New 3D printer creates detailed structures from multiple materials
A technique poised to advance the manufacture of micro-scale electronic and medical devices
WASHINGTON – Researchers have developed a new method of 3D printing precision microstructures with multiple materials. The new approach is poised to enable the fabrication of structures with complex functions for consumer products and medical devices.
“Our 3D printing method could be useful for fabricating a variety of devices, such as microcircuits, photonic devices, and microfluidics,” said Wen Qiao, member of the research team at University of Soochow in China. “For example, the ability to 3D print with multiple materials with different properties could be used to make micro-robots with sophisticated built-in functions. “
In the optical society (AOS) review Optical Express, researchers demonstrate their new technique, called roll-to-plate projection microstereolithography (PµSL). They show that it can be used to create a wide range of structures and detailed objects such as a miniature ear prosthesis, a tiny replica of the Great Wall of China, and a multi-material butterfly with foldable wings.
Make 3D printing more flexible
PµSL, also known as digital light processing, is an established additive manufacturing technique that typically involves placing a liquid photosensitive resin in a tank with a transparent bottom. A digital projector flashes a light pattern that cures – or cures – all UV-exposed spots in a resin layer simultaneously. This is repeated layer by layer until the entire object is formed in the resin.
Although PµSL is a powerful tool for the micropattern, it cannot be used to fabricate complex microstructures with multiple materials, nor to print efficiently with highly viscous resins as they take too long to settle after curing. The use of multiple resins with different viscosities is desirable to create structures made of different materials with discrete parts that have different degrees of flexibility.
To overcome these limitations, the researchers designed a printer that uses a flexible membrane to hold the photosensitive resin during its transfer and light-curing. “Using a membrane for transportation greatly expands the materials that can be used and enables fast printing with high viscosity materials,” Qiao said. “We also added several nozzles to deliver different materials and enable high resolution printing. “
The new printer uses a nozzle to dispense a few drops of photopolymer onto a flexible membrane. As the membrane moves on a guide roller, a blade evenly spreads the photopolymer. Adjusting the distance between the blade and the membrane makes it possible to vary the thickness of the photopolymer layer from 1 to 200 microns. The guide roller keeps the photopolymer coated membrane slightly stretched and transfers the membrane to the area where polymerization occurs.
After polymerization, the printed structure is peeled off from the flexible membrane. The surface energy of the membrane is carefully designed so that the solidified resin adheres to the sample while the uncured photopolymer residue remains on the flexible membrane and can be recycled. This process is repeated to build a structure layer by layer.
Creating tiny and complex objects
With the PµSL roll-to-plate, each layer can be made of a different material with unique physical or chemical properties. Using the flexible membranes to transfer various curable polymers eliminates the need for material exchange or chemical cleaning procedures when changing materials.
The researchers used the new printer to print a variety of complex structures. For example, they made a miniature version of the Great Wall of China measuring 0.86 × 2.34 × 1.11 cubic millimeters using layers 10 microns thick. They also created hollow cylinders
470 microns in height with a wall thickness of 10 microns, with no residue inside. A butterfly with wings that could be bent up to 45 degrees was made using materials of different viscosities to create a flexible seal and a stiff region.
Since the thickness of each layer can be adjusted over a wide range, the build rate can be increased by using thicker layers for parts of a structure that are less detailed and thinner layers for areas that are less detailed. require higher resolution printing. For example, the hollow channels of a microfluidic device could be printed with great precision while the inputs and outputs were printed at high speed.
Now that the researchers have demonstrated the feasibility of PµSL roll-to-plate, they plan to take it one step further by incorporating a light-based process called grayscale photolithography to eliminate the need for layered printing.
Article: X. Wu, W. Qiao, M. Zhu, J. Ren, D. Pu, L. Chen, “Roll-to-Plate Additive Manufacturing”, Opt. Express, 29, 14, 21833-21843 (2021).