Smart Microgel Studies. Interaction of Polyether-Modified Poly(Acrylic Acid) Microgels with Anticancer Drugs

Studies of submillimeter gels composed of covalently cross-linked poly(acrylic acid)-g-poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (Pluronic-PAA) networks are reviewed in light of potential applications of the microgels as drug carriers in oral delivery. The microgels are capable of volumetric transitions in response to environmental stimulae such as pH and temperature. It is shown that the type of Pluronic used in the microgel synthesis changes the structure of the resulting microgels, with the more hydrophobic Pluronic imparting porosity. Microgels based on Pluronic L92 (L92-PAA-EGDMA) possess higher ion-exchange capacity than microgels based on Pluronic F127 (F127-PAA-EGDMA), albeit the former are more hydrophobic. Analogously, more hydrophobic but heterogeneous L92-PAA-EGDMA exhibit superior capacity for equilibrium loading of hydrophobic drugs such as taxol, camptothecin and steroid hormones, as well as higher capacity for weakly basic drugs such as doxorubicin, mitomycin C, and mitoxantrone.Singapore-MIT Alliance (SMA

Surface Functionalization of Monodisperse Magnetic Nanoparticles

We present a systematic methodology to functionalize magnetic nanoparticles through surface-initiated atom-transfer radical polymerization (ATRP). The magnetite nanoparticles are prepared according to the method proposed by Sun et al. (2004), which leads to a monodisperse population of ~ 6 nm particles stabilized by oleic acid. The functionalization of the nanoparticles has been performed by transforming particles into macro-initiators for the ATRP, and to achieve this two different routes have been explored. The first one is the ligand-exchange method, which consists of replacing some oleic acid molecules adsorbed on the particle surface with molecules that act as an initiator for ATRP. The second method consists in using the addition reaction of bromine to the oleic acid double bond, which turns the oleic acid itself into an initiator for the ATRP. We have then grown polymer brushes of a variety of acrylic polymers on the particles, including polyisopropylacrylamide and polyacrylic acid. The nanoparticles so functionalized are water soluble and show responsive behavior: either temperature responsive behavior when polyisopropylacrylamide is grown from the surface or PH responsive in the case of polyacrylic acid. This methodology has potential applications in the control of clustering of magnetic nanoparticles.Singapore-MIT Alliance (SMA

Electrochemically-mediated adsorptive processes for CO2 capture

The capture of anthropogenic carbon dioxide CO2 from industrial and power generation sources, where the concentration of CO2 is relatively high, is an important component in an overall portfolio of low carbon energy sources for climate change mitigation. The US Department of Energy (DOE) acknowledges, for instance, that for the foreseeable future coal will continue to play a critical role in the national and global electricity generation, and that innovations in the field of carbon capture from high concentration sources such as coal combustion and coal gasification units are crucial. In addition, on-board carbon capture for reduced emission from vehicles and other mobile sources, which account for almost 30% of all emissions in the US, has garnered interest over the last few years by the automotive, and gas and oil industries. Other sources of much lower CO2 concentration collectively represent a large volume of carbon emissions, and there is thus a growing interest on the part of the DOE and private industries in capture technologies that operate over a wide range of CO2 concentrations, especially at concentrations below 1%. There is also a significant benefit to innovations in the removal of CO2 from enclosed spaces such as in buildings, aircraft, spacecraft and submarines, where the concentration of CO2 is in the 1,000-10,000 ppm range, and the small spaces available limit the types of capture technologies that can be used. The removal of CO2 from buildings to reduce its overall concentration to acceptable levels for human activity will obviate the need for frequent air exchanges and thereby reduce the energy needs for conditioning of fresh air brought into the buildings; this in turn results in fewer CO2 emissions from power plants. Please click Additional Files below to see the full abstract

Responsive Azobenzene-Containing Polymers and Gels

The photoviscosity effect in aqueous solutions of novel poly(4-methacryloyloxyazobenzene-co-N,N-dimethyl acrylamide) (MOAB-DMA) was demonstrated. The observed significant reduction in the zero-shear viscosity upon UV-irradiation of MOAB-DMA aqueous solutions was due to the dissociation of the interchain azobenzene aggregates. Such phenomena can be advantageously used in photoswitchable fluidic devices and in protein separation. Introduction of enzymatically degradable azo cross-links into Pluronic-PAA microgels allowed for control of swelling due to degradation of the cross-links by azoreductases from the rat intestinal cecum. Dynamic changes in the cross-link density of stimuli-responsive microgels enable novel opportunities for the control of gel swelling, of importance for drug delivery and microgel sensoric applications.Singapore-MIT Alliance (SMA

Synthesis and Properties of Novel Cationic, Temperature-Sensitive Block-Copolymers

Facile, one-step synthesis of self-assembling, cationic block copolymers of poly(2-N-(dimethylaminoethyl) methacrylate) (pDMAEMA) and PEO-PPO-PEO (Pluronic®) is developed. The copolymers are obtained via free-radical polymerization of DMAEMA initiated by Pluronic-radicals generated by cerium (IV). The copolymers possess surface activity, are polycationic at pH<7.1, and self-assemble into micelle-like aggregates when neutralized. Potential applications of the novel copolymers for DNA transfection in gene therapy are discussed.Singapore-MIT Alliance (SMA

