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Loading of Silica Nanoparticles in Block Copolymer Vesicles during Polymerization-Induced Self-Assembly: Encapsulation Efficiency and Thermally Triggered Release.

Mable CJ, Gibson RR, Prevost S, McKenzie BE, Mykhaylyk OO, Armes SP - J. Am. Chem. Soc. (2015)

Bottom Line: Silica has high electron contrast compared to the copolymer which facilitates TEM analysis, and its thermal stability enables quantification of the loading efficiency via thermogravimetric analysis.They may also serve as an active payload for self-healing hydrogels or repair of biological tissue.Finally, we also encapsulate a model globular protein, bovine serum albumin, and calculate its loading efficiency using fluorescence spectroscopy.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, University of Sheffield , Brook Hill, Sheffield, South Yorkshire S3 7HF, United Kingdom.

ABSTRACT
Poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) diblock copolymer vesicles can be prepared in the form of concentrated aqueous dispersions via polymerization-induced self-assembly (PISA). In the present study, these syntheses are conducted in the presence of varying amounts of silica nanoparticles of approximately 18 nm diameter. This approach leads to encapsulation of up to hundreds of silica nanoparticles per vesicle. Silica has high electron contrast compared to the copolymer which facilitates TEM analysis, and its thermal stability enables quantification of the loading efficiency via thermogravimetric analysis. Encapsulation efficiencies can be calculated using disk centrifuge photosedimentometry, since the vesicle density increases at higher silica loadings while the mean vesicle diameter remains essentially unchanged. Small angle X-ray scattering (SAXS) is used to confirm silica encapsulation, since a structure factor is observed at q ≈ 0.25 nm(-1). A new two-population model provides satisfactory data fits to the SAXS patterns and allows the mean silica volume fraction within the vesicles to be determined. Finally, the thermoresponsive nature of the diblock copolymer vesicles enables thermally triggered release of the encapsulated silica nanoparticles simply by cooling to 0-10 °C, which induces a morphological transition. These silica-loaded vesicles constitute a useful model system for understanding the encapsulation of globular proteins, enzymes, or antibodies for potential biomedical applications. They may also serve as an active payload for self-healing hydrogels or repair of biological tissue. Finally, we also encapsulate a model globular protein, bovine serum albumin, and calculate its loading efficiency using fluorescence spectroscopy.

No MeSH data available.


Related in: MedlinePlus

Effect of varying the initial silica concentration, [silica]0, on the concentration of encapsulated silica, as calculatedusing SAXS (green triangles, measured at 1.0% w/w copolymer) and TGA(red circles) for G58H250 diblock copolymervesicles prepared at 10% w/w in the presence of 0–35% w/w silicananoparticles (after six centrifugation–redispersion cycles).
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fig7: Effect of varying the initial silica concentration, [silica]0, on the concentration of encapsulated silica, as calculatedusing SAXS (green triangles, measured at 1.0% w/w copolymer) and TGA(red circles) for G58H250 diblock copolymervesicles prepared at 10% w/w in the presence of 0–35% w/w silicananoparticles (after six centrifugation–redispersion cycles).

Mentions: The concentrationof encapsulated silica nanoparticles (see Table 1) can be estimatedusing the volume fraction of silica nanoparticles (c2) obtained from the fitted SAXS patterns. In general,the SAXS data are in fairly good agreement with the correspondingTGA data (see Figure 7). However, SAXS tends to underestimate the concentration of encapsulatedsilica at higher [silica]0. In principle, this might bebecause TGA cannot distinguish between the silica nanoparticles locatedwithin the vesicles and any excess, non-encapsulated silica that mightremain in the aqueous continuous phase. In contrast, the two-populationSAXS model used in this work is mainly sensitive to silica nanoparticleslocated within the vesicle lumen. However, TEM studies coupled withgravimetric analysis of successive supernatants suggest that thereis relatively little, if any, non-encapsulated silica present aftersix centrifugation–redispersion cycles (see Figures 2 and S5, respectively). This discrepancy arises because DCP reports artificiallybroadened, highly asymmetric size distributions at higher [silica]0, as discussed earlier. This is essentially a polydispersityeffect: heavier vesicles containing relatively high silica loadingsappear larger in the DCP size distribution, whereaslighter vesicles containing fewer encapsulated silica nanoparticlesappear smaller, giving rise to an artificially skeweddistribution.


