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Size evolution of highly amphiphilic macromolecular solution assemblies via a distinct bimodal pathway.

Kelley EG, Murphy RP, Seppala JE, Smart TP, Hann SD, Sullivan MO, Epps TH - Nat Commun (2014)

Bottom Line: Herein we demonstrate that unequivocal step-change shifts in micelle populations occur over several weeks following transfer into a highly selective solvent.Notably, these results underscore fundamental similarities between assembly processes in amphiphilic polymer, small molecule and protein systems.Moreover, the non-equilibrium micelle size increase can have a major impact on the assumed stability of solution assemblies, for which performance is dictated by nanocarrier size and structure.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Chemical and Biomolecular Engineering, University of Delaware, 150 Academy Street, Newark, Delaware 19716, USA [2].

ABSTRACT
The solution self-assembly of macromolecular amphiphiles offers an efficient, bottom-up strategy for producing well-defined nanocarriers, with applications ranging from drug delivery to nanoreactors. Typically, the generation of uniform nanocarrier architectures is controlled by processing methods that rely on cosolvent mixtures. These preparation strategies hinge on the assumption that macromolecular solution nanostructures are kinetically stable following transfer from an organic/aqueous cosolvent into aqueous solution. Herein we demonstrate that unequivocal step-change shifts in micelle populations occur over several weeks following transfer into a highly selective solvent. The unexpected micelle growth evolves through a distinct bimodal distribution separated by multiple fusion events and critically depends on solution agitation. Notably, these results underscore fundamental similarities between assembly processes in amphiphilic polymer, small molecule and protein systems. Moreover, the non-equilibrium micelle size increase can have a major impact on the assumed stability of solution assemblies, for which performance is dictated by nanocarrier size and structure.

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Summary of micelle size evolutionSchematic representation of changes in micelle size after cosolvent addition and removal. (a) Poly(butadiene-b-ethylene oxide) [PB-PEO] micelles self-assemble in pure water, decrease in size following THF cosolvent addition (<10% by volume), and remain kinetically trapped after solvent transfer to pure water. Micelles prepared in solutions containing low THF contents are not perturbed far from their equilibrium size and therefore do not undergo significant size relaxation. (b) Increasing the THF content (e.g. 40% by volume) and subsequently removing the cosolvent perturbs the micelles far from their equilibrium size in water, leading to size relaxation through a bimodal pathway.
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Figure 7: Summary of micelle size evolutionSchematic representation of changes in micelle size after cosolvent addition and removal. (a) Poly(butadiene-b-ethylene oxide) [PB-PEO] micelles self-assemble in pure water, decrease in size following THF cosolvent addition (<10% by volume), and remain kinetically trapped after solvent transfer to pure water. Micelles prepared in solutions containing low THF contents are not perturbed far from their equilibrium size and therefore do not undergo significant size relaxation. (b) Increasing the THF content (e.g. 40% by volume) and subsequently removing the cosolvent perturbs the micelles far from their equilibrium size in water, leading to size relaxation through a bimodal pathway.

Mentions: The bimodal micelle growth behaviour in our PB-PEO micelle solutions has critical implications for block copolymer micelle stability in highly selective solvents. Specifically, we show that when micelle assemblies are perturbed far enough from their equilibrium size, the micelles can evolve through a fusion-controlled process, and moreover, through a distinct bimodal distribution that is separated by multiple fusion events (Fig. 7).


Size evolution of highly amphiphilic macromolecular solution assemblies via a distinct bimodal pathway.

Kelley EG, Murphy RP, Seppala JE, Smart TP, Hann SD, Sullivan MO, Epps TH - Nat Commun (2014)

Summary of micelle size evolutionSchematic representation of changes in micelle size after cosolvent addition and removal. (a) Poly(butadiene-b-ethylene oxide) [PB-PEO] micelles self-assemble in pure water, decrease in size following THF cosolvent addition (<10% by volume), and remain kinetically trapped after solvent transfer to pure water. Micelles prepared in solutions containing low THF contents are not perturbed far from their equilibrium size and therefore do not undergo significant size relaxation. (b) Increasing the THF content (e.g. 40% by volume) and subsequently removing the cosolvent perturbs the micelles far from their equilibrium size in water, leading to size relaxation through a bimodal pathway.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4225159&req=5

Figure 7: Summary of micelle size evolutionSchematic representation of changes in micelle size after cosolvent addition and removal. (a) Poly(butadiene-b-ethylene oxide) [PB-PEO] micelles self-assemble in pure water, decrease in size following THF cosolvent addition (<10% by volume), and remain kinetically trapped after solvent transfer to pure water. Micelles prepared in solutions containing low THF contents are not perturbed far from their equilibrium size and therefore do not undergo significant size relaxation. (b) Increasing the THF content (e.g. 40% by volume) and subsequently removing the cosolvent perturbs the micelles far from their equilibrium size in water, leading to size relaxation through a bimodal pathway.
Mentions: The bimodal micelle growth behaviour in our PB-PEO micelle solutions has critical implications for block copolymer micelle stability in highly selective solvents. Specifically, we show that when micelle assemblies are perturbed far enough from their equilibrium size, the micelles can evolve through a fusion-controlled process, and moreover, through a distinct bimodal distribution that is separated by multiple fusion events (Fig. 7).

Bottom Line: Herein we demonstrate that unequivocal step-change shifts in micelle populations occur over several weeks following transfer into a highly selective solvent.Notably, these results underscore fundamental similarities between assembly processes in amphiphilic polymer, small molecule and protein systems.Moreover, the non-equilibrium micelle size increase can have a major impact on the assumed stability of solution assemblies, for which performance is dictated by nanocarrier size and structure.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Chemical and Biomolecular Engineering, University of Delaware, 150 Academy Street, Newark, Delaware 19716, USA [2].

ABSTRACT
The solution self-assembly of macromolecular amphiphiles offers an efficient, bottom-up strategy for producing well-defined nanocarriers, with applications ranging from drug delivery to nanoreactors. Typically, the generation of uniform nanocarrier architectures is controlled by processing methods that rely on cosolvent mixtures. These preparation strategies hinge on the assumption that macromolecular solution nanostructures are kinetically stable following transfer from an organic/aqueous cosolvent into aqueous solution. Herein we demonstrate that unequivocal step-change shifts in micelle populations occur over several weeks following transfer into a highly selective solvent. The unexpected micelle growth evolves through a distinct bimodal distribution separated by multiple fusion events and critically depends on solution agitation. Notably, these results underscore fundamental similarities between assembly processes in amphiphilic polymer, small molecule and protein systems. Moreover, the non-equilibrium micelle size increase can have a major impact on the assumed stability of solution assemblies, for which performance is dictated by nanocarrier size and structure.

Show MeSH
Related in: MedlinePlus