Abstract
3D printing using conventional stereolithography is challenging because the polymerized layers adhere to the solid constraining interface. The mechanical separation forces lead to poor process reliability and limit the geometrical design space of the printed parts. Here, these challenges are overcome by utilizing a static inert immiscible liquid below the resin as the constraining interface. We elucidate the mechanisms that enable the static liquid to mitigate stiction in both discrete layer-by-layer and continuous layerless growth modes. The inert liquid functions as a dewetting interface during the discrete growth and as a carrier of oxygen to inhibit polymerization during the continuous growth. This method enables a wide range of process conditions, such as exposure and resin properties, which facilitates micrometer scale resolutions and dimensional accuracies above 95%. We demonstrate multi-scale microstructures with feature sizes ranging from 16 μm to thousands of micrometers and functional devices with aspect ratios greater than 50:1 without using sacrificial supports. This process can enable additive 3D microfabrication of functional devices for a variety of applications.
Highlights
1234567890():,; Recent advances in additive manufacturing have shown great potential to enable rapid fabrication of functional devices for diverse applications such as microelectronics[1], sensors[2], structural and optical metamaterials[3,4], micro-optics[5,6], and biomedical devices[7,8]
Within the context of this work and photolithography, the resolution is defined as the smallest feature size that can be printed for a range of process conditions and variations— known as the process window[22]
It is shown that discrete growth is advantageous for microfabrication since high spatial resolution and dimensional accuracies can be achieved because of reduced constraints over the process conditions such as exposure and resin properties—while continuous growth can be utilized when high vertical print speeds, smooth surface finish, and isotropic mechanical properties are desired
Summary
1234567890():,; Recent advances in additive manufacturing have shown great potential to enable rapid fabrication of functional devices for diverse applications such as microelectronics[1], sensors[2], structural and optical metamaterials[3,4], micro-optics[5,6], and biomedical devices[7,8]. High vertical print speeds have been demonstrated with continuous growth, the requirement of a stable dead zone and adequate resin replenishment places constraints on process conditions such as exposure energy, resin viscosity, and concentration of additives in the resin (resin properties), such as photoinitiator and absorbing dye[17,19,20,21]. Using a differential resin technique (see Methods), we characterized the dead zone thickness as a function of exposure intensity for Fluorinert (Fig. 2a).
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