Researchers from the Chinese Academy of Sciences and Massachusetts Institute of Technology have successfully investigated a 3D printing method to produce controllable 3D structures from a single resin droplet.
The process combines UV curing and droplet three-phase contact line (TCL) dewetting techniques to effectively grow 3D structures from a single droplet with improved 3D printing efficiency and precision while minimizing residual resin waste.
One-droplet 3D printing in AM
3D printing methods based on photocuring, where a 3D model is solidified at the curing interface, have become a promising technique for microfluid, sensor, bioprinting, and shape-morphing system applications. However, these techniques have low wet material utilization and net material utilization efficiency, in comparison to Fused Deposition Modelling (FDM), Digital Light Processing (DLP), and Stereolithography (SLA) technologies.
The drawback of these methods within this particular application, according to the researchers, is that uncured resin needs to cover the whole tank in an excessive quantity before the printing process takes place, which leads to higher costs, more waste, and insufficient heat dissipation.
Earlier this year, researchers from the University of Oxford developed a single-droplet resolution 3D bioprinting process which allowed them to create synthetic tissues with greater precision. Using a custom-built 3D printer, the researchers constructed 3D droplet networks made up of 224 droplets, which were automatically generated to create 3D lattices.
Elsewhere, researchers from the University of Montreal investigated a new droplet-based method of cell bioprinting, Laser Induced Side Transfer (LIST), which involved using a low energy nanosecond laser alongside the laws of microfluidic dynamics to jet living cells onto each other.
While the UV curing and TCL dewetting method have similarities with the single-droplet methods mentioned above, this technique involves the printing of an entire structure from a single droplet, as opposed to multilayer droplet networks. This, the researchers say, is what sets this particular method apart from other 3D printed single-droplet technologies.
The UV curing and TCL dewetting method
Inspired by natural lotus and pitcher plant surfaces, where air or liquid trapped at the surface can significantly reduce the adhesion between layers, the researchers investigated how the curing interface could be manipulated to manufacture 3D structures using a single droplet of resin.
The key to the success of this technique is the free contact surface property of the droplet system through introducing a receding TCL, which both increases the inner droplet liquid circulation and reduces the adhesion properties of the liquid resin, cured resin, and resin vat.
The printing setup involved the use of a UV projector, a UV-transparent curing interface, and an aluminum supporting plate mounted on a moving platform.
First, a liquid resin droplet was deposited on the curing interface – the upper surface of the bottom of the resin vat. Before printing, the supporting plate contacted the curing window with the resin droplet in between. UV illumination patterns were then continually projected onto the curing interface, while the supporting plate was elevated at a constant speed. Through this, the liquid resin could be cured into solid resin in the shape of the UV pattern.
Simultaneously, the TCL of the liquid resin droplet receded as it was consumed through the UV curing process, until eventually the liquid droplet was successfully cured into the desired solid 3D structure.
Encouraged by the results of their investigation, the scientists further demonstrated the UV curing and TCL dewetting single-droplet process by 3D printing a tooth structure for use in customized dental applications. To illustrate the controllability element of the method, the researchers printed molar, incisor, and canine teeth crown structures suitable for dental treatment.
According to the scientists, this strategy to produce controllable 3D structures from a single droplet will be “of great significance” for on-demand 3D fabrication and has many potential future applications.
More information on the study can be found in the article “Continuous 3D printing from one single droplet” in the Nature journal. The study is co-authored by Y. Zhang, Z. Dong, C. Li, H. Du, N. Fang, L. Wu, and Y. Song.
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Featured image shows the scheme of the curing of a single droplet into the desired 3D structure, and the sequence of optical images of the UV curing-induced TCL receding process. Image via Nature journal.