Three-dimensional substrate for microbial cultures

The present invention relates to a three-dimensional substrate with structural and compositional gradient for microbial cultures and cocultures, and to a method for preparing it, where said three-dimensional substrate comprises: - a diffusion system (1) which comprises a first compartment (2) and a second compartment (3), where said first compartment (2) is placed above said second compartment (3), said first and second compartments (2, 3) being separated by a semipermeable membrane (4); - a base solution which comprises polysaccharides, proteins and salts or a preformed hydrogel which comprises polysaccharides, proteins and salts; - a cross-linking medium which comprises salts, culture media and distilled water.