Cryo-TEM images (Figure ) were obtained for empty liposomal formulations as well as HIP loaded liposomes. Loaded liposomes were prepared at three different levels of HIP loading ranging from 8 -60 µg teriparatide per mg of liposomes (80 µg/mL -600 µg/mL teriparatide), corresponding to entrapment efficiencies between 18 -40%. From Figure it may be observed that with increasing teriparatide content, the formulation increases in heterogeneity. The empty formulations (Figure ) show the typical ring-shaped structure where high contrast regions represent the lipid bilayer . These formulations do not present a round but rather an angular shape, which is due to the phase transition temperature of the liposomes being above room temperature. Additionally, disk-like shapes are observed, which have previously been described to originate from the incorporation of PEGylated phospholipids forming additional colloidal structures (e.g. mixed micelles) .