Drug governs the morphology of polyalkylated block copolymer aggregates

Multicompartment Micro- and Nanoparticles Using Supramolecular Assembly of Core-Shell Bottlebrush Polymers

Multicompartment particles have been produced to date by the self-assembly of linear multiblock polymers. Besides the large diversity of structures that can be obtained with this approach, these are highly sensitive to dilution and environmental factors. Here we show that using core-shell bottlebrush polymers with a hydrophobic polyester core as starting materials it is possible to create compartmentalized particles from the micrometer size down to the molecular scale. These polymers can be used as building blocks to create multicompartment particles and networks via a self-assembly process. The polymers can encapsulate active compounds and slowly degrade in water into polymeric micelles, making them promising materials for drug delivery applications.

Revealing the mechanisms of vesicle formation with multiple spectral methods

The investigation of the self-assembly of amphiphilic molecules and the formation of micelles/vesicles has attracted significant attention. However, in situ and real-time methods for such studies are rare. Here, a surface-sensitive second harmonic generation (SHG) technique was applied to study the formation of vesicles in solutions of an anti-cancer drug, doxorubicin (DOX), and a generally used surfactant (sodium bis (2-ethylhexyl) sulfosuccinate, AOT). With the aid of two-photon fluorescence (TPF), Rayleigh scattering and TEM, we revealed the structural evolution of the aggregated micelles/vesicles. It was found that AOT and DOX molecules rapidly aggregated and formed micelles in the solution. The residual DOX then acted as a "glue" that induced the aggregating/growing of the micelles and the transformation from aggregates to vesicles. The existence of lipid films, which was considered as the necessary intermediate state for vesicle formation, was excluded via the SHG observations, indicating that hollow shells may be directly transformed from solid aggregated micelles in the self-assembly formation of complex vesicles. The combined spectroscopic methods were also used to investigate the formation of vesicles from a commonly used lipid (i.e., 1,2-dioleoyl-sn-glycero-3-phospho-rac-(1-glycerol) sodium salt, DOPG) from its stacked bilayers. The swelling, curving and sealing of the DOPG bilayers for vesicle formation was monitored and clear dynamics were revealed. This work shows that the vesicle formation mechanism varies with the initial state of the surfactant/lipid molecules. It not only demonstrates the capability of the combined spectroscopic methods in investigating the aggregated systems but also provides new insight for understanding the formation of vesicles.

Real-time monitoring of oil-induced micellar transitions in viscoelastic surfactants by small-angle X-ray scattering

HYPOTHESIS

Viscoelastic surfactant solutions with entangled wormlike micelles (WLMs) display dramatic changes in rheological properties when exposed to hydrophobic substances. This change is key in the oil and gas industry and for drug delivery. The changes in viscoelastic properties are believed to be a result of changes in micellar shape due to the oil solubilization. The time dependence of the process has practical importance, yet its mechanism is unknown. We set out to map the structural changes with time using small-angle x-ray scattering (SAXS).

EXPERIMENT

A surfactant system with erucamidopropyl hydroxypropyl sulfobetaine as the active ingredient was homogenized with three concentrations of n-decane (70 mM, 140 mM, 280 mM) in 600 mM CaCl₂. The samples were monitored with time using SAXS. Model fits were used to determine the structures present in the sample at each time interval.

FINDINGS

The entangled WLMs disappeared while spherical decane-swollen micelles formed with time, explaining the sharp decrease in viscosity. It was shown that the time at which the spherical swollen micelles appeared depends on the concentration of n-decane. This insight allows control of the spherical micelle appearance time, which is important for the successful application of WLMs in sectors that require WLMs to persist for a set time before they transform.

Polymersome formation induced by encapsulation of water-insoluble molecules within ABC triblock terpolymers

We found a morphological transition from spherical micelles to polymersomes induced by encapsulation of hydrophobic guest molecules.

