Amphiphilic poly(N-isopropylacrylamides) prepared by using a lipophilic radical initiator: synthesis and solution properties in water

Effect of End Groups on the Cloud Point Temperature of Aqueous Solutions of Thermoresponsive Polymers: An Inside View by Flory-Huggins Theory

In an effort to gain insight into the origin of the effects of end groups on the cloud point temperature (Tcp) as a function of the polymer molar mass of thermoresponsive polymers with lower critical solution behavior in dilute aqueous solutions, we use the Flory-Huggins (FH) theory amended for end groups. The theory was applied to available experimental data sets of poly(N-isopropylacrylamide) (PNIPAM), poly(4-vinylbenzyl methoxytris(oxyethylene) ether) (PTEGSt), and poly(α-hydro-ω-(4-vinylbenzyl)tetrakis(oxyethylene) ether) (PHTrEGSt). The theory relates the variations in TcpM,ϕcp for different end groups to the effective FH χ parameter of the end groups and explains the qualitative notion that the influence of the end groups is related to the hydrophobicity/hydrophilicity of the end groups relative to that of the so called intrinsic TcpM,ϕcp response of a polymer without end groups. The limits to the applicability of the FH theory are established, and a set of possible theoretical improvements is considered. The ultimate scrutiny of the simple FH theory and suggested improved theories must await the measurement of truly thermodynamic cloud points; the available cloud points are merely estimations of the thermodynamic cloud point, for which the deviation to the true cloud point cannot be established with sufficient accuracy.

5-Fluorouracil nano-delivery systems as a cutting-edge for cancer therapy

5-Fluorouracil (5-FU) is amongst the most commonly used antimetabolite chemotherapeutic agents in recent decades. However, its low bioavailability, short half-life, rapid metabolism and the development of drug resistance after chemotherapy limit its therapeutic efficiency. In this study, 5-FU applications as an anti-cancer drug for treating diverse types of cancers (e.g. colon, pancreatic and breast) have been reviewed. Different approaches lately designed to circumvent the drawbacks of 5-FU therapy are described herein, including 5-FU-loaded lipid-based nanoparticles (NPs), polymeric NPs (both stimuli and non-stimuli responsive), carbon-based nanostructures and inorganic NPs. Furthermore, co-delivery systems of 5-FU with other drugs (e.g. paclitaxel, gelatin-doxorubicin and naproxen) have been reviewed, which aid to attain better bioavailability, higher effectiveness at a lower concentration and lower toxicity. This review provides researchers with the latest progress on 5-FU-loaded nanocarriers, which show great potential as an advanced tool for cancer therapy.

Preparation and Characterization of Micelles

Nanoformulations in the past few decades have gained tremendous attention owing to their affirmative applications in increasing the bioavailability of poorly soluble drugs. Micelles in particular are favored due to their varied advantages which include thermodynamic stability, simple formulating steps, Newtonian flow, and enhanced biological barrier penetration. Owing to these advantages micellar nanosystems find extensive applications in oral, transdermal, and parenteral administration, and are now being explored for ocular and other noninvasive novel pathways of drug delivery such as nose to brain. In this chapter, we have discussed the protocol for the preparation of sumatriptan loaded micelles for the therapy of migraine. The inner core of these micelles comprises hydrophobic region of diblock polymer which holds the drug, while the hydrophilic region of the same provides conformational stability in the aqueous environment.

Tuning PNIPAm self-assembly and thermoresponse: roles of hydrophobic end-groups and hydrophilic comonomer

Systematic study of hydrophobic and hydrophilic modifications to poly(N-isopropylacrylamide) elucidates design rules for control over cloud point and aqueous self-assembly.

Phase Behavior of Co-Nonsolvent Systems: Poly( N-isopropylacrylamide) in Mixed Solvents of Water and Methanol

Cloud points of poly( N-isopropylacrylamide) in aqueous mixed solvents, with methanol as the cosolvent, are experimentally measured for polymer concentrations varied up to as high as the weight fraction 0.25. They are shown to form closed loops on the ternary phase plane in the temperature region between 5 and 30 °C, and hence co-nonsolvency is complete. Miscibility loops shrink by cooling, or equivalently, they exhibit lower critical solution temperature behavior. For a fixed polymer concentration, there is a composition of the mixed solvent at which the cloud-point temperature takes the lowest value. This minimum cloud-point temperature composition of the mixed solvent turned out to be almost independent of the polymer concentration, at least within the measured dilute region below the weight fraction 0.25. On the basis of the assumption that the phase separation is closely related to the preferential adsorption of the solvents by hydrogen bonding, we employ a model solution of Flory-Huggins type, augmented with direct and cooperative polymer-solvent hydrogen bonds, to construct the ternary phase diagrams. Theoretical calculation of the spinodal curves is performed, and the results are compared with the obtained experimental cloud-point data. The effect of molecular volume of the cosolvent is also studied within the same theoretical framework. Possibility for a upper critical solution temperature co-nonsolvency to appear for cosolvents with larger molecular volume is discussed.

