Equilibrium chain exchange kinetics in block copolymer micelle solutions by dissipative particle dynamics simulations

Li, Zhenlong; Dormidontova, Elena E.

doi:10.1039/c0sm01443e

Cited by 57 publications

(142 citation statements)

References 57 publications

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“…The difference in compressive modulus of SPEXA gels at the same n can be attributed to differences in diffusivity and residence time of the reactive acrylates in the micellar structures. The residence time of the acrylates in the micelles’ core was directly correlated to the effective interfacial tension between the chain ends and water (γ) [39, 40] in which γ increased with hydrophobicity of the monomers from G to D, L and C. Therefore, the residence time of the acrylates in SPELA and SPECA was higher than those of SPEDA and SPEGA which lead to the higher entrapment of reactive acrylates in the crosslinked micellar domains and faster gelation times for SPELA and SPECA (Figure 3b). The lower residence time of the acrylates in SPEGA and SPEDA led to higher diffusivity of the acrylates, slower but more uniform crosslinking throughout the solution, resulting in the higher compressive modulus of the gels.…”

Section: Resultsmentioning

confidence: 99%

Time dependence of material properties of polyethylene glycol hydrogels chain extended with short hydroxy acid segments

Barati

Moeinzadeh

Karaman

et al. 2014

Polymer

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The objective of this work was to investigate the effect of chemical composition and segment number (n) on gelation, stiffness, and degradation of hydroxy acid-chain-extended star polyethylene glycol acrylate (SPEXA) gels. The hydroxy acids included glycolide (G,), L-lactide (L), p-dioxanone (D) and -caprolactone (C). Chain-extension generated water soluble macromers with faster gelation rates, lower sol fractions, higher compressive moduli, and a wide-ranging degradation times when crosslinked into a hydrogel. SPEGA gels with the highest fraction of inter-molecular crosslinks had the most increase in compressive modulus with n whereas SPELA and SPECA had the lowest increase in modulus. SPEXA gels exhibited a wide range of degradation times from a few days for SPEGA to a few weeks for SPELA, a few months for SPEDA, and many months for SPECA. Marrow stromal cells and endothelial progenitor cells had the highest expression of vasculogenic markers when co-encapsulated in the faster degrading SPELA gel.

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Section: Resultsmentioning

confidence: 99%

Time dependence of material properties of polyethylene glycol hydrogels chain extended with short hydroxy acid segments

Barati

Moeinzadeh

Karaman

et al. 2014

Polymer

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“…11 A single exponential decay was also observed by dissipative particle dynamics simulation 12 but, in addition to single unimer exchange, contributions from small aggregate fragmentation/merging and unequal size fusion/fission as additional kinetic mechanisms were found. In order to explain the logarithmic decay, Lund et al 4,5 discussed different mechanisms including possible effects of polydispersity but none of them finally could sufficiently explain the observed behavior.…”

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confidence: 80%

Equilibrium exchange kinetics in n-alkyl–PEO polymeric micelles: single exponential relaxation and chain length dependence

