Small-angle X-ray scattering and light scattering study of hybrid nanoparticles composed of thermoresponsive triblock copolymer F127 and thermoresponsive statistical polyoxazolines with hydrophobic moieties

Pair Potential between Poloxamer 407 Micelles in 14 wt % Aqueous Solution Clarifying the Sol-Gel-Sol Transition by Temperature Rise

Poloxamer 407 (P407) is used as a safety-guaranteed, invaluable pharmaceutical nanocarrier. The aqueous solution of P407 exhibits sol-to-gel and gel-to-sol transitions, specifically during a temperature rise. Here, we develop a method to determine the pair potential between colloidal particles based primarily on experimental small-angle scattering data. Using this approach, the pair potential between the P407 micelles in the sol-gel-sol transition state is revealed without prelimiting any type of interaction forces. The results indicate that the increase in the attractive interaction contributes to enhancing the volume fraction, which is the decisive parameter for the gelation in terms of the Alder transition theory, i.e., the fluid-to-crystal phase transition of the hard-sphere model in the micelle system. This study demonstrates that one of the key mechanisms of the gel-to-sol transition upon heating is the enhancement of the structural fluctuation due to widening of the potential well in the intermicellar pair potential.

Reversible multilayered vesicle-like structures with fluid hydrophobic and interpolyelectrolyte layers

Hydrophobic blocks of amphiphilic block copolymers often form glassy micellar cores at room temperature with a rigid structure that limits their applications as nanocapsules for targeted delivery. Nevertheless, we prepared and analyzed core/shell micelles with a soft core, formed by a self-assembled block copolymer consisting of a hydrophobic block and a polycation block, poly(lauryl acrylate)-block-poly(trimethyl-aminoethyl acrylate) (PLA-QPDMAEA), in aqueous solution. By light and small-angle neutron scattering, by transmission electron microscopy and by fluorescence spectroscopy, we showed that these core/shell micelles are spherical and cylindrical with a fluid-like PLA core and a positively charged outer shell and that they can encapsulate and release hydrophobic solutes. Moreover, after mixing these PLA-QPDMAEA core/shell micelles with another diblock copolymer, consisting of a hydrophilic block and a polyanion block, namely poly(ethylene oxide)-block-poly(methacrylic acid) (PEO-PMAA), we observed the formation of novel vesicle-like multicompartment structures containing both soft hydrophobic and interpolyelectrolyte (IPEC) layers. By combining small-angle neutron scattering with self-consistent field modeling, we confirmed the formation of these complex vesicle-like structures with a swollen PEO core, an IPEC inner layer, a PLA soft layer, an IPEC outer layer and a loose PEO corona. Thus, these multicompartment micelles with fluid and IPEC layers and a hydrophilic corona may be used as nanocapsules with several tunable properties, including the ability to control the thickness of each layer, the charge of the IPEC layers and the stability of the micelles, to deliver both hydrophobic and multivalent solutes.

Unveiling the Interaction Potential Surface between Drug-Entrapped Polymeric Micelles Clarifying the High Drug Nanocarrier Efficiency

Polymeric micelles are invaluable media as drug nanocarriers. Although knowledge of an interaction between the micelles is a key to understanding the mechanisms and developing the superior functions, the interaction potential surface between drug-incorporated polymeric micelles has not yet been quantitatively evaluated due to the extremely complex structure. Here, the interaction potential surface between drug-entrapped polymeric micelles was unveiled by combining a small-angle scattering experiment and a model-potential-free liquid-state theory. Triblock copolymer composed of poly(ethylene oxide) and poly(propylene oxide) was investigated over a wide concentration range (0.5-10.0 wt %). Effects of the entrapment of a water-insoluble hydrophobic drug, cyclosporin A, on the interaction were explored by comparing the interactions with and without the drug. The results directly clarified the high drug carrier efficiency in terms of the interaction between the micelles. In addition, an investigation based on density functional theory provided a deeper insight into the monomer contribution to the extremely stable dispersion of the nanocarrier.

