Biomolecule-responsive Behavior of Smart Gels Having Biomolecular Complexes as Reversible Cross-links

Introduction Stimuli-responsive gels undergo abrupt changes in volume in response to environmental changes such as pH and temperature. Stimuli-responsive gels have attracted considerable attention as smart materials in the biochemical and biomedical fields, since they can sense environmental changes and induce structural changes by themselves. The fascinating properties of such stimuli-responsive gels suggest that they have many future opportunities as suitable materials for the design of smart biomaterials and self-regulated drug delivery systems [1]. Furthermore, several researchers focused on biologically stimuli-responsive gels that can respond to glucose for constructing self-regulated insulin delivery systems [2-6]. Recently, biomolecule-responsive gels that exhibit swelling/shrinking changes in response to specific signal biomolecules like tumor-specific markers have become increasingly important as smart devices for drug delivery systems and molecular diagnostics. Stimuli-responsive behavior of most gels reported previously was mainly based on changes in affinity of polymer chains for solvents or by changes in their charged groups. However, the cross-linking structure of a gel is also an important factor to determine its swelling behavior. This led us to a strategy that novel biomolecule-responsive gels can be prepared by using stimuli-responsive complexes as reversible cross-linking points. Based on this strategy, we have prepared two types of biomolecule-responsive gels (biomolecule-cross-linked gel and biomolecule-imprinted gel) by using biomolecular complexes as reversible cross-linking points [7-9]. This paper describes biomolecule-responsive behavior of biomolecule-cross-linked gels that were prepared using biomolecular complexes such as antigen-antibody complexes and DNA duplexes.