A structure for and method of manufacture of structures for implantation within the tissue of a mammalian subject are disclosed. These structures can be utilized in applications such as the delivery of therapeutic drugs to the tissue of the subject or the sampling of biofluids for the purposes of diagnosis. In one embodiment of the invention, a rigid structure has defined ingrowth features on a surface intended to contact tissue of the subject and defined passage features which provide a fluid path from the surface intended to contact tissue to another surface. The dimensions of these defined features vary based on the particular application, as the ingrowth features are of a dimension and spacing to promote ingrowth of the surrounding tissue, and the passage features are of a dimension to inhibit the passage through the structure of cells from the surrounding tissue.