Supramolecular structures and self-association processes in polymer systems

Self-organization in a polymer system appears when a balance is achieved between long-range repulsive and short-range attractive forces between the chemically different building blocks. Block copolymers forming supramolecular assemblies in aqueous media represent materials which are extremely useful for the construction of drug delivery systems especially for cancer applications. Such formulations suppress unwanted physicochemical properties of the encapsulated drugs, modify biodistribution of the drugs towards targeted delivery into tissue of interest and allow triggered release of the active cargo. In this review, we focus on general principles of polymer selforganization in solution, phase separation in polymer systems (driven by external stimuli, especially by changes in temperature, pH, solvent change and light) and on effects of copolymer architecture on the self-assembly process.

Thermoresponsive Polymers for Nuclear Medicine: Which Polymer Is the Best?

Thermoresponsive polymers showing cloud point temperatures (CPT) in aqueous solutions are very promising for the construction of various systems in biomedical field. In many of these applications these polymers get in contact with ionizing radiation, e.g., if they are used as carriers for radiopharmaceuticals or during radiation sterilization. Despite this fact, radiosensitivity of these polymers is largely overlooked to date. In this work, we describe the effect of electron beam ionizing radiation on the physicochemical and phase separation properties of selected thermoresponsive polymers with CPT between room and body temperature. Stability of the polymers to radiation (doses 0-20 kGy) in aqueous solutions increased in the order poly(N-vinylcaprolactam) (PVCL, the least stable) ≪ poly[N-(2,2-difluoroethyl)acrylamide] (DFP) < poly(N-isopropylacrylamide) (PNIPAM) ≪ poly(2-isopropyl-2-oxazoline-co-2-n-butyl-2-oxazoline) (POX). Even low doses of β radiation (1 kGy), which are highly relevant to the storage of polymer radiotherapeutics and sterilization of biomedical systems, cause significant increase in molecular weight due to cross-linking (except for POX, where this effect is weak). In the case of PVCL irradiated with low doses, the increase in molecular weight induced an increase in the CPT of the polymer. For PNIPAM and DFP, there is strong chain hydrophilization leading to an increase in CPT. From this perspective, POX is the most suitable polymer for the construction of delivery systems that experience exposure to radiation, while PVCL is the least suitable and PNIPAM and DFP are suitable only for low radiation demands.

Internal Nanoparticle Structure of Temperature-Responsive Self-Assembled PNIPAM-b-PEG-b-PNIPAM Triblock Copolymers in Aqueous Solutions: NMR, SANS, and Light Scattering Studies

In this study, we report detailed information on the internal structure of PNIPAM-b-PEG-b-PNIPAM nanoparticles formed from self-assembly in aqueous solutions upon increase in temperature. NMR spectroscopy, light scattering, and small-angle neutron scattering (SANS) were used to monitor different stages of nanoparticle formation as a function of temperature, providing insight into the fundamental processes involved. The presence of PEG in a copolymer structure significantly affects the formation of nanoparticles, making their transition to occur over a broader temperature range. The crucial parameter that controls the transition is the ratio of PEG/PNIPAM. For pure PNIPAM, the transition is sharp; the higher the PEG/PNIPAM ratio results in a broader transition. This behavior is explained by different mechanisms of PNIPAM block incorporation during nanoparticle formation at different PEG/PNIPAM ratios. Contrast variation experiments using SANS show that the structure of nanoparticles above cloud point temperatures for PNIPAM-b-PEG-b-PNIPAM copolymers is drastically different from the structure of PNIPAM mesoglobules. In contrast with pure PNIPAM mesoglobules, where solidlike particles and chain network with a mesh size of 1-3 nm are present, nanoparticles formed from PNIPAM-b-PEG-b-PNIPAM copolymers have nonuniform structure with "frozen" areas interconnected by single chains in Gaussian conformation. SANS data with deuterated "invisible" PEG blocks imply that PEG is uniformly distributed inside of a nanoparticle. It is kinetically flexible PEG blocks which affect the nanoparticle formation by prevention of PNIPAM microphase separation.

Interaction between bile salt sodium glycodeoxycholate and PEO–PPO–PEO triblock copolymers in aqueous solution

Bile salts can associate to PEO–PPO–PEO block copolymer micelles and disintegrate them depending on the relative block length and molecular weight of the copolymers and bile salt/copolymer molar ratio.

Novel thermosensitive telechelic PEGs with antioxidant activity: synthesis, molecular properties and conformational behaviour

We report on the tailor-made polymer conjugates, which are highly compelling for biomedical applications due to their antioxidant activity and the adjustable thermosensitive properties.