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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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SAXS study of micelle size evolutionSmall angle X-ray scattering (SAXS data for micelles prepared in various water/THF mixtures (0% to 50% by volume THF) on Day-1(before dialysis; a), Day 3 (after dialysis; b), and Day 30 (after dialysis; c). Triangles mark the peak location before dialysis into pure water. The dashed line highlights the peak location in the samples generated from the ≥10% by volume THF solutions 30d after dialysis into pure water. SAXS curves were shifted vertically for clarity.
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Figure 3: SAXS study of micelle size evolutionSmall angle X-ray scattering (SAXS data for micelles prepared in various water/THF mixtures (0% to 50% by volume THF) on Day-1(before dialysis; a), Day 3 (after dialysis; b), and Day 30 (after dialysis; c). Triangles mark the peak location before dialysis into pure water. The dashed line highlights the peak location in the samples generated from the ≥10% by volume THF solutions 30d after dialysis into pure water. SAXS curves were shifted vertically for clarity.

Mentions: Small angle X-ray scattering (SAXS) analyses reinforced the trends seen in the DLS results and provided insight into changes in the micelle size dispersity following cosolvent removal. The shift in primary peak location to higher q-values with increasing THF content (Fig. 3a) confirmed the inverse relationship between micelle size and THF content upon cosolvent addition. The disappearance of the main peak on Day 3 (Fig. 3b) for the specimens made from 30 % to 50 % by volume THF solutions suggested an appreciable increase in the size dispersity in the days immediately following cosolvent removal. The reappearance of the peak at lower q-values on Day 30 (Fig. 3c) indicated that micelles had coalesced into a final population of larger and nearly monodisperse assemblies. The initial increase and subsequent decrease in dispersity suggested the presence of multiple micelle populations during the growth process. Moreover, the final micelle sizes were similar for the specimens made from 10 % to 50 % by volume THF solutions, supporting the plateau in growth noted in the DLS results.


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)

SAXS study of micelle size evolutionSmall angle X-ray scattering (SAXS data for micelles prepared in various water/THF mixtures (0% to 50% by volume THF) on Day-1(before dialysis; a), Day 3 (after dialysis; b), and Day 30 (after dialysis; c). Triangles mark the peak location before dialysis into pure water. The dashed line highlights the peak location in the samples generated from the ≥10% by volume THF solutions 30d after dialysis into pure water. SAXS curves were shifted vertically for clarity.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 3: SAXS study of micelle size evolutionSmall angle X-ray scattering (SAXS data for micelles prepared in various water/THF mixtures (0% to 50% by volume THF) on Day-1(before dialysis; a), Day 3 (after dialysis; b), and Day 30 (after dialysis; c). Triangles mark the peak location before dialysis into pure water. The dashed line highlights the peak location in the samples generated from the ≥10% by volume THF solutions 30d after dialysis into pure water. SAXS curves were shifted vertically for clarity.
Mentions: Small angle X-ray scattering (SAXS) analyses reinforced the trends seen in the DLS results and provided insight into changes in the micelle size dispersity following cosolvent removal. The shift in primary peak location to higher q-values with increasing THF content (Fig. 3a) confirmed the inverse relationship between micelle size and THF content upon cosolvent addition. The disappearance of the main peak on Day 3 (Fig. 3b) for the specimens made from 30 % to 50 % by volume THF solutions suggested an appreciable increase in the size dispersity in the days immediately following cosolvent removal. The reappearance of the peak at lower q-values on Day 30 (Fig. 3c) indicated that micelles had coalesced into a final population of larger and nearly monodisperse assemblies. The initial increase and subsequent decrease in dispersity suggested the presence of multiple micelle populations during the growth process. Moreover, the final micelle sizes were similar for the specimens made from 10 % to 50 % by volume THF solutions, supporting the plateau in growth noted in the DLS results.

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