Internal structural characterization of triblock copolymer micelles with looped corona chains

Effects of Polymer 3D Architecture, Size, and Chemistry on Biological Transport and Drug Delivery In Vitro and in Orthotopic Triple Negative Breast Cancer Models

The size, shape, and underlying chemistries of drug delivery particles are key parameters which govern their ultimate performance in vivo. Responsive particles are desirable for triggered drug delivery, achievable through architecture change and biodegradation to control in vivo fate. Here, polymeric materials are synthesized with linear, hyperbranched, star, and micellar-like architectures based on 2-hydroxypropyl methacrylamide (HPMA), and the effects of 3D architecture and redox-responsive biodegradation on biological transport are investigated. Variations in "stealth" behavior between the materials are quantified in vitro and in vivo, whereby reduction-responsive hyperbranched polymers most successfully avoid accumulation within the liver, and none of the materials target the spleen or lungs. Functionalization of selected architectures with doxorubicin (DOX) demonstrates enhanced efficacy over the free drug in 2D and 3D in vitro models, and enhanced efficacy in vivo in a highly aggressive orthotopic breast cancer model when dosed over schedules accounting for the biodistribution of the carriers. These data show it is possible to direct materials of the same chemistries into different cellular and physiological regions via modulation of their 3D architectures, and thus the work overall provides valuable new insight into how nanoparticle architecture and programmed degradation can be tailored to elicit specific biological responses for drug delivery.

Self-Organization and Flow of Low-Functionality Telechelic Star Polymers with Varying Attraction

We combine state-of-the art synthesis, simulations, and physical experiments to explore the tunable, responsive character of telechelic star polymers as models for soft patchy particles. We focus on the simplest possible system: a star comprising three asymmetric block copolymer arms with solvophilic inner and solvophobic outer blocks. Our dilute solution studies reveal the onset of a second slow mode in the intermediate scattering functions as the temperature decreases below the θ-point of the outer block, as well as the size reduction of single stars upon further decreasing temperature. Clusters comprising multiple stars are formed and their average dimensions, akin to the single star size, counterintuitively decrease upon cooling. A similar phenomenology is observed in simulations upon increasing attraction between the outer blocks and is rationalized as a result of the interplay between interstar associations and steric repulsion between the star cores. Since our simulations are able to describe the experimental findings reliably, we can use them with confidence to make predictions at conditions and flow regimes that are inaccessible experimentally. Specifically, we employ simulations to investigate flow properties of the system at high shear rates, revealing shear thinning behavior caused by the breakup of interstar associations under flow. On the other hand, the zero-shear viscosity obtained experimentally exhibits a rather weak activation energy, which increases upon rising star concentration. These findings demonstrate the unusual properties of telechelic star polymers even in the dilute regime. They also offer a powerful toolbox for designing soft patchy particles and exploring their unprecedented responsive properties further on.

Toward Achieving Highly Ordered Fluorinated Surfaces of Spin-Coated Polymer Thin Films by Optimizing the Air/Liquid Interfacial Structure of the Casting Solutions

Thin polymer films with well-assembled fluorinated groups on their surfaces are not easily achieved via spin-coating film-fabrication methods because the solution solidifies very rapidly during spin-coating, which hinders the fluorinated moieties from segregating and organizing on the film surface. In this contribution, we have proposed a comprehensive strategy toward achieving well-ordered fluorinated thin films surfaces by optimizing the molecular organization at air/liquid interface of the film-formation solutions. To validate such a route, poly(methyl methacrylate) (PMMA) end-capped with several 2-perfluorooctylethyl methacrylate (FMA) units was employed as the model polymer for investigations. The air/solution interfacial structures were optimized by systematically changing the polymer chain structures and properties of the casting solvents. It was found that the polymers that form loosely associated aggregates (e.g., FMA₁- ec-PMMA₆₅- ec-FMA₁) and a solvent with better solubility to FMA while having not too low surface tension (i.e., toluene) can combine to produce solutions with well-assembled FMA at the interfaces. By spin-coating the solutions with well-organized interfaces, an ultrathin film with perfluorinated groups that were highly oriented toward the film surface was readily achieved, exhibiting surface energies as low as 7.2 mJ/m², which is among the lowest reported so far for the spin-coated thin films, and a very high F/C ratio (i.e., 0.98).

Synthesis of highly porous poly(tert-butyl acrylate)-b-polysulfone-b-poly(tert-butyl acrylate) asymmetric membranes

For the first time, self-assembly and non-solvent induced phase separation was applied to polysulfone-based linear block copolymers, reaching mechanical stability much higher than other block copolymer membranes used in this method, which were mainly based on polystyrene blocks.

