## 4 Materials for SLA
### Graphene Composites
#### 4.2.1 Overview of Graphene
Another important member of the graphene family is graphene quantum dots (GQDs), which are graphene sheets with a lateral dimension of <100 nm, but its potential is not consistently exploited in AM techniques yet. For in-depth details on the synthesis strategies and physical properties of graphene and its derivatives, we suggest some reviews for interested readers to refer to in the references [95; 96; 24; 97]. Graphene is the nanofiller of choice due to its layered structural fillers having a large surface area (up to 2630 m\({}^{2}\)/g) [98]. This is beneficial for obtaining high-performance composites as well as for loading drugs/biomolecules and brings the possibility of conjugating fluorescent dyes for bioimaging. Graphene reinforcement in AM offers a large spectrum of complex functional materials as a result of its inherent properties. However, the polymer matrix exhibits low dispersion efficiency, and therefore functionalization of graphene is required. In the oxidized form, the hydrophilic functional groups ensure a superior dispersion in an aqueous solution, increasing the accuracy and efficiency of the printing. Conversely, the graphene derivatives (GO, rGO, GQDs) offer a good dispersibility in polymer matrices and, for this reason, were selected as fillers in many polymer nanocomposite materials. GO stands out from this panel due to its unique hydrophilic, thermal, and electrical properties with high potential in medical science in stimuli-responsive materials [99; 100; 101; 102], antibacterial materials [103], membranes in wound dressings [104], tissue-engineering scaffolds [105]. GO shows promising antimicrobial activity against Gram-positive and Gram-negative bacteria, phytopathogens and biofilm-forming microorganisms [106]. The functional groups of graphene derivatives (carboxyl, epoxide, hydroxyl) result in higher surface energy and superior compatibility with polar polymer matrices, often used for healthcare products. The study of graphene derivative bioinks is a growing field. The electrical properties of graphene are advantageous for developing complex cell-laden scaffolds for neural tissue engineering. Loaded neural stem cells in the GelMA/graphene bioink (G-GelMA) had differentiated and showed neurites elongation within the printed scaffold after two weeks of culture [78]. The printed hydrogel showed well-defined architecture, with a homogeneous distribution of the neural cells. Other authors used graphene oxide as an inorganic delivery carrier for nanoscale molecule drugs to develop a 3D scaffold for cartilage tissue engineering. A collagen-chitosan hydrogel was mixed with GO nanoparticles loaded with bone morphogenetic protein 7 (BMP7) and bioprinted into a structure that successfully reproduced the microenvironment of native cartilage [107]. GO, one of the most common derivatives of graphene, has been used in additive manufacturing in solid- or liquid-like formulations. For example, composite filaments with thermoplastic polymers such as ABS and PLA [108] were printed using a fused deposition technique and pastes made with water, and different materials (polyvinyl alcohol, ceramic powders such as SiC and Al\({}_{2}\)O\({}_{3}\) and steel microspheres) were processed using robocasting [109]. The development of GO-based printing inks with high printability and biocompatibility is a major goal for 3D printing methods. Among the printing methods, stereolithography has emerged as a powerful tool to prepare structures with good resolution and high mechanical properties; therefore, the next section presents the graphene-based resin exclusively for SLA.