Wenwen Li

Carnegie Mellon University, Pittsburgh, Pennsylvania, United States

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Publications (15)56.3 Total impact

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    ABSTRACT: As an alternative to current methods of local nerve block, we studied the feasibility of producing ankle block in the rat with IV injection of magnetic nanoparticles (MNPs) associated with ropivacaine and application of a magnet at the ankle. The anesthetic effect of magnet-directed ropivacaine-associated MNPs (MNP/ Ropiv) was tested in the rat using paw withdrawal latencies from thermal stimuli applied to the hindpaw. The MNP/Ropiv complexes consisted of 0.7% w/v ropivacaine and 0.8% w/v MNPs containing 12% w/w magnetite (Fe3O4). The effect of IV injection of MNP/Ropiv with 15, 30, and 60-minute magnet application to the right ankle was compared with the effect without magnet application on the left hindpaw, to conventional ankle block with 0.1% or 0.2% ropivacaine, and to IV injection of MNPs alone with 30-minute magnet application to the right ankle. In addition, the pharmacokinetics of the MNP/Ropiv complexes were determined. IV injection of MNP/Ropiv with magnet application at the ankle significantly increased paw withdrawal latencies from thermal stimuli compared with pretreatment baselines in the same paw (P < 0.0001) and compared with the contralateral paw without magnet application (P < 0.0001). IV injection of MNPs alone had no significant effect on paw withdrawal latency. Absolute ropivacaine concentrations in ankle tissue, and ankle tissue-to-plasma concentration ratios were higher in the MNP/Ropiv group with 30-minute magnet application compared with MNP/Ropiv group without magnet application (mean ± SEM, 150 ± 10 ng/g vs 105 ± 15 ng/g, respectively, and 6.1 ± 0.8 vs 4.2 ± 0.7, respectively). The current study establishes proof of principle that it is possible to produce ankle block in the rat by IV injection of MNP/Ropiv complexes and magnet application at the ankle. The results indicate that further study of this approach is warranted.
    Anesthesia and analgesia 04/2014; · 3.08 Impact Factor
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    ABSTRACT: a b s t r a c t A series of porous polymers with different pore volumes, pore sizes, and crosslinking densities were synthesized by high internal phase emulsion (HIPE) polymerization. The crosslinked polymerized HIPEs (polyHIPEs) were formed by the copolymerization of 4-vinylbenzyl chloride and divinylbenzene using water droplets in conventional or Pickering HIPEs as the templates. These porous materials were further modified by quaternization and ion exchange to introduce quaternary ammonium hydroxide groups. The resulting polyHIPEs were utilized as sorbents for reversible CO 2 capture from air using the humidity swing. The effect of pore structure on the CO 2 adsorption and desorption processes was studied. The polyHIPEs containing large pores and interconnected porous structures showed improved swing sizes and faster adsorption/desorption kinetics of CO 2 compared to a commercial Excellion membrane with similar functional groups.
    08/2013;
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    ABSTRACT: Several polymeric materials were prepared for reversible CO2 capture. These materials contain quaternary ammonium ions and hydroxide counter ions, including polymers grafted from carbon black, crosslinked porous polymers templated by ordered colloidal crystals, and high internal phase emulsion systems. The porous polymers displayed an order of magnitude improvement in the kinetics of the absorption and desorption processes and a significant improvement in the swing sizes compared to a commercially available material with similar functional groups. This work suggests a new direction for the design of porous polymeric materials for CO2 air capture.
    Energy & Environmental Science 01/2013; 6(2):488-493. · 11.65 Impact Factor
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    ABSTRACT: Poly(methyl acrylate)-b-polystyrene with controlled molecular weight distribution of each block was synthesized via activators regenerated by electron transfer atom transfer radical polymerization. Polymers with tunable dispersity, in the range of Mw/Mn 1.32 to 2.0, were achieved by adjusting the concentration of the copper catalyst and reaction temperature, thereby controlling the rate of reversible deactivation reaction as well as the number of monomer units added during each activation cycle. Regardless of the increased dispersity, high chain-end functionality was retained and the livingness of the macroinitiators was confirmed by chain extension, resulting in diblock copolymers with controlled dispersity in each block. Liquid chromatography under critical conditions was employed to determine if any macroinitiator remained in the final product.
