## 3 Results
### Acrylic Cement Debris and Synovial Fluid  
The Raman spectra acquired from the surface of acrylic cement detached from the metallic stem is presented in Figure 7A,B in the low and high wavenumber region. The fingerprints of acrylic cement are the strongest band at 2953 cm\({}^{-1}\), which is the stretching mode attributable to \(\upsilon\) (C-H, CH\({}_{2}\), CH\({}_{3}\)) in PMMA, 1726 cm\({}^{-1}\), assigned to \(\upsilon\)(C=O) groups stretching mode, 1450 cm\({}^{-1}\) (strong intensity) due to CH\({}_{3}\) and CH\({}_{2}\) groups deformation and 812 cm\({}^{-1}\) (strong and sharp) due to the deformation of C-O-C group. Ten-year-old acrylic cement exhibited several bands that are slightly different from those of pristine PMMA, as shown in Table 2, in comparison with the previous Raman data reported on PMMA [29; 30; 31]. The intense band at 986 cm\({}^{-1}\), which is absent in pristine-PMMA, represent the signature of gentamicin (C-C stretching vibration) [32], while the characteristic band at 1648 cm\({}^{-1}\) reported by several authors [29; 31] was not observed here. However, this latter band was not reported in the first comprehensive vibrational IR and Raman characterization of PMMA available from [PERSON] et al. [30]. The slight changes in main band positions and occurrence of new band such as that observed at 1602 cm\({}^{-1}\) which is not observed in synovial fluid either, correlated with the yellow color of the retrieved acrylic cement, may suggest alteration in polymer composition and structural properties. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **New** & **Retrieved** \\ \hline C\% & \(46.22\pm 0.2\) & \(50.71\pm 0.2\) \\ A\% & \(53.52\pm 0.5\) & \(48.91\pm 0.3\) \\ OI & \(0.00\pm 0.1\) & \(0.37\pm 0.1\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Values of crystallinity, amorphous and oxidation index calculated according to the Equations (1)–(3) for unused and retrieved polymeric components (main value \(\pm\) standard deviation). \begin{table}
\begin{tabular}{c c c c c} \hline
**PMMA** & **PMMA** & **PMMA** & **Acrlic Cement Debris** & **Vibrational Assignment** \\
**Ref. [29]** & **Ref. [30]** & **Ref. [31]** & **(This Work) cm\({}^{-1}\)** & **[29–31]** \\
**cm\({}^{-1}\)** & **cm\({}^{-1}\)** & **cm\({}^{-1}\)** & **(This Work) cm\({}^{-1}\)** & **[29–31]** \\ \hline
833 & 818, & 853 & 812 & \(v_{\rm M}\)(C–O-C) \\  & 833 & & & \(\delta\) (CH\({}_{2}\)) \\ \hline  & & & 966 & Not assigned \\ \hline  & 991 & 925 & 1002 & \(v\) (C–O) \\
995 & 1161 & 999 & 1117 & \(\rho\) (O–CH\({}_{3}\)) \\  & 1188 & 1081 & 1180 & \(v_{\rm M}\)(C–O–C) \\  & 1234 & & 1234 & \\ \hline
1264 & 1276 & 1264 & & \(v\) (C–O) \\ \hline
1470 & 1456 & & 1450 & \(v\) C–H) \\  & 1490 & & 1602 & Not assigned \\ \hline
1645 & Not reported & 1648 & Not observed & \(v\)(C–C) and \(v\)(C-CO) \\ \hline
1739 & 1736 & 1736 & 1726 & \(v\) (C=O) of C-OO \\ \hline  & 2849 & 2848 & 2844 & \(v\)(CH\({}_{2}\)), combination band involving–O–CH\({}_{3}\) \\  & 2920 & 2848 & 2933 & \(v\) (C–H), CH\({}_{2}\) CH\({}_{3}\) \\ \hline
2952 & 2957 & 2957 & 2953 & \(v\) (C–H) of O-CH\({}_{3}\) \\ \hline
3001 & 2995 & 3001 & 3001 & \(v\) (C–H) of \(\rm{CH}_{3}\) \\ \hline \end{tabular} Abbreviations: \(v\)-stretching, \(\delta\)-deformation, \(\rho\)-rocking.  
\end{table} 
Table 2: Observed Raman bands/cm\({}^{-1}\) in aged acrylic cement from prosthetic retrieval compared to literature data of pristine polymethyl methacrylate (PMMA) and their assignment. Figure 7: Micro-Raman spectra collected in the low (**A**) and high wavenumber range (**B**) from the surface of acrylic cement debris detached from the metallic stem, characteristic for acrylic-bone interface; and (**C**,**D**) synovial fluid spectra from light (a) and dark (b) spotted points, accumulated in the stem of the tibial component. Averaged spectra of 10 distinct points acquisitions are given; spectra were background subtracted and normalized to unit; Excitation: 785 nm, 30 mW.