# Optimization of Mechanical and Setting Properties in Acrylic Bone Cements Added with Graphene Oxide
## 3 Results and Discussion
### Mechanical Properties
#### 3.2.2 Bending Properties  
* Bending strength  
The increase in sonication time and GO content increases ABCs' bending strength, as shown in Figure 8. In contrast, the rise in BPO content decreases this property. ISO  
5833-02 [51] establishes a minimum bending strength of 50 MPa, so formulations without GO and the highest GO content studied do not achieve this requirement. As mentioned earlier, for the compressive strength, a higher BPO content has an essential influence on the molecular weight and polymerization degree of PMMA [12] and, therefore, lower cement's mechanical performance. The size reduction generated by the longer sonication time generated a higher mechanical reinforcement [49] and a GO content of 0.3 wt. % produced the highest bending strengths, which coincides with the one reported by [PERSON] et al. [3] and by our group in other investigations [37; 38]. [PERSON]'s post-ANOVA test for the variable bending strength shown in Table 6 indicates that the formulations that maximize bending strength are those with GO contents between 0.1 and 0.3 wt.%. There are no significant differences in the bending strength value of the formulations to which the same letter is assigned so that all formulations grouped as A generate the highest possible values in this property and are above the minimum requirement in ISO 5833-02 [51]. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multicolumn{1}{c}{**Sonication Time \({}^{*}\)**} & \multicolumn{3}{c}{**Mean**} & \multicolumn{3}{c}{**Grouping \({}^{*}\)**} & \multicolumn{3}{c}{**BPO/Solid Ratio**} & \multicolumn{3}{c}{**Mean**} & \multicolumn{3}{c}{**Grouping \({}^{*}\)**} \\
**GO/Liquid Ratio** & & & & & \({}^{*}\) **GO/Liquid Ratio** & & & & \\ \hline
5-0.3 & 57.74 & A & & & 2.0-0.3 & 58.58 & A & & \\
1-0.3 & 57.01 & A & B & & 2.5-0.1 & 56.75 & A & & \\
1-0.1 & 55.10 & A & B & C & 2.5-0.3 & 56.17 & A & & \\
5-0.2 & 54.54 & A & B & C & 2.0-0.2 & 55.11 & A & B & \\
5-0.1 & 53.38 & A & B & C & 2.5-0.2 & 51.84 & B & C & \\
5-0.5 & 53.06 & & B & C & 2.0-0.1 & 51.72 & B & C & \\
1-0.2 & 52.41 & & C & 2.0-0.5 & 48.67 & & C & D \\
1-0.0 & 45.14 & & & D & 2.5-0.5 & 48.56 & & C & D \\
5-0.0 & 45.14 & & & D & 2.0-0.0 & 45.91 & & D \\
1-0.5 & 44.17 & & & D & 2.5-0.0 & 44.37 & & D \\ \hline \hline \end{tabular}  
* Means that do not share a letter are significantly different.  
\end{table} 
Table 6: Grouping information for bending strength using [PERSON]’s test and 95% confidence. Figure 8: Interaction plot between the effect sonication time vs. GO/liquid ratio and BPO/solid ratio vs. GO/liquid ratio for the variable bending strength. On the other hand, the addition of 0.5 wt.% of GO does not benefit the ABC from the bending strength perspective. The results of [PERSON]'s test show that the addition of the maximum GO content statistically has the same effect on this property as the basic formulation without the addition of GO (Group D in both interactions) and that both GO contents are below the minimum strength required in the standard (50 MPa). * Bending modulus According to Figures 7 and 9, the bending modulus and the compression modulus increase with higher BPO content, shorter sonication time, and higher GO content up to 0.3 wt.%. The higher the polymer chains during polymerization, the larger particle size, and GO nanoparticles' presence increases the ABCs' stiffness [66]. Other researchers found a similar modulus behavior concerning the BPO content in ABCs formulations [1; 57]. In addition, it has been reported the increase in the mechanical properties of ABCs [3; 35; 67] and other types of polymeric materials with the addition of GO thanks to the presence of hydroxyl, carboxylic, and epoxy groups on their surface and is consequently more accessible to disperse [47; 68; 69]. Concerning the sonication time, [PERSON] et al. [70] reported an improvement in the cement mechanical properties by mixing multilayer carbon nanotubes in the liquid phase with ultrasound due to the homogenization and dispersion of the nanotubes in the liquid phase.