A substrate (12) for delivering a biologically active substance. the substrate (12) comprising: a cross-linked silicone matrix formed by cross-linking a silicone polymer using at least one crosslinking agent comprising a tetraalkoxysilane, the cross-linked silicone matrix defining a plurality of domains, and a composition contained within the domains of the cross-linked silicone matrix, wherein the composition comprises: at least one monomeric glycol and at least one biologically active substance.