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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 theinitial silica concentration, [silica]0, during the insitu loading of silica nanoparticles intoG58H250 diblock copolymer vesicles preparedvia RAFT aqueous dispersion polymerization at 70 °C. (a) Comparisonof the theoretical maximum number of silica nanoparticles encapsulatedper vesicle with that calculated experimentally from DCP data. (b)Comparison of DCP-derived silica encapsulation efficiency (EEDCP) and the TGA-derived loading efficiency(LETGA).
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fig5: Effect of varying theinitial silica concentration, [silica]0, during the insitu loading of silica nanoparticles intoG58H250 diblock copolymer vesicles preparedvia RAFT aqueous dispersion polymerization at 70 °C. (a) Comparisonof the theoretical maximum number of silica nanoparticles encapsulatedper vesicle with that calculated experimentally from DCP data. (b)Comparison of DCP-derived silica encapsulation efficiency (EEDCP) and the TGA-derived loading efficiency(LETGA).

Mentions: SAXS analysisof the G58H250 diblock copolymervesicles prepared in the presence of silica nanoparticles indicatedvolume-average vesicle diameters of 295–335 nm, which are comparableto the mean diameter of 291 ± 7 nm obtained for empty vesicles(see Table 1). Thissuggests that the presence of the silica nanoparticles does not significantlyaffect the PISA synthesis. Taking the SAXS diameter of the empty vesiclesto be the true DCP diameter for both empty and silica-loaded vesicles,the effective vesicle density (ρeff) must vary from1.071 to 1.141 g cm–3 on increasing the [silica]0 from 0 to 35% w/w (see Figure 4b). This difference in ρeff allowscalculation of (i) the mean number of silica nanoparticles encapsulatedper vesicle (Nsv), (ii) the volume ofthe vesicle lumen occupied by silica nanoparticles (Vsl), and (iii) the encapsulation efficiency (EEDCP, see eqs S1–S8 in the Supporting Information for calculations). This analysis suggests that Nsv increases from 0 to 133 (see Figure 5a and Table 1), Vsl increasesfrom 0 to 4.76%, and EEDCP increases from0 to 27% on increasing [silica]0 from 0 to 35% w/w (see Figure 5b and Table 1). The Nsv increases monotonically with [silica]0. However, Nsv is lower than the theoretical Nsv calculated from geometric considerations. Naively,we expected that the Nsv would be simplycomparable to the number of silica nanoparticles that occupy a certainvolume for a given [silica]0. However, the silica concentrationinside the vesicle lumen is lower than that outsidethe vesicles. This suggests a mass transport problem: diffusion ofthe silica nanoparticles within the jellyfish during PISA appearsto be relatively slow on the time scale of vesicle formation. Thus,only approximately 27% of the theoretical maximum amount of silicais actually encapsulated within the vesicle lumen (see Figure 5b).


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 theinitial silica concentration, [silica]0, during the insitu loading of silica nanoparticles intoG58H250 diblock copolymer vesicles preparedvia RAFT aqueous dispersion polymerization at 70 °C. (a) Comparisonof the theoretical maximum number of silica nanoparticles encapsulatedper vesicle with that calculated experimentally from DCP data. (b)Comparison of DCP-derived silica encapsulation efficiency (EEDCP) and the TGA-derived loading efficiency(LETGA).
© Copyright Policy
Related In: Results  -  Collection

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

fig5: Effect of varying theinitial silica concentration, [silica]0, during the insitu loading of silica nanoparticles intoG58H250 diblock copolymer vesicles preparedvia RAFT aqueous dispersion polymerization at 70 °C. (a) Comparisonof the theoretical maximum number of silica nanoparticles encapsulatedper vesicle with that calculated experimentally from DCP data. (b)Comparison of DCP-derived silica encapsulation efficiency (EEDCP) and the TGA-derived loading efficiency(LETGA).
Mentions: SAXS analysisof the G58H250 diblock copolymervesicles prepared in the presence of silica nanoparticles indicatedvolume-average vesicle diameters of 295–335 nm, which are comparableto the mean diameter of 291 ± 7 nm obtained for empty vesicles(see Table 1). Thissuggests that the presence of the silica nanoparticles does not significantlyaffect the PISA synthesis. Taking the SAXS diameter of the empty vesiclesto be the true DCP diameter for both empty and silica-loaded vesicles,the effective vesicle density (ρeff) must vary from1.071 to 1.141 g cm–3 on increasing the [silica]0 from 0 to 35% w/w (see Figure 4b). This difference in ρeff allowscalculation of (i) the mean number of silica nanoparticles encapsulatedper vesicle (Nsv), (ii) the volume ofthe vesicle lumen occupied by silica nanoparticles (Vsl), and (iii) the encapsulation efficiency (EEDCP, see eqs S1–S8 in the Supporting Information for calculations). This analysis suggests that Nsv increases from 0 to 133 (see Figure 5a and Table 1), Vsl increasesfrom 0 to 4.76%, and EEDCP increases from0 to 27% on increasing [silica]0 from 0 to 35% w/w (see Figure 5b and Table 1). The Nsv increases monotonically with [silica]0. However, Nsv is lower than the theoretical Nsv calculated from geometric considerations. Naively,we expected that the Nsv would be simplycomparable to the number of silica nanoparticles that occupy a certainvolume for a given [silica]0. However, the silica concentrationinside the vesicle lumen is lower than that outsidethe vesicles. This suggests a mass transport problem: diffusion ofthe silica nanoparticles within the jellyfish during PISA appearsto be relatively slow on the time scale of vesicle formation. Thus,only approximately 27% of the theoretical maximum amount of silicais actually encapsulated within the vesicle lumen (see Figure 5b).

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