One-Pot Grayscale Patterning of Sacrificial Polymer Networks to Enable Supportless 3D Printing

Recent advances in additive manufacturing (AM) have demonstrated the fabrication of complex geometries with high degrees of freedom and rapid processing times. Projection based micro-stereolithography (PµSL) is a popular AM technique due to its high precision and high efficiency in patterning micron-scale structures. Demand for high resolution AM encompasses many fields from rapid prototyping to microelectronics, tissue engineering, and metamaterials. However, fabricating features that are unsupported by previous cured layers is difficult to achieve due to the risk of collapse, misshaping, and misalignment of subsequent layers under gravity. This limits the ability of AM to construct some geometries, including overhangs, arches, and channels, which may require the digital generation of support structures. While these structures improve upon the geometric fidelity of manufactured parts, they can also lead to unnecessary material consumption and result in a loss of relevant features. Upon completion of the print process, support structures must be removed from the final product which lengthens processing time and often results in surface irregularities or structural damage.<br/>To overcome this challenge, we study a dual cure radical-cationic resin to print geometries with soluble supports in a single pot. The resin patterns permanent features using deep blue light (405 nm) at high intensity and sacrificial support structures at low intensity to be dissolved under basic conditions. By simply irradiating a grayscale pattern, the permanent cationic network is localized to areas that are brightly illuminated, while the sacrificial radical network is patterned under dim light. The cationic network consists of an epoxide crosslinker and comonomer, while the radical network consists of a methacrylated sebacic acid (MSA) crosslinker and comonomer. The MSA crosslinker hydrolyzes by simply soaking it in basic conditions (0.1-1 M NaOH), thereby dissolving the supporting structures patterned with low intensity light. FTIR data shows conversion of only the radical network at low power (30 mW/cm²), while conversion of both the radical and cationic network is observed at high power (90 mW/cm²). The FTIR results were further confirmed by photorheological measurements which show gelation of the radical network at low light intensity and gelation of the cationic network at high light intensity. Finally, 3D printed structures patterned with low light intensities (&lt; 39 mW/cm²) were sacrificed under basic conditions (1M NaOH, ~15 min), while structures patterned with high light intensities (&gt; 40 mW/cm²) survived basic conditions which indicates the presence of the cationic network. This AM approach to pattern sacrificial structures could be easily adapted to commercial printers that use 405 nm visible light to enable supportless 3D printing of complex geometries.