Binding of amino acids to "smart" sorbents: where does hydrophobicity come into play?

One-Shot Preparation of Thermoresponsive Comb Polyurethane Hydrogel for Both Excellent Toughness and Large Volume Switching

Thermoresponsive degradable polyurethane (PU) hydrogels are expected as the next-generation biomedical devices, although they have an important trade-off relationship between toughness and thermoresponsive properties. Tough and thermoresponsive comb PU hydrogels are prepared by one-shot poly-addition between hexamethylene diisocyanate, triethylene glycol tartrate ester, poly(ethylene glycol) 300 (PEG300), and glycerol. The swelling ratio change between 4 and 40 °C decreases as the proportion of PEG300 increases and is maintained at 600% switching within 30% PEG300. Moreover, the one-shot preparation of comb PU hydrogel with PEG300 improves toughness up to 100 times compared to the original comb PU hydrogel. Rheological analysis suggests that the bimodal toughening phenomenon for the proportion of PEG300 is due to the network structure and the hydrophobic aggregation domain. This simple toughening method using a heteronetwork based on the kinetic difference of step-growth PU is expected to apply to other chemical structures.

Phase transition characterization of poly(oligo(ethylene glycol)methyl ether methacrylate) brushes using the quartz crystal microbalance with dissipation

Heterogeneous non-linear poly(ethylene glycol) analogs, like poly(oligo(ethylene glycol)methyl ether methacrylate) (POEGMA), are of particular interest in the fabrication of smart biocompatible coatings as they undergo a reversible macromolecular rearrangement in response to external heat stimuli. The phase transition dynamics of POEGMA coatings in response to external temperature stimuli have been poorly investigated. The quartz crystal microbalance with dissipation (QCM-D) can be used to investigate the phase transition of these functional coatings as polymer brushes in a dynamic and noninvasive in situ measurement. POEGMA brushes with different thickness are synthesized from the surface of a QCM-D sensor following a living radical polymerization technique by varying the monomer molecular weight. Investigations on the thermoresponsive collapse and swelling of POEGMA brushes grafted from the surface of a QCM-D sensor reveal the reversible phase transition nature of these coatings. Furthermore, the potential of these smart coatings in the field of biotechnology was explored by investigating the absorption and desorption of a model drug. A pulsatile drug release profile triggered by an increase in temperature is observed from POEGMA brushes. POEGMA brushes have the potential to be utilized as polymer coatings for controlled and programable drug release.

Solubility behaviour of random and gradient copolymers of di- and oligo(ethylene oxide) methacrylate in water: effect of various additives

Poly[oligo(ethylene oxide)] based gradient and random copolymers with different compositions are synthesized via Cu-based atom transfer radical polymerization. The solubility behavior of these copolymers in pure water and in the presence of different salts, surfactants and ethanol is investigated. According to dynamic light scattering results, the lower critical solution temperature (LCST) depends on the structure of the copolymer and changes slightly in the presence of additives. Good cosolvents like ethanol can increase the LCST through dissolving the collapsed copolymer chains to some extent. The same effect is observed for surfactants that make the copolymer solution more stable by preventing aggregation. Above a certain concentration of surfactant, depending on the copolymer structure, the solution is stable at all temperatures (no LCST). The effect of salts on the solubility of the copolymers follows the Hofmeister series and it is related linearly to the salt concentration. Based on their affinity to the copolymer, the salts can increase or decrease the LCST. There is a considerable difference in phase transition changes for gradient or random copolymers after salt addition. While both copolymers show a two-step phase transition in the presence of different salts, the changes in the hydrodynamic radius and normalized scattering intensity are rather broad for random compared to gradient copolymers. Contrary to what was expected, varying the cations has no distinguishable effect on the LCST for both copolymers. All chlorides decrease the LCST. This decrease is almost the same for gradient copolymers and fluctuates for random copolymers.

