Mixed self-assembly of poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers and sodium dodecyl sulfate in aqueous solution

The in vivo fate of polymeric micelles

This review aims to provide a systemic analysis of the in vivo, as well as subcellular, fate of polymeric micelles (PMs), starting from the entry of PMs into the body. Few PMs are able to cross the biological barriers intact and reach the circulation. In the blood, PMs demonstrate fairly good stability mainly owing to formation of protein corona despite controversial results reported by different groups. Although the exterior hydrophilic shells render PMs "long-circulating", the biodistribution of PMs into the mononuclear phagocyte systems (MPS) is dominant as compared with non-MPS organs and tissues. Evidence emerges to support that the copolymer poly(ethylene glycol)-poly(lactic acid) (PEG-PLA) is first broken down into pieces of PEG and PLA and then remnants to be eliminated from the body finally. At the cellular level, PMs tend to be internalized via endocytosis due to their particulate nature and disassembled and degraded within the cell. Recent findings on the effect of particle size, surface characteristics and shape are also reviewed. It is envisaged that unraveling the in vivo and subcellular fate sheds light on the performing mechanisms and gears up the clinical translation of PMs.

Interaction between sodium dodecylsulfate (SDS) and pluronic L61 in aqueous medium: assessment of the nature and morphology of the formed mixed aggregates by NMR, EPR, SANS and FF-TEM measurements

The interaction of copolymer L61 i.e., (EO)2(PO)32(EO)2 (where EO and PO are ethylene and propylene oxides, respectively) with surfactant SDS (sodium dodecylsulfate) in relation to their self-aggregation, dynamics and microstructures has been physicochemically studied in detail employing the Nuclear Magnetic Resonance (NMR), Electron Paramagnetic Resonance (EPR), Small-Angle Neutron Scattering (SANS), and Freeze-Fracture Transmission Electron Microscopy (FF-TEM) methods. The NMR self-diffusion study indicated a synergistic interaction between SDS and L61 forming L61-SDS mixed complex aggregates, and deuterium (2H) NMR pointed out the nonspherical nature of these aggregates with increasing [L61]. EPR spectral analysis of the motional parameters of 5-doxyl steraric acid (5-DSA) as a spin probe provided information on the microviscosity of the local environment of the L61-SDS complex aggregates. SANS probed the geometrical aspects of the SDS-L61 assemblies as a function of both [L61] and [SDS]. Progressive evolution of the mixed-aggregate geometries from globular to prolate ellipsoids with axial ratios ranging from 2 to 10 with increasing [L61] was found. Such morphological changes were further corroborated with the results of 2H NMR and FF-TEM measurements. The strategy of the measurements, and data analysis for a concerted conclusion have been presented.

Association between Nonionic Amphiphilic Polymer and Ionic Surfactant in Aqueous Solutions: Effect of Polymer Hydrophobicity and Micellization

The interaction in aqueous solutions of surfactants with amphiphilic polymers can be more complex than the surfactant interactions with homopolymers. Interactions between the common ionic surfactant sodium dodecyl sulfate (SDS) and nonionic amphiphilic polymers of the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) type have been probed utilizing a variety of experimental techniques. The polymer amphiphiles studied here are Pluronic F127 (EO₁₀₀PO₆₅EO₁₀₀) and Pluronic P123 (EO₁₉PO₆₉EO₁₉), having the same length PPO block but different length PEO blocks and, accordingly, very different critical micellization concentrations (CMC). With increasing surfactant concentration in aqueous solutions of fixed polymer content, SDS interacts with unassociated PEO-PPO-PEO molecules to first form SDS-rich SDS/Pluronic assemblies and then free SDS micelles. SDS interacts with micellized PEO-PPO-PEO to form Pluronic-rich SDS/Pluronic assemblies, which upon further increase in surfactant concentration, break down and transition into SDS-rich SDS/Pluronic assemblies, followed by free SDS micelle formation. The SDS-rich SDS/Pluronic assemblies exhibit polyelectrolyte characteristics. The interactions and mode of association between nonionic macromolecular amphiphiles and short-chain ionic amphiphiles are affected by the polymer hydrophobicity and its concentration in the aqueous solution. For example, SDS binds to Pluronic F127 micelles at much lower concentrations (~0.01 mM) when compared to Pluronic P123 micelles (~1 mM). The critical association concentration (CAC) values of SDS in aqueous PEO-PPO-PEO solutions are much lower than CAC in aqueous PEO homopolymer solutions.

