title: Size Determination of a Liposomal Drug by Small-Angle X-ray Scattering Using Continuous Contrast Variation.
abstract: The continuously growing complexity of nanodrugs urges for complementary characterization techniques which can elude the current limitations. In this paper, the applicability of continuous contrast variation in small-angle X-ray scattering (SAXS) for the accurate size determination of a complex nanocarrier is demonstrated on the example of PEGylated liposomal doxorubicin (Caelyx). The mean size and average electron density of Caelyx was determined by SAXS using a gradient of aqueous iodixanol (Optiprep), an iso-osmolar suspending medium. The study is focused on the isoscattering point position and the analysis of the Guinier region of the scattering curves recorded at different solvent densities. An average diameter of (69 ± 5) nm and electron density of (346.2 ± 1.2) nm(-3) were determined for the liposomal formulation of doxorubicin. The response of the liposomal nanocarrier to increasing solvent osmolality and the structure of the liposome-encapsulated doxorubicin after the osmotic shrinkage of the liposome are evaluated with sucrose contrast variation in SAXS and wide-angle X-ray scattering (WAXS). In the case of using sucrose as contrast agent, a clear osmolality threshold at 670 mOsm kg(-1) was observed, above which the liposomal drug carriers start to shrink, though preserving the intraliposomal doxorubicin structure. The average size obtained by this technique is smaller than the value measured by dynamic light scattering (DLS), though this difference is expected due to the hydrodynamic size of the PEG moieties attached to the liposomal surface, which are not probed with solvent contrast variation in SAXS. The advantages and drawbacks of the proposed technique are discussed in comparison to DLS, the most frequently used sizing method in nanomedicine.
authors.affiliation: Physikalisch-Technische Bundesanstalt (PTB) , 10587 Berlin, Germany.
authors.forename: Raul
authors.initials: R
authors.lastname: Garcia-Diez
authors.affiliation: Physikalisch-Technische Bundesanstalt (PTB) , 10587 Berlin, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Gollwitzer
authors.affiliation: Physikalisch-Technische Bundesanstalt (PTB) , 10587 Berlin, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Krumrey
authors.affiliation: Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences , H-1117 Budapest, Hungary.
authors.forename: Zoltan
authors.initials: Z
authors.lastname: Varga
mesh_terms: D004317:Doxorubicin / Q000031:analogs & derivatives* / Q000737:chemistry; D004337:Drug Carriers / Q000737:chemistry*; D008081:Liposomes / Q000737:chemistry*; D050997:Nanomedicine / Q000379:methods*; D009994:Osmolar Concentration; D010316:Particle Size; D011092:Polyethylene Glycols / Q000737:chemistry; D053838:Scattering, Small Angle; D014283:Triiodobenzoic Acids / Q000737:chemistry; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D004337:Drug Carriers; D008081:Liposomes; D014283:Triiodobenzoic Acids; C506643:liposomal doxorubicin; D014867:Water; D011092:Polyethylene Glycols; D004317:Doxorubicin; C044834:iodixanol