title: Reproducibility of scratch assays is affected by the initial degree of confluence: Experiments, modelling and model selection.
abstract: Scratch assays are difficult to reproduce. Here we identify a previously overlooked source of variability which could partially explain this difficulty. We analyse a suite of scratch assays in which we vary the initial degree of confluence (initial cell density). Our results indicate that the rate of re-colonisation is very sensitive to the initial density. To quantify the relative roles of cell migration and proliferation, we calibrate the solution of the Fisher-Kolmogorov model to cell density profiles to provide estimates of the cell diffusivity, D, and the cell proliferation rate, λ. This procedure indicates that the estimates of D and λ are very sensitive to the initial density. This dependence suggests that the Fisher-Kolmogorov model does not accurately represent the details of the collective cell spreading process, since this model assumes that D and λ are constants that ought to be independent of the initial density. Since higher initial cell density leads to enhanced spreading, we also calibrate the solution of the Porous-Fisher model to the data as this model assumes that the cell flux is an increasing function of the cell density. Estimates of D and λ associated with the Porous-Fisher model are less sensitive to the initial density, suggesting that the Porous-Fisher model provides a better description of the experiments.
authors.affiliation: School of Mathematical Sciences, Queensland University of Technology (QUT) Brisbane, Queensland, Australia.
authors.forename: Wang
authors.initials: W
authors.lastname: Jin
authors.affiliation: Ghrelin Research Group, Translational Research Institute, QUT, 37 Kent St, Woolloongabba, Queensland, Australia.
authors.forename: Esha T
authors.initials: ET
authors.lastname: Shah
authors.affiliation: School of Mathematical Sciences, Queensland University of Technology (QUT) Brisbane, Queensland, Australia.
authors.forename: Catherine J
authors.initials: CJ
authors.lastname: Penington
authors.affiliation: School of Mathematical Sciences, Queensland University of Technology (QUT) Brisbane, Queensland, Australia.
authors.forename: Scott W
authors.initials: SW
authors.lastname: McCue
authors.affiliation: Ghrelin Research Group, Translational Research Institute, QUT, 37 Kent St, Woolloongabba, Queensland, Australia.
authors.forename: Lisa K
authors.initials: LK
authors.lastname: Chopin
authors.affiliation: School of Mathematical Sciences, Queensland University of Technology (QUT) Brisbane, Queensland, Australia; Ghrelin Research Group, Translational Research Institute, QUT, 37 Kent St, Woolloongabba, Queensland, Australia. Electronic address: matthew.simpson@qut.edu.au.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Simpson
mesh_terms: D000465:Algorithms; D001681:Biological Assay / Q000379:methods; D002452:Cell Count; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000502:physiology*; D049109:Cell Proliferation / Q000502:physiology*; D006801:Humans; D008954:Models, Biological; D015203:Reproducibility of Results; D013314:Stress, Mechanical; D013997:Time Factors
keywords: Cell diffusivity; Cell proliferation rate; Reproducibility; Scratch assay