Hydrogels, chemically responsive results

Chemical polymerization bypasses some issues of stimuli-responsive hydrogels, as the resulting material has stable chemical bonds and the gel formation depends on molecular chemistry rather than on uncontrollable physiological parameters. Likewise, chemical gelation requires the injection of the whole reaction system, where each component in the mixture (eg, monomer, catalyst) must satisfy the basic requirements of biocompatibility. Furthermore, the cross-linking reaction should reach a high conversion to eliminate the possibility of unreacted precmsors leaching from the implant. 

Figure 2.2 A simplified scheme of events that define and influence a bio-responsive hydrogel system. An input of a stimulus (step 1) leads to the binding of the receptor to the ligand within the gel network resulting in molecular biorecognition events (step 2). Molecular actuation is stimulated in step 3 to trigger further micro and macroscopic events, i.e. swelling. Molecular actuation results in a response (step 4) that can be mechanical, chemical, optical or electronic.

---