Topographical features, such as projections or recesses, having a maximum dimension which is less than 3 μm, with the features being separated by a distance which is less than 10 μm are transferred to polyetheretherketone, on an industrial scale, by injection moulding relatively low viscosity PEEK, using a mould in which is arranged a master structure which carries the desired topography. The topographical features increase the water contact angle of a surface which includes them and such a modified surface has been shown to influence cell attachment and differentiation. Parts which incorporate the topographical features may be used in medical devices such as implantable medical devices for cardiology or for neuromodulation.