Serum-Stable, Long-Circulating, pH-Sensitive PEGylated Liposomes

pH-sensitive liposomes have been designed to deliver active compounds, specifically to acidic intracellular organelles, and to augment their cytoplasmic concentrations. These systems combine the protective effects of other liposomal formulations with specific environment-controlled drug release. They are stable at physiological pH, but abruptly discharge their contents when endocytosed into acidic compartments, allowing the drug to be released before it is exposed to the harsh environment of the lysosomes.Serum-stable formulations with minimal leakage at physiological pH and rapid drug release at pH 5.0 to 5.5 can be easily prepared by inserting a hydrophobically modified N-isopropylacrylamide/methacrylic acid copolymer (poly(NIPAM-co-MAA)) in the lipid bilayer of sterically stabilized liposomes. The present chapter describes polymer synthesis, as well as the preparation and characterization of large unilamellar pH-sensitive vesicles.

Core Cross-linked Star Polymers for Temperature/pH Controlled Delivery of 5-Fluorouracil

RAFT polymerization with cross-linking was used to prepare core cross-linked star polymers bearing temperature sensitive arms. The arms consisted of a diblock copolymer containingN-isopropylacrylamide (NIPAAm) and 4-methacryloyloxy benzoic acid (4MBA) in the temperature sensitive block and poly(hexyl acrylate) forming the second hydrophobic block, while ethyleneglycol dimethacrylate was used to form the core. The acid comonomer provides pH sensitivity to the arms and also increases the transition temperature of polyNIPAAm to values in the range of 40 to 46°C. Light scattering and atomic force microscopy studies suggest that loose core star polymers were obtained. The star polymers were loaded with 5-fluorouracil (5-FU), an anticancer agent, in values of up to 30 w/w%.In vitrorelease experiments were performed at different temperatures and pH values, as well as with heating and cooling temperature cycles. Faster drug release was obtained at 42°C or pH 6, compared to normal physiological conditions (37°C, pH 7.4). The drug carriers prepared acted as nanopumps changing the release kinetics of 5-FU when temperatures cycles were applied, in contrast with release rates at a constant temperature. The prepared core cross-linked star polymers represent advanced drug delivery vehicles optimized for 5-FU with potential application in cancer treatment.

An unusual role of folate in the self-assembly of heparin-folate conjugates into nanoparticles

Tumor targeting agents including antibodies, peptides, and small molecules, are often used to improve the delivery efficiency of nanoparticles. Despite numerous studies investigating the abilities of targeting agents to increase the accumulation of nanosized therapeutics within diseased tissues, little attention has been focused on how these ligands can affect the self-assembly of the nanoparticle's modified polymer constituents upon chemical conjugation. Here we present an actively tumor targeted nanoparticle constructed via the self-assembly of a folate modified heparin. Folate conjugation unexpectedly allowed the self-assembly of heparin, where a majority of the folate molecules (>80%) resided inside the core of the nanoparticle. The folate-heparin nanoparticles could also physically encapsulate lipophilic fluorescent dyes, enabling the use of the constructs as activatable fluorescent probes for targeted in vivo tumor imaging.

Water soluble polythiophenes: preparation and applications

Different synthetic procedures for water soluble polythiophenes and their applications in sensing, detection of biomolecules and optoelectronic devices are discussed.

End-group-functionalized poly(N,N-diethylacrylamide) via free-radical chain transfer polymerization: Influence of sulfur oxidation and cyclodextrin on self-organization and cloud points in water

In this work we report the synthesis of thermo-, oxidation- and cyclodextrin- (CD) responsive end-group-functionalized polymers, based on N,N-diethylacrylamide (DEAAm). In a classical free-radical chain transfer polymerization, using thiol-functionalized 4-alkylphenols, namely 3-(4-(1,1-dimethylethan-1-yl)phenoxy)propane-1-thiol and 3-(4-(2,4,4-trimethylpentan-2-yl)phenoxy)propane-1-thiol, poly(N,N-diethylacrylamide) (PDEAAm) with well-defined hydrophobic end-groups is obtained. These end-group-functionalized polymers show different cloud point values, depending on the degree of polymerization and the presence of randomly methylated β-cyclodextrin (RAMEB-CD). Additionally, the influence of the oxidation of the incorporated thioether linkages on the cloud point is investigated. The resulting hydrophilic sulfoxides show higher cloud point values for the lower critical solution temperature (LCST). A high degree of functionalization is supported by ¹H NMR-, SEC-, FTIR- and MALDI–TOF measurements.

