Research ArticleHEALTH AND MEDICINE

Encapsulation-free controlled release: Electrostatic adsorption eliminates the need for protein encapsulation in PLGA nanoparticles

See allHide authors and affiliations

Science Advances  27 May 2016:
Vol. 2, no. 5, e1600519
DOI: 10.1126/sciadv.1600519
  • Fig. 1 Two different PLGA np systems are compared for controlled protein release.

    (A) Protein encapsulated in PLGA np dispersed in a hydrogel. (B) Protein and blank PLGA np dispersed in a hydrogel. For the latter, protein adsorbs to the PLGA np but is not encapsulated within them.

  • Fig. 2 Controlled sustained release of positively charged proteins from PLGA np does not require encapsulation.

    (A to C) Three different proteins show nearly identical release profiles whether encapsulated within PLGA np or simply mixed with blank PLGA np in a hydrogel: (A) SDF (pI 10.9, molecular mass of 8 kD, 200 ng/release), (B) NT-3 (pI 9.5, molecular mass of 27 kD, 1000 ng/release), and (C) BDNF (pI 10.9, molecular mass of 27 kD, 300 ng/release). The cumulative percentage released is significantly greater for soluble proteins with no PLGA np compared to soluble proteins with blank PLGA np or proteins encapsulated in PLGA np at all time points (P < 0.05, n = 3 for all releases, mean ± SD plotted). Asterisks indicate significant differences between release of soluble protein with PLGA np and release of protein encapsulated in PLGA np (*P < 0.05, **P < 0.01, ***P < 0.001). Curves for soluble SDF with no PLGA np and SDF encapsulated in PLGA np were taken with permission (15). (D) EPO (pI ~4, molecular mass of 30 kD, 84 ng/release) shows no attenuated release when mixed into HAMC with PLGA np versus just HAMC alone (without PLGA np), indicating that the phenomena observed with SDF, NT-3, and BDNF are based on short-range electrostatic interactions between positively charged proteins and negatively charged PLGA (n = 3, mean ± SD plotted).

  • Fig. 3 Sustained release of BDNF from agarose containing PLGA np is disrupted by increased salt.

    (A) BDNF shows the same delayed- and sustained-release profile from agarose containing PLGA np as from HAMC with PLGA np while diffusional release from agarose alone is still fast. (B) Almost all soluble BDNF is adsorbed to PLGA np after incubation, even at short times. (C) NaCl (0.5 M) completely disrupts the interaction of BDNF with PLGA np, resulting in purely diffusional release (P > 0.05 for all time points, n = 3 for all releases, mean ± SD plotted).

  • Fig. 4 Release of positively charged proteins from composite HAMC can be tuned by changing the available nanoparticle surface area.

    (A) Cumulative percentage release of BDNF from composite HAMC is higher with 1000-nm-diameter PLGA np than with 300-nm-diameter PLGA np while keeping PLGA np mass constant. (B) (i) Release of NT-3 from composite HAMC with 0, 0.1, 0.5, 1, and 10 wt % PLGA np. Cumulative percentage of NT-3 released is significantly lower for 10 wt % PLGA np than for all other curves at t > 1 day (P < 0.05). Cumulative percentage of NT-3 released is significantly higher with 0 wt % PLGA np than with 0.1 wt % (t = 1 day, P < 0.05), 0.5 wt % (1 day ≤ t ≤ 3 days, P < 0.05), and 1 wt % (t > 3 hours, P < 0.05). (ii) Release of 0.5, 1, or 10 μg of NT-3 from composite HAMC with 10 wt % PLGA np. The concentration of NT-3 incorporated can be increased up to 20 times with virtually no change in release profile. Cumulative percentage of NT-3 released is significantly higher for 10 μg than for 1 and 0.5 μg at 10 and 14 days (P < 0.05) and is significantly lower for 0.5 μg than for 1 and 10 μg at 21 and 28 days (P < 0.05) (n = 3 for all releases, mean ± SD plotted).

  • Fig. 5 Release of positively charged proteins can be tuned by changing the environmental pH.

    (A) Release of SDF from composite XMC into media at pH 3, pH 5, or pH 7. Cumulative percentage release of SDF is significantly greater at pH 3 than at pH 5 (t < 10 days, P < 0.01) and pH 7 (t > 0 days, P < 0.0001), likely because PLGA carboxylate anions are protonated to carboxylic acids, thereby reducing electrostatic interactions with positively charged proteins. (B) Release of BDNF from HAMC with PLGA np with or without encapsulated magnesium carbonate (MgCO3). Release is delayed with encapsulated MgCO3 (a basic salt), which neutralizes acidic degradation products and thereby maintains a higher/neutral local pH (n = 3 for all releases, mean ± SD plotted).

  • Fig. 6 Monte Carlo simulations agree well with experimental results.

    Release of NT-3 from HAMC with 10 wt % PLGA np (Fig. 4B, i) was fitted using three-dimensional on-lattice Monte Carlo simulations. Simulations were then run for all other nanoparticle concentrations in Fig. 4B(i) using the same parameters. The combined reduced χ2 value for all simulations was 3.9. Symbols represent data, whereas solid lines represent the simulation results.

  • Fig. 7 Adsorption may be rate-limiting for the release of positively charged proteins from PLGA np.

    (i) Initially, the protein is fully adsorbed to the negatively charged nanoparticle surface. (ii) As the nanoparticle begins to degrade, acidic components build up and decrease the local pH. (iii) At a certain threshold, the nanoparticle surface becomes neutral, weakening the electrostatic interactions with the positively charged proteins and initiating release.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/5/e1600519/DC1

    fig. S1. Release of NT-3 from a PLGA np/hydrogel DDS containing encapsulated NT-3 and soluble NT-3.

    fig. S2. Bioactivity of proteins released from hydrogels with embedded PLGA np.

    fig. S3. Characteristics of PLGA np used in this study.

    fig. S4. Swelling of HAMC hydrogel with and without PLGA np.

    fig. S5. Release of soluble SDF from XMC alone into aCSF at pH 3, pH 5, or pH 7.

    fig. S6. Mass loss of PLGA from the release system at pH 3 and pH 7.

    movie S1. Two-dimensional Monte Carlo simulations of protein release from a hydrogel with embedded cubic degrading nanoparticles.

    Calculation of the relative surface area for PLGA np of different sizes

    Calculation for maximum surface coverage

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Release of NT-3 from a PLGA np/hydrogel DDS containing encapsulated NT-3 and soluble NT-3.
    • fig. S2. Bioactivity of proteins released from hydrogels with embedded PLGA np.
    • fig. S3. Characteristics of PLGA np used in this study.
    • fig. S4. Swelling of HAMC hydrogel with and without PLGA np.
    • fig. S5. Release of soluble SDF from XMC alone into aCSF at pH 3, pH 5, or pH 7.
    • fig. S6. Mass loss of PLGA from the release system at pH 3 and pH 7.
    • Legend for movies S1
    • Calculation of the relative surface area for PLGA np of different sizes
    • Calculation for maximum surface coverage

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • movie S1 (.avi format). Two-dimensional Monte Carlo simulations of protein release from a hydrogel with embedded cubic degrading nanoparticles.

    Files in this Data Supplement:

Stay Connected to Science Advances

Navigate This Article