Abstract: The present invention relates to 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 &mgr;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 density of at least 3.0 g/ml, said polymeric base matrix including pendant groups which are positively charged at pH 4.0 or which are affinity ligands for a bio-molecule. Possible pendant groups include polyethyleneimine (PEI), diethylaminoethyl (DEAE) and quaternary aminoethyl (QAE). The materials are useful in expanded bed or fluidized bed chromatography processes, in particular for purification of bio-macromolecules such as plasmid DNA, chromosomal DNA, RNA, viral DNA, bacteria and viruses.