Research ArticleAPPLIED SCIENCES AND ENGINEERING

Three-dimensional microarchitected materials and devices using nanoparticle assembly by pointwise spatial printing

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Science Advances  03 Mar 2017:
Vol. 3, no. 3, e1601986
DOI: 10.1126/sciadv.1601986
  • Fig. 1 Analogy of the natural growth of Desert Rose and the 3D buildup of nanoparticles by pointwise printing to realize microarchitectures.

    (A) An illustration of the Desert Rose formation process by condensation of sulfur-containing fog along with the elevated temperature of the desert climate. Desert Rose photo courtesy of O. Apostolidou (reprinted with permission). (B) In a process inspired by that shown in (A), we used successive condensation of droplets of nanoparticle ink in the spatial dimension followed by solvent evaporation and sintering to create controlled 3D microarchitectures with hierarchical porosity. The scanning electron microscopy (SEM) image resembles a petal-shaped structure (right). The truss element diameter is about 40 μm.

  • Fig. 2 An illustration of physical models developed to study the stability and control of pointwise printing and their experimental verification.

    (A) A simplified free-body diagram of a critical droplet at the edge of a structure and the illustration of a designed experiment to verify the models. (B) The predicted angle of growth as a function of droplet radius for different measured dried droplet heights. (C) The half-life time of the microdroplet was numerically calculated by evaporation rate estimation as a function of substrate temperature. (D) SEM images showing a series of inclined pillars fabricated at different angles to verify the model predictions. A magnified side view of the last inclined pillar establishes the critical angle (smallest angle to the horizontal for the assembled pillar by this method) at 37° that matches reasonably well with the model prediction. Scale bar, 250 μm.

  • Fig. 3 Pointwise-printed 3D microarchitectures with different network topologies.

    (A) An open octahedral microarchitecture with truss elements having a diameter of about 35 μm. Scale bars, 50 μm. (B) Pointwise-fabricated microarchitecture with a combination of octahedral and hexagonal structures. Scale bars, 50 μm. (C) Top surface of an octahedral scaffold structure at different magnifications and (D) truss elements of the 3D-printed scaffold after binder escape and nanoparticle sintering and possible grain growth.

  • Fig. 4 The pointwise printing in combination with controlled sintering technique.

    The printed material is designed to contain the first level of macroporosities. Coalescence of sintered nanoparticles starts to form the second level of porosity and could be stopped before pore closure and grain growth. Scale bars, 100 nm.

  • Fig. 5 Pointwise-printed hierarchical materials with 3D microarchitectures having features that span over five orders of magnitudes in length scale.

    (A) SEM images of octahedral and hexagonal microlattices at a bulk view at a length scale of millimeters. (B) High aspect ratio truss elements forming the architecture of sintered structures introducing the first level of porosity. (C) The engineered surface of truss elements of the lattice induced by different sintering profiles featuring a high level of porosity to near dense materials. (D) The final order of controlled surface features and porosity for different sintering temperature profiles that show several microscale to nanoscale voids.

  • Fig. 6 Demonstration of flexibility of nanoparticle buildup using pointwise printing for a wide range of applications.

    (A) Hierarchical porous scaffold and the topography of porous surfaces that is useful for tissue engineering and cell proliferation. (B) Stretchable spatial interconnect assembled between two micro-LEDs. Scale bars, 100 μm. (C) SEM image of array of pillars with different diameters (35 to 100 μm) and heights (85 to 500 μm). (D) (Left to right) Four spiral high aspect ratio hollow columns forming a dome show the flexibility of this method in fabrication of spatial interconnects. Fine silver interconnects with a thickness of 30 μm and an aspect ratio of over 20.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/3/e1601986/DC1

    section S1. Aerosol Jet printing technique

    section S2. Physical model for the critical angle of growth

    section S3. Droplet evaporation rate

    section S4. Voids/porosity as a function of the sintering conditions

    section S5. Compression tests

    fig. S1. An illustration of the Aerosol Jet printing technique.

    fig. S2. Schematic of pointwise printing process.

    fig. S3. A droplet at the edge of supporting plane.

    fig. S4. Porosity evolution for two different particle sizes and sintering conditions.

    fig. S5. Mechanical behavior of the 3D-printed hierarchical scaffolds fabricated by the pointwise printing method.

    table. S1. Properties of ethylene glycol, the solvent used for the nanoparticle ink.

    table. S2. Information about compression test samples and test results.

    movie S1. Video showing compressive loading of a 3D microlattice fabricated by the pointwise printing method.

    References (3136)

  • Supplementary Materials

    This PDF file includes:

    • section S1. Aerosol Jet printing technique section
    • S2. Physical model for the critical angle of growth section
    • S3. Droplet evaporation rate section
    • S4. Voids/porosity as a function of the sintering conditions section
    • S5. Compression tests
    • fig. S1. An illustration of the Aerosol Jet printing technique.
    • fig. S2. Schematic of pointwise printing process.
    • fig. S3. A droplet at the edge of supporting plane.
    • fig. S4. Porosity evolution for two different particle sizes and sintering conditions.
    • fig. S5. Mechanical behavior of the 3D-printed hierarchical scaffolds fabricated by the pointwise printing method.
    • table S1. Properties of ethylene glycol, the solvent used for the nanoparticle ink.
    • table S2. Information about compression test samples and test results.
    • Legend for movie S1
    • References (31–36)

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    Other Supplementary Material for this manuscript includes the following:

    • movie S1 (.wmv format). Video showing compressive loading of a 3D microlattice fabricated by the pointwise printing method.

    Files in this Data Supplement:

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