Pancreatic cancer contains both fibrotic tissue and tumor cells with embedded vasculature. Therefore anti-cancer nanoparticles need to extravasate from tumor vasculature and permeate thick fibrotic tissue to target tumor cells. To date, permeation of drugs has been investigated in vitro using monolayer models. Since three-dimensional migration of nanoparticles cannot be analyzed in a monolayer model, we established a novel, three-dimensional, multilayered, in vitro model of tumor fibrotic tissue, using our hierarchical cell manipulation technique with K643f fibroblasts derived from a murine pancreatic tumor model. NIH3T3 normal fibroblasts were used in comparison. We analyzed the size-dependent effect of nanoparticles on permeation in this experimental model using fluorescent dextran molecules of different molecular weights. The system revealed permeation decreased as number of layers of cultured cells increased, or as molecule size increased. Furthermore, we showed changes in permeation depended on the source of the fibroblasts. Observations of this sort cannot be made in conventional monolayer culture systems. Thus our novel technique provides a promising in vitro means to investigate permeation of nanoparticles in fibrotic tissue, when both type and number of fibroblasts can be regulated. (C) 2012 Elsevier Inc. All rights reserved.