Micropeel dynamics of cells - correlations with substrate compliance and cytoskeletal structures

Novel, micropipette-based cell peeling methods have been used to assess the relative adhesion strengths and mechanisms of both skeletal and smooth muscle cells. Patterned substrates as well as substrates of variable stiffness were examined. In a first method, the shear stress of the aspirating fluid into a large bore micropipette peels micro-patterned cells from their substrates. The rate at which cells detach from the surface, or the peeling velocity, is measured as a function of the imposed tension created by fluid shear. The peeling velocities and zero-velocity peeling tension of cells growing on flexible polyacrylamide gel (PAG) substrates are compared to the velocities of cells growing on rigid glass. Some C2C12 cells on glass also exhibit spontaneous peeling along their lengths after one end of the myotube is mechanically detached. The results indicate progressive development of a prestress as these contractile cells differentiate on stiff substrates. Additionally, smooth muscle cells (SMC) transfected with GFP-actin or GFP-paxillin were peeled from glass-based substrates. Results indicate a discontinuous peeling in which focal adhesions and actin stress fibers fracture above sites of strong attachment which remain behind. Myocyte adhesion thus appears to depend on both cell type and compliance of the growth substrate.