Background: This work aimed to provide useful information on the incidence of the choice of formulation in semisolid\npreparations of iron-oxide nanoparticles (IONs). The appropriate analytical methods to assess the IONs physical\nstability and the effect of the semi-solid preparations on IONs human skin penetration were discussed. The physical\nstability of IONs (Dh = 31 Ã?± 4 nm; Ã?¶ = âË?â??65 Ã?± 5 mV) loaded in five semi-solid preparations (0.3% w/v), namely\nCarbopol gel (CP), hydroxyethyl cellulose gel (HEC), carboxymethylcellulose gel (CMC), cetomacrogol cream (Cet)\nand cold cream was assessed by combining DLS and low-field pulsed NMR data. The in vitro penetration of IONs was\nstudied using human epidermis or isolated stratum corneum (SC).\nResults: Reversible and irreversible IONs aggregates were evidenced only in HEC and CMC, respectively. IONs diffused\nmassively through SC preferentially by an intercellular pathway, as assessed by transmission electron microscopy.\nThe semi-solid preparations differently influenced the IONs penetration as compared to the aqueous suspension.\nCet cream allowed the highest permeation and the lowest retained amount, while cold cream and CP favored\nthe accumulation into the skin membrane.\nConclusion: Basic cutaneous semi-solid preparations could be used to administer IONs without affecting their permeation\nprofile if they maintained their physical stability over time. This property is better discriminated by low-field\npulsed NMR measurements than the commonly used DLS measurements.
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