Multiscale morphology of organic semiconductor thin films controls the adhesion and viability of human neural cells.

We investigate how multiscale morphology of functional thin films affects the in vitro behavior of human neural astrocytoma 1321N1 cells. Pentacene thin film morphology is precisely controlled by means of the film thickness, Theta (here expressed in monolayers (ML)). Fluorescence and atomic force microscopy allow us to correlate the shape, adhesion, and proliferation of cells to the morphological properties of pentacene films controlled by saturated roughness, sigma, correlation length, xi, and fractal dimension, d(f). At early incubation times, cell adhesion exhibits a transition from higher to lower values at Theta approximately 10 ML. This is explained using a model of conformal adhesion of the cell membrane onto the growing pentacene islands. From the model fitting of the data, we show that the cell explores the surface with a deformation of the membrane whose minimum curvature radius is 90 (+/- 45) nm. The transition in the adhesion at approximately 10 ML arises from the saturation of xi accompanied by the monotonic increase of sigma, which leads to a progressive decrease of the pentacene local radius of curvature and hence to the surface area accessible to the cell. Cell proliferation is also enhanced for Theta < 10 ML, and the optimum morphology parameter ranges for cell deployment and growth are sigma <or= 6 nm, xi > 500 nm, and d(f) > 2.45. The characteristic time of cell proliferation is tau approximately 10 +/- 2 h.