Poly-D-Lysine (PDL) are synthetic molecules used to enhance cell attachment to plastic and glass surfaces. For many anchorage-dependent cells, the nature of the culture substrate has a major effect on cell growth and the requirement for serum proteins. Tissue culture plastic has a net negative surface charge, which is produced by plasma treatment of the polystyrene. Over the years, many researchers have shown that serum-free or reduced serum cultures can be dramatically improved by coating the culture surface with positively charged polymers (i.e., PDL). Poly-Lysine surface treatment improves adhesive properties by altering the charge on the vessel surface from negative to positive. In addition to promoting cell adhesion, Poly-Lysine also enhances the adsorption of serum or extracellular matrix proteins to the culture substrate.