Abstract: Described herein are fluid treatment devices for use in tangential flow filtration, comprising a housing unit and a composite material, wherein the composite material comprises: a support member comprising a plurality of pores extending through the support member; and a non-self-supporting macroporous cross-linked gel comprising macropores having an average size of 10 nm to 3000 nm, said macroporous gel being located in the pores of the support member. The invention also relates to a method of separating a substance from a fluid, comprising the step of placing the fluid in contact with an inventive device, thereby adsorbing or absorbing the substance to the composite material contained therein.