Self-assembly of the triblock copolymer 17R4 poly(propylene oxide)₁₄-poly(ethylene oxide)₂₄-poly(propylene oxide)₁₄ in D₂O

Our recent investigation of the three regions of the phase diagram of 17R4 in D2O (Huff et al., 2011) has led us to study the copolymer structure in this system by small-angle neutron scattering, rheometry, and dynamic light scattering. In region I at low temperatures and copolymer concentrations (0-30°C, 0.1-0.2 mass fraction ω), the cloudy solution contains the copolymer in large clusters made of hydrophobic PPO-rich "knots" bridged by dissolved hydrophilic PEO chains. These clusters vanish in region I at the lower temperatures and concentrations (below 39°C and ω=0.01). In region I over long times (weeks) at 25°C, a white liquid/gel film forms at the air-D2O interface. In region II at temperatures above the micellization line (above about 35°C, at ω=0.22) the large clusters dissipate and unimers coexist with "flower micelles," where the PPO blocks are the centers of the micelles and the PEO blocks loop into the solvent. In region III at still higher temperatures (above about 40°C at ω=0.2), the solution separates into coexisting liquid phases, where the upper phase of higher copolymer concentration is in region II, and the lower phase is in region I. The concentrated upper phase may contain micelles so crowded as to form a network.

Structural Characteristics of Amphiphilic Cyclic and Linear Block Copolymer Micelles in Aqueous Solutions

The structural characteristics of aqueous micelles composed of amphiphilic cyclic poly(n-butyl acrylate-b-ethylene oxide) (cyclic PBA-b-PEO) or a linear analogue (i.e., linear poly(n-butyl acrylate-b-ethylene oxide-b-n-butyl acrylate) (linear PBA-b-PEO-b-PBA)) were examined for the first time using synchrotron X-ray scattering techniques and quantitative data analysis. The scattering data were analyzed using a variety of methodologies in a comprehensive complementary manner. These analyses provided details of the structural information about the micelles. Both micelles were found to consist of a core and a fuzzy shell; however, the cyclic block copolymer had a strong tendency to form micelles with core and shell parts that were more compact and dense than the corresponding parts of the linear block copolymer micelles. The PBA block of the cyclic copolymer was found to form a hydrophobic core with a density that exceeded the density of the homopolymer in the bulk state. The structural differences originated primarily from the topological difference between the cyclic and linear block copolymers. The elimination of the chain end groups (which introduced entropy and increased the excess excluded volume) from the amphiphilic block copolymer yielded more stable dense micelles in solution.

Seeded dispersion RAFT polymerization and synthesis of well-defined ABA triblock copolymer flower-like nanoparticles

Flower-like triblock copolymer nanoparticles containing a central looped solvophilic block and two outer solvophobic blocks are prepared by seeded dispersion RAFT polymerization.

Looped structure of flowerlike micelles revealed by 1H NMR relaxometry and light scattering

We present experimental proof that so-called "flowerlike micelles" exist and that they have some distinctly different properties compared to their "starlike" counterparts. Amphiphilic AB diblock and BAB triblock copolymers consisting of poly(ethylene glycol) (PEG) as hydrophilic A block and thermosensitive poly(N-isopropylacrylamide) (pNIPAm) B block(s) were synthesized via atom transfer radical polymerization (ATRP). In aqueous solutions, both block copolymer types form micelles above the cloud point of pNIPAm. Static and dynamic light scattering measurements in combination with NMR relaxation experiments proved the existence of flowerlike micelles based on pNIPAm(16kDa)-PEG(4kDa)-pNIPAm(16kDa) which had a smaller radius and lower mass and aggregation number than starlike micelles based on mPEG(2kDa)-pNIPAm(16kDa). Furthermore, the PEG surface density was much lower for the flowerlike micelles, which we attribute to the looped configuration of the hydrophilic PEG block. (1)H NMR relaxation measurements showed biphasic T(2) relaxation for PEG, indicating rigid PEG segments close to the micelle core and more flexible distal segments. Even the flexible distal segments were shown to have a lower mobility in the flowerlike micelles compared to the starlike micelles, indicating strain due to loop formation. Taken together, it is demonstrated that self-assemblies of BAB triblock copolymers have their hydrophilic block in a looped conformation and thus indeed adopt a flowerlike conformation.

Structure of micelles formed by highly asymmetric polystyrene-b-polydimethylsiloxane and polystyrene-b-poly[5-(N,N-diethylamino)isoprene] diblock copolymers

The internal structure of polystyrene(PS)-shell micelles having core-forming blocks consisting of polydimethylsiloxane (PDMS) or poly[5-(N,N-diethylamino)isoprene] (PAI) was determined in detail by accessing the multilevel structural organization using static and dynamic light scattering and small-angle X-ray scattering techniques. Well-defined PS-b-PDMS and PS-b-PAI diblock copolymers with molar masses in the range of 12.0k-18.2k g/mol were dispersed in cyclohexane, dimethylacetamide, or dimethylformamide. Colloidal nanoparticles exhibiting either swollen core with a large surface area per corona chain that enables the PS chains to assume a random coil conformation with gaussian statistics, or compact core and slightly stretched PS chains in the corona were obtained. Therefore, the results of this study provide an interesting alternative allowing for precise control of the core and corona properties of PS-b-PDMS and PS-b-PAI micelles in selective solvents. Admittedly, such differences in terms of micellar properties can dictate the potential of block copolymer micelles for generating thin films from preformed nano-objects, as well as the capability to function as nanoreactors in organic medium.