Optically controlled hybrid metamaterial of plasmonic spiky gold inbuilt graphene sheets for bimodal imaging guided multimodal therapy

The development of multifunctional molecular diagnostic platforms for the concordant visualization and treatment of diseases with high sensitivity and resolution has recently become a crucial strategy in cancer management. Thus, engineering functional metamaterials with high therapeutic and imaging capabilities to elucidate diseases from their morphological behaviors to physiological mechanisms is an unmet need in the current scenario. Here, we report the design of a unique hybrid plasmonic nanoarchitecture for targeted multiple phototherapies of breast cancer by simultaneous real-time monitoring through fluorescence and surface-enhanced Raman scattering (SERS) techniques. The nanoframework consisted of plasmonic gold-graphene hybrids tethered with folic acid-ligated chitosan-modified photosensitizer (PpIX) to afford target-specific localized photothermal and photodynamic therapy. The hybrid vehicle also served as an excellent nanocarrier for the efficient loading and stimuli-responsive release of the chemotherapeutic drug doxorubicin (DOX) to enhance the therapeutic efficacy, thereby forming a trimodal nanomedicine against cancer. The cytotoxic effects induced by the cumulative action of the triplet therapeutic tools were visualized through both fluorescence and SERS imaging channels. Moreover, it also generated synchronized therapeutic effects resulting in the effective regression of tumor volume without propagating any toxic effects to other organs of the animals. Taken together, by virtue of strong light-matter interactions, the nanoprobe showed enhanced photoadsorption, which facilitated amplified light-reactive therapeutic and imaging efficacies along with targeted and enhanced chemotherapy, both in vitro and in vivo, which may offer promising outcomes in clinical research.

Core-shell Structure and Aggregation Number of Micelles Composed of Amphiphilic Block Copolymers and Amphiphilic Heterografted Polymer Brushes Determined by Small-Angle X-ray Scattering

A large group of functional nanomaterials employed in biomedical applications, including targeted drug delivery, relies on amphiphilic polymers to encapsulate therapeutic payloads via self-assembly processes. Knowledge of the micelle structures will provide critical insights into design of polymeric drug delivery systems. Core-shell micelles composed of linear diblock copolymers poly(ethylene glycol)-b-poly(caprolactone) (PEG-b-PCL), poly(ethylene oxide)-b-poly(lactic acid) (PEG-b-PLA), as well as a heterografted brush consisting of a poly(glycidyl methacrylate) backbone with PEG and PLA branches (PGMA-g-PEG/PLA) were characterized by dynamic light scattering (DLS) and small angle X-ray scattering (SAXS) measurements to gain structural information regarding the particle morphology, core-shell size, and aggregation number. The structural information at this quasi-equilibrium state can also be used as a reference when studying the kinetics of polymer micellization.

Improved Photodynamic Therapy Efficacy of Protoporphyrin IX-Loaded Polymeric Micelles Using Erlotinib Pretreatment

Photodynamic therapy (PDT) has attracted widespread attention in recent years as a noninvasive and highly selective approach for cancer treatment. We have previously reported a significant increase in the 90-day complete response rate when tumor-bearing mice are treated with the epidermal growth factor receptor (EGFR) inhibitor erlotinib prior to PDT with the photosensitizer benzoporphyrin-derivative monoacid ring A (BPD-MA) compared to treatment with PDT alone. To further explore this strategy for anticancer therapy and clinical practice, we tested whether pretreatment with erlotinib also exhibited a synergistic therapeutic effect with a nanocarrier containing the clinically relevant photosensitizer protoporphyrin IX (PpIX). The PpIX was encapsulated within biodegradable polymeric micelles formed from the amphiphilic block copolymer poly(ethylene glycol)-polycaprolactone (PEG-PCL). The obtained micelles were characterized systematically in vitro. Further, an in vitro cytotoxicity study showed that PDT with PpIX loaded micelles did exhibit a synergistic effect when combined with erlotinib pretreatment. Considering the distinct advantages of polymeric nanocarriers in vivo, this study offers a promising new approach for the improved treatment of localized tumors. The strategy developed here has the potential to be extended to other photosensitizers currently used in the clinic for photodynamic therapy.

