Definition of "prolongated"

However, those approaches are hindered by low cell yield, limited plasticity, and differentiation capacity following prolongated expansion in vitro [ 24 ].

2015 June 4, Juliana Lott de Carvalho et al., “Production of Human Endothelial Cells Free from Soluble Xenogeneic Antigens for Bioartificial Small Diameter Vascular Graft Endothelization”, in BioMed Research International‎, volume 2015