Finally, we observe that for both PLGA 50:50 and PLGA 75:25 the value of T g,α increases in the order of blank < low polypeptide loaded < high polypeptide loaded microspheres (Figure ). This suggests that at high temperature, sufficient activation energy and free volume must be available to facilitate mobility of the polymer and polypeptide. Thus, with increase in exendin-4 loading, due to steric hinderance the threshold for mobility increases, as reflected in the raised value of T g,α . Ideally if it were possible to produce a stable freezedried exendin-4 product, it may be feasible to determine whether the exendin alone could aggregate and lead to the changes observed.