Research ArticleAPPLIED PHYSICS

Grayscale digital light processing 3D printing for highly functionally graded materials

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Science Advances  03 May 2019:
Vol. 5, no. 5, eaav5790
DOI: 10.1126/sciadv.aav5790
  • Fig. 1 g-DLP 3D printing of FGM via two-stage curing.

    (A) Schematics showing the g-DLP printing of graded material via a two-stage curing process. A hybrid ink was used for DLP 3D printing first followed by thermal curing the printed part in a heating oven. (B) Predicted normalized conversion of cured material under different grayscale light with only one exposure (solid lines) and multiexposure (dashed lines) by the model using the exposure time of 20 s and curing thickness of 60 μm per layer. (C) Gel fraction of hybrid ink after the first- and second-stage curing. (D) Tensile stress-strain curves of printed materials using different grayscale during printing (sample size, >3). (E) Young’s modulus and glass transition temperature of printed materials as functions of grayscale. (F and G) Design, print part under bending, and corresponding FEM simulation of graded materials enabled by g-DLP using a discrete gradient (F) and a continuous gradient (G) grayscale pattern. Scale bars, 5 mm.

  • Fig. 2 Graded metamaterial via g-DLP for multifunctional applications.

    (A and B) Design, print part, experimental compression test, and FEM of a 2D lattice and cellular metamaterial for controlled buckling (A) and pattern transformation (B), respectively. (C) Design and print part of a 3D lattice metamaterial. (D and E) Synchronous deformation (D) and sequential deformation (E) of the 3D lattice in the x and z axes, respectively. (F) Compression stress-strain curves of the anisotropic 3D lattice in the x and z axes. (G) Design and print part of a limb-mimic structure with soft muscle (G88), moderate skin (G70), and stiff bone (G0) as well as hollow channels. (H) The limb-mimic structure was easily compressed in the thickness direction. (I) The limb-mimic structure was loaded heavyweight (1 kg) without obvious bending across the length direction (z axis). (J) Design and print part of a small-scale artificial limb structure with soft muscle (G85) and stiff bone (G0). Scale bars, 1 cm. Photo credit: Xiao Kuang, Georgia Tech.

  • Fig. 3 Applications of g-DLP–printed composites for sequential SMP components and 4D printing.

    (A) Design and print part of a helical SMP component with increasing grayscale level on the hinge from G20 to G80. (B) Snapshot showing the sequential shape recovery process of the helical SMP component with graded hinge materials in hot water (~60°C). (C) Design and print part of a sequential SMP as an artificial arm. (D and E) Snapshot showing sequential shape recovery of a single artificial arm (D) and artificial arms for soft robotics to lift a stick (E) by a heat gun. (F) Schematic of a shape-shifting film by cold drawing of printed lamina fiber-reinforced composites with asymmetric fiber distribution and recovery process. (G) Pictures of the printed strip with 0° of fiber orientation: original shape and bending shapes by applied stretching strain at room temperature. Scale bars, 1 cm. Photo credit: Xiao Kuang, Georgia Tech.

  • Fig. 4 Encryption via diffusion-assisted coloring for graded materials.

    (A) Two-stage cured films enabled by a continuous gradient grayscale pattern (inside G80 to outside G0) across the radius were immersed in fluorescein (B) or dye (C) solution followed by washing and drying to visualize the grayscale pattern by UV light and visible light, respectively. (D) Coloring kinetics of the film in (A) by analyzing the red value (RGB color) of the images. (E) Two-stage cured films using the design of staggered discrete gradient grayscale (G80 and G0) concentric circle pattern. The samples in (E) were colored using cyan dye solution and corresponding red value of image across the sample (F) as well as fluorescein solution and the green value of image across the section (G). (H) Design of a grayscale pattern for QR code and corresponding images of the colored pattern using fluorescein under UV light. (I) Design of a grayscale pattern for a name card colored with black dye solution. Scale bars, 5 mm. Photo credit: Xiao Kuang, Georgia Tech.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/5/eaav5790/DC1

    Supplementary Text

    Fig. S1. Photopolymerization of acrylate and thermal curing reactions in the hybrid resin.

    Fig. S2. Model reaction using a stoichiometric mixture of GMA and D230 by FTIR.

    Fig. S3. Model reaction kinetics by 1H NMR.

    Fig. S4. Experiment and modeling of grayscale light photocuring kinetics.

    Fig. S5. Printing resolution of g-DLP.

    Fig. S6. FTIR spectra showing the two-stage curing for practical printing.

    Fig. S7. Grayscale-dependent thermomechanical properties of g-DLP–printed samples.

    Fig. S8. Helical SMP component without recovery sequence.

    Fig. S9. Design, morphology, and properties of in situ–printed laminate composites.

    Table S1. Grayscale-dependent tensile properties of g-DLP printed after the first and second curing stages.

    Movie S1. Single-point bending of a discrete and continuous gradient strip.

    Movie S2. Compression of 2D lattice metamaterial.

    Movie S3. Compression of pattern switch metamaterial.

    Movie S4. Compression of 3D anisotropic lattice.

    Movie S5. Shape recovery of helical SMP components.

    Movie S6. Soft robotics by sequential SMPs.

    Movie S7. Scanning QR code by a smartphone.

  • Supplementary Materials

    The PDF file includes:

    • Supplementary Text
    • Fig. S1. Photopolymerization of acrylate and thermal curing reactions in the hybrid resin.
    • Fig. S2. Model reaction using a stoichiometric mixture of GMA and D230 by FTIR.
    • Fig. S3. Model reaction kinetics by 1H NMR.
    • Fig. S4. Experiment and modeling of grayscale light photocuring kinetics.
    • Fig. S5. Printing resolution of g-DLP.
    • Fig. S6. FTIR spectra showing the two-stage curing for practical printing.
    • Fig. S7. Grayscale-dependent thermomechanical properties of g-DLP–printed samples.
    • Fig. S8. Helical SMP component without recovery sequence.
    • Fig. S9. Design, morphology, and properties of in situ–printed laminate composites.
    • Table S1. Grayscale-dependent tensile properties of g-DLP printed after the first and second curing stages.
    • Legends for movies S1 to S7

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mp4 format). Single-point bending of a discrete and continuous gradient strip.
    • Movie S2 (.mp4 format). Compression of 2D lattice metamaterial.
    • Movie S3 (.mp4 format). Compression of pattern switch metamaterial.
    • Movie S4 (.mp4 format). Compression of 3D anisotropic lattice.
    • Movie S5 (.mp4 format). Shape recovery of helical SMP components.
    • Movie S6 (.mp4 format). Soft robotics by sequential SMPs.
    • Movie S7 (.mp4 format). Scanning QR code by a smartphone.

    Files in this Data Supplement:

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