# A Systematic Experimental and Computational Analysis of Commercially Available Aliphatic Polyesters
## 3 Results  
The experimental protocol here involves the systematic determination of number and weight, average molecular weights, copolymer composition, glass transition temperature, water uptake, and mass loss as a function of degradation time. Mathematical modeling is subsequently employed in order to provide a more quantitative estimation of degradation kinetics. Degradation experiments were carried out at 37 \({}^{\circ}\)C in a phosphate buffer solution, in order to best reproduce in vivo conditions, as commonly done in scientific literature. The investigated polymers, along with their initial properties (after thermal treatment for sample preparation but before degradation onset) are summarized in Table 1.  
PDLG 5002, 5004, 5010, and RG505 materials belong to the PLGA 50/50 family, since the copolymer contains the same amount of lactic (LA) and glycolide (GA) units. PDLG 7507 belongs to the PLGA 75/25 polymer family and thus exhibits an increased content in lactic units in the backbone. The impact of hydroxyapatite addition (in form of nanoparticles) was investigated for PDLG 5004 and RG505. The use of HA is not uncommon for orthopedic applications because of its two main effects: It enhances polymer mechanical properties and slows down degradation, since HA is basic and counterbalances the acid-based autocatalysis [22]. In this way, it is possible to avoid the use of slow-degrading polymers, which possess adequate mechanical properties but would remain in situ too long before complete adsorption. For this reason, the effect of hydroxyapatite was investigated only with PDLG 5004 and RG505 materials, which emerged as the best candidates for their degradation time and the foreseen improvement of their mechanical properties. In the following sections, data are plotted as an average of three independent measurements with error bars, related to standard deviation. For the sake of completeness, the properties of the raw materials (i.e., before thermal treatment), as well as the entire experimental data sets, are reported in the Supporting Information. It is worth mentioning that not all measurements could be performed at the late degradation stage due to the relevant mass loss. Missing data are highlighted in Supplementary Materials. Number average molecular weight, weight average molecular weight, and polydispersity as a function of degradation time are depicted in Figure 2.  
PDLG 5002 and 5004 are rapidly degraded after about three weeks, by virtue of their low molecular weight. RG505 needs about five weeks to be fully degraded, while PDLG 5010 experiences complete hydrolysis after about 8 weeks. Molecular weight of PDLG 5010 after three weeks is much lower \begin{table}
\begin{tabular}{c c c c c c} \hline
**Polymer** & **LA:GA** & \(MW_{u}\) **(g mol\({}^{-1}\))** & \(MW_{w}\) **(g mol\({}^{-1}\))** & **PD (-)** & \(T_{g}\) **(\({}^{\circ}\)C)** \\ \hline PDLG 5002 & 50:50 & 9000 \(\pm\) 300 & 16,500 \(\pm\) 100 & 1.8 \(\pm\) 0.1 & 36.6 \(\pm\) 0.04 \\ \hline PDLG 5004 & 50:50 & 24,900 \(\pm\) 400 & 40,800 \(\pm\) 800 & 1.6 \(\pm\) 0.02 & 43.7 \(\pm\) 0.5 \\ \hline PDLG 5010 & 50:50 & 69,700 \(\pm\) 5800 & 126,000 \(\pm\) 9600 & 1.8 \(\pm\) 0.01 & 48.5 \(\pm\) 0.4 \\ \hline RG505 & 50:50 & 43,300 \(\pm\) 700 & 75,100 \(\pm\) 900 & 1.7 \(\pm\) 0.01 & 48.7 \(\pm\) 0.1 \\ \hline PDLG 7507 & 75:25 & 51,000 \(\pm\) 1600 & 91,400 \(\pm\) 3300 & 1.8 \(\pm\) 0.02 & 49.7 \(\pm\) 0.4 \\ \hline RG505 + HA & 50:50 & 48,000 \(\pm\) 1100 & 82,700 \(\pm\) 1800 & 1.7 \(\pm\) 0.01 & 48.2 \(\pm\) 0.2 \\ \hline PDLG 5004 + HA & 50:50 & 21,500 \(\pm\) 400 & 40,100 \(\pm\) 1600 & 1.9 \(\pm\) 0.04 & 41.4 \(\pm\) 0.7 \\ \hline \end{tabular}
\end{table} 
Table 1: Investigated polymers and their initial properties. Values are expressed as average \(\pm\) standard deviation. Figure 2: Number (**a**) and weight (**b**) average molecular weights and polydispersity (**c**) as a function of degradation time; values are expressed as arithmetic average of three independent measurements \(\pm\) standard deviation. than expected.