A prodrug of a general formula: A-X I wherein A is a biologically active agent or an agent capable of being metabolised to a biologically active agent; and X is selected from the group consisting of a substituent according to formula (a), a substituent according to formula (b), a substituent according to formula (c) and a substituent according to formula (d): R- (a) R-Y 1 - (b) wherein R has a chain length equivalent to 10 to 30 carbon atoms and is selected from a group consisting of alkyl, alkenyl, alkynyl, branched alkyl, branched alkenyl, branched alkynyl, hydroxylated alkyl, hydroxylated alkenyl, and alpha-tocopherol groups; Y 1 is a linker group that is covalently attached to the group R at one attachment site and to A at a second attachment site; Y 2 is a linker group that is covalently attached to two R groups (which may be identical or different) at two independent attachment sites and is attached to A at a third attachment site; and Y 3 is a linker group that is covalently attached to three R groups (which may be identical or different) at three independent attachment sites and is attached to A at a fourth attachment site characterised in that A-X is a compound according to formula and wherein the R group is capable of conferring self-assembly properties to the prodrug under physiological conditions into a lamellar, inverse hexagonal phase or inverse cubic phase. A is a biologically active agent or an agent capable of being metabolised to a biologically active agent; and X is selected from the group consisting of a substituent according to formula (a), a substituent according to formula (b), a substituent according to formula (c) and a substituent according to formula (d): R- (a) R-Y 1 - (b) wherein R has a chain length equivalent to 10 to 30 carbon atoms and is selected from a group consisting of alkyl, alkenyl, alkynyl, branched alkyl, branched alkenyl, branched alkynyl, hydroxylated alkyl, hydroxylated alkenyl, and alpha-tocopherol groups; Y 1 is a linker group that is covalently attached to the group R at one attachment site and to A at a second attachment site; Y 2 is a linker group that is covalently attached to two R groups (which may be identical or different) at two independent attachment sites and is attached to A at a third attachment site; and Y 3 is a linker group that is covalently attached to three R groups (which may be identical or different) at three independent attachment sites and is attached to A at a fourth attachment site characterised in that A-X is a compound according to formula and wherein the R group is capable of conferring self-assembly properties to the prodrug under physiological conditions into a lamellar, inverse hexagonal phase or inverse cubic phase. R has a chain length equivalent to 10 to 30 carbon atoms and is selected from a group consisting of alkyl, alkenyl, alkynyl, branched alkyl, branched alkenyl, branched alkynyl, hydroxylated alkyl, hydroxylated alkenyl, and alpha-tocopherol groups; Y 1 is a linker group that is covalently attached to the group R at one attachment site and to A at a second attachment site; Y 2 is a linker group that is covalently attached to two R groups (which may be identical or different) at two independent attachment sites and is attached to A at a third attachment site; and Y 3 is a linker group that is covalently attached to three R groups (which may be identical or different) at three independent attachment sites and is attached to A at a fourth attachment site