Measurement of membrane elasticity of azithromycin and diltiazem chloride loaded liposomes

Svrha ovog rada bila je provesti fizikalnu karakterizaciju različitih tipova liposoma s uklopljenim lipofilnim ili hidrofilnim lijekom (azitromicin ili diltiazemklorid). Poseban naglasak stavljen je na ispitivanje membranske elastičnosti budući da su formulacije namijenjene primjeni na kožu i sluznicu. Ispitivanjem se željelo utvrditi kako fosfolipidni sastav, prisustvo surfaktanta (natrijev deoksikolat) ili suotapala (propilenglikol) u liposomima utječe na fizikalna svojstva liposoma: veličinu, naboj na površini te elastičnost/rigidnost njihovih dvoslojeva. Liposomi s azitromicinom pripravljeni su film metodom, dok su liposomi s diltiazemkloridom pripremljeni proliposomskom i metodom razrjeđenja poliola. Pokazano je da metoda priprave i fosfolipidni sastav značajno doprinose fizikalnim svojstvima liposoma. Film metodom dobivene su izrazito heterogene disperzije liposoma, a provedena ekstruzija rezultirala je liposomima značajno manjeg srednjeg promjera i niskog indeksa polidisperznosti. Ispitivanja membranske elastičnosti pokazala su najveću elastičnost deformabilnih liposoma s azitromicinom. Elastičnost propilenglikol liposoma s azitromicinom je bila manja od deformabilnih liposoma, ali značajno veća od anionskih, konvencionalnih, te pogotovo kationskih liposoma. Potvrđeno je da fosfolipidni sastav liposoma, prisustvo surfaktanta ili suotapala te lipofilnost uklopljene djelatne tvari značajno utječu na stupanj membranske elastičnosti liposoma.The main objective of this study was physical characterization of the different types of liposomes loaded with either a lipophilic or hydrophilic drug (azithromycin or diltiazem chloride). The focus was placed on determination of membrane (liposome bilayer's) elasticity, because the investigated nanoformulations are destined for skin and mucosal drug delivery. The specific aims were to determine influence of the phospholipid composition, surfactant (sodium deoxycholate) or co-solvent (propylene glycol) on liposomal physical characteristics: size, surface charge and bilayer’s elasticity. Liposomes containing azithromycin were prepared by the film method, while liposomes with diltiazem chloride were prepared by proliposome and polyol dilution method. The results have shown that the phospholipid composition and method used for the preparation of liposomes significantly influence physical characteristics of the liposomes. Liposomes prepared by the film method were significantly more heterogenic than liposomes prepared by proliposome and polyol dilution method, respectively. Extrusion of the originally prepared liposomes resulted in the liposomes of significantly smaller mean diameters and polydispersity indexes. Deformable liposomes with azithromycin were characterized with the most elastic bilayers. Propylene glycol liposomes had less elastic bilayers than deformable liposomes, but significantly more elastic bilayers than anionic, conventional and cationic liposomes encapsulating azithromycin. On the contrary, propylene glycol liposomes with diltiazem chloride were more elastic than propylene glycol liposomes encapsulating azithromycin. This study confirmed that phospholipid composition, presence of surfactant and co-solvent, as well as the lipophilicity of the drug have a significant impact on liposome membrane elasticity