The present invention relates to a method of evaluating fluid shear stress acting on cells in real-time in a bioprocess and/or during the operation of a biotechnological device or system, comprising the steps of subjecting a cell to said bioprocess and/or to operation of said biotechnological device or system, wherein said cell comprises an isolated nucleic acid molecule or a nucleic acid vector comprising said isolated nucleic acid molecule, wherein said isolated nucleic acid molecule comprises a functional mammalian EGR-1 (early growth response protein 1) promoter region that is operatively linked to a gene encoding a fluorescent protein, or a gene encoding an siRNA directed against a constitutively expressed fluorescent protein, and controls expression of said gene; determining a level of fluid shear stress acting on cells during said bioprocess and/or during operation of said biotechnological device or system using said cell in real-time at any given time, and determining said level of fluid shear stress as the level of fluid shear stress that is acting on any cells subjected to said bioprocess and/or to operation of said biotechnological device or system at said given time.