Recent insights in magnetic hyperthermia: From the "hot-spot" effect for local delivery to combined magneto-photo-thermia using magneto-plasmonic hybrids

Magnetic hyperthermia which exploits the heat generated by magnetic nanoparticles (MNPs) when exposed to an alternative magnetic field (AMF) is now in clinical trials for the treatment of cancers. However, this thermal therapy requires a high amount of MNPs in the tumor to be efficient. On the contrary the hot spot local effect refers to the use of specific temperature profile at the vicinity of nanoparticles for heating with minor to no long-range effect. This magneto-thermal effect can be exploited as a relevant external stimulus to temporally and spatially trigger drug release. In this review, we focus on recent advances in magnetic hyperthermia. Indirect experimental proofs of the local temperature increase are first discussed leading to a good estimation of the temperature at the surface (from 0.5 to 6 nm) of superparamagnetic NPs. Then we highlight recent studies illustrating the hot-spot effect for drug-release. Finally, we present another recent strategy to enhance the efficacity of thermal treatment by combining photothermal therapy with magnetic hyperthermia mediated by magneto-plasmonic nanoplatforms.

Doxorubicin Intracellular Remote Release from Biocompatible Oligo(ethylene glycol) Methyl Ether Methacrylate-Based Magnetic Nanogels Triggered by Magnetic Hyperthermia

Hybrid nanogels, composed of thermoresponsive polymers and superparamagnetic nanoparticles, are attractive nanocarriers for biomedical applications, being able-as a polymer matrix-to uptake and release high quantities of chemotherapeutic agents and-as magnetic nanoparticles-to be heated when exposed to an alternative magnetic field (AMF), better known as magnetic hyperthermia. Herein, biocompatible, pH-responsive, magnetoresponsive, and thermoresponsive nanogels, based on oligo(ethylene glycol) methyl ether methacrylate monomers and a methacrylic acid comonomer were prepared by conventional precipitation radical copolymerization in water, post-assembled by complexation with iron oxide magnetic nanoparticles (MNPs) of maghemite (γ-Fe₂O₃), and loaded with an anticancer drug (doxorubicin, DOX), for remotely controlled drug release by a "hot spot", as an athermal magnetic hyperthermia strategy against cancer. These nanogels, denoted MagNanoGels, with a hydrodynamic diameter from 328 to 460 nm, as a function of the MNP content, have a swelling-deswelling behavior at their volume phase temperature transition around 47 °C in a physiological medium (pH 7.5), which is above the human body temperature (37 °C). Applying an alternative magnetic field increases the release of DOX by 2-fold, while no macroscopic heating was recorded. This enhanced drug release is due to a shrinking of the polymer network by local heating, as illustrated by the MagNanoGel size decrease under an AMF. In cancer cells, not only do the DOX-MagNanoGels internalize DOX more efficiently than free DOX, but also DOX intracellular release can be remotely triggered under an AMF, in athermal conditions, thus enhancing DOX cytotoxicity.

Thermoresponsive diblock glycopolymer by RAFT polymerization for lectin recognition

A thermoresponsive double-hydrophilic diblock glycopolymer, poly(diethyl- eneglycol methacrylate)-block-poly(6-O-vinyladipoyl-d-glucose) (PDEGMA-b-POVAG), was successfully prepared by a combination of enzymatic synthesis and reversible addition-fragment chain transfer (RAFT) polymerization protocols using poly(diethyl- eneglycol methacrylate) (PDEGMA) as macro-RAFT agent. The block glycopolymer was characterized by (1)H NMR and GPC. UV-vis, DLS and TEM studies revealed that the glycopolymer PDEGMA-b-POVAG was thermoresponsive with LCST at 31.0°C, and was able to self-assemble into spherical micelles of various sizes in aqueous solution. The glucose pendants in the glycopolymer could interact with the lectin Concanavalin A (Con A), the average hydrodynamic diameters of glycopolymer micelles increased to 170nm from 110nm after recognizing Con A. The diblock glycopolymer micelles have excellent biocompatibility with pig iliac endothelial cells, as measured using the MTT assay, but micelles loaded with Con A could be used to induce apoptosis in human hepatoma SMMC-7721 cells.

Fast and facile one-step synthesis of monodisperse thermo-responsive core–shell microspheres and applications

Highly monodisperse PMMA microspheres covered with a thermo-responsive shell were synthesized in a single step by means of photoinitiated RAFT dispersion polymerization at room temperature.

