Research ArticleMATERIALS SCIENCE

Nanocomposite capsules with directional, pulsed nanoparticle release

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Science Advances  08 Dec 2017:
Vol. 3, no. 12, eaao3353
DOI: 10.1126/sciadv.aao3353
  • Fig. 1 Schematic of the capsule formation process.

    Polymer (P)–nanoparticle (NP) solutions are emulsified into droplets in a microfluidic flow-focusing junction, followed by capsule formation via solvent extraction and directed solidification. A range of internal and external morphologies are accessible by varying drop size and (ternary) composition. For the data presented here, the polymer was NaPSS, the nanoparticles were silica (22 nm in diameter), and the solvent (S), carrier, and nonsolvent (NS) were water, hexadecane, and ethyl acetate, respectively. Scale bar, 100 μm.

  • Fig. 2 Optical images and kinetics of solvent extraction.

    Time series of solvent extraction from droplets of (A) pure H2O, (B) 1% (w/v) NaPSS (P), (C) 10% (w/v) silica (S), and (D) 1% (w/v) NaPSS + 10% (w/v) silica droplets; the initial droplet radius was R0 ≃ 250 μm. (E to G) Higher-magnification images of spinodal decomposition and coarsening of surface morphology of (D) within 120 to 140 s; inset in (F) shows corresponding FFT of the structure. (H) Evolution of droplet radius with time during extraction for data in (A) to (D). The symbol “+” indicates the completion of the extraction process (or dissolution for pure water). Droplets and then capsules remain approximately spherical in all cases at these compositions. Extraction kinetics for droplets with R0 ≃ 140 μm is provided in fig. S2. (I) Structure factor obtained from FFT of images (E to G), with the inset showing the evolution of dominant length scale (λ ≡ 2π/q*) with time, where q* is the wave number of the peak position indicated with “*”. A linear λ ∝ t1 dependence is expected for hydrodynamic coarsening in three dimensions. a.u., arbitrary units.

  • Fig. 3 Kinetics of capsule formation for various NaPSS/silica initial compositions.

    (A) Droplet extraction kinetics for a composition of 5% (w/v) NaPSS + 12% (w/v) silica, yielding anisotropic capsules with major and minor radii indicated. Vertical dashed lines and optical images indicate the regions of liquid droplets, capsule shell formation and shape deformation, and solidification. The evolution of area and deformation [D = (Rmajor + Rminor)/(RmajorRminor)] with time, for the droplet, is shown in fig. S3. (B and C) Linear dependence of final capsule size, bifurcation time, td, and extraction time, τ, on initial droplet radius, R0, for a composition of 5% (w/v) NaPSS + 12% (w/v) silica. (D) Effect of polymer concentration on extraction kinetics at 12% (w/v) silica. Pure H2O and NaPSS 1% (w/v) are included for reference. A graph of deformation versus time for each CNaPSS showing an increase in deformation with polymer concentration is shown in fig. S4B. (E) Effect of silica concentration on extraction kinetics at a constant NaPSS [1% (w/v)] concentration. Results for nanoparticle of 2 to 20% (w/v) overlap. (F) Ratio of final capsule size R to initial droplet size R0. (G) Corresponding extraction time obtained in (E). Only major axis (Rmajor) is shown in (B), (D), and (E) for clarity. Minor axis (Rminor) data are shown in figs. S4A and S5.

  • Fig. 4 Morphology diagram.

    Phase map and accompanying SEM images of shape and internal structure of polymer-silica composite capsules as a function of NaPSS and SiO2 content for a fixed initial droplet size (R = 150 μm). Spherical polymer capsules with increasing size and smaller pore dimensions are obtained with increasing NaPSS concentration (Δ), shown in the gray region. Compact and dimpled capsules are obtained in the absence of polymer, with increasing size with silica content ( □), shown in the pink region. At most NaPSS/SiO2 compositions, nonspherical capsules with folded geometries (analogous to pollen grains and tricorns) are found, shown in the light blue region. Within a narrow composition range, indicated in dark blue, dimpled capsules with a bicontinuous internal structure are obtained, comprising hierarchical silica microparticles and a composite polymer-nanoparticle shell and scaffold.

  • Fig. 5 Dissolution of NaPSS/silica composite capsules.

