WO 00/57982 discloses a particulate material having a density of at least 2.5 g/mL, where the particles of the particulate material have an average diameter of 5-75 ??m, and the particles of the particulate material are essentially constructed of a polymeric base matrix, e.g. a polysaccharide such as agarose, and a non-porous core material, e.g. steel and titanium, said core material having a dens