Synergistic enhancement in the drug sequestration power and reduction in the cytotoxicity of surfactants

Surfactants in supramolecular assemblies show a significant increase in their drug sequestration power with a remarkably reduced cytotoxicity.

Influence of mixed CTABr–C16E20 nanoparticles on relative counterion binding constants in aqueous solutions of inert salts (2-NaOC6H4CO2Na and NaBr): kinetic and rheometric study

A semi-empirical kinetic technique has been used to obtain the ratios of pure CTABr (cationic nanoparticle) and mixed CTABr–C₁₆E₂₀ (cationic–nonionic nanoparticle) micellar binding constants of counterions X and Br, K_X/K_Br (=KBrX or RBrX) for X = salicylate ion.

Physicochemical perspectives (aggregation, structure and dynamics) of interaction between pluronic (L31) and surfactant (SDS)

The influence of the water soluble non-ionic tri-block copolymer L31 on the microstructure and self-aggregation dynamics of the anionic surfactant sodium dodecylsulfate (SDS) in aqueous solution was investigated.

Copolymer micelles and nanospheres with different in vitro stability demonstrate similar paclitaxel pharmacokinetics

Paclitaxel loaded amphiphilic block copolymer nanoparticles have been demonstrated to enhance the aqueous solubility and improve the toxicity profile as compared to the commercially available product Taxol; however, in many cases long circulation of the drug is not achieved due to rapid partitioning of the drug from the carrier and/or carrier instability upon injection. In this work we investigated the effect of increasing the hydrophobic block length of methoxy poly(ethylene glycol)-block-poly(ε-caprolactone) (MePEG-b-PCL) copolymers on the physicochemical properties and in vitro stability of the formed nanoparticles as well as the pharmacokinetics and biodistribution of both the copolymer and solubilized drug. We hypothesized that copolymers composed of high molecular weight hydrophobic blocks (MePEG₁₁₄-b-PCL₁₀₄) that form nanoparticles with a kinetically "frozen core" (which we term nanospheres) would better retain their PTX payload as compared to micelles composed of shorter hydrophobic blocks (MePEG₁₁₄-b-PCL₁₉), thus leading to prolonged drug circulation. Nanospheres solubilized PTX more efficiently, released the drug in a more sustained fashion and were characterized by enhanced stability and drug retention in the presence of plasma proteins as compared to micelles. Using radiolabeled copolymers and PTX, it was found that, upon injection, MePEG₁₁₄-b-PCL₁₀₄ circulated for longer than MePEG₁₁₄-b-PCL₁₉; however, the drug was rapidly eliminated from the blood regardless of the formulation. These results suggest that, despite formulation in more stable nanospheres, PTX was still rapidly extracted from these nanoparticles.

Tumor-homing photosensitizer-conjugated glycol chitosan nanoparticles for synchronous photodynamic imaging and therapy based on cellular on/off system

Herein, we developed the photosensitizer, protoporphyrin IX (PpIX), conjugated glycol chitosan (GC) nanoparticles (PpIX-GC-NPs) as tumor-homing drug carriers with cellular on/off system for photodynamic imaging and therapy, simultaneously. In order to prepare PpIX-GC-NPs, hydrophobic PpIXs were chemically conjugated to GC polymer and the amphiphilic PpIX-GC conjugates formed a stable nanoparticle structure in aqueous condition, wherein conjugated PpIX molecules formed hydrophobic inner-cores and they were covered by the hydrophilic GC polymer shell. Based on the nanoparticle structure, PpIX-GC-NPs showed the self-quenching effect that is 'off' state with no fluorescence signal and phototoxicity with light exposure. It is due to the compact crystallized PpIX molecules in the nanoparticles as confirmed by dynamic light scattering and X-ray diffraction methods. However, after cellular uptake, compact nanoparticle structure gradually decreased to generate strong fluorescence signal and singlet oxygen generation when irradiated. Importantly, PpIX-GC-NPs-treated mice presented prolonged blood circulation, enhanced tumor targeting ability, and improved in vivo therapeutic efficiency in tumor-bearing mice, compared to that of free PpIX-treated mice. These results proved that this tumor-homing cellular 'on/off' nanoparticle system of PpIX-GC-NPs has a great potential for synchronous photodynamic imaging and therapy in cancer treatment.

