Hi there-
By "Pegylation", I assume you mean poly-ethylene-glycol linking of TNF to your
substrate?
There are number of ways to do, but the best known method I know was invented by Brewer. He crosslinks PolyLysine to his
substrate in a pattern use an intermediate peg layer.
For specifics please check out the following references:
Chang, J.C., Brewer, G.J., Wheeler, B.C. (2003), A Modified Microstamping Technique Enhances Polylysine Transfer and Neuronal Cell Patterning, Journal of Biomaterials, 24/17, pp. 2863-2870.
Chang, J.C., Brewer, G.J., and Wheeler, B.C. (2001), "Modulation of Neural Network Activity by Patterning," Biosensors and Bioelectronics, 16/7-8, pp. 527-533..
You might also check out Gelest's website (www.gelest.com).
They sell PEG in a variety of formats I believe and they also have protocols posted on their website.