Poly[tri(ethylene glycol) ethyl ether methacrylate]-coated surfaces for controlled fibroblasts culturing

Well-defined thermosensitive poly[tri(ethylene glycol) monoethyl ether methacrylate] (P(TEGMA-EE)) brushes were synthesized on a solid substrate by the surface-initiated atom transfer radical polymerization of TEGMA-EE. The polymerization reaction was initiated by 2-bromo-2-methylpropionate groups immobilized on the surface of the wafers. The changes in the surface composition, morphology, philicity, and thickness that occurred at each step of wafer functionalization confirmed that all surface modification procedures were successful. Both the successful modification of the surface and bonding of the P(TEGMA-EE) layer were confirmed by X-ray photoelectron spectroscopy (XPS) measurements. The thickness of the obtained P(TEGMA-EE) layers increased with increasing polymerization time. The increase of environmental temperature above the cloud point temperature of P(TEGMA-EE) caused the changes of surface philicity. A simultaneous decrease in the polymer layer thickness confirmed the thermosensitive properties of these P(TEGMA-EE) layers. The thermosensitive polymer surfaces obtained were evaluated for the growth and harvesting of human fibroblasts (basic skin cells). At 37 °C, seeded cells adhered to and spread well onto the P(TEGMA-EE)-coated surfaces. A confluent cell sheet was formed within 24 h of cell culture. Lowering the temperature to an optimal value of 17.5 °C (below the cloud point temperature of the polymer, TCP, in cell culture medium) led to the separation of the fibroblast sheet from the polymer layer. These promising results indicate that the surfaces produced may successfully be used as substrate for engineering of skin tissue, especially for delivering cell sheets in the treatment of burns and slow-healing wounds.

Thermodynamic studies of partitioning behavior of cytochrome c in ionic liquid-based aqueous two-phase system

The ionic liquid/aqueous two-phase extraction systems (ATPSs) based on imidazolium ionic liquids were used to extract cytochrome c. Effects of the alkyl chain length of the ionic liquid cations, concentration of potassium citrate, temperature and pH on the extraction efficiency have been investigated. The thermodynamic parameters (ΔG(T)°, ΔH(T)° and ΔS(T)°) associated with Cyt-c partitioning in aqueous two phase systems were determined. Thermodynamic studies indicated that the partitioning of Cyt-c was driven by both hydrophobic and electrostatic interactions in the extraction process. Under the optimum conditions, experiment results showed that 94% of the cytochrome c could be extracted into the ionic liquid-rich phase in a one-step extraction. The structural characterization of Cyt-c in the IL ATPS was investigated by UV-vis and circular dichroism (CD) spectra. The results demonstrated that no direct bonding interaction observed between ionic liquid and cytochrome c, while the native properties of the cytochrome c were not altered. Compared with traditional liquid-liquid extractions based on toxic organic solvents, ionic liquid/aqueous two phase extraction offers clear advantages due to no use of volatile organic solvent and low consumption of imidazolium ionic liquids.

Assembly and degradation of low-fouling click-functionalized poly(ethylene glycol)-based multilayer films and capsules

Nano-/micrometer-scaled films and capsules made of low-fouling materials such as poly(ethylene glycol) (PEG) are of interest for drug delivery and tissue engineering applications. Herein, the assembly and degradation of low-fouling, alkyne-functionalized PEG (PEG(Alk) ) multilayer films and capsules, which are prepared by combining layer-by-layer (LbL) assembly and click chemistry, are reported. A nonlinear, temperature-responsive PEG(Alk) is synthesized, and is then used to form hydrogen-bonded multilayers with poly(methacrylic acid) (PMA) at pH 5. The thermoresponsive behavior of PEG(Alk) is exploited to tailor film buildup by adjusting the assembly conditions. Using alkyne-azide click chemistry, PEG(Alk)/PMA multilayers are crosslinked with a bisazide linker that contains a disulfide bond, rendering these films and capsules redox-responsive. At pH 7, by disrupting the hydrogen bonding between the polymers, PEG(Alk) LbL films and PEG(Alk) -based capsules are obtained. These films exhibit specific deconstruction properties under simulated intracellular reducing conditions, but remain stable at physiological pH, suggesting potential applications in controlled drug release. The low-fouling properties of the PEG films are confirmed by incubation with human serum and a blood clot. Additionally, these capsules showed negligible toxicity to human cells.

