Single-digit-micrometer-resolution continuous liquid interface production

Abstract

To date, a compromise between resolution and print speed has rendered most high-resolution additive manufacturing technologies unscalable with limited applications. By combining a reduction lens optics system for single-digit-micrometer resolution, an in-line camera system for contrast-based sharpness optimization, and continuous liquid interface production (CLIP) technology for high scalability, we introduce a single-digit-micrometer-resolution CLIP-based 3D printer that can create millimeter-scale 3D prints with single-digit-micrometer-resolution features in just a few minutes. A simulation model is developed in parallel to probe the fundamental governing principles in optics, chemical kinetics, and mass transport in the 3D printing process. A print strategy with tunable parameters informed by the simulation model is adopted to achieve both the optimal resolution and the maximum print speed. Together, the high-resolution 3D CLIP printer has opened the door to various applications including, but not limited to, biomedical, MEMS, and microelectronics.

Fig. 1.. Single-digit-micrometer-resolution CLIP-based 3D printer setup schematic and printing process.

(A) Schematic of the single-digit-micrometer-resolution CLIP-based 3D printer. The 3D printer consists of a UV projector, a projection lens, a resin vat that contains an oxygen-permeable window, and a translation stage. (B) Projection optics system includes a UV camera and a computer for real-time monitoring, where the projected UV light path (purple) is reflected through the beam splitter, and the reflected projection (yellow) is captured by the UV camera, thereby allowing for real-time monitoring of the projected images and enabling fine adjustment of the focal plane. (C) CLIP process contains an oxygen-permeable window, which is not only highly transmissive to UV (385 nm) but also permeable to oxygen. The permeated oxygen forms a thin layer of dead-zone above the window, where photopolymerization is inhibited, allowing a continuous 3D print.

Fig. 2.. Contrast-based focus algorithm for optimization of the projection focal plane.

(A) Focus on the build platform with strobe light by finely adjusting the tube lens (highlighted in green). (i) Build platform is out of focus; (ii) build platform is in focus. Scale bars, 2.5 mm. (B) Focus on a projected pattern by finely adjusting the vertical position of the build platform (highlighted in green). (i) Projected pattern on the build platform is out of focus; (ii) adjusted build platform brings the projected pattern into focus. Scale bars, 2.5 mm. (C) Edge profile of the projected pattern. (D) The calculated MTF of the edge profile. (E) Through-focus sharpness performance obtained from scanning near a rough estimation of the optimal focal plane of 400 μm. Best focal plane with the highest sharpness performance is found and compared with actual prints. The z position with the highest sharpness also has the best resolved 3D print. Scale bars, 1.0 mm.

Fig. 3.. Schematic of CLIP setup and printing process.

(A) Schematic of a general CLIP printing setup. The setup includes (from bottom to top) a UV light engine that illuminates UV projection at a wavelength of 385 nm, an oxygen-permeable window, a dead-zone (height h) where uncured resin flows through, cured resin, and a build platform that travels at a pulling rate U. (B) Schematic of the stepped printing processes containing the (i) initial step, (ii) stage movement, (iii) stage stoppage, and (iv) UV exposure that are (v) repeated throughout the print process.

Fig. 4.. CLIP printing process model includes projection optics, velocity flow field, polymerization gradient, and final 3D printed structure.

(A) Simulation of PSF from Zemax and Gaussian approximation [for (i) 30-μm-pixel projection lens] and Gaussian approximation[(for (ii) 1.5-μm-pixel projection lens]. Insets are 2D visualizations of the PSF. (B) Simulations of a full 3D print that combines optical Gaussian approximation and photopolymerization to predict the overall printing performance of a square pyramid structure (width of 500 μm and height of 1000 μm). Insets are SEM images of an actual 3D printed part for comparison. Scale bars, 250 μm.

Fig. 5.. CLIP printing process: Kinetics modeling.

(A)Transient photopolymerization gradient simulation. (i) Transient oxygen concentration profile in the dead-zone regime. (ii) Transient converted oligomer concentration in the dead-zone regime. (iii) Concentration of all components in the dead-zone regime at t = 0.1 (−). (B) Steady-state oxygen concentration in the dead-zone regime for both the analytical expression and numerical solution from PDEs. (C) Dead-zone thickness at various values of the Damköhler number (Da) from both the analytical expression and the numerical solution of the PDEs. (D) Parameters used in this study.

Fig. 6.. CLIP printing process: Mass transport modeling using lubrication theory.

(A) (i) Velocity flow profile in the dead-zone regime for Newtonian fluid using the analytical expression derived. (A) (ii) Velocity flow profile in the dead-zone regime for non-Newtonian fluid using the analytical expression derived. Notice that the non-Newtonian fluid is modeled with a power-law fluid with shear-thinning coefficient of n = 0.87. (B) Direct measurement of Stefan force. Experimental data are obtained through recording the Stefan force during the print process for different 3D print part radius, ranging from 0.5 mm to 2.2 cm. Inset: Load-cell experimental setup for Stefan force measurement.

Fig. 7.. Demonstration prints from the single-digit-micrometer-resolution CLIP-based 3D printer.

(A) David by Michelangelo (1.2 cm in height) (Florence, Italy). (B) Rocky Statue (2 cm in height) (Philadelphia, PA, USA). (C) Statue of Liberty (1.5 cm) (New York, NY, USA). (D) Lattice twisted bar (1.25 cm in height). (E) Eiffel Tower (Paris, France). (F) Terraced microneedle. (G) Square block array. (H) Lattice block. Scale bars, 1 mm.

Fig. 8.. Resolution and print speed characterization.

(A) Comparison plot of print speed and resolution between high-resolution CLIP and other high-resolution 3D printing technologies. (B) Twisted lattice bar. The high-resolution CLIP 3D print and TPP (Nanoscribe, Germany) show that the CLIP technology completed the full print in a much shorter print time compared to the TPP technology. (C) Sample images of 1.5-μm-resolution CLIP printer resolution characterization designs for lines of (top row) 30 μm (20 pixels), 15 μm (10 pixels), and 7.5 μm (5 pixels). Insets: Side view of lines resolvability. Bottom row: Holes ranging from 37.5 μm (15 pixels) to 18 μm (12 pixels). (D) Summary table of resolution characterization for single-digit-micrometer-resolution CLIP-based 3D printer.