Haptotaxis's the directional motility or outgrowth of cells, for example in the case of axonal outgrowth, usually up a gradient of cellular adhesion sites or substrate-bound chemoattractants. These gradients are naturally present in the extracellular matrix (ECM) of the body during processes such as angiogenesis or artificially present in biomaterials where gradients are established by altering the concentration of adhesion sites on a polymer substrate.… (More on Haptotaxis)