N-heterocyclic carbene-induced zwitterionic ring-opening polymerization of ethylene oxide and direct synthesis of alpha,omega-difunctionalized poly(ethylene oxide)s and poly(ethylene oxide)-b-poly(epsilon-caprolactone) block copolymers

An N-heterocyclic carbene (NHC), namely, 1,3-bis-(diisopropyl)imidazol-2-ylidene (1), was demonstrated to bring about the metal-free ring-opening polymerization of ethylene oxide at 50 degrees C in dimethyl sulfoxide, in absence of any other reagents. Poly(ethylene oxide) (PEO) of polydispersities <1.2 and molar masses perfectly matching the [monomer]/[(1)] ratio could thus be obtained in quantitative yields, attesting to the controlled/living character of such carbene-initiated polymerizations. It is argued that (1) adds to ethylene oxide to form a zwitterionic species, namely 1,3-bis-(diisopropyl)imidazol-2-ylidinium alkoxide, that further propagates by a zwitterionic ring-opening polymerization (ZROP) mechanism. Through an appropriate choice of terminating agent NuH or NuSiMe(3) at the completion of the polymerization, a variety of end-functionalized PEO chains could be generated. In particular, alpha,omega-bis(hydroxy)-telechelic PEO, alpha-benzyl,omega-hydroxy, and alpha-azido,omega-hydroxy-difunctionalized PEOs were synthesized by NHC (1)-initiated ZROP, using H(2)O, PhCH(2)OH, and N(3)SiMe(3) as terminating agent, respectively. Characterization of these alpha,omega-difunctionalized PEOs by techniques such as (1)H NMR spectroscopy, MALDI-TOF spectrometry, and size exclusion chromatography confirmed the quantitative introduction of functional groups at both alpha and omega positions of the PEO chains and the formation of very narrow molar mass polymers. Finally, the synthesis of a poly(ethylene oxide)-b-poly(epsilon-caprolactone) diblock copolymer by sequential ZROP of the corresponding monomers was successfully achieved using (1) as organic initiator without isolation of the PEO block intermediate.

Comparison of surfactants used to prepare aqueous perfluoropentane emulsions for pharmaceutical applications

Perfluoropentane (PFP), a very hydrophobic, nontoxic, noncarcinogenic fluoroalkane, has generated much interest in biomedical applications, including occlusion therapy and controlled drug delivery. For most of these applications, the dispersion within aqueous media of a large quantity of PFP droplets of the proper size is critically important. Surprisingly, the interfacial tension of PFP against water in the presence of surfactants used to stabilize the emulsion has rarely, if ever, been measured. In this study, we report the interfacial tension of PFP in the presence of surfactants used in previous studies to produce emulsions for biomedical applications: polyethylene oxide-co-polylactic acid (PEO-PLA) and polyethylene oxide-co-poly-epsilon-caprolactone (PEO-PCL). Because both of these surfactants are uncharged diblock copolymers that rely on the mechanism of steric stabilization, we also investigate for comparison's sake the use of the small-molecule cationic surfactant cetyl trimethyl ammonium bromide (CTAB) and the much larger protein surfactant bovine serum albumin (BSA). The results presented here complement previous reports of the PFP droplet size distribution and will be useful for determining to what extent the interfacial tension value can be used to control the mean PFP droplet size.

Mixed micelles of Triton X-100, sodium dodecyl dioxyethylene sulfate, and synperonic l61 investigated by NOESY and diffusion ordered NMR spectroscopy

