The development of advanced techniques of fabrication of three-dimensional (3D) microenvironments for the study of cell growth and proliferation has become one of the major motivations of material scientists and bioengineers in the past decade. Here, we present a novel residueless 3D structuration technique of poly(dimethylsiloxane) (PDMS) by water-in-PDMS emulsion casting and subsequent curing process in temperature-/pressure-controlled environment. Scanning electron microscopy and X-ray microcomputed tomography allowed us to investigate the impact of those parameters on the microarchitecture of the porous structure. We demonstrated that the optimized emulsion casting process gives rise to large-scale and highly interconnected network with pore size ranging from 500 μm to 1.5 mm that turned out to be nicely adapted to 3D cell culture. Experimental cell culture validations were performed using SaOS-2 (osteosarcoma) cell lines. Epifluorescence and deep penetration imaging techniques as two-photon confocal microscopy unveiled information about cell morphology and confirmed a homogeneous cell proliferation and spatial distribution in the 3D porous structure within an available volume larger than 1 cm³. These results open alternative scenarios for the fabrication and integration of porous scaffolds for the development of 3D cell culture platforms.