Much research has imparted specific functionalities, such as encouraging proliferation or differentiation, to biomaterials by grafting, incorporating or delivering molecules with defined biologic functions. An alternative approach might have been to use rational design to construct biomaterials with those functions, but that is very difficult, although it is a goal of some aspects of glycomics (62)-the study of infomation encoded in the structure of carbohydrates-and structural biochemistry. Instead, some investigators have used highthroughput methods to perfom rapid nanoliter-scale synihesis of thousands of cell-polymer interactions on chip-like systems (63) (Fig. 2). This approach revealed that some polymers were markedly better than others in making human embryonic stem cells differentiate into epithelial cells. Furthermore hermore, the various polymers had widely differing effects on the cellular response to a bioactive molecule, retinoic acid. It is possible, as has been suggested, that the effects of the biomaterials were actually mediated by adsorbed proteins (64) or other factors, but that does not alter the fact that the variety in polymeric structure. It is possible that approaches of this sort will allow for rapid identification of biomaterials-with or without addition of specific ligands-for specific tissuc engineering applications.