Mixed micelles formed from nonionic surfactant Triton X-100 (TX100), anionic surfactant sodium dodecyl dioxyethylene sulfate (SDP2S), and triblock copolymer Synperonic L61 (SL61) were investigated by 1H NMR spectroscopy. The size and shape of the aggregates were determined by diffusion ordered NMR spectroscopy (DOSY), while 2D nuclear Overhauser enhanced spectroscopy (NOESY) NMR was used to study the mutual spatial arrangement of the surfactant molecules in the aggregated state. An average micellar hydrodynamic radius of 3.6 nm, slightly increasing upon increasing TX100 molar fraction, was found for the mixed systems without additives. Addition of SL61 to the mixed micellar systems results in a slight increase of micellar radii. In the presence of AlCl3, an increase of TX100/SDP2S micellar sizes from 4 to 10 nm was found when increasing the SDP2S molar fraction. The mixed TX100/SDP2S micelles in the presence of both AlCl3 and polymer SL61 are almost spherical, with a radius of 4.5 nm. 2D NOESY data reveal that, as the individual TX100 micelles, mixed TX100/SDP2S and TX100/SDP2S/SL61/AlCl3 micelles also have a multilayer structure, with partially overlapping internal and external layers of TX100 molecules. In these mixed micelles, the SDP2S molecules are located at the level of the external layer of TX100 molecules, whereas the SL61 polymer is partially incorporated inside of the micellar core.

Effects of SDS on the thermo- and pH-sensitive structural changes of the poly(acrylic acid)-based copolymer containing both poly(N-isopropylacrylamide) and monomethoxy poly(ethylene glycol) grafts in water

The effects of SDS on the structural changes of the thermally induced polymeric micelles from a graft copolymer comprising poly(acrylic acid) (PAAc) as the backbone and poly(N-isopropylacrylamide) (PNIPAAm) and monomethoxy poly(ethylene glycol) (mPEG) as the grafts in aqueous solution are studied. At low temperature, SDS micelles form via the hydrophobic association of SDS molecules with the PNIPAAm grafts at a critical aggregation concentration of SDS (cac(SDS)) much lower than its critical micelle concentration. Consequently, the critical aggregation temperature of the graft copolymer is elevated. The corresponding structure of the thermally induced polymeric micelles is characterized by an abrupt reduction in the particle size and an increased tendency toward formation of the monocore structure with a more compact and hydrophobic PNIPAAm microdomain being developed. On the other hand, upon the polymeric micelle formation at high temperature, the copolymer-bound SDS micelle structure is disrupted and the dissociated SDS molecules migrate to the core-shell interface with their alkyl chains residing in the liquidlike region of the hydrophobic PNIPAAm microdomain. The correlation between the polymeric particles and copolymer-bound micelles is further substantiated by showing the change of the colloidal particle size in response to changes in cac(SDS) via adjusting the pH of the aqueous copolymer/SDS solutions.

Effect of SDS on the Self-Assembly Behavior of the PEO−PPO−PEO Triblock Copolymer (EO)20(PO)70(EO)20

The mixed micellar system comprising the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)-based triblock copolymer (EO)(20)(PO)(70)(EO)(20) (P123) and the anionic surfactant sodium dodecyl sulfate (SDS) has been investigated in aqueous media by small-angle neutron scattering (SANS) and viscosity measurements. The aggregation number of the copolymer in the micelles decreases upon addition of SDS, but a simultaneous enhancement in the degree of micellar hydration leads to a significant increase in the micellar volume fraction at a fixed copolymer concentration. This enhancement in the micellar hydration leads to a marked increase in the stability of the micellar gel phase until it is destroyed at very high SDS concentration. Mixed micellar systems with low and intermediate SDS concentrations form the micellar gel phase in much wider temperature and copolymer concentration ranges than the pure copolymer micellar solution. A comparison of the observed results with those for the copolymers (EO)(26)(PO)(40)(EO)(26) (P85) and (EO)(99)(PO)(70)(EO)(99) (F127) suggests that the composition of the copolymers plays a significant role in determining the influence of SDS on the gelation characteristics of the aqueous copolymer solutions. Copolymers with high PO/EO ratios show an enhancement in the stability of the gel phase, whereas copolymers with low PO/EO ratios show a deterioration of the same in the presence of SDS.

Influence of temperature on the mixed micelles of Pluronic F127 and P103 with dimethylene-bis-(dodecyldimethylammonium bromide)

The steady state fluorescence measurements have been performed on Pluronic F127 and P103 with dimethylene-bis-(dodecyldimethylammonium bromide) (12-2-12) mixtures at 21-40 degrees C. From the pyrene fluorescence, the critical micelle concentration (cmc), micelle mole fraction (x), micropolarity, and aggregation number have been computed for both mixtures over the whole mixing range at different temperatures. These micelle parameters indicate that the mixed micelle formation between the unlike components of both mixtures takes place due to the synergistic interactions and which increase with an increase in temperature.