    Optical images of dissolution of capsules of (A) 1% (w/v) NaPSS, (B) 1% (w/v) NaPSS + 0.5% (w/v) silica, (C) 1% (w/v) NaPSS + 5% (w/v) silica, and (D) 1% (w/v) NaPSS + 10% (w/v) SiO2 at pH 5 and (E) pH 9.4. The final capsule radius was ≃250 μm in all cases. (F) High-magnification images of the surface cracks of the capsule and (G) the emanating micrometer-sized nanoparticle clusters. (H) The droplet radius of the composite 1% (w/v) NaPSS/10% (w/v) SiO2 capsule was found to remain approximately constant over time, and the release of micrometer-sized nanoparticle clusters occurs in bursts, over long time scales, tunable with pH. Lines shown are fits of the well-known Weibull empirical model [I = 1 − exp(−a(tti))b, where I is the integrated intensity in our case; a and b are the scale and shape parameters, respectively; t is time; and ti is the induction time] to the experimental data. DI, deionized.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/12/eaao3353/DC1

    fig. S1. Phase diagram of NaPSS/SiO2/H2O mixtures.

    fig. S2. Kinetics of composite capsule formation at initial CNaPSS, 1% (w/v).

    fig. S3. Deformation and area change of capsule obtained from 5% (w/v) NaPSS + 12% (w/v) silica droplet.

    fig. S4. Kinetics of composite capsule formation at initial Formula, 12% (w/v).

    fig. S5. Corresponding minor axis Rminor data for Fig. 2C (main text).

    fig. S6. Evolution of droplet radius and deformation parameter with time during extraction for various NaPSS/silica compositions.

    fig. S7. SEM showing the morphology of anisotropic composite NaPSS/silica capsule.

    fig. S8. SEM images showing the morphology and internal microstructure of polymer-nanoparticle capsules as a function of NaPSS and SiO2 content.

    fig. S9. High-magnification SEM images showing the internal morphology of neat polymer and composite polymer-nanoparticle capsules as a function of NaPSS and SiO2 content.

    fig. S10. Wide-view SEM images showing neat polymer and composite polymer-nanoparticle capsules as a function of NaPSS and SiO2 content.

    fig. S11. EDS analysis of neat and composite NaPSS/silica capsules.

    fig. S12. Dissolution of 3% (w/v) NaPSS and 3% (w/v) NaPSS + 10% (w/v) SiO2 capsules.

    fig. S13. Pulsatile release of nanoparticle clusters from selected active sites of a capsule obtained from 1% (w/v) NaPSS + 10% (w/v) SiO2 initial droplet composition.

    fig. S14. Pulsatile release of nanoparticle clusters from specific sectors of capsules obtained from 1% (w/v) NaPSS + 10% (w/v) SiO2 and 1% (w/v) NaPSS + 15% (w/v) SiO2 initial droplet composition.

    fig. S15. Analysis of release of nanoparticle clusters from a capsule obtained from 1% (w/v) NaPSS + 10% (w/v) SiO2 initial droplet composition.

    fig. S16. Analysis of release of nanoparticle clusters from a capsule obtained from 1% (w/v) NaPSS + 15% (w/v) SiO2 initial droplet composition.

    fig. S17. Formation and SEM images of internal microstructure of composite NaPSS/SWCNT and NaPSS/Au capsules.

    fig. S18. Release of SWCNT and Au nanoparticles from composite NaPSS/SWCNT and NaPSS/Au capsules.

    table S1. Viscosity measurements of NaPSS/SiO2/H2O mixtures.

    note S1. Microfluidic device fabrication.

    note S2. Phase diagram of NaPSS/SiO2/H2O mixtures.

    note S3. Estimation of Péclet number.

    note S4. Additional analysis for data shown in the main text.

    note S5. Additional SEM images of capsules.

    note S6. EDS of neat and composite NaPSS/silica capsules.

    note S7. Analysis of dissolution of neat and composite NaPSS/silica capsules immersed in deionized water (pH 5 to 6).

    note S8. Spatiotemporal analysis of pulse release of nanoparticle clusters from bicontinuous capsules immersed in deionized water (pH 5 to 6).

    note S9. Impact of payload type on composite capsule morphology and release profile.

    movie S1. Video depicting the mechanism and kinetics of solvent extraction of 1% (w/v) NaPSS + 10% (w/v) SiO2 aqueous droplet of 250 μm radius in neat ethyl acetate over a period of 360 s (video 10 times faster).

    movie S2. Video showing the immersion of bicontinuous capsule above in deionized water (pH 5 to 6), depicting the pulsed release of nanoparticle clusters, over a time scale of 10,000 s (video 300 times faster).

    movie S3. As above, following immersion in deionized water with pH 9.35 over a time scale of 7000 s (video 200 times faster; air bubbles result from the immersion of the dried capsule in water and are not a result of dissolution).

    movie S4. Video depicting the mechanism and kinetics of solvent extraction of 1% (w/v) NaPSS + 0.3% (w/v) SWCNT aqueous droplet of ≃250 μm radius in neat ethyl acetate over a period of 250 s (video 25 times faster).

    movie S5. Video depicting the mechanism and kinetics of solvent extraction of 1% (w/v) NaPSS + 0.025% (w/v) Au nanoparticle aqueous droplet of ≃250 μm radius in neat ethyl acetate over a period of 250 s (video 10 times faster).

