Polyvinyl alcohol particle superficial morphology.

We appreciated the research by Derdeyn et al (1) from the Mallinckrodt Institute of Radiology concerning the size and suspension characteristics of polyvinyl alcohol (PVA) particles. We do agree that both size and suspension characteristics of PVA represent relevant parameters affecting the aggregation of particles during injection. In addition to these two variables, we considered further parameters that could influence particle behavior. Using scanning electron microscopy and differential scanning calorimetry, we observed some differences between dry and suspended particles and between particles produced by different manufacturers. We noticed that particles of Contour Emboli (720 to 1000 mm) (produced in dry form by Interventional Therapeutics Corp, Fremont, Calif) are characterized by a very homogeneous, smooth, regularly punched surface (Fig 1). On the contrary, Ivalon particles of the corresponding size (600 to 1000 mm) (produced in both dry and suspended form by Nycomed Ingenor, Paris, France) demonstrate an irregular, rough surface with folded lamellas (Fig 1B). Such spicules are less pronounced in the dry form of Ivalon, which is less irregular than the suspended one. Moreover, calorimetric analysis showed that both forms of Ivalon particles had a glass transition temperature exceeding that of the Contour Emboli by 10°C. Such significant delta suggests the presence of structural differences between the PVA particles produced by the two manufacturers, which could be related to different production processes. We are carrying on further studies to understand whether these morphological and structural differences affect aggregation characteristics both during injection and after interaction with blood. In fact, although surface irregularities can hamper the injection procedure, the same factor could interfere favorably with thrombogenic processes.