Concomitant adsorption of poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers and sodium dodecyl sulfate at the silica-water interface

Upon addition of silica to aqueous solutions of poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers (PEO-b-PCL) and sodium dodecyl sulfate (SDS), adsorption of the solutes occurs at the silica-water interface. The amount of the adsorbed constituents has been measured by the total concentration depletion method. Small-angle neutron scattering experiments (SANS) have been carried out to investigate the structure of the adsorbed layer. Although SDS is not spontaneously adsorbed onto hydrophilic silica, adsorption is observed in the presence of PEO-b-PCL diblocks, in relation to the relative concentration of the two compounds. Conversely, SDS has a depressive effect on the adsorption of the copolymer, whose structure at the interface is modified. Copolymer desorption is however never complete at high SDS content. These observations have been rationalized by the associative behavior of PEO-b-PCL and SDS in water.

Small-Angle X-ray Scattering, Light Scattering, and NMR Study of PEO−PPO−PEO Triblock Copolymer/Cationic Surfactant Complexes in Aqueous Solution

The formation of triblock copolymer/surfactant complexes upon mixing a nonionic Pluronic polymer (PEO-PPO-PEO) with a cationic surfactant, hexadecyltrimethylammonium chloride (CTAC), has been studied in dilute aqueous solutions using small-angle X-ray scattering, static and dynamic light scattering, and self-diffusion NMR. The studied copolymer (denoted P123, EO(20)PO(68)EO(20)) forms micelles with a radius of 10 nm and a molecular weight of 7.5 x 10(5), composed of a hydrophobic PPO-rich core of radius 4 nm and a water swollen PEO corona. The P123/CTAC system has been investigated between 1 and 5 wt % P123 and with varying surfactant concentration up to approximately 170 mM CTAC (or a molar ratio n(CTAC)/n(P123) = 19.3). When CTAC is mixed with micellar P123 solutions, two different types of complexes are observed at various CTAC concentrations. At low molar ratios (>/=0.5) a "P123 micelle-CTAC" complex is obtained as the CTAC monomers associate noncooperatively with the P123 micelle, forming a spherical complex. Here, an increased interaction between the complexes with increasing CTAC concentration is observed. The interaction has been investigated by determining the structure factor obtained by using the generalized indirect Fourier transformation (GIFT) method. The interaction between the P123 micelle-CTAC complexes was modeled using the Percus-Yevick closure. For the low molar ratios a small decrease in the apparent molecular weight of the complex was obtained, whereas the major effect was the increase in electrostatic repulsion between the complexes. Between molar ratios 1.9 and 9 two coexisting complexes were found, one P123 micelle-CTAC complex and one "CTAC-P123" complex. The latter one consists of one or a few P123 unimers and a few CTAC monomers. As the CTAC concentration increases above a molar ratio of 9, the P123 micelles are broken up and only the CTAC-P123 complex that is slightly smaller than a CTAC micelle exists. The interaction between the P123/CTAC complexes was modeled with the hypernetted-chain closure using a Yukawa type potential in the GIFT analysis, due to the stronger electrostatic repulsion.

The nociceptin pharmacophore site for opioid receptor binding derived from the NMR structure and bioactivity relationships

Nociceptin, a 17 amino acid opioid-like peptide that has an inhibitory effect on synaptic transmission in the nervous system, is involved in learning, memory, attention, and emotion and is also implicated in the perception of pain and visual, auditory, and olfactory functions. In this study, we investigated the NMR solution structure of nociceptin in membrane-like environments (trifluoroethanol and SDS micelles) and found it to have a relatively stable helix conformation from residues 4-17 with functionally important N-terminal residues being folded aperidoically on top of the helix. In functional assays for receptor binding and calcium flux, alanine-scanning variants of nociceptin indicated that functionally important residues generally followed helix periodicity, consistent with the NMR structural model. Structure-activity relationships allowed identification of pharmacophore sites that were used in small molecule data base searches, affording hits with demonstrated nociceptin receptor binding affinities.