et al. 2012

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In this communication we present first results on the chain exchange kinetics of n-alkyl-PEO polymeric micelles by time-resolved small angle neutron scattering. We found that the rate strongly depends on the alkyl-chain length and that the relaxation function almost perfectly follows the single exponential decay predicted by theory. The key achievement of this study is the experimental verification that core block polydispersity accounts for the almost logarithmic time decay in block copolymer micelles as recently suggested by Choi et al. The results thus directly show that unimer exchange is the main mechanism for molecular exchange in block copolymer micelles.An important issue in the understanding of the self-assembling behavior of diblock copolymers in selective solvents is the kinetics of chain exchange between individual micellar entities in thermodynamic equilibrium.1 The exchange can be monitored by timeresolved small angle neutron scattering (TR-SANS) applying a sophisticated contrast variation technique. Significant perturbations as often required for other methods here are limited to simple hydrogen/deuterium isotope labelling.2-9 In an earlier work by using this technique we have studied the chain exchange kinetics of poly (ethylene-alt-propylene)-poly(ethylene oxide) (PEP-PEO) micelles in water/N,N-dimethylformamide mixtures.4,5,10 There we found that the measured relaxation curves follow a logarithmic time dependence in contradiction to the single exponential decay predicted by the theory of Halperin and Alexander.11 A single exponential decay was also observed by dissipative particle dynamics simulation 12 but, in addition to single unimer exchange, contributions from small aggregate fragmentation/merging and unequal size fusion/fission as additional kinetic mechanisms were found. In order to explain the logarithmic decay, Lund et al.4,5 discussed different mechanisms including possible effects of polydispersity but none of them finally could sufficiently explain the observed behavior. More recently Choi et al.8 succeeded in describing the logarithmic relaxation by taking properly into account the polydispersity of the core forming block. Following these ideas also the data of Lund et al.7 could be successfully re-evaluated thereafter. As put forward by Choi et al. the enormous effect of polydispersity on the kinetics can be rationalized by a double exponential dependence of the exchange rate on the core chain length: R(t) ¼ exp(Àkt) with k $ exp(ÀE a /k B T) where the activation energy E a is a function of the degree of polymerization N of the core block. Thus polydispersity effects become crucial even though M w /M n (where M w and M n the weight and number average molecular weight) is generally very small in micelle forming model polymers. However, direct experimental evidence is still missing due to the lack of suitable model compounds which should ideally consist of a monodisperse core polymer. As polymerization is a statistical process inherently leading to materials with a chain length dist...

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“…The identity of a nanocluster at any time t remains unchanged until more than half of its constituent molecules have left. The evolution of cluster composition with time is monitored using a molecular expulsion autocorrelation function f ( t ) 37,47 . In this function, all tH molecules in a given cluster (a cluster is defined here as an aggregate of four or more peptides) of specific size were marked as “native” at t’ .…”

Section: Methodsmentioning

confidence: 99%

Formation and Domain Partitioning of H-ras Peptide Nanoclusters: Effects of Peptide Concentration and Lipid Composition

Janosi

Gorfe

2012

J. Am. Chem. Soc.

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Experiments have shown that homologous Ras proteins containing different lipid-modification, which is required for membrane binding, form non-overlapping nanoclusters on the plasma membrane. However, the physical basis for clustering and lateral organization remained poorly understood. We have begun to tackle this issue using coarse-grained molecular dynamics simulations of the H-ras lipid anchor (tH), a triply lipid-modified heptapeptide embedded in a domain-forming mixed bilayer [Janosi L. et al., Proc. Natl. Acad. Sci. U. S. A. 2012 109:8097]. Here we use the same simulation approach to investigate the effect of peptide concentration and bilayer composition on the clustering and lateral distribution of tH. We found no major difference in the clustering behavior of tH above a certain concentration. However, the simulations predict the existence of a critical concentration below which tH does not form nanoclusters. Moreover, our data demonstrate that cholesterol enhances the stability of tH nanoclusters but is not required for their formation. Finally, analyses of peptide distributions and partition free energies allowed us to quantitatively describe how clustering facilitates the accumulation of tH at the interface between ordered and disordered domains of the simulated bilayer systems. These thermodynamic insights represent some of the key elements for a comprehensive understanding of the molecular basis for the formation and stability of Ras signaling platforms.

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Equilibrium chain exchange kinetics in block copolymer micelle solutions by dissipative particle dynamics simulations

Cited by 57 publications

References 57 publications

Time dependence of material properties of polyethylene glycol hydrogels chain extended with short hydroxy acid segments

Time dependence of material properties of polyethylene glycol hydrogels chain extended with short hydroxy acid segments

Equilibrium exchange kinetics in n-alkyl–PEO polymeric micelles: single exponential relaxation and chain length dependence

Formation and Domain Partitioning of H-ras Peptide Nanoclusters: Effects of Peptide Concentration and Lipid Composition

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