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Phase diagram of NaPSS/SiO2/H2O mixtures.
    • fig. S2. Kinetics of composite capsule formation at initial CNaPSS, 1% (w/v).
    • fig. S3. Deformation and area change of capsule obtained from 5% (w/v) NaPSS + 12% (w/v) silica droplet.
    • fig. S4. Kinetics of composite capsule formation at initial CSiO2 , 12% (w/v).
    • fig. S5. Corresponding minor axis Rminor data for Fig. 2C (main text).
    • fig. S6. Evolution of droplet radius and deformation parameter with time during extraction for various NaPSS/silica compositions.
    • fig. S7. SEM showing the morphology of anisotropic composite NaPSS/silica capsule.
    • fig. S8. SEM images showing the morphology and internal microstructure of polymer-nanoparticle capsules as a function of NaPSS and SiO2 content.
    • fig. S9. High-magnification SEM images showing the internal morphology of neat polymer and composite polymer-nanoparticle capsules as a function of NaPSS and SiO2 content.
    • fig. S10. Wide-view SEM images showing neat polymer and composite polymernanoparticle capsules as a function of NaPSS and SiO2 content.
    • fig. S11. EDS analysis of neat and composite NaPSS/silica capsules.
    • fig. S12. Dissolution of 3% (w/v) NaPSS and 3% (w/v) NaPSS + 10% (w/v) SiO2 capsules.
    • fig. S13. Pulsatile release of nanoparticle clusters from selected active sites of a capsule obtained from 1% (w/v) NaPSS + 10% (w/v) SiO2 initial droplet composition.
    • fig. S14. Pulsatile release of nanoparticle clusters from specific sectors of capsules obtained from 1% (w/v) NaPSS + 10% (w/v) SiO2 and 1% (w/v) NaPSS + 15% (w/v) SiO2 initial droplet composition.
    • fig. S15. Analysis of release of nanoparticle clusters from a capsule obtained from 1% (w/v) NaPSS + 10% (w/v) SiO2 initial droplet composition.
    • fig. S16. Analysis of release of nanoparticle clusters from a capsule obtained from 1% (w/v) NaPSS + 15% (w/v) SiO2 initial droplet composition.
    • fig. S17. Formation and SEM images of internal microstructure of composite NaPSS/SWCNT and NaPSS/Au capsules.
    • fig. S18. Release of SWCNT and Au nanoparticles from composite NaPSS/SWCNT and NaPSS/Au capsules.
    • table S1. Viscosity measurements of NaPSS/SiO2/H2O mixtures.
    • note S1. Microfluidic device fabrication.
    • note S2. Phase diagram of NaPSS/SiO2/H2O mixtures.
    • note S3. Estimation of Péclet number.
    • note S4. Additional analysis for data shown in the main text.
    • note S5. Additional SEM images of capsules.
    • note S6. EDS of neat and composite NaPSS/silica capsules.
    • note S7. Analysis of dissolution of neat and composite NaPSS/silica capsules immersed in deionized water (pH 5 to 6).
    • note S8. Spatiotemporal analysis of pulse release of nanoparticle clusters from bicontinuous capsules immersed in deionized water (pH 5 to 6).
    • note S9. Impact of payload type on composite capsule morphology and release profile.

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    Other Supplementary Material for this manuscript includes the following:

    • movie S1 (.mp4 format). Video depicting the mechanism and kinetics of solvent extraction of 1% (w/v) NaPSS + 10% (w/v) SiO2 aqueous droplet of 250 μm radius in neat ethyl acetate over a period of 360 s (video 10 times faster).
    • movie S2 (.avi format). Video showing the immersion of bicontinuous capsule above in deionized water (pH 5 to 6), depicting the pulsed release of nanoparticle clusters, over a time scale of 10,000 s (video 300 times faster).
    • movie S3 (.avi format). As above, following immersion in deionized water with pH 9.35 over a time scale of 7000 s (video 200 times faster; air bubbles result from the immersion of the dried capsule in water and are not a result of dissolution).
    • movie S4 (.mp4 format). Video depicting the mechanism and kinetics of solvent extraction of 1% (w/v) NaPSS + 0.3% (w/v) SWCNT aqueous droplet of ≃250 μm radius in neat ethyl acetate over a period of 250 s (video 25 times faster).
    • movie S5 (.mp4 format). Video depicting the mechanism and kinetics of solvent extraction of 1% (w/v) NaPSS + 0.025% (w/v) Au nanoparticle aqueous droplet of ≃250 μm radius in neat ethyl acetate over a period of 250 s (video 10 times faster).

    Files in this Data Supplement:

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