# How Does the Biocompatibility of Molybdenum Compare to the Gold Standard Titanium?--An In Vivo Rat
## 3 Results
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**Score** & \multicolumn{2}{c}{**Total (\(n=30\))**} & \multicolumn{2}{c}{**Ti (\(n=17\))**} & \multicolumn{2}{c}{**Mo (\(n=13\))**} \\ \hline \hline \multicolumn{2}{c}{S synovial covering of the cell layer} & \(n\) & \% & \(n\) & \% & \(n\) & \% \\ \hline \multirow{5}{*}{Cll density of the synovial stroma} & 0 & 2 & 6.57 & 0 & 0.0 & 2 & 15.4 \\  & 1 & 13 & 43.3 & 7 & 41.2 & 6 & 46.2 \\  & 2 & 9 & 30.0 & 7 & 41.2 & 2 & 15.4 \\  & 3 & 6 & 20.0 & 3 & 17.6 & 3 & 23.1 \\  & & \(n\) & \% & \(n\) & \% & \(n\) & \% \\ \hline \multirow{5}{*}{Leukocytic infiltrate} & 0 & 8 & 26.7 & 4 & 23.5 & 4 & 30.8 \\  & 1 & 17 & 56.7 & 11 & 64.7 & 6 & 46.2 \\  & 2 & 4 & 13.3 & 1 & 5.9 & 3 & 23.1 \\  & 3 & 1 & 3.3 & 1 & 5.9 & 0 & 0.0 \\  & & \(n\) & \% & \(n\) & \% & \(n\) & \% \\ \hline \multirow{5}{*}{[PERSON] score} & 0 & 3 & 10.0 & 1 & 5.9 & 2 & 15.4 \\  & 1 & 20 & 66.7 & 13 & 76.5 & 7 & 53.8 \\ \cline{1-1}  & 2 & 7 & 23.3 & 3 & 17.6 & 4 & 30.8 \\ \hline \end{tabular}
\end{table} 
Table 1: Overview of the evaluation of the capsules according to [PERSON] et al. (synovial covering of the cell layer and the cell density of the synovial stroma and the leucocytic infiltrates). Figure 9: Synovitis assessment according to [PERSON] at the time points of T2, T3, and T4. We examined the spleens, kidneys, and livers of all 84 animals. Two of the eighty-four kidneys showed slight abnormalities in the form of infarcted areas. One animal was from the titanium cohort and the other from the cohort with molybdenum, and both were euthanized after 52 weeks. Otherwise, the kidneys were inconspicuous, and no deposits of molybdenum or titanium were found. Neither the spleen nor the liver showed any organic changes, but 7 of 84 organs showed capsular necrosis, which, according to an investigation at the Institute of Pathology of the University clinic Dusseldorf, Germany, occurred post mort mortem due to cardiac arrest. For all explanted molybdenum samples, surface colorations varying from yellow/golden to blue/violet were observed (Figure 10). Various colors were observed among the samples from each cohort, with no clear tendency towards a specific coloration within any of the cohorts. For molybdenum, the surface coloration was a first indication of the thickness of the degradation product layer on the surface. Yellow/golden coloration roughly corresponded to a thickness of around 50 nm, while blue/violet colorations corresponded to a thickness above 50 nm and below 100 nm. For a thickness higher than 0.8-1.0 um, the degraded surface appeared black. The colorations of the explanted samples thus indicate that only a very thin layer of degradation products formed over 3-12 months. Correspondingly, only a very small amount of molybdenum would have dissolved, since the soluble product of the oxidation cascade of molybdenum, MoO\({}_{3}\), was formed within the degradation layer and then was transferred into a solution in the form of MoO\({}_{4}\)\({}^{2-}\) (molybate ion). The analysis of the metallographic cross-sections (Figure 11) of the explanted molybdenum samples confirmed that there were only miniscule degradation product layers, irrespective of the total duration of implantation. Due to the thickness of the degradation layers, far below 1 um and likely in the range of 50-100 nm, it was not possible to distinguish the implanted samples from the samples in the as-manufactured state. The thin dark \"layer\" at the interface of Mo and the embedding resin was not the degradation product layer, but a small fissure that formed during embedding. This is supported by the fact that this fissure also appeared in the as-manufactured state. Five samples from each cohort were analyzed, with no marked differences either within a cohort or between cohorts. The cross-sections of all the as-manufactured samples and the samples explanted after 3 or 6 months showed internal cracks and pores.