## 3 Graphene Oxide
### Biomedical Properties  
A study by [PERSON] et al. [21] showed that the activation of inflammosomes does not depend on the lateral dimensions of GO sheets. Inflammosomes, are receptors/sensors of the innate immune system that regulate the activation of caspase-1 and are responsible for the activation of inflammatory responses, such as IL-1B [1]. [PERSON] et al. [21] also show that when GO sheets (small and large) are exposed to primary human macrophages, they are not cytotoxic for primary human macrophages and do not trigger a typical Th1 cytokine (i.e., TNF-\(\alpha\), IL-6, or IL-1B) or Th2 cytokine (i.e., IL-4, IL-5, and IL-13) response in macrophages. From these observations, it was concluded that endotoxin-free GO is biocompatible and proinflammatory. GO can be gradually degraded through enzyme-induced oxidization by, for example, horseradish peroxidase (HRP). Due to the remote possibility of toxicity to macrophages,  
Figure 4: Quantification of MC3T3-E1 preosteoblast metabolic activity in contact with chitosan and chitosan/GO films. Statistical significance: # \(p<0.05\) (CHT/GO 0.5 wt% 7 days vs. CHT 7 days); ### \(p\) < 0.001 [(CHT/GO 0.5 wt% 2 days vs. CHT 2 days); (CHT/GO 3 wt% 2 days vs. CHT 2 days); (CHT/GO 3 wt% 7 days vs. CHT 7 days)]; \"\"\" \(p\) < 0.001 (CHT/GO 3 wt% 7 days vs. CHT/GO 0.5 wt% 7 days) [20]. Figure 3: Cell viability of modified GO-loaded films with different concentrations [3]. coating GO with biocompatible macromolecules can be a method to reduce its level of cytotoxicity. However, at the same time, coating can limit the degradability of GO due to steric hindrance. Therefore, more recent studies have attempted to design a surface-modified GO carrier that will degrade and provide drug delivery functionality while maintaining an acceptable level of toxicity [22; 23]. In one study conducted by [PERSON] et al. [24], chitosan film completely degraded in 3 days, while chitosan/GO films degraded after 28 days. By adding a small amount of GO, and through an interaction of the COOH functional groups of GO with chitosan, crystallinity of the composite film increases, leading to reduction in the degradation rate, which make it a good candidate for bone replacement in orthopedic applications. In another study, enzymatic hydrolysis in the presence of lysozyme was performed for evaluation of biodegradability of chitosan/GO films. It was observed that the degradability of the chitosan decreased by increasing the amount of GO, which is probably because GO sheets postpone the penetration of the enzyme inside a polymer matrix [25]. [PERSON] et al. [26] investigated the antibacterial activity of GO and reduced graphene oxide (rGO) against _P. aeruginosa_. rGO sample was synthesized from GO using btemercapto-ethanol (BME) as a novel reducing agent, which is known to be less cytotoxic than hydrazine. The results showed that both GO and rGO had significant antibacterial activity in a concentration- and time-dependent manner. They also realized that oxidative stress is a key mechanism for antibacterial activity of GO and rGO. In another study by [PERSON] et al. [27], the antibacterial activity of GO sheets with different sizes and shapes was evaluated against _Escherichia coli_. The results indicated that the antibacterial activity of GO depended on the specimen's lateral size. Larger-sized GO sheets had more antibacterial activity compared to smaller-sized ones. They also had different time- and concentration-dependent antibacterial activities. The antibacterial activity of different graphene-based materials, including graphite (Gt), graphite oxide (GtO), graphene oxide (GO), and reduced graphene oxide (rGO), were investigated against _Escherichia coli_, and the results showed that GO had the highest antibacterial activity, followed by rGO, Gt, and GtO [28]. Angiogenesis is another key property to accelerate the wound healing process. [PERSON] et al. demonstrated that GO and rGO have promising angiogenesis properties [29].