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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

TEM imagesobtained for G55H270 diblock copolymervesicles prepared via PISA at 10% w/w copolymer at 37 °C in the(a) absence of BSA and (b) presence of 5% w/w BSA (after six centrifugation–redispersioncycles to remove non-encapsulated BSA). (c) In order to calculatethe BSA loading efficiency within the vesicles, fluorescence emissionspectra were recorded for both the empty G55H270 vesicles and the BSA-loaded G55H270 vesiclesbefore and after centrifugation. The background fluorescence emissionspectrum of water was also recorded (the sharp signal at 305 nm isa Raman water band). [N.B. BSA exhibits weak intrinsic fluorescence;absorption at 278 nm and emission at 337 nm].50,51
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fig10: TEM imagesobtained for G55H270 diblock copolymervesicles prepared via PISA at 10% w/w copolymer at 37 °C in the(a) absence of BSA and (b) presence of 5% w/w BSA (after six centrifugation–redispersioncycles to remove non-encapsulated BSA). (c) In order to calculatethe BSA loading efficiency within the vesicles, fluorescence emissionspectra were recorded for both the empty G55H270 vesicles and the BSA-loaded G55H270 vesiclesbefore and after centrifugation. The background fluorescence emissionspectrum of water was also recorded (the sharp signal at 305 nm isa Raman water band). [N.B. BSA exhibits weak intrinsic fluorescence;absorption at 278 nm and emission at 337 nm].50,51

Mentions: We wishedto examine whetherthe above findings with silica nanoparticles could be extended toinclude a model globular protein (bovine serum albumin, BSA). Thus,we conducted RAFT aqueous dispersion polymerization of HPMA at 37°C using a low-temperature initiator (VA-044) to obtain G55H270 diblock copolymer vesicles. These relativelymild conditions were essential in order to avoid denaturation of theprotein cargo. The rate of HPMA polymerization was significantly slowerat 37 °C, but nevertheless essentially full conversion (>99%)was achieved within 8 h as judged by 1H NMR studies (see Figure S10a). GPC studies confirmed that a near-monodispersediblock copolymer was obtained with minimal macro-CTA contaminationand a high blocking efficiency (Mw/Mn = 1.16; see Figure S10b). TEM images (see Figure 10a) reveal a pure vesicular morphology, as expected when targetingsuch an asymmetric G55H270 diblock copolymercomposition. The vesicles are not affected by this low-temperaturePISA formulation, suggesting that it may be possible to encapsulateproteins or other delicate biomolecules (e.g., DNA, RNA, antibodies,enzymes etc.) intact under mild conditions. To examine this hypothesis,G55H270 diblock copolymer vesicles were synthesizedat 37 °C in the presence of 5% w/w BSA. GPC studies indicatedthat near-monodisperse diblock copolymers were obtained with a comparable Mn, minimal macro-CTA contamination, and highblocking efficiencies (Mw/Mn = 1.17; see Figure S10b),despite the presence of BSA. After removal of the non-encapsulatedBSA via six centrifugation–redispersion cycles, TEM imagesconfirmed the expected vesicular morphology (see Figure 10b). Moreover, encapsulatedBSA is discernible within the vesicle lumen. It should be noted thatBSA is a monothiol-functional protein, which in principle can participatein radical-based polymerizations.52−54 However, GPC, TEM, and 1H NMR studies suggest that this 37 °C PISA formulationis not adversely affected by the presence of 5% w/w BSA.


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)

TEM imagesobtained for G55H270 diblock copolymervesicles prepared via PISA at 10% w/w copolymer at 37 °C in the(a) absence of BSA and (b) presence of 5% w/w BSA (after six centrifugation–redispersioncycles to remove non-encapsulated BSA). (c) In order to calculatethe BSA loading efficiency within the vesicles, fluorescence emissionspectra were recorded for both the empty G55H270 vesicles and the BSA-loaded G55H270 vesiclesbefore and after centrifugation. The background fluorescence emissionspectrum of water was also recorded (the sharp signal at 305 nm isa Raman water band). [N.B. BSA exhibits weak intrinsic fluorescence;absorption at 278 nm and emission at 337 nm].50,51
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4697924&req=5

fig10: TEM imagesobtained for G55H270 diblock copolymervesicles prepared via PISA at 10% w/w copolymer at 37 °C in the(a) absence of BSA and (b) presence of 5% w/w BSA (after six centrifugation–redispersioncycles to remove non-encapsulated BSA). (c) In order to calculatethe BSA loading efficiency within the vesicles, fluorescence emissionspectra were recorded for both the empty G55H270 vesicles and the BSA-loaded G55H270 vesiclesbefore and after centrifugation. The background fluorescence emissionspectrum of water was also recorded (the sharp signal at 305 nm isa Raman water band). [N.B. BSA exhibits weak intrinsic fluorescence;absorption at 278 nm and emission at 337 nm].50,51
Mentions: We wishedto examine whetherthe above findings with silica nanoparticles could be extended toinclude a model globular protein (bovine serum albumin, BSA). Thus,we conducted RAFT aqueous dispersion polymerization of HPMA at 37°C using a low-temperature initiator (VA-044) to obtain G55H270 diblock copolymer vesicles. These relativelymild conditions were essential in order to avoid denaturation of theprotein cargo. The rate of HPMA polymerization was significantly slowerat 37 °C, but nevertheless essentially full conversion (>99%)was achieved within 8 h as judged by 1H NMR studies (see Figure S10a). GPC studies confirmed that a near-monodispersediblock copolymer was obtained with minimal macro-CTA contaminationand a high blocking efficiency (Mw/Mn = 1.16; see Figure S10b). TEM images (see Figure 10a) reveal a pure vesicular morphology, as expected when targetingsuch an asymmetric G55H270 diblock copolymercomposition. The vesicles are not affected by this low-temperaturePISA formulation, suggesting that it may be possible to encapsulateproteins or other delicate biomolecules (e.g., DNA, RNA, antibodies,enzymes etc.) intact under mild conditions. To examine this hypothesis,G55H270 diblock copolymer vesicles were synthesizedat 37 °C in the presence of 5% w/w BSA. GPC studies indicatedthat near-monodisperse diblock copolymers were obtained with a comparable Mn, minimal macro-CTA contamination, and highblocking efficiencies (Mw/Mn = 1.17; see Figure S10b),despite the presence of BSA. After removal of the non-encapsulatedBSA via six centrifugation–redispersion cycles, TEM imagesconfirmed the expected vesicular morphology (see Figure 10b). Moreover, encapsulatedBSA is discernible within the vesicle lumen. It should be noted thatBSA is a monothiol-functional protein, which in principle can participatein radical-based polymerizations.52−54 However, GPC, TEM, and 1H NMR studies suggest that this 37 °C PISA formulationis not adversely affected by the presence of 5% w/w BSA.

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