a medical device , for example a stent , has a surface which in use contacts body tissue , wherein said surface has on it a biocompatible coating layer comprising a polymer having covalently bound allyl - terminated pendent groups , said pendent groups comprising a moiety selected from - 0 - ch 2 — ch ═ ch 2 — s — ch 2 — ch ═ ch 2 — s - ch 2 — ch ═ ch 2 — se — ch 2 — ch ═ ch 2 and — se (= 0 j - ch 2 — ch ═ ch 2 . this surface has good biocompatibility and can bind strongly to a metallic surface . the polymer may be made from an electropolymerisable monomer , e . g . a pyrrole .