Described are composite materials and methods of using them for mixed-mode chromatography. In certain embodiments, the composite material comprises a support member, comprising a plurality of pores extending through the support member; and a multi-functional cross-linked gel. The multi-functional cross-linked gel possesses at least two of the following functions or characteristics: cationic, anionic, hydrophobic, hydrophilic, thiophilic, hydrogen bond donating, hydrogen bond accepting, pi-pi bond donating, pi-pi bond accepting, or metal chelating. The composite materials may be used in the separation or purification of a biological molecule or biological ion.