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On the formation of inclusion complexes at the solid/liquid interface of anchored temperature-responsive PNIPAAM diblock copolymers with γ-cyclodextrin.

ABSTRACT: The thermal responsive behavior of adsorbed layers of diblock copolymers of poly(N-isopropylacrylamide) (PNIPAAM) and poly((3-acrylamidopropyl)trimethylammonium chloride) (PAMPTMA(+)) with γ-cyclodextrin (γ-CD) at the solid/liquid interface has been investigated using three in situ techniques: null ellipsometry, quartz-crystal microbalance with dissipation monitoring, and neutron reflectometry. The measurements provided information about the adsorbed amounts, the layer thickness, hydration and viscoelastic properties, and the interfacial structure and composition. The copolymers adsorb to silica with the cationic PAMPTMA(+) blocks sitting as anchors in a flat conformation and the PNIPAAM chains extending into the solution. The copolymer system alone exhibits reversible collapse above the lower critical solution temperature of PNIPAAM. The addition of γ-CD to pre-adsorbed copolymer layers results in a highly extended conformation as well as some loss of copolymer from the surface, which we discuss in terms of the formation of surface-invoked lateral steric repulsion of formed inclusion complexes.

SUBMITTER: Lazzara G

PROVIDER: S-EPMC5519650 | biostudies-other | 2017

REPOSITORIES: biostudies-other

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Project description:INTRODUCTION:Intracellular delivery is a key step for many applications in medicine and for investigations into cellular function. This is particularly true for immunotherapy, which often requires controlled delivery of antigen and adjuvants to the cytoplasm of immune cells. Due to the complex responses generated by the stimulation of diverse immune cell populations, it is critical to monitor which cells are targeted during treatment. To address this issue, we have engineered an immunotheranostic polymersome delivery system that fluorescently marks immune cells following intracellular delivery. METHODS:N-(3-bromopropyl)phthalimide end-capped poly(ethylene glycol)-bl-poly(propylene sulfide) (PEG-PPS-PI) was synthesized by anionic ring opening polymerization and linked with PEG-PPS-NH2 via a perylene bisimide (PBI) bridge to form a tetrablock copolymer (PEG-PPS-PBI-PPS-PEG). Block copolymers were assembled into polymersomes by thin film hydration in phosphate buffered saline and characterized by dynamic light scattering, cryogenic electron microscopy and fluorescence spectroscopy. Polymersomes were injected subcutaneously into the backs of mice, and draining lymph nodes were extracted for flow cytometric analysis of cellular uptake and disassembly. RESULTS:Modular self-assembly of tetrablock / diblock copolymers in aqueous solutions induced ?-? stacking of the PBI linker that both red-shifted and quenched the PBI fluorescence. Reactive oxygen species within the endosomes of phagocytic immune cell populations oxidized the PPS blocks, which disassembled the polymersomes for dequenching and shifting of the PBI fluorescence from 640 nm to 550 nm emission. Lymph node resident macrophages and dendritic cells were found to increase in 550 nm emission over the course of 3 days by flow cytometry. CONCLUSIONS:Immunotheranostic polymersomes present a versatile platform to probe the contributions of specific cell populations during the elicitation of controlled immune responses. Flanking PBI with two oxidation-sensitive hydrophobic PPS blocks enhanced ? stacking and introduced a mechanism for disrupting ?-? interactions to shift PBI fluorescence in response to oxidative conditions. Shifts from red (640 nm) to green (550 nm) fluorescence occurred in the presence of physiologically relevant concentrations of reactive oxygen species and could be observed within phagocytic cells both in vitro and in vivo.

Project description:Quantitatively understanding the self-assembly of amphiphilic macromolecules at liquid-liquid interfaces is a fundamental scientific concern due to its relevance to a broad range of applications including bottom-up nanopatterning, protein encapsulation, oil recovery, drug delivery, and other technologies. Elucidating the mechanisms that drive assembly of amphiphilic macromolecules at liquid-liquid interfaces is challenging due to the combination of hydrophobic, hydrophilic, and Coulomb interactions, which require consideration of the dielectric mismatch, solvation effects, ionic correlations, and entropic factors. Here we investigate the self-assembly of a model block copolymer with various charge fractions at the chloroform-water interface. We analyze the adsorption and conformation of poly(styrene)-block-poly(2-vinylpyridine) (PS-b-P2VP) and of the homopolymer poly(2-vinylpyridine) (P2VP) with varying charge fraction, which is controlled via a quaternization reaction and distributed randomly along the backbone. Interfacial tension measurements show that the polymer adsorption increases only marginally at low charge fractions (<5%) but increases more significantly at higher charge fractions for the copolymer, while the corresponding randomly charged P2VP homopolymer analogues display much more sensitivity to the presence of charged groups. Molecular dynamics (MD) simulations of the experimental systems reveal that the diblock copolymer (PS-b-P2VP) interfacial activity could be mediated by the formation of a rich set of complex interfacial copolymer aggregates. Circular domains to elongated stripes are observed in the simulations at the water-chloroform interface as the charge fraction increases. These structures are shown to resemble the spherical and cylindrical helicoid structures observed in bulk chloroform as the charge fraction increases. The self-assembly of charge-containing copolymers is found to be driven by the association of the charged component in the hydrophilic block, with the hydrophobic segments extending away from the hydrophilic cores into the chloroform phase.

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On the formation of inclusion complexes at the solid/liquid interface of anchored temperature-responsive PNIPAAM diblock copolymers with γ-cyclodextrin.

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