This article demonstrates the tuning of the biological activity of a surface functionalized by a polyelectrolyte multilayer. The interaction of protein A with macrophages is used as the model system. The film consists of two polypeptides, poly(lysine) and poly(glutamic acid); each “build-up” solution is a mixture of the respective D- and L-enantiomers (d and l enantiomers). Cells are deposited on top of the film, and they produce tumor necrosis factor alpha (TNF-α) as they come into contact with the protein. Depending upon the d/l-enantiomer ratio of the polyelectrolyte solutions used for the film build-up, and the embedding depth of the protein, the production of TNF-α commences after a varying induction time and displays a transition from no-production to full-production, which takes place over a period of time that depends on the film's composition and embedding depth. Thus, it is shown that by changing these two parameters the timing of the protein's activity can be accurately tuned.
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