## 3 Results and Discussion
### Release Kinetics of BSA in MPs  
In vitro release profiles of BSA from MPs in SVB, along with the results of numerical simulations, are shown in Figures 2 and 3. When polymer concentration in the organic phase of the emulsion was 20% \(w/v\), the presence of POLOX influenced the protein release kinetics. Indeed, the 20-100 formulation showed considerable initial release, which can be attributed to the porous surface of the MPs. The residual protein discharge was sustained for 4 weeks. In the case of 20-90 MPs, BSA was released in a similar time, but with a very attenuated initial release. Protein release from the 20-70 MPs was found to be unsatisfactorily reproducible, as indicated by the high standard deviations. Likewise, the BSA release profiles from the 24-90 and 24-100 formulations were essentially similar, with complete delivery within 4 weeks, while, in the case of the 24-70 formulation, protein discharge was slightly quicker. Interestingly, no substantial initial was detected for the 24-70, 24-90 and 24-100 formulations, while a moderate acceleration of protein release was seen between 7 and 14 days, which implies that considerable fractions of bulk BSA were present for these formulations in the specified timeframe. \begin{table}
\begin{tabular}{c c c c} \hline
**Formulation** & **Mean Diameter (\(\upmu\)m) (\(\pm\)SD)** & **E.E. (\%) (\(\pm\)SD)** & **Yield (\(\pm\)SD)** \\ \hline
20–100 & 30 \(\pm\) 8.4 & 49 \(\pm\) 4 & 27 \(\pm\)12 \\
20–90 & 14 \(\pm\) 6.0 & 63 \(\pm\) 13 & 38 \(\pm\)10 \\
20–70 & 14 \(\pm\) 6.0 & 43 \(\pm\) 1.0 & 43 \(\pm\)24 \\
24–100 & 31 \(\pm\) 5.0 & 61 \(\pm\) 10 & 30 \(\pm\)15 \\
24–90 & 15 \(\pm\) 7.0 & 68 \(\pm\) 19 & 35 \(\pm\)21 \\
24–70 & 15 \(\pm\) 6.2 & 81 \(\pm\) 18 & 27 \(\pm\)15 \\ \hline \end{tabular}
\end{table} 
Table 2: Overall technological features of the produced MPs. Figure 1: SEM images of (**A**) 20–70 (**B**) 20–90 and (**C**) 20–100 (**D**) 24–70 (**E**) 24–90 and (**F**) 24–100 MPs. The bar is 2 \(\upmu\)m in (**A**,**B**,**D**,**E**) and 10 \(\upmu\)m in (**C**,**F**). The released fraction was modeled as described in Section 2.5 and the best fit parameters are summarized in Table 3. The values of the solubilization rate constant \(k_{S}\) were relatively close for all formulations, which indicates that superficial phenomena within MPs during release are comparable irrespective of the polymer concentration and POLOX presence. When the polymer concentration was 20% \(w/v\) in the organic phase of the emulsion, \(\varphi_{S,\infty}\) increased with increasing PLGA:POLOX ratio. This is related to the extent of the initial BSA release and consistent with the strong initial release observed in the 20-100 formulation. As for MPs produced with a 24% \(w/v\) polymer concentration in the organic phase of the emulsion, no clear trend of \(\varphi_{S,\infty}\) with POLOX percentage was seen, indicating that the  
Figure 3: Representative DSC thermograms of PLGA powder (**A**); F68 powder (**B**); F127 powder (**C**); 20–100 (**D**), 20–90 (**E**), 20–70 (**F**) microparticles. Exotherm is directed upward. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **20–70** & **20–90** & **20–100** & **24–70** & **24–90** & **24–100** \\ \hline \(k_{S}\) [day\({}^{-1}\)] & 4.60 & 4.41 & 4.86 & 4.40 & 4.33 & 4.33 \\ \(\varphi_{S,\infty}\) & 0.031 & 0.089 & 0.429 & 0.204 & 0.080 & 0.146 \\ \(k_{E}\) [day\({}^{-1}\)] & 0.234 & 0.241 & 0.202 & 0.391 & 0.262 & 0.229 \\ \(t_{MAX}\) [day] & 9.78 & 11.7 & 9.89 & 14.0 & 11.0 & 11.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Best fit results of BSA release kinetics modelling for the six MP formulations. Figure 2: In vitro protein release kinetics from PLGA—based microparticles at 20% (**left**) and 24% (**right**) \(w/v\) overall polymer content in the organic phase of the emulsion. Solid lines represent numerical simulations. dense MP matrix associated with a high polymer concentration effectively hampers BSA diffusion and subsequent release.