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1. Introduction
Since the development of digital design and manufacturing technologies such as computer-aided design (CAD), -aided manufacturing and additive manufacturing (AM) techniques, the 3D printing (3DP) has gained more attention and has been widely applied for medical and dental purposes (Khorsandi et al., 2021; Pruksakorn et al., 2015; Melchels et al., 2010). These include use for the production of personalized implants for organ replacement (Turna et al., 2014), endoprosthesis (Pruksakorn et al., 2015), tissue engineering scaffolds (Melchels et al., 2010) and single-use surgical instruments (Hu et al., 2020). The concept of 3DP is to deposit the material to create the physical workpiece layer-by-layer. There are several systems of 3DP which can be classified into processed material forms, i.e. power-based, solid-based and liquid-based principles (Chantarapanich et al., 2013). In addition to the material extrusion, a solid-based 3DP which has been seen widespread use in medical applications, a liquid-based technology known as vat photopolymerization (VPP) is another 3DP system which has been recognized for its potential in manufacturing medical parts and instruments. This is due to its advantages in accuracy, a precise and smooth fabrication process and high mechanical strength. Also, various liquid photopolymer resins have been certified for medical use (Formlabs, 2021; Formlabs, 2016). Examples of use include orthopaedic surgical drilling/osteotomy guides (Anunmana et al., 2020; Takeyasu et al., 2013), clear orthodontic aligners (Tartaglia et al., 2021), bone tissue scaffolds (Melchels et al., 2010) and so forth.
The manufacturing principle of VPP is to solidify liquid photopolymer resin from energy dissipated from ultraviolet (UV) light source. It currently has bottom-up and top-down working concepts (Schmidleithner and Kalaskar, 2018), as shown in Figure 1. For the bottom-up concept, the build platform is upside down, and the built part is then hung above. The top-down concept is a conventional part-building principle, whereby the part is upright on the platform. In either concept, the solidification begins at the near-build platform layer, which is the bottom layer. Then, the successive build surfaces are solidified one by one until reaching the topmost layer (Chantarapanich et al., 2013). The photopolymer resin used in the VPP are those such as DSM’s Somos WaterShed (Puebla et al., 2012), Surgical...