Surface Modification of Titanium by Atomic Transfer Radical Polymerization (ATRP)

Titanium is commonly used as an orthopedic biomaterial due to its unique mechanical properties and good corrosion resistance. However, after implantation into the body, titanium does not always integrate completely with bone. Its performance can be improved by surface modification with an osteointegrative, bioactive coating such as poly(sodium styrene sulfonate) (pNaSS). Thin films of NaSS were grafted onto rough polished Ti foil as well as smooth, thin Ti layers (~50nm thickness) evaporated onto Si wafers. These substrates were first modified with a chloroform solution of methacryloxypropyltrimethoxysilane (MPS) and then immersed into different NaSS solutions. The grafted surfaces were characterized by a colorimetric assay and X-ray photoelectron spectroscopy. The atomic transfer radical polymerization (ATRP) reaction was catalyzed by either heating the solution to 90°C or by using CuBr at room temperature; the latter resulted Cu contamination in the grafted layer. The reaction kinetics were studied and 15 hrs was found to be an optimum duration for grafting the NaSS layers. It was also found that unlike grafting under nitrogen flow, grafting under vacuum produces reproducible NaSS films.