A Fluorescence Recovery After Photobleaching (FRAP) Technique for the Measurement of Solute Transport Across Surfactant-Laden Interfaces

The technique of Fluorescence Recovery After Photobleaching (FRAP) has been applied to the measurement of interfacial transport in two-phase systems. FRAP exploits the loss of fluorescence exhibited by certain fluorophores when over-stimulated (photobleached), so that a two-phase system, originally at equilibrium, can be perturbed without disturbing the interface by strong light from an argon-ion laser and its recovery monitored by a microscope-mounted CCD camera as it relaxes to a new equilibrium. During this relaxation, the concentration profiles of the probe solute are measured on both sides of the interface as a function of time, yielding information about the transport characteristics of the system. To minimize the size of the meniscus between the two phases, a photolithography technique is used to selectively treat the glass walls of the cell in which the phases are contained. This allows concentration measurements to be made very close to the interface and increases the sensitivity of the FRAP technique

A Review of Electrospun Carbon Fibers as Electrode Materials for Energy Storage

The applications of electrospun carbon fiber webs to the development of energy storages devices, including both supercapacitors and lithium ion batteries (LIB) , are reviewed. Following a brief discussion of the fabrication process and characterization methods for ultrafine electrospun carbon fibers, recent advances in their performance as supercapacitors and LIBs anode materials are summarized. Optimization of the overall electrochemical properties of these materials through choice of thermal treatment conditions, incorporation of additional active components (such as carbon nanotubes, metal oxides, and catalysts), and generation of novel fibrous structures (such as core-shell, multi-channel or porous fibers) is highlighted. Further challenges related to improving the conductivity, surface area, and mechanical properties of the carbon nanofiber webs, as well as the scale-up ability of the fabrication technique, are discussed.United States. Dept. of Energ

Dynamic Surface Tension Behaviour in a Photoresponsive Surfactant System

We report on the surface properties of a photoresponsive surfactant that incorporates the light-sensitive azobenzene group into its tail. Cis-trans photo-isomerization of this group alters the ability of the surfactant to pack into adsorbed monolayers at an air-water interface or into aggregates in solution, causing a significant variation in bulk and surface properties upon changes in the illumination conditions. NMR studies indicate that a solution left in the dark for an extended period of time contains trans isomer almost exclusively, while samples exposed to light of fixed wavelength eventually reach a photostationary equilibrium with significant amounts of both isomers present. Dynamic surface tension studies performed on this system under different illumination conditions (dark, UV light, visible light) show profoundly different approaches to equilibrium. At concentrations well above the CMC, the same equilibrium tension is reached in all three cases, presumably corresponding to a surface saturated with the trans (more surface active) isomer. The dark sample shows a simple, single-step relaxation in surface tension after creation of a fresh interface, while the UV and visible samples exhibit a more rapid initial decrease in tension, followed by a plateau of nearly constant tension, and end with a final relaxation to equilibrium. It is hypothesized that this behavior of the UV and visible samples is caused by competitive adsorption between the cis and trans isomers present in these mixtures. Presumably the cis surfactant reaches the interface more quickly, leading to a cis-dominated interface having a tension value corresponding to the intermediate plateau, but is ultimately displaced by the trans isomer. Diffusional time scale arguments which consider the extremes of possible micellar dissolution rates are used to analyze the relaxation data of the dark sample, and the results indicate that micellar dissolution in these samples is slow.Singapore-MIT Alliance (SMA

Measurement of resistance to solute transport across surfactant-laden interfaces using a Fluorescence Recovery After Photobleaching (FRAP) technique

A noninvasive fluorescence recovery after photobleaching (FRAP) technique is under development to measure interfacial transport in two phase systems without disturbing the interface. The concentration profiles of a probe solute are measured in both sides of the interface by argon-ion laser, and the system relaxation is then monitored by a microscope-mounted CCD camera

Polyacrylonitrile-based electrospun carbon paper for electrode applications

Polyacrylonitrile (PAN)-based carbon paper with fiber diameters of 200–300 nm was developed through hot-pressing, pre-oxidation, and carbonization of electrospun fiber mats. Changes in morphology, crystallinity, and surface chemistry of the hot-pressed carbon paper were investigated. More junctions between fibers were formed with increasing hot-press time, which is attributed to melting and bonding of fibers. The bulk density increased to 0.5–0.6 g/cm[superscript 3], which could help to improve the volume energy density for electrode applications. The conductivity of the carbon paper was found to be about 40 S/cm when the surface area was ∼ 2 m[superscript 2]/g, and depends not only on the conductivity of the individual nanofibers but also on the contacts between the nanofibers. The performance of the electrospun carbon paper as an electrode for electrochemical reactions involving ferrocene molecules was affected by the preparation protocol: the higher surface area of the electrodes formed with shorter hot-press times provided a higher current generated per unit mass than that obtained with electrodes prepared using longer hot-press time, but electrodes prepared with longer hot-press times exhibited higher electrical conductivity and faster electron transfer kinetics