Temperature-responsive glass coverslips with an ultrathin poly(N-isopropylacrylamide) layer

A temperature-responsive cross-linked polymer gel was covalently grafted onto glass coverslips by electron beam irradiation. The grafted thickness and amount of polymer as well as the surface wettability increased with the initial monomer concentration. When the monomer concentration was 5 wt.%, the grafted polymer density was 0.84microgcm(-2), and cells adhered and spread on the surface at 37 degrees C, but detached at 20 degrees C. In contrast, when the monomer concentration was 35 wt.%, the polymer density was 1.28microgcm(-2), and the surfaces were cell repellent even at 37 degrees C. These results show a remarkable contrast to those obtained from temperature-responsive polymer-grafted tissue culture polystyrene dishes, since various types of cells showed temperature-dependent cell adhesion/detachment when the grafted density was around 2microgcm(-2) on these surfaces. We discuss the possible molecular mechanisms underlying this discrepancy.

Factors affecting ionic liquids based removal of anionic dyes from water

Liquid--liquid extraction with imidazolium based ionic liquids--[C4mim][PF6], [C6miml][PF6], [C6mim[BF4], and [C8mim][PF6--is proposed for removal of anionic dyes including methyl orange, eosin yellow, and orange G from aqueous solutions. The effects of extraction time, pH of aqueous phase, structure of the ionic liquids, temperature, and KCl concentration on the extraction efficiencies have been studied. Extraction efficiencies of dyes were strongly affected by the pH of the aqueous phase. Under the optimized pH condition, 85-99% of methyl orange, almost 100% eosin yellows, and 69% of orange G in tested water samples were transferred into the ionic liquids in a single extraction. Extraction efficiency for a given dye was found to increase with increasing temperature and increasing alkyl chain length of cation of the ionic liquids. Presence of a small amount of KCl in the aqueous phase did not considerably improve the extraction efficiency of the dyes. Thermodynamic studies revealed that the extraction process was driven by hydrophobic interaction of the anionic dyes and the ionic liquids.

Adsorption of zwitterionic drugs onto oxidized cellulose

Adsorption of zwitterionic drugs (beta-lactam antibiotics and amino acids) onto samples of oxidized cellulose (OC) with various carboxyl contents and structural characteristics from aqueous and water/alcohol solutions was investigated. The adsorption process can be described according to the theory of localized stoichiometric adsorption and represented by Langmuir isotherms. It was established that the constants of interfacial distribution mainly increase with increased relative sorbate hydrophobicity. The dependencies of adsorption on pH of equilibrium drug solution have a maximum at pH 3-3.5, which is caused by peculiarities of dissociation of OC and sorbates. The drug uptake is shown to increase with an increase of alcohol mole fraction in the solution and transfer to the binary water/isopropanol from water/ethanol solutions. The dominant contribution to the increase of uptake is the desolvation of ionic groups of zwitterions in the solution, which increases with increased alcohol content. The degree of crystallinity of the sorbent has no considerable effect on drug adsorption from aqueous solutions. In water/alcohol solutions the adsorption of drugs by OC samples with similar exchange capacity increases with reducted uniformity of carboxylic group distribution in the volume of the polymer, which is connected with increased accessibility of carboxylic groups for sorbate molecules.

Multilayer adsorption of amino acids on oxidized cellulose

The adsorption of amino acids (AA) (glycine, L-alanine, L-proline) on oxidized cellulose (OC) with various carboxyl contents and degrees of crystallinity from aqueous and water/ethanol solutions was studied. It was found that multilayer adsorption occurs in concentrated solutions of AA. It proceeds according to successive mechanisms via adsorption of AA zwitterions onto carboxyls of already adsorbed AA. This leads to formation of chain AA associates in the OC phase. A sharp increase in swelling accompanies multilayer adsorption. It was established that structural characteristics and degree of polymerization of OC are the main factors that affect multilayer adsorption. The distribution of carboxyls in the OC phase also plays an important role. Multilayer adsorption does not proceed in water/ethanol solutions and in the case of the cationic form of AA.

Survey of the year 2004: literature on applications of isothermal titration calorimetry

The market for commercially available isothermal titration calorimeters continues to grow as new applications and methodologies are developed. Concomitantly the number of users (and abusers) increases dramatically, resulting in a steady increase in the number of publications in which isothermal titration calorimetry (ITC) plays a role. In the present review, we will focus on areas where ITC is making a significant contribution and will highlight some interesting applications of the technique. This overview of papers published in 2004 also discusses current issues of interest in the development of ITC as a tool of choice in the determination of the thermodynamics of molecular recognition and interaction.