For each material we report the number of particles counted and the circular equivalent (CE) diameter D[n, 0.1], D[n, 0.5] and D[n, 0.9] percentiles. As shown from Table , preparing the microspheres using an oil-in-water emulsification yields products with a relatively broad size distribution for both the blank microspheres and the exendin-4 loaded microspheres before lyophilisation. Following lyophilisation, the particle size distribution is significantly more narrow than before. This could be due to the removal water and moisture. The Karl Fischer measurements we conducted revealed that the residual moisture for each vial was less than 1%. Notably, upon lyophilisation, as water molecules are removed peptides and copolymers, for example, exendin-4 and PLGA microspheres, can form an extensive hydrogen bonding network leaving few sites for bonding with water molecules.