Fabrication of fillable microparticles and other complex 3D microstructures

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Science  15 Sep 2017:
Vol. 357, Issue 6356, pp. 1138-1142
DOI: 10.1126/science.aaf7447
  • Fig. 1 Assembly of 3D microstructures using the SEAL process.

    (A) Microstructures are fabricated by pressing and heating polymer into a patterned PDMS base mold and delaminating these structures onto a substrate to create the first layer. A second layer is then formed by using a similar molding process against a Teflon surface, which allows the features to remain in the PDMS mold after cooling. The second layer is aligned, placed into contact with the first layer, and sintered by using a mild heating step. (B) Schematic depicting the alignment and sintering equipment, consisting of a mask aligner retrofitted with a Peltier heater. A glass slide containing the first layer is suspended upside down from a fixed mask holder by means of a vacuum while the second layer, still in the PDMS mold, is placed on the wafer chuck, aligned using the stage rotation and translation knobs, put into contact, and heated until they fuse. This approach can be used to create a variety of microstructures, including (C and D) stars, (E and H) letters spelling “MiT,” (F and I) two-layered tables, and (G and J) three-layered chairs. Scale bars indicate 200 μm for scanning electron microscopy (SEM) images and 1 mm for optical images. Optical images were stitched together from multiple images to enable a better depth of focus. The interfaces between images are denoted by thin red lines.

  • Fig. 2 SEAL-fabricated controlled-release microparticles.

    Particles are fabricated by (A) heating and pressing polymer between a patterned PDMS base mold and a Teflon surface, (B) transferring these bases to a new substrate and filling them with a model drug of interest, then (C) aligning an array of particle caps with drug-filled bases and briefly applying a low amount of heat to sinter the two layers. SEM images of (D) a single particle, (E) the core of a particle, and (F) a sealed particle. (G) A cross section of a single particle and (H) an array of sealed particles. Optical images of (I) an array of bases, (J) an array of filled particles, and (K) a side view of a single filled particle.

  • Fig. 3 Single-injection vaccination concept and release from SEAL-fabricated PLGA microparticles.

    (A) Schematic of a syringe containing multiple micromolded particles sufficiently small to pass through an 18-gauge needle that each produce a discrete, delayed pulse of antigen release to mimic current bolus vaccination regimens. (B) In vitro and in vivo pulsatile release of encapsulated Alexa Fluor 680–labeled 10-kD dextran from SEAL-fabricated particles composed of PLGA1, PLGA2, and PLGA3, respectively, from left to right. The top row shows the in vitro cumulative release of fluorescently labeled dextran at 37°C (normalized average, n = 10 particles). Graphs in the second row depict the in vivo cumulative release (normalized average, n = 7 to 10 particles). Note that this yields a broader release curve even though each particle exhibits a sharp pulse because the onset of release can differ slightly in each animal. Error bars indicate the standard error of the mean. The third row shows representative images of mice collected with an in vivo imaging system after injection of a single SEAL-fabricated PLGA particle containing fluorescently labeled dextran.

  • Fig. 4 Ovalbumin (OVA) vaccination and storage stability.

    (A) Longitudinal geometric mean antibody titers and (B) peak antibody titers achieved by mice treated with a single injection of OVA-containing particles or two bolus injections of OVA in solution (n = 5 mice). All peak titer groups were significantly different from those of the control group receiving only methyl cellulose (MC; P < 0.001), but significance markers are not shown for clarity. All other differences are indicated by *P < 0.05 and **P < 0.01. These results show that a single injection of core-shell particles can induce an immune response that is not only noninferior to two dose-matched boluses, but also noninferior to two boluses with double the cumulative dose. (C) Core-shell particles stored desiccated for 30 days at 4°C release the same amount of ELISA-reactive OVA as freshly prepared particles (n = 4 particles). Error bars indicate standard error of the geometric mean in (A) and (B) and standard error of the mean in (C).

Supplementary Materials

  • Fabrication of fillable microparticles and other complex 3D microstructures

    Kevin J. McHugh, Thanh D. Nguyen, Allison R. Linehan, David Yang, Adam M. Behrens, Sviatlana Rose, Zachary L. Tochka, Stephany Y. Tzeng, James J. Norman, Aaron C. Anselmo, Xian Xu, Stephanie Tomasic, Matthew A. Taylor, Jennifer Lu, Rohiverth Guarecuco, Robert Langer, Ana Jaklenec

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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    • Materials and Methods
    • Figs. S1 to S10
    • Table S1
    • References
    • Captions for Movies S1 to S4

    Images, Video, and Other Media

    Movie S1
    The SEAL process. The StampEd Assembly of polymer Layers, or “SEAL� method, combines computer-chip manufacturing technology with a new layer-by-layer assembling method to create an array of core-shell polymer particles. First, the polymer of choice, PLGA in this example, is melt pressed using a prefabricated silicone mold. The mold with the particles is then transferred to another substrate where it is peeled off, leaving behind an array of polymer base particles. These are then filled with any drug or vaccine using an ink jet piezoelectric nozzle and then dried. To seal the filled particles, a cap mold is aligned, sealed with the base, and delaminated. The resulting array of core-shell particles are then removed from the base and stored until use.
    Movie S2
    Visual inspection of diffraction patterns during sintering. Adjacent microstructure layers, such as the particle base and cap shown here, are placed into contact resulting in a diffraction pattern due to a small air gap. Layers begin to fuse as the polymer is heated above its glass transition temperature thereby eliminating the small air gap and causing the diffraction pattern to resolve.
    Movie S3
    Particle ink jet filling. Micromolded particle bases with a 100 x 100 μm core and 400 x 400 x 200 μm external dimension are filled prior to sealing using a BioJet Ultra ink jet piezoelectric nozzle that can rapidly dispense picoliter volumes of model drug, such as the blue dye seen here, into the particle core. Filling shown at the default of 4 drops/sec for the purposes of visualization, but the equipment is capable of achieving rates up to 50 drops/sec.
    Movie S4
    Flow through a 3D microfluidic channel produced using SEAL. A solution of 1 mg/ml Alexa Fluor 488-labeled 10 kD dextran was manually injected into a 50 μm microfluidic device using a 500 μl syringe and 30-gauge needle. The solution is seen filling the channel both laterally and vertically through the continuous 3D serpentine channel

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