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In this paper, we show that vertical, high-aspect-ratio 1-D photonic crystals (PhCs), consisting of periodic arrays of 3-μm-thick silicon walls separated by 5-μm-wide gaps with depth of 50 μ m (U-grooves), fabricated by electrochemical micromachining, can be combined with mesenchymal cells directly grown into the gaps. Silicon micromachined dice incorporating side-by-side regions with 2- and 3-D structures, namely, flat silicon, shallow (1-2 μm deep) V-grooves, and high-aspect-ratio U-grooves were used as microincubators for culturing SW613-B3, HeLa, SW480, and MRC-5V1 cell lines. Fluorescence microscopy images, obtained after cell fixation, highlight that all the tested cell lines, characterized by different morphologies, are able to grow and proliferate on 2-D microstructures as well as on the “extreme” environment of the PhC structure. More important, SW480 and MRC-5V1 cell lines exhibit the peculiar ability to penetrate into the PhC structure, extending their body deeply in the narrow gaps between adjacent silicon walls, and to grow attached to the vertical surfaces of such 3-D microstructures. This last result represents a first significant step toward the realization of a new class of cell-based biosensors, exploiting cells as bioreceptors and high-aspect-ratio PhCs as transducers, for label-free optical detection of cellular activities involving changes in cell morphology and/or adhesion.