Research Article3D PRINTING

Self-assembled micro-organogels for 3D printing silicone structures

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Science Advances  10 May 2017:
Vol. 3, no. 5, e1602800
DOI: 10.1126/sciadv.1602800
  • Fig. 1 Block copolymer self-assemblies and micro-organogels.

    (A) Organogel support materials are formulated with light mineral oil, polystyrene-block-polyethylene/propylene diblock copolymers, and polystyrene-block-polyethylene/butylene-block-polystyrene triblock copolymers (polymers drawn are extended to illustrate their contour lengths). (B) High concentrations of diblock copolymers result in a fluid phase of packed micelles, unable to support printed structures. (C) Diblock micelles consist of polystyrene cores (red dots) surrounded by ethylene/propylene coronas. (D) At high concentrations of triblock copolymers, the support bath becomes globally cross-linked, and the printing nozzle causes permanent damage as it moves across the gel. (E) Ethylene/butylene midblocks assemble either into cross-link “bridges,” in which the polystyrene endblocks are found in different cores, or into “loops,” in which both polystyrene endblocks are located in the same core. (F and G) An equal blend of diblock and triblock copolymers results in closely packed microgels. Packed microgels provide a self-healing environment, allowing a printing nozzle to repeatedly transverse the same region while simultaneously supporting printed structures. (H) The micro-organogels form when the diblock copolymers replace the triblock copolymers, reducing the number of ethylene/butylene bridges that form until the material is no longer a continuous network.

  • Fig. 2 Rheological characterization of block copolymer phases.

    The rheological properties, including frequency sweep (A) and yield stress (B) of block copolymer assemblies, are highly dependent on the ratio of diblock to triblock copolymers. At high diblock concentrations, the material demonstrates rheological properties associated with a liquid, including a crossover in the shear modulus at high frequencies and no determinable yield stress. At high triblock concentrations, the material shows rheological properties associated with an irreversibly cross-linked gel, including separated elastic and viscous shear modulus at high values and irrecoverable yielding at high stresses. Block copolymer blends show rheological properties favorable for 3D printing of soft materials, including separated elastic and viscous shear moduli with low elastic modulus, a low yield stress, and a fast recovery of elasticity after shearing. (C) Thixotropic response time of the block copolymer microgel system. (D) The samples exhibiting rheology suitable for 3D printing are found to be composed of 2- to 4-μm microgels, as seen in phase-contrast microscopy.

  • Fig. 3 Control of printed features.

    (A) The width and height of printed lines are measured using confocal microscopy at flow rates and tangential velocities of 5000 μl/hour at 2 mm/s, 5000 μl/hour at 10 mm/s, 1000 μl/hour at 3.5 mm/s, 1000 μl/hour at 10 mm/s, and 5 μl/hour at 6 mm/s. (B) Feature size of printed objects can be controlled by the tangential velocity of the nozzle (v) and the flow rate of the ink through the nozzle (Q). The printed feature size shows nearly ideal behavior across a wide range of velocities and flow rates. (C) The critical feature size in which neat silicone oil remains stable is controlled by the yield stress of the organogel; increasing the yield stress of the organogel decreases the critical feature size necessary to maintain stable features. (D) The time at which features printed below the critical feature size will begin to break up can be increased by increasing the shear viscosity of the silicone ink.

  • Fig. 4 Surfaces and mechanical properties of printed structures.

    (A to C) SWLI of a printed silicone surface shows a surface roughness of 150 nm [2D scan (A), slice along the x axis (B), and slice along the y axis (C)]. (D) Stress-strain curve of printed silicone dog-bone specimens; printed silicone structures are capable of enduring more than 700% strain before mechanical failure. Tensile tests maintain a linear stress-strain relationship at low strains (inset). (E) Scanning electron microscopy of the cross section of a printed silicone structure demonstrates the uniformity of printed structures. (F) Macrophotographic image of a dog-bone specimen printed from silicone elastomer for tensile testing. (G) Macrophotographic images of printed dog-bone structures in the relaxed and highly strained states.

  • Fig. 5 Printed silicone structures.

    (A) Model trachea implants printed from RTV silicone elastomers into the micro-organogel support matrix retain their integrity and robustness once removed from the support material. (B) Cross section of the model trachea implant demonstrates the ability to print perfusable tubes with a wall thickness of 400 μm. (C) Silicone scaffold with sinusoidal wave pattern in both the x-y and x-z directions. (D) Top-down view of the silicone scaffold shows 250-μm-diameter features. (E) Macroscopic image of a perfusable network of hollow vessels being 3D-printed into the micro-organogel support material. (F) Macroscopic image of the completed, uncured silicone structure in the micro-organogel support material. The structure transitions from one large base with a diameter of 25 mm to six smaller tentacles with a diameter of 3 mm. (G) Once cured, the printed structure is removed from the organogel support material and cleaned. Fluid is pumped through the tubular network, demonstrating the capability of printed structure to support fluid flow. (H) Multiple parts are printed together to form a silicone pump with encapsulated ball valves supported by the micro-organogel material. (I) Scheme depicting the flow of fluid through the printed silicone pump. Applying repetitive compressive forces to the lower chamber pushes the fluid into the upper chamber and out the top of the pump.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/5/e1602800/DC1

    fig. S1. Small-angle x-ray scattering.

    fig. S2. Rheological measurements.

    fig. S3. Effects of elevated temperature on rheological properties.

    fig. S4. Measuring interfacial tension using the pendant drop method and contact angles.

    fig. S5. Loading and unloading stress-strain curves.

    fig. S6. Layer-to-layer and lateral adhesion between printed filaments.

    movie S1. Phase-contrast microscopy of dilute sample.

    movie S2. 3D printing a model trachea.

    movie S3. Removal of a cured silicone structure.

    movie S4. Fluid flow through a 3D-printed perfusable tube network.

    movie S5. Fluid pumped through a 3D-printed silicone valve.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Small-angle x-ray scattering.
    • fig. S2. Rheological measurements.
    • fig. S3. Effects of elevated temperature on rheological properties.
    • fig. S4. Measuring interfacial tension using the pendant drop method and contact angles.
    • fig. S5. Loading and unloading stress-strain curves.
    • fig. S6. Layer-to-layer and lateral adhesion between printed filaments.
    • Legends for movies S1 to S5

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • movie S1 (.mov format). Phase-contrast microscopy of dilute sample.
    • movie S2 (.mov format). 3D printing a model trachea.
    • movie S3 (.mov format). Removal of a cured silicone structure.
    • movie S4 (.mov format). Fluid flow through a 3D-printed perfusable tube network.
    • movie S5 (.mov format). Fluid pumped through a 3D-printed silicone valve.

    Files in this Data Supplement:

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