Dendrimicelles with pH-controlled aggregation number of core-dendrimers and stability

Synthesis of β-Cyclodextrin-Decorated Dendritic Compounds Based on EDTA Core: A New Class of PAMAM Dendrimer Analogs

In this work, two dendritic molecules containing an ethylenediaminetetraacetic acid (EDTA) core decorated with two and four β-cyclodextrin (βCD) units were synthesized and fully characterized. Copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) click chemistry under microwave irradiation was used to obtain the target compounds with yields up to 99%. The classical ethylenediamine (EDA) core present in PAMAM dendrimers was replaced by an EDTA core, obtaining platforms that increase the water solubility at least 80 times compared with native βCD. The synthetic methodology presented here represents a convenient alternative for the rapid and efficient construction of PAMAM analogs. These molecules are envisaged for future applications as drug carriers.

Controlling Trapping, Release, and Exchange Dynamics of Micellar Core Components

Whereas the formation and overall stability of hierarchically organized self-assembled supramolecular structures have been extensively investigated, the mechanistic aspects of subcomponent dynamics are often poorly understood or controlled. Here we show that the dynamics of polyamidoamine (PAMAM) dendrimer based micelles can be manipulated by changes in dendrimer generation, pH, and stoichiometry, as proven by NMR and FRET. For this, dendrimers were functionalized with either fluorescein (donor) or rhodamine (acceptor) and encapsulated into separate micelles. Upon mixing, exchange of dendrimers is revealed by an increase in FRET. While dendrimicelles based on dendrimer generations 4 and 5 show a clear increase in FRET in time, revealing the dynamic exchange of dendrimers between micellar cores, generation 6 based micelles appear to be kinetically trapped systems. Interestingly, generation 6 based dendrimicelles prepared at a pH of 7.8 rather than 7.0 do show exchange dynamics, which can be attributed to about 25% less charge of the dendrimer, corresponding to the charge of a virtual generation 5.5 dendrimer at neutral pH. Changing the pH of dendrimicelle solutions prepared at a pH of 7.8 to 7.0 shows the activated release of dendrimers. High-resolution NMR spectra of the micellar core are obtained from a 1.2 GHz spectrometer with sub-micromolar sensitivity, with DOSY discriminating released dendrimers from dendrimers still present in the micellar core. This study shows that dendrimer generation, charge density, and stoichiometry are important mechanistic factors for controlling the dynamics of complex coacervate core micelles. This knowledge can be used to tune micelles between kinetically trapped and dynamic systems, with tuning of exchange and/or release speeds, to be tailored for applications in, e.g., material science, sensors, or drug delivery.

Hierarchical polyion complex vesicles from PAMAM dendrimers

Hierarchical dendrimer-based polyion complex (PIC) vesicles with multiple compartments have attracted considerable attention as functional delivery vehicles and nano-carriers. Formation of these vesicles relies on the electrostatic assembly of asymmetric polyelectrolytes, namely branched dendrimers with linear polyion-neutral diblock copolymers. However, successful incorporation of dendrimers in vesicle lamellae is challenging due to the compact structure of dendrimers, and therefore, vesicles reported so far are prepared mainly with low generation dendrimers which lack the cavity required for carrier functions. Here, we present a new assembly combination of amine-terminated dendrimer polyamidoamine (PAMAM) with polyion-neutral diblock copolymer poly (styrene sulphonate-b-ethylene oxide) (PSS-b-PEO). The strong charge interaction between the building blocks leads to stable and well-defined PIC vesicles that can tolerate not only different PSS block lengths but, more importantly, also different dendrimer generations from 2 to 7. As a consequence, high generation dendrimers with a cavity can be packed in the vesicle wall, and one obtains hierarchical PIC vesicles with multiple compartments, namely the dendrimer cavity for loading small hydrophobic cargo, and the vesicle lumen for encapsulating hydrophilic macromolecules. Our study demonstrates that combining proper building blocks enables to manipulate the charge interactions, which is essential for controlling the dendrimer packing and the formation of PIC vesicles. These findings should be helpful for understanding the assembly of asymmetric (linear / branched) polyelectrolyte complexes, as well as for designing new hierarchical PIC vesicles for controlled delivery of multiple active substances.

Self-Assembly of a Triazolylferrocenyl Dendrimer in Water Yields Nontraditional Intrinsic Green Fluorescent Vesosomes for Nanotheranostic Applications

The promising field of nanomedicine stimulates a continuous search for multifunctional nanotheranostic systems for imaging and drug delivery. Herein, we demonstrate that application of supramolecular chemistry's concepts in dendritic assemblies can enable the formation of advanced dendrimer-based nanotheranostic devices. A dendrimer bearing 81 triazolylferrocenyl terminal groups adopts a more compact shell-like structure in polar solvents with the ferrocenyl peripheral groups backfolding toward the hydrophobic dendrimer interior, while exposing the more polar triazole moieties as the dendritic shell. Akin to lipids, the compact dendritic structure self-assembles into uniform nanovesicles that in turn self-assemble into larger vesosomes in water. The vesosomes emit green nontraditional intrinsic fluorescence (NTIL), which is an emerging property as there are no classical fluorophores in the dendritic macromolecular structure. This work confirms the hypothesis that the NTIL emission is greatly enhanced by rigidification of the supramolecular assemblies containing heteroatomic subluminophores (HASLs) and by the presence of electron rich functional groups on the periphery of dendrimers. This work is the first one detecting NTIL in ferrocenyl-terminated dendrimers. Moreover, the vesosomes are stable in biological medium, are uptaken by cells, and show cytotoxic activity against cancer cells. Accordingly, the self-organization of these dendrimers into tertiary structures promotes the emergence of new properties enabling the same component, in this case, ferrocenyl group, to function as both antitumoral drug and fluorophore.

