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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

DCP data recorded for G58H250 diblockcopolymervesicles prepared in the presence of increasing amounts of silicananoparticles (0–35% w/w silica). (a) Uncorrected weight-averagevesicle size distributions for which an arbitrary vesicle densityof 1.10 g cm–3 was utilized. (b) Corrected weight-averagevesicle size distributions whereby the weight-average diameter washeld constant at 291 nm (as calculated from SAXS analysis of vesiclesprepared in the absence of any silica nanoparticles) by adjustingthe vesicle density from 1.071 to 1.141 g cm–3,see Table 1. Thesedensities were then used to calculate the silica content of the vesicles.N.B. The apparent broadening of these DCP size distributionsis an artifact caused by the superposition of a density distributionon the size distribution (because larger vesicles will contain moresilica nanoparticles, see main text for details).
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fig4: DCP data recorded for G58H250 diblockcopolymervesicles prepared in the presence of increasing amounts of silicananoparticles (0–35% w/w silica). (a) Uncorrected weight-averagevesicle size distributions for which an arbitrary vesicle densityof 1.10 g cm–3 was utilized. (b) Corrected weight-averagevesicle size distributions whereby the weight-average diameter washeld constant at 291 nm (as calculated from SAXS analysis of vesiclesprepared in the absence of any silica nanoparticles) by adjustingthe vesicle density from 1.071 to 1.141 g cm–3,see Table 1. Thesedensities were then used to calculate the silica content of the vesicles.N.B. The apparent broadening of these DCP size distributionsis an artifact caused by the superposition of a density distributionon the size distribution (because larger vesicles will contain moresilica nanoparticles, see main text for details).

Mentions: Assuming a spherical particle morphology, a DCP weight-averagediameter can be calculated, provided that the particle density isaccurately known. Since the PHPMA membrane is highly plasticized bywater38 the vesicle density was estimated to be 1.10 g cm–3. When arbitrarilyfixing the vesicle density at this value, the mean vesicle diameterincreases monotonically and the vesicle size distribution becomessignificantly broader when the [silica]0 is increased from0 to 35% w/w (see Figure 4a). Given that the silica density is 2.06(5) g cm–3 (as judged by helium pycnometry), this suggests that the numberof silica nanoparticles encapsulated per vesicle increases at higher[silica]0, as expected. Hence, the effective vesicle densityincreases, resulting in much faster sedimentation of the vesiclesrelative to the non-encapsulated silica nanoparticles. This meansthat DCP analyses can be conducted on the as-synthesized dispersions,since the excess silica nanoparticles cannot be detected on the same(short) time scale as the vesicles. However, the vesicle size distributionhas finite width, and larger vesicles contain many more silica nanoparticlesthan smaller vesicles. This leads to a density distribution beingsuperimposed on the vesicle size distribution, which results in itsartificial broadening. In principle, this problem can be correctedby calculating the particle density for a given diameter, as reportedby Fielding et al.43 However, this refinementwas not considered necessary in the present work.


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)

DCP data recorded for G58H250 diblockcopolymervesicles prepared in the presence of increasing amounts of silicananoparticles (0–35% w/w silica). (a) Uncorrected weight-averagevesicle size distributions for which an arbitrary vesicle densityof 1.10 g cm–3 was utilized. (b) Corrected weight-averagevesicle size distributions whereby the weight-average diameter washeld constant at 291 nm (as calculated from SAXS analysis of vesiclesprepared in the absence of any silica nanoparticles) by adjustingthe vesicle density from 1.071 to 1.141 g cm–3,see Table 1. Thesedensities were then used to calculate the silica content of the vesicles.N.B. The apparent broadening of these DCP size distributionsis an artifact caused by the superposition of a density distributionon the size distribution (because larger vesicles will contain moresilica nanoparticles, see main text for details).
© Copyright Policy
Related In: Results  -  Collection

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

fig4: DCP data recorded for G58H250 diblockcopolymervesicles prepared in the presence of increasing amounts of silicananoparticles (0–35% w/w silica). (a) Uncorrected weight-averagevesicle size distributions for which an arbitrary vesicle densityof 1.10 g cm–3 was utilized. (b) Corrected weight-averagevesicle size distributions whereby the weight-average diameter washeld constant at 291 nm (as calculated from SAXS analysis of vesiclesprepared in the absence of any silica nanoparticles) by adjustingthe vesicle density from 1.071 to 1.141 g cm–3,see Table 1. Thesedensities were then used to calculate the silica content of the vesicles.N.B. The apparent broadening of these DCP size distributionsis an artifact caused by the superposition of a density distributionon the size distribution (because larger vesicles will contain moresilica nanoparticles, see main text for details).
Mentions: Assuming a spherical particle morphology, a DCP weight-averagediameter can be calculated, provided that the particle density isaccurately known. Since the PHPMA membrane is highly plasticized bywater38 the vesicle density was estimated to be 1.10 g cm–3. When arbitrarilyfixing the vesicle density at this value, the mean vesicle diameterincreases monotonically and the vesicle size distribution becomessignificantly broader when the [silica]0 is increased from0 to 35% w/w (see Figure 4a). Given that the silica density is 2.06(5) g cm–3 (as judged by helium pycnometry), this suggests that the numberof silica nanoparticles encapsulated per vesicle increases at higher[silica]0, as expected. Hence, the effective vesicle densityincreases, resulting in much faster sedimentation of the vesiclesrelative to the non-encapsulated silica nanoparticles. This meansthat DCP analyses can be conducted on the as-synthesized dispersions,since the excess silica nanoparticles cannot be detected on the same(short) time scale as the vesicles. However, the vesicle size distributionhas finite width, and larger vesicles contain many more silica nanoparticlesthan smaller vesicles. This leads to a density distribution beingsuperimposed on the vesicle size distribution, which results in itsartificial broadening. In principle, this problem can be correctedby calculating the particle density for a given diameter, as reportedby Fielding et al.43 However, this refinementwas not considered necessary in the present work.

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