    Macromolecular Chemistry and Physics 12/2012; 213(24). · 2.39 Impact Factor
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    ABSTRACT: A water soluble monomer, oligo(ethylene glycol) monomethyl ether methacrylate (OEOMA), was successfully polymerized in an inverse microemulsion system via the activator generated by electron transfer atom transfer radical polymerization (AGET ATRP) technique. Stable colloidal particles with a readily tunable size, ranging from ca. 35 to 200 nm, were obtained by adjusting the amount and the type of reducing agent used for the generation of activators in the AGET ATRP and by adjusting the aqueous phase fraction in the inverse microemulsion system. The formed particles contained well-defined water-soluble polymers with relatively narrow molecular weight distribution (Mw/Mn < 1.5). The introduction of a small amount of divinyl cross-linkers into the system allowed the synthesis of cross-linked hydrogel nanoparticles. The cross-linked particles retained their morphology when they were redispersed in methanol or water, as evidenced by the constant particle size determined by dynamic light scattering (DLS).
    Polym. Chem. 06/2012; 3(7):1813-1819.
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    ABSTRACT: Polymer biomolecule hybrids represent a powerful class of highly customizable nanomaterials. Here, we report star-polymer conjugates with DNA using a "ligandless" Cu(I) promoted azide-alkyne cycloaddition click reaction. The multivalency of the star-polymer architecture allows for the concomitant conjugation of other molecules along with the DNA, and the conjugation method provides control over the DNA orientation. The star-polymer DNA nanoparticles are shown to assemble into higher-order nanoassemblies through hybridization. Further, we show that the DNA strands can be utilized in controlled disassembly of the nanostructures.
    Bioconjugate Chemistry 08/2011; 22(10):2030-7. · 4.58 Impact Factor
  • Macromolecular Chemistry and Physics 08/2011; 212(15). · 2.39 Impact Factor
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    ABSTRACT: A series of star-shaped poly(ethylene oxide) (PEO) with azide groups at the end of each arm were synthesized by combination of anionic ring-opening polymerization (AROP) and aqueous activators generated by electron transfer for atom transfer radical polymerization (AGET ATRP). First, α-azido, ω-hydroxy heterofunctional PEOs were prepared by AROP of ethylene oxide (EO) using tetrabutylammonium azide as initiator and triisobutylaluminum as catalyst. Then, a clickable PEO ATRP macroinitiator, α-azido, ω-bromoisobutyryl heterofunctional PEO, was synthesized by an esterification of the ω-hydroxy end group with 2-bromoisobutyryl bromide. Finally, an AGET ATRP of ethylene glycol diacrylate (EGDA) was carried out in water using the α-azido, ω-bromoisobutyryl heterofunctional PEOs as macroinitiator and surfactant. The absolute molecular weights of the products were characterized by static laser light scattering in water. Azide PEO stars with Mw = 6.58 × 106 and average 309 arms were obtained using azide PEO macroinitiators with Mn = 9800 and [EGDA]/[MI] = 58. However, control over topology was lost for [EGDA]/[MI] > 100, resulting in irregular aggregates. The core−shell morphology of the functional star PEOs was observed by transmission electron microscopy. Fluorescent PEO stars were obtained by “clicking” dansyl probes onto the star shell, as verified by fluorescence spectra.
    Macromolecules. 03/2011;
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    ABSTRACT: The influence of dilution on the degree of intra- or intermolecular cross-linking reactions during the copolymerization of a monomer and a divinyl cross-linker via atom transfer radical polymerization (ATRP) technique was studied. To maximize intramolecular cross-linking, highly dilute systems with 0.5−10 vol % of monomer plus cross-linker vs solvent were used. The fraction of branched polymers formed through intermolecular consumption of pendant vinyl groups was calculated for each system through multipeak splitting of the gel permeation chromatography (GPC) curves. Progressive dilution of the reaction media resulted in the formation of products containing less branched polymers. Absolute molecular weights and compactness of the formed polymers determined by GPC with a multiangle laser light scattering (MALLS) detector further confirmed the formation of majority nonbranched polymer structures in more dilute systems, indicating an enhanced level of intramolecular cross-linking reactions in this case.
    Macromolecules 01/2011; · 5.93 Impact Factor
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    ABSTRACT: Amphiphilic star shaped polymers with poly(ethylene oxide) (PEO) arms and cross-linked hydrophobic core were synthesized in water via either conventional free radical polymerization (FRP) or atom transfer radical polymerization (ATRP) techniques using a simple "arm-first" method. In FRP, PEO based macromonomers (MM) were used as arm precursors, which were then cross-linked by divinylbenzene (DVB) using 2,2'-azoisobutyronitrile (AIBN). Uniform star polymers (Mw/Mn < 1.2) were achieved through adjustment of the ratio of PEO MM, DVB, and AIBN. While in case of ATRP, both PEO MM, and PEO based macroinitiator (MI) were used as arm precursors with ethylene glycol diacrylate as cross-linker. Even more uniform star polymers with less contamination by low MW polymers were obtained, as compared to the products synthesized by FRP.
