Radiopaque hydrogel microspheres

Spherical, hydrophilic microspheres prepared from crosslinked poly(methyl methacrylate) (PMMA) by alkaline hydrolysis have been made radiopaque by impregnating with barium sulphate by the precipitation technique. Microspheres having carboxyl functions as their alkali metal salt were swollen in sodium sulphate solution and barium sulphate entrapment was effected by treating with barium chloride solution. The swelling characteristics of the microspheres could be controlled by acidification and further by anhydride formation thereby trapping the barium sulphate firmly inside the microspheres. Barium sulphate loading of up to 70 wt-per cent could be achieved by this technique. These microspheres have been found to possess excellent X-ray contrast properties and may find application as particulate emboli in endovascular embolization.