According to an aspect of the invention, medical devices are provided which contain at least one polymeric region. The polymeric region contains at least one copolymer, which includes at least one high Tg vinyl aromatic monomer and at least one low Tg monomer. Moreover, the polymeric region contains at least one surface sub-region that is crosslinked and at least one bulk sub-region that is substantially non-crosslinked. According to another aspect of the invention, a method is provided which includes exposing a polymeric region of a medical device to energetic species such that at least one surface sub-region of the polymeric region becomes crosslinked and at least one bulk sub-region remains substantially non-crosslinked. The polymeric region contains at least one copolymer, which includes at least one high Tg vinyl aromatic monomer and at least one low Tg monomer.