The teriparatide entrapment efficiency within the different liposomal formulations can be found in Figure . For all formulations entrapment efficiencies between 30-53 % were obtained representing peptide loadings between 25 -100 µg per mg of phospholipid. Compared to previous entrapment achieved by hydrophobic ion pairing (>70%, see section 3.1), the entrapment of teriparatide is significantly lower (p < 0.05, One-way ANOVA). This effect is mainly attributed to the increase in peptide loading (see Figure ). In addition, in the current experiment liposomes were prepared in 100 mM phosphate buffer (pH = 7.4) in order to improve physiological relevance and cellular biocompatibility. The subsequent increase in ionic strength (and pH) may further contribute to the decrease in entrapment efficiency by favouring de-complexation of the ion-pairs during the rehydration process. Indeed, de-complexation is driven by counter-ion competition (e.g. through salts) or through pH-dependant charge negation . Nevertheless, entrapment efficiencies are still comparable to those observed when loading hydrophilic compounds by other methods such as reverse phase evaporation . Overall, peptide loadings (250 -1000 μg/mL corresponding to 12-50 doses / mL) were deemed satisfactory and encapsulation efficiencies comparable to the most successful techniques for passive entrapment of hydrophilic molecules (30-50%) .