Goodbye Layered 3D Printing: The Method That Makes It Disappear in Just 20 Seconds

A group of researchers from the University of Utah, affiliated with the John and Marcia Price College of Engineering, has developed a new approach to 3D printing capable of overcoming one of the historical limitations of layered printing techniques: the formation of joints between layers, often responsible for leaks and structural weaknesses.

The technique, described in an article published in the journal Nature Communications, utilizes a nanometer-scale mask that diffracts laser light to generate a holographic pattern corresponding to the desired shape, allowing the material to solidify in a single exposure. The entire process takes about 20 seconds, a significantly shorter time compared to the hours required by other laser-based printing methods.

Rajesh Menon, a professor in the Department of Electrical and Computer Engineering, led the research alongside laboratory collaborator Dajun Lin. During the experiments, the team demonstrated the possibility of printing multiple shapes in sequence, in a mode reminiscent of how a conveyor belt operates.

The Principle: From 2D Photolithography to the Third Dimension

The project draws inspiration from photolithography, a well-established technique in microfabrication, but extends its principles to three-dimensionality. The material used for the prints is a photosensitive substrate called SU-8, widely employed in photolithographic applications. It is a polymer organized into filamentous molecular chains that, when exposed to laser light, crosslink and harden. The portions of the substrate that are not exposed to light remain free of this bond and can be washed away, leaving only the desired shape.

In traditional two-dimensional photolithography, the final shape is defined by an opaque mask that prevents light from reaching the areas of the substrate that should not harden. This approach works well in two dimensions because the light only needs to interact with the surface of the material. However, the leap to three-dimensionality introduces a non-trivial complication: the laser must penetrate the entire volume of the substrate to harden it at depth, and since the material is not perfectly transparent, the beam undergoes deflections during its path, generating blur effects that would compromise printing precision.

A Nanostructured Lens to Compensate for Diffraction

To address this issue, the research group led by Menon designed a mask based on a nanostructured lens, capable of pre-compensating for the diffraction introduced by the substrate itself. Positioned in front of the light source, this mask directs the laser energy exclusively toward the volume of material that will constitute the final shape, countering the dispersion effects that would otherwise degrade the result.

Thanks to this enhancement, the researchers were able to create complex microstructures with dimensional ratios of up to 120:1. Menon himself described these structures as "extended 2D" rather than true three-dimensional structures: while they possess length, width, and height, the direct control of the experimenters only regards the first two dimensions. To illustrate the concept, Menon used a culinary metaphor: the mask would act like a cookie cutter that cuts a complex shape from a thick dough, while the laser "bakes" the inside of the structure at the same time, giving the final result adequate mechanical solidity.

Applications on Microtubules and Strength Testing

The intrinsic characteristics of the technique make it particularly suitable for creating lattice patterns of microtubules, structures that exhibit extremely fine details in two dimensions extended as far as possible along the third. Using this method, the team printed assemblies of microtubules with individual diameters of up to 6 micrometers, subsequently subjecting them to a series of tests.

The researchers illustrated various lattice models for their microtubule arrays. The tests included both the mechanical strength of the structures, via compression tests, and their functionality as channels for transporting liquids utilizing capillary action, with positive results in both cases.

Future Prospects

Currently, the research group is working to surpass the limit of "extended 2D" and develop a version of the technique capable of independently controlling geometry along all three spatial dimensions, a step that could further expand the range of practical applications of the method, from microfluidics to the fabrication of components on a microscale.