In the former case, the relative concentrations of gel and monomer 16 are unaffected by the coupled reaction and thus, although a non-equilibrium steady state can be established in which the concentrations of 15 and 16 relative to 14 are distorted, the gel is "at equilibrium" with monomer 16 at any given instant and its properties are essentially identical to the structure achieved by simply mixing the same proportions of 14, 15 and 16. In the latter case, the self-assembled state is directly influenced by the coupled reaction, as in ATP-actin polymerization. Prins and co-workers have suggested systems that correspond to the former situation be described as forming under "dissipative conditions" to differentiate them from those in which selfassembly is directly coupled to a driving reaction, which they term "dissipative self-assembly". The open question as to whether self-assembly is directly coupled to the spontaneous reaction is one that applies, to our knowledge, to most if not all artificial systems reported to date. This is at least in part because, unlike in the case of molecular motor 6, there is no simple observable (e.g., directed motion), even when working in a stepwise regime, that would unequivocally confirm the nature of the network. For example, under different conditions, the same authors reported the gelation of monoester 15 generated from 14 by reaction with SO4Me2. In this case the material formed displayed intriguing properties including non-linear dissolution kinetics of gel fibers and their simultaneous growth and shrinkage under some regimes. Although these properties are reminiscent of the behavior of ATP-actin, 33 or GTP-tubulin, 40 the only absolute confirmation that the selfassembled structure is produced in a non-equilibrium steady state requires the rate constants for ester formation/hydrolysis in the solution and gel states to be determined. Such studies, which are not trivial in a multiphase system, would establish the form of the reaction network and whether the required kinetic asymmetry is present. Summary. Based on the above, it is hard to escape the conclusion that the assembly of artificial supramolecular materials that can in theory achieve a non-equilibrium steady state with respect to their monomers has yet to be unambiguously demonstrated. That is not to say that the systems reported are not elegant or excitingmany have unusual transient propertiesbut just that it is not clear if the self-assembly process is coupled to the driving reaction and if kinetic asymmetry is present because the required data have not yet been reported.