A plethora of stimuli-responsive micellar aggregates with a compartmentalized shell can be formed in aqueous solution from ABC triblock terpolymers with tunable hydrophilicity. Polybutadiene-blockpoly(tert-butyl methacrylate)-block-poly(2-(dimethylamino)ethyl methacrylate) (PB-b-PtBMA-b-PDMAEMA) and, after modifications by hydrolysis to poly(methacrylic acid) (PMAA) or quaternization to PDMAEMAq, PB-b-PMAA-b-PDMAEMAq terpolymers self-assemble in water, depending on pH and temperature. We demonstrate control over micellar shape, size, and charge via three different preparation pathways. Even more, the micelles are capable of undergoing rearrangements in both the shell and the corona in response to external stimuli like pH or salinity. In that way, different structures such as multicompartment, core-shell-corona or flower-like micelles were identified and characterized via cryogenic transmission electron microscopy (cryo-TEM) and dynamic light scattering (DLS). The presence of two oppositely charged polyelectrolyte blocks within the structures leads to the formation of intramicellar interpolyelectrolyte complexes (im-IPECs) in the shell of the particles. Surprisingly, the im-IPEC formed between PMAA and PDMAEMAq can be redissolved by changes in pH, even in the absence of additional salt.
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.
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).
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.
We present a new nanoporous multilayer system with a reversible pH-triggered swelling transition. Using the layer-by-layer approach, pH-responsive block copolymer micelles with a hydrophobic core, a weak polyanion shell and a strong polycation corona formed from an ABC triblock terpolymer are included within multilayer films. The approach of complexing the strong polycationic corona with a strong polyanion leads to the creation of novel double-end-tethered polyelectrolyte brush structures confined between the hydrophobic micellar cores and the interpolyelectrolyte complexes. The swelling degree, morphology as well as the mechanical properties of the coatings are reversibly tunable by the solution pH due to the ionization-induced swelling of the pH-sensitive polyelectrolyte-brush-like shell of the incorporated micelles resulting in large-scale volumetric changes of the film. Moreover, controlling the internal film architecture by the number of deposition steps allows tuning the properties of the porous multilayers such as the density of incorporated micelles, the porosity, and the equilibrium swelling degree to more than 1200%.
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