Critical aspects related to the use of FlFFF and SdFFF techniques for size characterizing biodegradable PLA nanospheres

Biodegradable polymer micro and nano sized particles have become an important area of research in the field of the drug delivery because of their ability to deliver a wide range of drugs to varying areas of the body, for sustained period of time1. Poly(lactic acid) (PLA) is traditionally one of the most studied polymer because its biodegradation leads to pharmacologically inactive substances, which are adsorbable by the body or removable by the metabolism2. The size of colloidal drug carrier spheres is a crucial task since depending on it different organs are target2; the size greatly influences also the drug efficacy and its release. Several are the experimental parameters during the whole formulation process which should be taken into account to control the size of the nanospheres. Usually the size characterization of pharmaceutical nanospheres is carried out by electron microscopy, even if also light scattering techniques are frequently used. These techniques tend to be rapid but of low resolution since they are non-fractionation methods3 and measurements are made of the entire particle mixture. More useful are instead the separation methods, which recently include Field-Flow Fractionation, for which an higher resolution is achieved since the different particle populations are first separated and then sized. Field Flow Fractionation (FFF) is a well known and established family of elution techniques, which differ by the type of used external physical field force4. FFF techniques are useful for the separation and the characterization of a broad range of colloidal particles, polymers and biological macromolecules and have been successfully applied for the size characterization of particle of pharmaceutical interest5-12. The aim of this study was to use the Flow and the Sedimentation FFF (FlFFF and SdFFF) techniques in order check variations in the particle size distribution (PSD) of nano-sized PLA samples, made encapsulating 5’-esters of N6-cyclopentyladenosine (CPA), a prodrug which has a neuroprotective role13-14. The considered PLA samples differ for the surfactant used during their formulation and for the recovery-purification methods. These parameters affect the PDS of the nanoparticles, the prodrug loading, its release modalities and the related stabilisation in whole blood. The morphology of the nanoparticles was also controlled by using a scanning electron microscope (SEM)