## 4 Materials for SLA
### Three-Dimensional SLA Printing of Functionalized Graphene Composites  
The interactions between GO and hydrophobic polymer matrix are relatively weak, based on non-covalent interactions, such as hydrogen bonds or van der Waals forces [124]. Consequently, the mechanical toughness of graphene nanocomposites, required for some applications, is lower than expected. The unique opportunities offered by graphene are fully exploited after the functionalization of GO with molecules that enable creation of strong covalent interactions with the surrounding polymer matrix. Some authors reported the functionalization of graphene with photosensitive groups, such as azobenzene [125], and their findings can be implemented in the design of new photocurable resins for SLA. The chemical functionalization of graphene with photoactive units led to the formation of the so-called \"photoactive graphene\", which undergo a chemical or physical reaction upon exposure to sunlight and/or ultraviolet light [126]. Therefore, their applications are predominantly in the fields of optoelectronics and photocatalysis. Interested readers are referred to other review papers to know more details about the functionalization of graphene and GO [127], as this article pays particular attention to the design of new resins for graphene-based polymer composites. The analysis of selected peer-reviewed literature revealed that the incorporation of unmodified GO into a resin for SLA printing is prevalent. A promising approach refers to the surface modification of graphene, which is helpful for the formation of covalent bonds between nanofiller and polymer matrix, which further determine the effective improvement of mechanical properties. Table 3 summarizes the studies with the most representative results. [PERSON] et al. [128] synthesized 2-hydroxyethyl methacrylate-grafted graphene oxide (HEMA-g-GO) and dispersed it in an acrylate photosensitive resin to prepare nanocomposites via SLA. The results showed that improvements in mechanical strength were obtained by adding small amounts of HEMA-g-GO (0.01, 0.003 and 0.06 wt%). The tensile strength and flexural strength of nanocomposites were increased by 67% and 32%, respectively, for the nanocomposite with 0.06 wt% HEMA-g-GO. Later, [PERSON] et al. [129] has successfully grafted acrylate groups on GO, resulting in improved thermal stability of the filler. The functionalized GO (fGO) was homogeneously dispersed into commercial methacrylate resin and generated good interfacial adhesion that causes effective load transmission from the matrix to the filler in the 3D-printed structure. This material exhibited excellent tensile strength, ductility, and fracture energy with a minor loading of 0.2 wt% GO. Very recently, [PERSON] et al. demonstrated that surface modification reactions of GO with chitosan and alkaline phosphatase could be made after manufacturing the 3D-printed objects [130]. The authors stated that introducing GO in concentration below 1 wt% results in nanocomposites with higher strength and toughness when compared to the pristine resin. The obtained nanocomposites were considered suitable as platforms for the selective immobilization of functional biomolecules. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Functionalization** & **Polymer Matrix** & **Resin Preparation** & **3D Printing** & **Post-Processing** & **Applications** & **Ref.** \\
**Agent** & & & & **Conditions** & **Steps** & & \\ \hline \multirow{6}{*}{2-Hydroxyethyl methacrylate} & \multirow{6}{*}{Arylate photosensitive resin synthesized by radical polymerization} & \multirow{6}{*}{Basiphenol-A epoxyacrylate (E-4) and methylene glycol (male ratio of 10:1) was mixed with butyled hydroxyloethylene (0.1 wt%) at 70 \(\lx@math@degree\) for 1 h.} & \multirow{6}{*}{SLA printer (Hygieo WIZART (BLDF/SLA, China), UV-light irradiation & & \\  & & & & & \\ \cline{1-1}  & & & & & \\ \cline{1-1}  & & & & & \\ \cline{1-1}  & & & & & \\ \cline{1-1}  & & & & & \\ \hline \hline \end{tabular}
\end{table}