Recent advances in glycopolypeptide synthesis

Stimuli-sensitive hydrogels have attracted considerable attention as intelligent materials in the biochemical and biomedical fields, since they can sense environmental changes and induce structural changes by themselves. In particular, biomolecule-sensitive hydrogels that undergo swelling changes in response to specific biomolecules have become increasingly important because of their potential applications in the development of biomaterials and drug delivery systems. This article provides an overview of the important and historical research regarding the synthesis and applications of glucose-sensitive hydrogels which exhibit swelling changes in response to glucose concentration. Enzymatically degradable hydrogels and antigen-sensitive hydrogels are also described in detail as protein-sensitive hydrogels that can respond to larger biomolecules. The synthetic strategies of other biomolecule-sensitive hydrogels are summarized on the basis of molecular imprinting and specific interaction. The biomolecule-sensitive hydrogels reviewed in this paper are expected to contribute significantly to the exploration and development of newer generations of intelligent biomaterials and self-regulated drug delivery systems.

Many natural polymeric materials (particularly structural proteins) display a hierarchy of structure over several length scales. Block copolymers are able to self-assemble into ordered nanostructures, but the random-coiled nature of their polymer chains usually suppresses any further levels of organization. The use of components with regular structures, such as rigid-rod polymers, can increase the extent of spatial organization in self-assembling materials. But the synthesis of such polymeric components typically involves complicated reaction steps that are not suitable for large-scale production. Proteins form hierarchically organized structures in which the fundamental motifs are generally alpha-helical coils and beta-sheets. Attempts to synthesize polypeptides with well-defined amino-acid sequences, which might adopt similar organized structures, have been plagued by unwanted side reactions that give rise to products with a wide range of molecular weights, hampering the formation of well-defined peptide block copolymers. Here I describe a polymerization strategy that overcomes these difficulties by using organonickel initiators which suppress chain-transfer and termination side reactions. This approach allows the facile synthesis of block copolypeptides with well-defined sequences, which might provide new peptide-based biomaterials with potential applications in tissue engineering, drug delivery and biomimetic composite formation.