Unified Scaling of the Structure and Loading of Nanoparticles Formed by Diffusion-Limited Coalescence

The present study establishes the scaling laws describing the structure of spherical nanoparticles formed by diffusion-limited coalescence. We produced drug-loaded nanoparticles from a poly(ethylene glycol)-poly(d,l-lactic acid) diblock polymer (PEG- b-PLA) by the nanoprecipitation method using different types of micromixing chambers to explore multiple mixing regimes and characteristic times. We first show that the drug loading of the nanoparticles is not controlled by the mixing time but solely by the drug-to-polymer ratio (D:P) in the feed and the hydrophobicity of the drug scaled via the partition coefficient P. We then procure compelling evidence that particles formed via diffusion/coalescence exhibit a relative distribution of PEG blocks between the particle core and its shell that depends only on mixing conditions (not on D:P). Scaling laws of PEG relative distribution and chain surface density were derived in different mixing regimes and showed excellent agreement with experimental data. In particular, results made evident that PEG blocks entrapment in the core of the particles occurs in the slow-mixing regime and favors the overloading (above the thermodynamic limit) of the particles with hydrophilic drugs. The present analysis compiles effective guidelines for the scale up of nanoparticles structure and properties with mixing conditions, which should facilitate their future translation to medical and industrial settings.

Unveiling the Aggregation Behavior of Doxorubicin Hydrochloride in Aqueous Solution of 1-Octyl-3-methylimidazolium Chloride and the Effect of Bile Salt on These Aggregates: A Microscopic Study

In this article, we have unveiled the aggregation behavior of a potent chemotherapeutic drug, doxorubicin hydrochloride (Dox) in a well-known imidazolium based surface active ionic liquid (SAIL), 1-octyl-3-methylimidazolium chloride (C₈mimCl). The aggregates formed by Dox in C₈mimCl have been characterized using dynamic light scattering (DLS), fluorescence lifetime imaging microscopy (FLIM), high-resolution transmission electron microscopy (HR-TEM), analytical transmission electron microscopy (analytical TEM), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and Fourier-transform infrared spectroscopy (FTIR) measurements. It is found that Dox forms large spherical aggregates in the presence of C₈mimCl SAIL. We have also explored the driving force behind this aggregation behavior of Dox in C₈mimCl. Furthermore, it is observed that in the presence of a common bile salt, sodium cholate (NaCh), Dox/C₈mimCl spherical aggregates disrupt to form rodlike fibrillar aggregates. Therefore, formation of spherical aggregates and also its disruption into rodlike fibrillar aggregates have been performed, and this is expected to open a new scope for the design of a new generation smart drug delivery system where the drug itself aggregates to form the delivery system.

Self-Assembled Ligands Targeting TLR7: A Molecular Level Investigation

Toll-like receptors (TLRs) are pattern recognition transmembrane proteins that play an important role in innate immunity. In particular, TLR7 plays a role in detecting nucleic acids derived from viruses and bacteria. The huge number of pathologies in which TLR7 is involved has led to an increasing interest in developing new compounds targeting this protein. Several conjugation strategies were proposed for TLR7 agonists to increase the potency while maintaining a low toxicity. In this work, we focus the attention on two promising classes of TLR7 compounds derived from the same pharmacophore conjugated with phospholipid and polyethylene glycol (PEG). A multidisciplinary investigation has been carried out by molecular dynamics (MD), dynamic light scattering (DLS), electron paramagnetic resonance (EPR), and cytotoxicity assessment. DLS and MD indicated how only the phospholipid conjugation provides the compound abilities to self-assemble in an orderly fashion with a maximal pharmacophore exposition to the solvent. Further EPR and cytotoxicity experiments highlighted that phospholipid compounds organize in stable aggregates and well interact with TLR7, whereas PEG conjugation was characterized by poorly stable aggregates at the cells surface. The methodological framework proposed in this study may be used to investigate, at a molecular level, the interactions generally occurring between aggregated ligands, to be used as drugs, and protein receptors.