Tantalum loaded silicone microspheres as particulate emboli.

Chloroform solutions of medical grade silicone resin were cured in an aqueous dispersion medium containing poly(vinyl alcohol) (PVA) as the drop stabilizer at 40-60 degrees C to generate smooth, spherical, elastic microspheres. The microspheres were encapsulated with tantalum powder to render them radiopaque. Tantalum loaded microspheres having diameter more than 1.00 mm could be prepared by this technique. Incorporation of radiopaques such as barium sulphate and methyl iothalamate resulted in the instability of the suspension giving rise to an agglomerated product. Microspheres were grafted with hydrophilic monomers such as 2-hydroxyethyl methacrylate (HEMA) and N-vinyl pyrrolidone (NVP) using ionizing radiation from a 60Co source in an effort to make their surfaces hydrophilic. While the graft yield was very little when HEMA alone was used for grafting, a combination of HEMA/NVP in a 1:1 ratio produced better graft yields resulting in improved surface hydrophilicity. The tantalum loaded microspheres were found to be very resistant to surface modification. Microspheres could be dispersed in water with the aid of small quantities of surfactants such as Tween 20. These microspheres may find use in particulate embolization.