distinct components in a single compartment and control their stability and release properties. Such vesosome structures based on polymers that can be termed “polymersomes in polymersomes” have recently been reported. One of the most recent approaches consisted in forming the larger polymersomes by solvent-displacement method (or nanoprecipitation) with a suspension of smaller polymersomes previously formed by film rehydration as a water phase. The drawback of this technique lies essentially in the poor encapsulation yield during nanoprecipitation. To overcome this limitation, other options, such as emulsions or double-emulsion techniques, have been investigated. The first team taking up this challenge used two successive emulsions. Even if very original, such a process is not the most easy to use and may suffer from a lack of reproducibility and homogeneity. Weitz and co-workers formed another type of complex polymersomes, aggregates of polymersomes, or multicompartment vesicles using microfluidics. Such an approach allows a high level of control and reproducibility that has recently been extended further to fully multicompartmentalized polymersomes. Herein, we demonstrate the generation of polymer vesosomes, that is, polymersomes in polymersomes, with an original, facile, versatile, reproducible, and low-time and lowproduct-consuming technique. Our method allows multiple compartment encapsulation and the formation of systems that have controlled permeability, as they present a significant decrease in the release rate of the anticancer drug doxorubicin (DOX) encapsulated in the inner polymersomes. The inner polymersomes are formed by nanoprecipitation of poly(trimethylene carbonate)-b-poly(l-glutamic acid) (PTMC-b-PGA) synthesized following a reported method. This suspension is then loaded in larger polymersomes of poly(butadiene)-b-poly(ethylene oxide) (PB-bPEO) by emulsion–centrifugation with a quantitative loading efficiency. The procedure for forming giant PB-bPEO polymersomes was inspired from Li and co-workers. Briefly (Scheme 1, Part 1), a small fraction of an inverted emulsion of aqueous solution (in this case a nanosize polymersome suspension of PTMC-b-PGA with 380 mOsm sucrose) in toluene is poured over an interface of toluene and an aqueous solution of 380 mOsm glucose. (Scheme 1, Part 2) The PB-b-PEO diblock copolymer is dissolved in toluene at 3 mgmL 1 and stabilizes the emulsion droplets (forming the inner leaflet of the final bilayer) of this interface. (Scheme 1, Part 3) In a final step, both centrifugal force and denser sucrose (as compared to glucose) inside the droplets, force these droplets to cross the interface and to be enveloped by a second leaflet of amphiphilic PB-b-PEO block copolymer, resulting in the final giant polymersomes or polymer vesosomes (if a nanosize polymersome suspension is used as aqueous inner solution as reported herein). The control provided by this process enabled imaging the compartmentalized polymersome structure by spinning disk confocal microscopy. In Figure 1 the Alexa Fluor 568 (red) labeled inner polymersomes are visibly encapsulated in a green giant polymersome (with 10 wt% of anAlexa Fluor 488 conjugated polybutadiene). The red inner polymersomes in [*] M. Marguet, L. Edembe, Prof. S. Lecommandoux Universit de Bordeaux/IPB, ENSCBP 16 avenue Pey Berland, 33607 Pessac Cedex (France) and CNRS, Laboratoire de Chimie des Polym res Organiques (UMR5629) Pessac (France) E-mail: [email protected] Homepage: http://www.lcpo.fr