Load-collapse-release cascades of amphiphilic guest molecules in charged dendronized polymers through spatial separation of noncovalent forces

The ability to pack guest molecules into charged dendronized polymers (denpols) and the possibility to release these guest molecules from subsequently densely aggregated denpols in a load-collapse-release cascade is described. Charged denpols, which constitute molecular objects with a persistent, well-defined envelope and interior, are capable of incorporating large amounts of amphiphilic guest molecules. Simultaneously, multivalent ions can coordinate to the surfaces of charged denpols, leading to counterion-induced aggregation of the already guest-loaded host structures. Thus, although the local guest concentration in denpol-based molecular transport might already be initially high due to the dense guest packing inside the dendritic denpol scaffolding, the "local" guest concentration can nonetheless be further increased by packing (through aggregation) of the host-guest complexes themselves. Subsequent release of guest compounds from densely aggregated dendronized polymers is then possible (e.g., through increasing the solution concentration of imidazolium-based ions). Augmented with this release possibility, the concept of twofold packing of guests, firstly through hosting itself and secondly through aggregation of the hosts, gives rise to a load-collapse-release cascade that strikingly displays the high potential of dendronized macromolecules for future molecular transport applications.

Self-Assembly of Cholesterol-Containing Water-Soluble Polymers

Self-assembly of amphiphilic polymers containing cholesteryl groups has proved to be attractive in the field of nanotechnology research. Some cholesterol derivatives are known to form ordered structures which indicate thermotropic and lyotropic liquid-crystalline, monolayers, multilayers, micelles, and liposomes. This paper involves the synthesis and characterization of various kinds of amphiphilic polymers bearing cholesteryl moieties.

Serum-stable, long-circulating, pH-sensitive PEGylated liposomes

pH-sensitive liposomes have been designed to deliver active compounds, specifically to acidic intracellular organelles and to augment their cytoplasmic concentrations. These systems combine the protective effects of other liposomal formulations with specific environment-controlled drug release. They are stable at physiological pH, but abruptly discharge their contents when endocytosed into acidic compartments, allowing the drug to be released before it is exposed to the harsh environment of lysosomes. Serum-stable formulations with minimal leakage at physiological pH and rapid drug release at pH 5.0-5.5 can be easily prepared by inserting a hydrophobically modified N-isopropylacrylamide/methacrylic acid copolymer (poly(NIPAM-co-MAA)) in the lipid bilayer of sterically stabilized liposomes. The present chapter describes polymer synthesis, as well as the preparation, and characterization of large unilamelar pH-sensitive vesicles.

Polymeric micelles for drug targeting

Polymeric micelles are nano-delivery systems formed through self-assembly of amphiphilic block copolymers in an aqueous environment. The nanoscopic dimension, stealth properties induced by the hydrophilic polymeric brush on the micellar surface, capacity for stabilized encapsulation of hydrophobic drugs offered by the hydrophobic and rigid micellar core, and finally a possibility for the chemical manipulation of the core/shell structure have made polymeric micelles one of the most promising carriers for drug targeting. To date, three generations of polymeric micellar delivery systems, i.e. polymeric micelles for passive, active and multifunctional drug targeting, have arisen from research efforts, with each subsequent generation displaying greater specificity for the diseased tissue and/or targeting efficiency. The present manuscript aims to review the research efforts made for the development of each generation and provide an assessment on the overall success of polymeric micellar delivery system in drug targeting. The emphasis is placed on the design and development of ligand modified, stimuli responsive and multifunctional polymeric micelles for drug targeting.

