The pycnometry data shows that increasing exendin-4 loading increases the density of the material (Table ). Our helium pycnometry measurements are in agreement with values reported in the literature. 4 FTIR was performed for the PLGA 75:25 microsphere samples (Figure ). The absorbance of the peaks at around 3300 cm -1 and 2950 cm -1 increased in intensity with an increase in polypeptide loading. The peak at 3300 cm -1 originates from the -OH stretch in exendin-4, and the peak at 2950 cm -1 is assigned to the C-H stretching modes in exendin-4. The amide I band at 1600 -1700 cm -1 can be attributed to the -C=O stretch, with contributions from the out-of-phase -CN stretch, -CCN deformation, and -NH in-plane bend and is sensitive to the structure of the protein backbone. Additionally, there is an increase in absorption in the amide I region around 1600-1700 cm -1 , and a shift in the frequency of the mode for the sample with a high polypeptide loading, which is indicative of changes in the hydrogen bonding network. Thus, the FTIR spectra confirm the increase in exendin-4 loading between the blank, low and high polypeptide formulations, and, with this, a change in the hydrogen bonding network. Notably, it was not possible to investigate an only exendin-4 control, as a stable product could not be freeze-dried.