Loading of Silica Nanoparticles in Block Copolymer Vesicles during Polymerization-Induced Self-Assembly: Encapsulation Efficiency and Thermally Triggered Release.

Mable CJ, Gibson RR, Prevost S, McKenzie BE, Mykhaylyk OO, Armes SP - J. Am. Chem. Soc. (2015)

Effect of varying the initial silica concentration, [silica]0, on the concentration of encapsulated silica, as calculatedusing SAXS (green triangles, measured at 1.0% w/w copolymer) and TGA(red circles) for G58H250 diblock copolymervesicles prepared at 10% w/w in the presence of 0–35% w/w silicananoparticles (after six centrifugation–redispersion cycles).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4697924&req=5

fig7: Effect of varying the initial silica concentration, [silica]0, on the concentration of encapsulated silica, as calculatedusing SAXS (green triangles, measured at 1.0% w/w copolymer) and TGA(red circles) for G58H250 diblock copolymervesicles prepared at 10% w/w in the presence of 0–35% w/w silicananoparticles (after six centrifugation–redispersion cycles).
Mentions: The concentrationof encapsulated silica nanoparticles (see Table 1) can be estimatedusing the volume fraction of silica nanoparticles (c2) obtained from the fitted SAXS patterns. In general,the SAXS data are in fairly good agreement with the correspondingTGA data (see Figure 7). However, SAXS tends to underestimate the concentration of encapsulatedsilica at higher [silica]0. In principle, this might bebecause TGA cannot distinguish between the silica nanoparticles locatedwithin the vesicles and any excess, non-encapsulated silica that mightremain in the aqueous continuous phase. In contrast, the two-populationSAXS model used in this work is mainly sensitive to silica nanoparticleslocated within the vesicle lumen. However, TEM studies coupled withgravimetric analysis of successive supernatants suggest that thereis relatively little, if any, non-encapsulated silica present aftersix centrifugation–redispersion cycles (see Figures 2 and S5, respectively). This discrepancy arises because DCP reports artificiallybroadened, highly asymmetric size distributions at higher [silica]0, as discussed earlier. This is essentially a polydispersityeffect: heavier vesicles containing relatively high silica loadingsappear larger in the DCP size distribution, whereaslighter vesicles containing fewer encapsulated silica nanoparticlesappear smaller, giving rise to an artificially skeweddistribution.

Bottom Line: Silica has high electron contrast compared to the copolymer which facilitates TEM analysis, and its thermal stability enables quantification of the loading efficiency via thermogravimetric analysis.They may also serve as an active payload for self-healing hydrogels or repair of biological tissue.Finally, we also encapsulate a model globular protein, bovine serum albumin, and calculate its loading efficiency using fluorescence spectroscopy.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, University of Sheffield , Brook Hill, Sheffield, South Yorkshire S3 7HF, United Kingdom.

ABSTRACT
Poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) diblock copolymer vesicles can be prepared in the form of concentrated aqueous dispersions via polymerization-induced self-assembly (PISA). In the present study, these syntheses are conducted in the presence of varying amounts of silica nanoparticles of approximately 18 nm diameter. This approach leads to encapsulation of up to hundreds of silica nanoparticles per vesicle. Silica has high electron contrast compared to the copolymer which facilitates TEM analysis, and its thermal stability enables quantification of the loading efficiency via thermogravimetric analysis. Encapsulation efficiencies can be calculated using disk centrifuge photosedimentometry, since the vesicle density increases at higher silica loadings while the mean vesicle diameter remains essentially unchanged. Small angle X-ray scattering (SAXS) is used to confirm silica encapsulation, since a structure factor is observed at q ≈ 0.25 nm(-1). A new two-population model provides satisfactory data fits to the SAXS patterns and allows the mean silica volume fraction within the vesicles to be determined. Finally, the thermoresponsive nature of the diblock copolymer vesicles enables thermally triggered release of the encapsulated silica nanoparticles simply by cooling to 0-10 °C, which induces a morphological transition. These silica-loaded vesicles constitute a useful model system for understanding the encapsulation of globular proteins, enzymes, or antibodies for potential biomedical applications. They may also serve as an active payload for self-healing hydrogels or repair of biological tissue. Finally, we also encapsulate a model globular protein, bovine serum albumin, and calculate its loading efficiency using fluorescence spectroscopy.

No MeSH data available.


Related in: MedlinePlus