Advances in hydrogel photonics and their applications

Hydrogels are three-dimensional, hydrophilic networks of cross-linked polymers that can retain water molecules in the structures and respond to physical/chemical stimulus by changing their phase and volume. Recent progress shows hydrogels with optical clarity and good processability to construct various microstructures/nanostructures, which are attractive for photonics-based environmental and biological sensing applications. Moreover, hydrogel-based photonic structures formed by biocompatible and biodegradable polymers are capable of delivering light into living tissues for diagnosis, therapy, and stimulus. We introduce recent studies of hydrogel-based photonic structures, including waveguides, optical fibers, photonic crystals, and plasmonic structures. Optically active photonic devices have been reported by doping luminescent agents into the hydrogel. In addition to introducing important demonstrations of the photonic components, the recent progress in new applications using the hydrogel-based photonic platforms is discussed. Development in the technology of hydrogel photonics will provide a solution to the convergence of scientific fields where the use of conventional photonic devices has been limited.