The entrapment efficiency of teriparatide ion pairs within the DPPC:DSPC liposomes appears to be higher with lower DSPC content, however this observation was not significant (p>0.05, One-way ANOVA). Incorporation of hydrophobic molecules within the lipid bilayer generally depends on physicochemical properties of the cargo molecule as well as bilayer composition and volume . The average size of the individual formulations ranged between 100 -200 nm, with the exception of DSPC-2, which presented a size of 85 ± 12 nm (see Figure ). The difference is likely to be related to the extrusion process. Initially, formulations (DSPC-2) were extruded through 100 nm membranes. It was observed that increasing Tc led to more resistance during the extrusion process, thus more manual strain. As extrusion through 100 nm membranes was not required to achieve small (<200 nm) liposomes, the final extrusion of all other formulation was achieved with 200 nm membranes.