    Macromolecular Rapid Communications 01/2011; 32(1):74-81. · 4.93 Impact Factor
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    ABSTRACT: The effect of dilution on random living copolymerization of vinyl- and divinyl monomers with fast initiation and slow propagation was simulated and compared with the experiments. Two Monte Carlo simulation methods have been used: one, purely statistical, based on the Flory–Stockmayer (FS) theory and the second using the dynamic lattice liquid model (DLL). The results were compared with experiments using atom transfer radical polymerization (ATRP), one of controlled/living radical polymerization methods. Molecular weights, polydispersities and the crosslinking/cyclization of macromolecules were analyzed as a function of conversion and time for various solvent concentrations and initiator crosslinker/monomer ratios. The results obtained by the DLL method are in good agreement with the experiment, showing an increase of conversion and time at gel point with dilution, i.e., with the increase of solvent concentration. The FS theory was found to be unable to reproduce even qualitatively the dilution effect on gelation. It is shown that intrachain crosslinking becomes more and more important with increasing solvent concentration, preventing macroscopic gelation at high dilutions, even if the number of crosslinks per primary chain is much greater than one (Flory criterion).DLL simulations give an insight into the mechanism of crosslinking processes near the gel point (leading to gelation) and/or microgel formation when solvent concentration is too high. At very high solvent concentration polymerization is slow and side effects like deactivation of radicals become important. Taking such effects into account, the simulation gives better agreement with the experimental data.
    Polymer. 01/2011; 52(22):5092-5101.
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    ABSTRACT: Dual-functional amphiphilic block copolymers, alpha-azido-omega-2-chloroisobutyrate-poly(oligo(ethylene oxide) monomethyl ether methacrylate)-b-poly(n-butyl methacrylate), prepared by atom-transfer radical polymerization were used as dual-reactive surfactants (i.e., macroinitiators for a miniemulsion copolymerization of a monovinyl monomer and divinyl cross-linker as well as surfactants with latent functionality). Because of the amphiphilic nature of the block copolymers used as surfactant/initiators, the polymerization was initiated at the oil-water interface, with polymer chains slowly growing inward in a controlled manner after activation by the catalyst. Polymeric nanocapsules with cross-linked shells and the latent azido functionality were obtained. Introduction of various degradable cross-linking agents into the system resulted in the formation of nanocapsules that were cleaved under specific conditions. The preserved latent alpha-terminal azido groups in the dual-reactive surfactant were utilized to attach a fluorescent dansyl probe and/or atom-transfer radical polymerization initiators to grow linear polymer chains forming an additional shell covalently connected to the nanocapsules.
    Journal of the American Chemical Society 06/2010; 132(23):7823-5. · 10.68 Impact Factor
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    ABSTRACT: Stable hollow polymeric nanocapsules with a cross-linked shell were prepared through an interfacially confined copolymerization of a monovinyl monomer and divinyl cross-linker via an activator generated by electron transfer atom transfer radical polymerization (AGET ATRP) in a miniemulsion system. An amphiphilic block copolymer poly(ethylene oxide)-b-poly(n-butyl methacrylate) (PEO−PBMA−Cl) was used as a stabilizer/macroinitiator. The amphiphilic nature of the macroinitiator ensures that the polymerization starts from the aqueous/monomer droplet interface with polymer chains slowly growing inward in a controlled manner by an AGET initiated ATRP. Characterization of the resulting particles by TEM, Cryo-SEM, and AFM provided direct evidence that nanoparticles with a hollow structure were successfully prepared. Introduction of cross-linking units to the shell of the particles improved the stability of the particles, which could be easily redispersed in some common organic solvents.
    Macromolecules. 11/2009;
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    ABSTRACT: Amphiphilic star polymers with low polydispersity (PDI) and high molecular weight were synthesized by an activator generated by electron transfer atom transfer radical polymerization (AGET ATRP) in aqueous dispersed media using a simple "arm-first" method and linear block copolymers poly(ethylene oxide)-b-polystyrene (PEO-PS-Cl) as arm precursors. The amphiphilic block copolymers PEO-PS-Cl with halogen chain-end functionality formed micelles in water and then were cross-linked by the divinyl cross-linkers. Due to the formation of cross-linker swollen micelles before the polymerization was initiated, star-star or star-linear chain reactions were not required for the star formation. The suppressed star-star coupling reactions resulted in the formation of star polymers with low PDI (M(w)/M(n) < 1.1) but still high molecular weight (over 1000 kg/mol).
    Journal of the American Chemical Society 07/2009; 131(30):10378-9. · 10.68 Impact Factor
  • Macromolecules. 04/2009; 42(7).