Furthermore, with the ionised liposomes -as described above -it is likely that teriparatide loading is predominantly achieved by association via electrostatic interactions with oleic acid, thus further explaining the increase in zeta potential from -24.0 ± 2.4 mV to -16.1 ± 2.6 mV . It is uncertain whether a temperature-dependant release of the peptide could be achieved from an adsorbed therapeutic. Therefore, physical entrapment of the peptide within the liposomal bilayer may be preferable, presenting higher chances of demonstrating temperature-dependant release upon gel-sol transition of the phospholipids. The use of hydrophobic ion pairing is a versatile approach, which has been successfully employed to generate hydrophobic complexes of many peptides and proteins . Through the choice of an appropriate counter-ion, the approach is applicable to both positively and negatively charged peptides and proteins and could further be extended to biomolecules (e.g. RNA). Indeed, current mRNA delivery systems employ a similar strategy where ionisable/cationic lipids allow complexation with the negatively charged mRNA and consequently encapsulation within lipid nanoparticles .