In the polymer dispersion, exendin-4 can form hydrogen-bonds with PLGA. Intuitively, an increase in exendin-4 loading would correspondingly increase the hydrogen bonding interactions between the polypeptide and PLGA, reduce the molecular mobility of the system, which would raise the value of T g,β . 9,50 Indeed, we observe a significant increase in T g,β for the high polypeptide loaded microspheres, compared to the T g,β value observed for the blank and low polypeptide loaded microspheres. Notably, for the blank and low exendin-4 loaded 50:50 microspheres, the onset for local mobility occurs at approximately the same value of T g,β . This could suggest that the low polypeptide loaded microsphere behave similarly to the blank microspheres, due to the limited interaction between peptide and polymer. For the blank microspheres and low exendin-4 loaded microspheres, the onset for local mobility occurs at approximately the same value of T g,β , (T g,β = 167 K). For the high exendin-4 loaded microspheres, T g,β increases significantly (T g,β = 219 K). As more polypeptide is added to the PLGA matrix it forms an extensive hydrogen bonding network, which in turn reduces the configurational entropy of the system. The resultant interactions between exendin-4