Multicompartment Micelles

Comparison between block copolmer micelle and multicompartment micelle
© A.Gröschel

Multicompartment micelles are block copolymers micelles with a compartmentalized core, i.e. the core is not homogeneous but divided into nanocompartments with different chemical environments. Compartmentalization is an essential requirement for life (e.g. cells and organelles), and synthetic mimics promise the separate storage of incompatible materials with nanometre distance (e.g. catalysts). Polymer blocks are intrinsically incompatible and therefore ideal candidates to form MCMs. To create MCMs, three domains are needed: 1) one soluble block that forms a stabilizing corona (green in schematics but not visible in TEM); 2) two insoluble blocks that form the core compartments. Naturally, ABC triblock terpolymers (linear or µ-arm stars) consisting of three covalently linked polymer blocks are the best choice for this job.

  • Hierarchical self-assembly process
    © A.Gröschel

    Hierarchical Self-Assembly

    We developed a hierarchical self-assembly strategy for ABC triblock terpolymers resulting in high control over size, shape, and inner structure of MCMs. To be able to control the structure will allow to identify structure-property relations in drug delivery. The process is general and applicable to almost any polymer chemistry. The main requirements is a polarity sequence that needs to be programmed synthetically into the polymer chain, e.g. A = nonpolar, B = most non-polar, and C = polar. Using now solvents with increasing polarity, the polymer blocks will collapse sequentially starting with the B middle block thereby forming precursor micelles with a corona of A and C. in the second step, these precursor micelles then aggregate to form the final MCM. The ratio of A to C thereby controls the aggregation number that can be surprisingly uniform. For instance, the evaluation of the sample shown above gave 96 % of MCMs with trigonal planar arrangement of the B compartments, while the remaining MCMs consisted either of four or two B compartments. Choosing different solvent sequences allowed to form MCMs from a variety of ABC triblock terpolymers with pH- and thermoresponsive dis-/assembly properties, stealthy corona, fluorescent core domains and catalytic core domains.

  • MCMs by combining micelle shape and inner structure
    © A.Gröschel

    Multicompartment Library

    We developed a set of simple design rules that allow to synthetically program the micelle shape and inner morphology of the final structure into the polymer chains. For instance, the length of the C corona will determine the overall shape of the MCM from sphere to cylinder, to disc to vesicle (or polymersome). The ratio between the core blocks A and B (more precisely the volume fractions φA=1-φB) determine the morphology inside the core with similarities to bulk morphologies. Together with the proper sequence of polarities along the chain and the matching solvent polarity, these parameters allow the systematic screening of a combinatorial table containing (so far) 13 distinct multicompartment nanostructures. These include: spheres-on-spheres, spheres-on-cylinders, spheres-on-discs, spheres-on-polymersome, double helix-on-cylinders, striped discs, striped polymersomes, perforated discs (likely the gyroidal phase), perforated polymersomes, as well as core shell spheres, cylinders, discs, and polymersomes.
    These materials are mostly studied for their potential as multifunctional delivery vehicles in nanomedicine. However, the nanoscale compartmentalization could be beneficial for templating inorganic nanostructures as well.