The present invention generally relates to modified substrates such as membranes for use in bioartificial organs, such as bioartificial kidneys, and other applications. Certain aspects are generally directed to a membrane or other substrate modified to facilitate the attachment of cells. In one set of embodiments, the substrate or membrane may be at least partially coated with an adhesive such as 3,4-dihydroxy-L-phenylalanine (DOPA), poly(dopamine), or other adhesive comprising a molecule having a catechol moiety, for example on one side of the membrane or substrate. On at least a portion of the adhesive coated portion of the substrate, a protein may be coated, such as an extracellular matrix protein (for example, a collagen), to which cells such as primary human renal proximal tubule cells may be adhered. Surprisingly, such a dual coating may be used to promote the attachment of such cells to a membrane or other substrate that otherwise may not promote cell adhesion. In certain embodiments, the coating may also facilitate or promote not only cell adhesion, but also cell proliferation and/or differentiation. Such membranes or other substrates may be useful, for example, in bioartificial organs such as bioartificial kidneys, hemodialysis cartridges, bioimplants, biosensors, bioreactors, etc. In certain embodiments, cells may be attached to a membrane or other substrate on only one side, while the other side may be kept free of attached cells.