Responding to change: thermo- and photo-responsive polymers as unique biomaterials.

Responsive polymer systems that react to thermal and light stimuli have been a focus in the biomaterials literature because they have the potential to be less invasive than currently available materials and may perform well in the in vivo environment. Natural and synthetic polymer systems created to exhibit a temperature-sensitive phase transition lead to in situ forming hydrogels that can be degradable or non-degradable. These systems typically yield physical gels whose properties can be manipulated to accommodate specific applications while requiring no additional solvents or cross-linkers. Photo-responsive isomerization, dimerization, degradation, and triggered processes that are reversible and irreversible may be used to create unique gel, micelle, liposome, and surface-modified polymer systems. Unique wavelengths induce photo-chemical reactions of polymer-bound chromophores to alter the bulk properties of polymer systems. The properties of both thermo- and photo-responsive polymer systems may be taken advantage of to control drug delivery, protein binding, and tissue scaffold architectures. Systems that respond to both thermo- and photo-stimuli will also be discussed because their multi-responsive properties hold the potential to create unique biomaterials.