Methods for seeding live cells onto spatially defined regions of a substrate including multiple features (e.g., microwells or other microenvironments) utilize a stencil embodied in a hole-defining sacrificial film. A sacrificial film devoid of holes may be applied over features of a substrate, and a hole generating mechanism (e.g., hot needle or laser) aligned with features may be used to define holes in the film. Alternatively, holes may be predefined in a sacrificial film to form a stencil, and the stencil may be assembled to the substrate with the holes registered with features thereof. Thereafter, cells are seeded through holes in the film. Seeded cells are subject to incubation, further processing, and/or performance of one or more assays, and the hole-defining sacrificial film (stencil) may be removed.