A polymer, possibly fabricated as part of a medical device or as part of a medical prostheses (such as a contact lens) is functionalized to facilitate the introduction of functional groups, such as biomedical species including heparin. The polymer is reacted in an aqueous medium with a water soluble azo compound (such as cyanovaleric acid or 2-methylpropionamidine) to produce oxygen centered radicals responsible for introducing functional groups into the polymer.