3D Printing and In Situ Surface Modification via Type I Photoinitiated Reversible Addition-Fragmentation Chain Transfer Polymerization

The present protocol describes the digital light processing-based 3D printing of polymeric materials using type I photoinitiated reversible addition-fragmentation chain transfer polymerization and the subsequent in situ material post-functionalization via surface-mediated polymerization. Photoinduced 3D printing provides materials with independently tailored and spatially controlled bulk and interfacial properties.

This protocol allows the bulk and interfacial properties of 3D-printed materials to be independently tuned. This gives greater flexibility to design and fabricate complex 3D-printed materials. This technique doesn't require stringent reaction conditions and can be performed using commercially available equipment.

As a result, this technique makes it significantly easier to fabricate complex 3D-printed materials. To begin, prepare the bulk resin by weighing 0.36 grams of BTPA into a clean 50 milliliter amber vial. Add 13.63 milliliters of polyethylene glycol diacrylate and 14.94 milliliters of DMAm to the amber vial using a micropipette.

In a separate 20 milliliter clean glass vial covered with aluminum foil, add 0.53 grams of TPO. Using a micropipette, add 10 milliliters of DMAm to the 20 milliliter glass vial containing the TPO and seal the vial using the cap. Thoroughly homogenize the solution of TPO in DMAm by mixing using a vortex mixer for 10 seconds and then using a standard laboratory sonic bath to sonicate the mixture for 2 minutes at room temperature.

Using a glass pipette and rubber pipette bulb, transfer the solution from the 20 milliliter glass vial to the 50 milliliter amber vial and seal the vial with a cap and moldable plastic film. Gently shake the 50 milliliter amber vial and then placed the vial in a sonic bath for 2 minutes at room temperature to ensure the mixture is homogenous. Place the sealed amber vial filled with the bulk resin in a fume hood for later use.

Prepare the surface resin as described previously for the preparation of the bulk resin. After preparing the surface resin, place the sealed amber vile filled with the surface resin in a fume hood for later use. To perform 3D printing, pour the previously prepared bulk resin into the 3D printer vat, ensuring that the solution completely covers the bottom film in the vat without any air bubbles or other inhomogeneities, and then close the 3D printer case.

Navigate the USB using the 3D printer screen and select the sliced model file by clicking on the triangle Play button to begin the 3D printing process. By watching the 3D printer screen, take careful note of the number of layers printed and pause the printing program by pressing the two vertical lines Pause button during 3D printing of the last layer of the base substrate. Remove the entire build stage and gently rinse the build stage and printed material with undenatured 100%ethanol from a wash bottle for 10 seconds to remove residual bulk resin from the 3D-printed material and the build stage.

Using compressed air, gently dry the 3D-printed material and build stage to remove residual ethanol and then reinsert the build stage into the 3D printer. Remove the vat from the 3D printer and pour the remaining bulk resin into an amber vile, and store the vile in a cool, dark place. Using undenatured 100%ethanol from a wash bottle, carefully rinse the vat to remove any residual bulk resin.

Dry the vat using a stream of compressed air to remove any residual ethanol and reinsert the vat into the 3D printer. To perform surface functionalization, pour the previously prepared surface resin into the 3D printer vat, ensuring that the solution completely covers the bottom film without any air bubbles or other inhomogeneities, and then close the 3D printer case. Resume the 3D printing program by clicking on the triangle Play button to allow the predetermined surface patterning to occur.

Once the printing program has been completed, remove the build stage from the 3D printer and wash for 10 seconds with undenatured 100%ethanol using a wash bottle to remove residual surface resin from the 3D-printed material and the build stage. Using compressed air, gently dry the 3D-printed material and build stage to remove residual ethanol. While still attached to the build stage, post-cure the material by inverting the entire build stage and placing it under 405 nanometer light for 15 minutes.

Gently remove the surface-functionalized 3D-printed material from the build stage using a thin metal plate or paint scraper. To perform the fluorescence analysis, place the 3D-printed surface-functionalized material under a 312 nanometer ultraviolet gas discharge lamp in a dark place, ensuring the surface-functionalized layer is facing up. Turn the lamp on to continuously irradiate the surface layer with 312 nanometer light and observe the fluorescent pattern.

To perform the tensile property analysis, place the dog bone-shaped specimens between the grips of a tensile testing machine, ensuring the 3D-printed material is equally placed at a distance of 50.3 millimeters. Start the program to acquire force versus travel data. After 3D printing and surface functionalization, the material was post-cured under 405 nanometer irradiation.

It was observed that the functionalized materials were yellow but highly transparent with well-defined shapes. The functionalized materials show no fluorescence in the dark. However, upon ultraviolet irradiation, spatially-resolved surface fluorescence was observed in the regions irradiated with light during the surface functionalization step, visible as a slightly raised yin-yang pattern.

Fluorescence images showed that the underside of the material showed no fluorescence under ultraviolet light irradiation. However, the top side of the material showed strong fluorescence in the yin-yang pattern. The mechanical properties of the 3D-printed dog bone-shaped samples were analyzed and a stress-strain curve was obtained.

The material showed an elastic deformation, providing yield stress of approximately 25 megapascal, and then a plastic deformation before failure. The elongation at break was approximately 12%while the stress at break was about 22 megapascal. The Young's modulus was calculated to be approximately 7 megapascal, while the toughness was approximately 115 megajoule per cubic meter.

It's important to make sure that the surface resident completely covers the vat film and is free from air bubbles or other imperfections that may lead to deviations from the intended surface pattern.