Researchers from Stanford University have conducted a study on microfabrication using additive manufacturing, which increases the emerging paradigm shift of building microstructures with AM to revolutionize device design in fields such as medicine and energy storage.
The study, published recently in Science Advances, describes a new approach by engineers to addressing multiple microfabrication issues in AM and enabling 3D printed objects with characteristics as small as 1.5 microns—one-fifth the size of a red blood cell. The new single-digit-micron resolution technology, dubbed micro-CLIP, allows for 50X smaller part features than commercial CLIP printers while retaining the commercial printers’ high print speed, which is more than 100X quicker than other “state-of-art” high-resolution 3D printing methods suited for microfabrication.
What does the research highlight?
The researchers developed and implemented a custom projection lens system consisting of a tube lens and microscope objectives to attain the single-digit-micrometer resolution. Furthermore, due to the extremely narrow depth of field (tens of micrometers) of the high-magnification microscope objectives, the team used a focused algorithm that included an in-line beam splitter and a customizable tube lens to visualize the projection pattern with a CCD camera.
To find the optimal focal plane position, the team employed a contrast-based algorithm and digitally designed mesh pattern. The team cited the optimum sharpness location and confirmed the performance with actual print results after scanning through a depth of 400 μm and assessing the through-focus projected image stacks. This contrast-based focusing system, according to the team, solves the challenge of focusing on the narrow depth of field from high-magnification projection optics and enables them to effortlessly readjust to the ideal focal plane.
The resolution performance of the CLIP-based 3D printer with single-digit micrometer resolution was assessed utilizing hole and line patterns with dimensions varying from 4.5 to 135 μm. Although the optical resolution was developed to be 1.5 μm, the smallest features which were repeatedly and successfully printed were 18-μm holes and 6-μm lines. It has been discovered that resin formulation, design patterns, optical resolution, printing strategies, and finally, cleaning strategies have a strong influence on printer resolution and print performance.
Following that, the team created a simulation model to offer a deeper understanding of the CLIP printing process as well as directions for creating optimal printing strategies for different designs and materials. The model includes an optical simulation of projection optics through a PSF estimated with a Gaussian distribution, and a lubrication theory prediction of momentum transport and flow field. It also consists of cured height, oxygen concentration gradient, and photopolymerization kinetics modeling to assess dead-zone thickness.
The model offers insights into how to enhance the printing process, such as using a step-by-step printing strategy (for instance, stop-move-expose) to enable effective resin reflow and estimating the necessary interlayer moment to remove resin convection-induced print artifacts. The model also estimates the parameters (oxygen diffusion coefficient and light intensity) needed to keep a constant dead zone for constant printing. Finally, the team demonstrated 3D printing with single-digit-micrometer-resolution CLIP-based 3D printers and the capability to print with viscous elastomeric material.
Micron resolution 3D printing
Previously, Nanofabrica, a Tel Aviv-based developer of precision additive manufacturing technologies, introduced two industrial 3D printers with micron-level resolution, namely, the Workshop System and the Industrial System. Both systems incorporate the company’s patented process, which is based on a Digital Light Processing (DLP) engine, along with Adaptive Optics (AO), a technology used to enhance image discrepancies in optical devices like telescopes. This technology is intended for use in the medical, automotive, aerospace, optics, and semiconductor industries to develop parts with micron and sub-micron resolution and surface finishes.
Furthermore, French ultra-high-resolution 3D printer manufacturer Microlight3D released the Altraspin sub-micron 3D printer. The machine has a resolution of 0.2µm, which is 100 times smaller than the thickness of human hair. Altraspin 3D printer, which is useful in the fields of micro-robotics, bioengineering, and microsensors, is developed to meet the increasing demand for sub-micron fabrication. The company’s CEO, Denis Barbier, comments, “Microlight3D designed Altraspin to respond to manufacturing demands for more customization and the rapid prototyping of submicron parts that are not constrained by their geometric or organic shape.”
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Feature image shows Single-digit-micrometer-resolution CLIP-based 3D printer setup schematic and printing process. Image via Stanford University.