Splitting of Surface-Immobilized Multicompartment Micelles into Clusters upon Charge Inversion.

We investigate a morphological transition of surface-immobilized triblock terpolymer micelles: the splitting into well-defined clusters of satellite micelles upon pH changes. The multicompartment micelles are formed in aqueous solution of ABC triblock terpolymers consisting of a hydrophobic polybutadiene block, a weak polyanionic poly(methacrylic acid) block, and a weak polycationic poly(2-(dimethylamino)ethyl methacrylate) block. They are subsequently immobilized on silicon wafer surfaces by dip-coating. The splitting process is triggered by a pH change to strongly basic pH, which goes along with a charge reversal of the micelles. We find that the aggregation number of the submicelles is well-defined and that larger micelles have a tendency to split into a larger number of submicelles. Furthermore, there is a clear preference for clusters consisting of doublets and triplets of submicelles. The morphology of surface-immobilized clusters can be "quenched" by returning to the original pH. Thus, such well-defined micellar clusters can be stabilized and are available as colloidal building blocks for the formation of hierarchical surface structures. We discuss the underlying physicochemical principles of the splitting process considering changes in charge and total free energy of the micelles upon pH change.

A paradigm change: efficient transfection of human leukemia cells by stimuli-responsive multicompartment micelles.

The controlled nonviral delivery of genetic material using cationic polymers into cells has been of interest during the past three decades, yet the ideal delivery agent featuring utmost transfection efficiency and low cytotoxicity still has to be developed. Here, we demonstrate that multicompartment micelles from stimuli-responsive triblock terpolymers, polybutadiene-block-poly(methacrylic acid)-block-poly(2-(dimethylamino)ethyl methacrylate) (BMAAD), are promising candidates. The structures exhibit a patchy shell, consisting of amphiphilic (interpolyelectrolyte complexes, MAA and D) and cationic patches (excess D), generating a surface reminiscent to those of certain viruses and capable of undergoing pH-dependent changes in charge stoichiometry. After polyplex formation with plasmid DNA, superior transfection efficiencies can be reached for both adherent cells and human leukemia cells. Compared to the gold standard PEI, remarkable improvements and a number of advantages were identified for this system, including increased cellular uptake and an improved release of the genetic material, accompanied by fast and efficient endosomal escape. Furthermore, high sedimentation rates might be beneficial regarding in vitro applications.

Cavitation engineered 3D sponge networks and their application in active surface construction.

The design of the 3D architecture surfaces with both space- and time-dependent functionality (cell attraction, pH-trigged self-cleaning, antiseptic/disinfection) is in the focus. The innovative story includes: sonochemical surface activation, formation of feedback surface component (pH-responsible micelles), proof of responsive activity (time resolved cell adhesion and bacteria deactivation) and space adhesion selectivity (surface patterning).

Interpolyelectrolyte complexes of dynamic multicompartment micelles.

Dynamic core-shell-shell-corona micelles are formed between two oppositely charged block copolymer systems. Preformed polybutadiene-block-poly(N-methyl-2-vinylpyridinium)-block-poly(methacrylic acid) (PB-P2VPq-PMAA) block terpolymer micelles with a soft polybutadiene core, an interpolyelectrolyte complex (IPEC) shell made out of poly(N-methyl-2-vinylpyridinium) and poly(methacrylic acid), and a negatively charged PMAA corona were mixed in different ratios at high pH with positively charged poly(N-methyl-2-vinylpyridinium)-block-poly(ethylene oxide) (P2VPq-PEO) diblock copolymers. Under these conditions, mixing results in the formation of a second IPEC shell onto the PB-P2VPq-PMAA precursor micelles, surrounded by a PEO corona. The resulting multicompartmented IPECs exhibit dynamic behavior, highlighted by a structural relaxation within a period of 10 days, investigated by dynamic light scattering (DLS), cryogenic transmission electron microscopy (cryo-TEM), and scanning force microscopy (SFM). After a short mixing time of 1 h, the IPECs exhibit a star-shaped structure, whereas after 10 days, spherical core-shell-shell-corona objects could be observed. To further increase complexity and versatility of the presented systems, the in situ formation of gold nanoparticles (Au NPs) in both the precursor micelles and the equilibrated IPEC was tested. For the PB-P2VPq-PMAA micelles, NP formation resulted in narrowly distributed Au NPs located within the PMAA shell, whereas for the core-shell-shell-corona IPEC, the Au NPs were confined within the IPEC shell and shielded from the outside through the PEO corona.