Dendroids, Discrete Covalently Cross-Linked Dendrimer Superstructures

A versatile method is presented to form dendrimer superstructures by exploiting coacervate-core micelles as a template to confine and organize the hyperbranched macromolecules. First, complex coacervate-core micelles are formed from negative-neutral block copolymers and positively charged polyamidoamine dendrimers. The dendrimers inside the micellar core are then covalently cross-linked with each other upon addition of glutaraldehyde. After removal of the block copolymer from the assembly by increasing the salt concentration, consecutively, the formed Schiff bases cross-linking the dendrimers are reduced to amines, followed by a final dialysis step. This leads to well-defined covalently cross-linked nanostructures, coined dendroids, with a size of around 30 nm in diameter and a molecular weight of approximately 2.5 MDa. By incorporating dendrimer-encapsulated gold nanoparticles (AuDENs) into the micelle template strategy, the aggregation number of dendrimers inside the dendroids is determined by counting the nanoparticles in TEM micrographs. Furthermore, TEM performed at different tilt angles and AFM analysis corroborate formation of stable, covalently linked three-dimensional structures. Reconstruction of the TEM tilt series results in a tomogram further illustrating the 3D distribution of the gold nanoparticles, and hence the individual dendrimers, in the nanostructure. These dendroids appear to have a hard, poorly compressible core and a relatively soft outside. The versatility of the hierarchical building up of the supermolecules is illustrated by the controlled and synchronous incorporation of empty dendrimers and AuDENs into a single hybrid dendroid structure. The presented strategy allows for the preparation of a variety of classes of supermolecules, depending on the type of micellar-core macromolecule, e.g., dendrimer, cross-linker, and nanoparticles, used. Considering the broad interest in dendrimers as well as micelles in a plethora of research areas, e.g., (targeted) drug delivery, biomedical imaging, theragnostics, and catalysis, there is a great potential for dendroids and related classes of covalently linked macromolecules, viz., supermolecules.

Molecular Modelling Guided Modulation of Molecular Shape and Charge for Design of Smart Self-Assembled Polymeric Drug Transporters

Nanomedicine employs molecular materials for prevention and treatment of disease. Recently, smart nanoparticle (NP)-based drug delivery systems were developed for the advanced transport of drug molecules. Rationally engineered organic and inorganic NP platforms hold the promise of improving drug targeting, solubility, prolonged circulation, and tissue penetration. However, despite great progress in the synthesis of NP building blocks, more interdisciplinary research is needed to understand their self-assembly and optimize their performance as smart nanocarriers. Multi-scale modeling and simulations provide a valuable ally to experiment by mapping the potential energy landscape of self-assembly, translocation, and delivery of smart drug-loaded NPs. Here, we highlight key recent advances to illustrate the concepts, methods, and applications of smart polymer-based NP drug delivery. We summarize the key design principles emerging for advanced multifunctional polymer topologies, illustrating how the unusual architecture and chemistry of dendritic polymers, self-assembling polyelectrolytes and cyclic polymers can provide exceptional drug delivery platforms. We provide a roadmap outlining the opportunities and challenges for the effective use of predictive multiscale molecular modeling techniques to accelerate the development of smart polymer-based drug delivery systems.

Dendritic Macromolecular Architectures: Dendrimer-Based Polyion Complex Micelles

Polymeric micelles are nanoassemblies that are formed by spontaneous arrangement of amphiphilic block copolymers in aqueous solutions at critical micelle concentration (CMC). They represent an effective system for drug delivery of, for instance, poorly water-soluble anticancer drugs. Then, the development of polyion complexes (PICs) were emphasized. The morphology of these complexes depends on the topology of the polyelectrolytes used and the way they are assembled. For instance, ionic-hydrophilic block copolymers have been used for the preparation of PIC micelles. The main limitation in the use of PIC micelles is their potential instability during the self-assembly/disassembly processes, influenced by several parameters, such as polyelectrolyte concentration, deionization associated with pH, ionic strength due to salt medium effects, mixing ratio, and PIC particle cross-linking. To overcome these issues, the preparation of stable PIC micelles by increasing the rigidity of their dendritic architecture by the introduction of dendrimers and controlling their number within micelle scaffold was highlighted. In this original concise Review, we will describe the preparation, molecular characteristics, and pharmacological profile of these stable nanoassemblies.