Research ArticleMATERIALS ENGINEERING

Direct 4D printing via active composite materials

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Science Advances  12 Apr 2017:
Vol. 3, no. 4, e1602890
DOI: 10.1126/sciadv.1602890
  • Fig. 1 The concept of direct 4D printing and its experimental demonstration.

    (A) Previous SMP-based 4D printing requires five steps to achieve the programmed shape. (B) The direct 4D printing approach exploits the ability to print controlled multimaterial composites to integrate the five steps into a single one. (C) Experimental demonstration of two-layer strips (80 mm × 5 mm × 0.6 mm, with each layer 0.3 mm) that have been designed and fabricated to be printed as a flat strip (the temporary shape) and then, when heated, transform into a curved shape (the permanent shape) that remains largely unchanged upon further cooling and heating. (D) Measured curvature of the bilayer as a function of temperature during heating to deploy the bilayer from its flat to the curved shape. Both continuous and discrete heating achieve the same curvatures: The former are heated from 18°C at a rate of 2°C/min, whereas the latter are immersed in water for 20 s at a prescribed temperature.

  • Fig. 2 Basic understanding of the parameters involved in direct 4D printing.

    (A) Measured (symbols) and fitted (curves) compressive strain built into each material (strips of dimensions 60 mm × 8 mm × 1.2 mm) as a function of the printing time for each layer. (B) Measured permanent shape of printed flat bilayer samples (60 mm × 6 mm × 0.6 mm, with each layer having equal thickness) as a function of layer printing time. (C) Measured (symbols) and simulated (curves) curvature of bilayers (60 mm × 5 mm × t mm) with elastomer and SMP layers of equal thickness as a function of total layer thickness (t) and layer printing time. (D) Measured (symbols) and simulated (curves) curvature of bilayers (60 mm × 5 mm × 1.2 mm) as a function of volume (thickness) fraction of elastomer. The curvatures in (B) to (D) were measured after the samples were heated to 62°C and held for 20 s.

  • Fig. 3 Direct 4D printing of structural elements with deformation modes dictated by the 3D-printed architecture.

    (A) A printed flat strip (150 mm × 10 mm × 0.7 mm) that transforms into a wavy structure. The SMP/elastomer thicknesses are 0.2/0.5 mm, and the pattern pitch is 15 mm. (B) A printed flat strip (120 mm × 8 mm × 0.7 mm) that transforms into a helix. The SMP/elastomer thicknesses are 0.2/0.5 mm, and a 0.5-mm-wide SMP separator is oriented at 45°. (C) A ring of 120/68.6-mm outer/inner diameter and 1.2-mm thickness that transforms into a wavy structure. The SMP/elastomer thicknesses are 0.4/0.8 mm, and the pattern pitch is 15 mm. In all cases, the layer printing time is 68 s. Details of the composite architecture are shown in exploded views, where blue represents the elastomer and cyan represents the glassy polymer [see the Supplementary Materials (section S3) for geometry parameters]. Both the temporary (as-printed) and permanent (after heating) configurations from experiments are shown as corresponding finite element simulations.

  • Fig. 4 Direct 4D printing of structures consisting of multiple elements.

    (A) Lattice structure printed in a collapsed configuration (180 mm × 25.2 mm × 7 mm) that deploys into an open configuration upon heating. The SMP/elastomer thicknesses are 0.35/0.35 mm. (B) Similar lattice (192 mm × 6.3 mm × 6 mm) structure that not only expands upon heating but also bends because of the designed architecture. The SMP/elastomer thicknesses are 0.8/0.8, 0.6/0.6, 0.3/0.9, and 0.2/0.6 mm, respectively, from top to bottom. (C) Flat star-shaped structure that deploys into a 3D dome. Each equilateral triangle has an outer/inner side length of 60/44.4 mm. The SMP/elastomer thicknesses are 0.88/1.77 mm. (D) Printed flower consisting of multiple petals at multiple layers that blooms into a configuration, where petals at different layers assume final configurations with different curvatures. The SMP/elastomer thicknesses of all petals are 0.3/0.3 mm. Three different radii (42, 48, and 51 mm) are designed for petals in different layers. Details of the composite architecture are shown in exploded views, where blue represents the elastomer and cyan represents the glassy polymer [see the Supplementary Materials (section S3) for geometry parameters].

  • Fig. 5 Demonstration of the ability for a 4D-printed structure to be reprogrammed from its permanent shape into many different configurations that are structurally stiff at room temperature and then to be returned to its permanent shape upon heating.

    (A) The deployed permanent configuration of a compact lattice after heating, which is same with the activated structure in Fig. 4A. This shape is also the recovered shape after reprogramming and heating. (B) The reprogrammed saddle-cylinder shape. (C) The reprogrammed compressed-twisted compact shape. (D) The reprogrammed semisphere/dome shape. (E) The reprogrammed in-plane fan shape.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/4/e1602890/DC1

    section S1. Thermomechanical properties of polymers

    section S2. Additional results

    section S3. Geometry of printed samples

    section S4. Modeling and simulation

    fig. S1. Thermomechanical properties of elastomer (TangoBlack+) and glassy polymer SMP (VeroClear) as determined by DMA.

    fig. S2. Contribution in overall curvature from CTE mismatch strain and built-in compressive strain.

    fig. S3. A lattice structure (dimensions in mm) printed in an open configuration and then deployed into a compact configuration upon heating.

    fig. S4. Design of the printed sample in Fig. 3A.

    fig. S5. Design of the printed sample in Fig. 3B.

    fig. S6. Design of the printed sample in Fig. 3C.

    fig. S7. Design of the printed sample in Fig. 4A.

    fig. S8. Design of the printed sample in Fig. 4B.

    fig. S9. Design of the printed sample in Fig. 4C.

    fig. S10. Design of the printed sample in fig. S3.

    table S1. List of parameters for constitutive model.

  • Supplementary Materials

    This PDF file includes:

    • section S1. Thermomechanical properties of polymers
    • section S2. Additional results
    • section S3. Geometry of printed samples
    • section S4. Modeling and simulation
    • fig. S1. Thermomechanical properties of elastomer (TangoBlack+) and glassy polymer SMP (VeroClear) as determined by DMA.
    • fig. S2. Contribution in overall curvature from CTE mismatch strain and built-in compressive strain.
    • fig. S3. A lattice structure (dimensions in mm) printed in an open configuration and then deployed into a compact configuration upon heating.
    • fig. S4. Design of the printed sample in Fig. 3A.
    • fig. S5. Design of the printed sample in Fig. 3B.
    • fig. S6. Design of the printed sample in Fig. 3C.
    • fig. S7. Design of the printed sample in Fig. 4A.
    • fig. S8. Design of the printed sample in Fig. 4B.
    • fig. S9. Design of the printed sample in Fig. 4C.
    • fig. S10. Design of the printed sample in fig. S3.
    • table S1. List of parameters for constitutive model.

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