Uniform, functional polymer patches can be attached to a fraction of the surface area of living individual cells. These surface-modified cells remain viable after attachment of the functional patch. The patch does not completely occlude the cellular surface from the surrounding environment. Functional payloads carried by the patch may include, for example, drugs or other small molecules, peptides, proteins, thermally responsive polymers, and nanoparticles, or any other material that can be incorporated in a polymer patch of subcellular dimensions. The patch can include one or more polyelectrolyte multilayers (PEMs).