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The use of mechanically robust nanoporous alumina capsules, with highly uniform pores of 25 nm to 55 nm, for controled drug delivery is demonstrated. The nanoporous alumina capsules were fabricated by anodization of an aluminum tube, resulting in a highly uniform, large surface area, relatively inexpensive device suitable for biofiltration applications. Characterization of diffusion from the nanoporous capsules using fluorescein isothiocyanate and dextran conjugates of varying molecular weight, showed that molecular transport could be readily controlled by selection of capsule pore size. A branched membrane structure, with a stepwise change in pore size from large to small, is used to provide small pore-sized membranes with sufficient mechanical strength for handling.