Hydrophilic Monodisperse Magnetic Nanoparticles Protected by an Amphiphilic Alternating Copolymer

Iron oxide nanoparticles (NPs) with diameters of 16.1, 20.5, and 20.8 nm prepared from iron oleate precursors were coated with poly(maleic acid-alt-1-octadecene) (PMAcOD). The coating procedure exploited hydrophobic interactions of octadecene and oleic acid tails while hydrolysis of maleic anhydride moieties allowed the NP hydrophilicity. The PMAcOD nanostructure in water and the PMAcOD-coated NPs were studied using transmission electron microscopy, zeta-potential measurements, small-angle X-ray scattering, and fluorescence measurements. The combination of several techniques suggests that independently of the iron oxide core and oleic acid shell structures, PMAcOD encapsulates NPs, forming stable hydrophilic shells which withstand absorption of hydrophobic molecules, such as pyrene, without shell disintegration. Moreover, the PMAcOD molecules are predominantly attached to a single NP instead of self-assembling into the PMAcOD disklike nanostructures or attachment to several NPs. This leads to highly monodisperse aqueous samples with only a small fraction of NPs forming large aggregates due to cross-linking by the copolymer macromolecules.

Mixed micelles formed from graft and diblock copolymers for application in intracellular drug delivery

A novel mixed micelle that comprised of poly(N-isopropylacrylamide-co-methacrylic acid)-graft-poly(D,L-lactide) (P(NIPAAm-co-MAAc)-g-PLA) with methoxy poly(ethylene glycol)-b-poly(D,L-lactide) (mPEG-b-PLA) was developed for application in cancer therapy. The mixed micelle had an multi-functional inner core of P(NIPAAm-co-MAAc)-g-PLA to enable intracellular drug delivery and an extended hydrophilic outer shell of mPEG to hide the inner core. Stability analysis of the mixed micelles in bovine serum albumin (BSA) solution indicates that the diblock copolymer mPEG efficiently protected the BSA adsorption on the mixed micelles because the hydrophobic groups of graft copolymer were efficiently screened by mPEG. From the drug release study, the mPEG-PLA diblock copolymer in mixed micelles slightly affected the functionalities of the P(NIPAAm-co-MAAc)-g-PLA graft copolymer; the graft copolymer still exhibited pH- and thermo-sensitivities in this core-shell structure. A change in pH deformed the structure of the inner core from that of aggregated P(NIPAAm-co-MAAc), causing the release of a significant quantity of doxorubicin (Dox) from mixed micelles. Clear differences between free Dox and Dox-mixed micelles were observed using confocal laser scanning microscopy (CLSM). This study presents not only a new micelle structure for a graft-diblock copolymer system, but also a method for overcoming some of the limitations on biomaterials used in intravenous injection.

Characterization of self-assembling copolymers in aqueous solutions using Electron Paramagnetic Resonance and Fluorescence spectroscopy

Electron Paramagnetic Resonance and fluorescence spectroscopy have been used to determine the micropolarity and microviscosity of self-assembling systems based on mmePEG-p(CL-co-TMC) having different PEG chain lengths and different CL/TMC ratios and PEG/MOG/SA (45/5/50) polymers with different PEG chain lengths. Four reporter probes have been used: two spin probes, 16-doxyl stearic acid and 5-doxylstearic acid, and two fluorescent probes, pyrene and 1,3-bis(1-pyrenyl) propane (P3P). We found that the micelles based on mmePEG-p(CL-co-TMC) polymers are of a biphasic nature. The micelles are made of a hydrophilic corona with low viscosity while the core of the micelle is more hydrophobic and more viscous. The outer shell is made up of PEG chains, the hydrophobic part of the chains making the core. The partial hydration of the shell seems to lead to a looser chain network than that associated with deeper domains in the micelles. By contrast, in micelles composed of PEG/MOG/SA, there is no clear domain separation. This is consistent with a spatial configuration of random polymeric chains forming a loose network. In these micelles, the microviscosity is low and the hydrophobicity is high.

Functionalization of single-walled carbon nanotube by the covalent modification with polymer chains

A single-walled carbon nanotube (SWNT), which had been oxidized by incubation with a mixture of nitric acid and sulfuric acid to afford carboxyl groups at its ends, was incubated with an azo-type radical initiator carrying poly(2-methacryloyloxyethyl D-glucopyranoside) blocks at both ends (PMEGlc-initiator). Due to its high radical trapping activity, the SWNT could be coated with glycopolymers corresponding to the cloven macro-initiator (PMEGlc-SWNT). The PMEGlc-SWNT indicated a lectin (concanavalin A, Con A)-induced aggregation, and a buckey sheet composed of PMEGlc-SWNT could be used for the recovery of Con A from its aqueous solution. Furthermore, the carboxylated SWNT was also incubated with a terminal-aminated poly(N-isopropyl acrylamide) (PIPA) and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide HCl salt (PIPA-SWNT). The PIPA-SWNT indicated a definite temperature-responsiveness in the turbidity of its dispersion. These methods would be promising to modify SWNT with various functional polymers.