*2.3.1. Continuous liquid interface production (CLIP)*

Continuous liquid interface production (CLIP) is a type of constrained surface DLP process, where a thin film between building platform and the material tray is not cured and remains liquid. The so-called dead zone at the interface can be generated by utilizing a vat with a floor that is permeable to oxygen. This inhibits curing, and the resin in contact with oxygen remains liquid. Recoating mechanisms are thereby superfluous and continuous elevation of the building platform can be achieved, which improves surface quality and drastically increases printing speed up to 500 mm/h [44]. Similarly, to attain a liquid interface film, a high-density inert and an immiscible liquid layer such as brine has been proposed [45]. CLIP has been commercialized by Carbon Inc., and is establishing itself in the AM market due to its reduced printing times [46].

#### **2.4. Liquid crystal display stereolithography**

Since its development in 1997 by Bertsch *et al.* [47], using an LCD device as a dynamic mask for SLA has been almost completely replaced by the DLP counterpart. The latter benefits are from superior switching speeds at higher accuracy [48]. Nevertheless, it merits mentioning as a low-cost alternative to DLP with commercially available LCD printers primarily catering to the laypersons demographic as opposed to the industry [49].
