Photoresponsive shape-memory polymers

Unlike several of the other stimuh considered in this chapter, pH is an internal stimulus and thus requires alteration of the chemical environment. As a result, the use of pH triggers is limited, particularly for basic ceU studies that are confined to a narrow pH range. The complexity of reversibility is another drawback that arises with the use of pH-responsive materials, as the solution must be removed or extracted before reuse and this may also alter the physical environment. 

Nonetheless, pH-responsive materials have shown promise in fields such as drug dehvery and microprocessing [40], 

Temperature variations may result in reversible changes in properties such as structural arrangement, size, solubihty, and shape. Many materials designed for biomedical or biotechnology appHcations are confined to a narrow temperature spectrum in order to be effective in a physiological environment. The following thermoresponsive materials are discussed in the next section poly(N-iso-propylacrylamide (PNIPAAm), polymer brushes, and shape-memory polymers. 

Temperature-Dependent Switching Based on Poly(N-iso-propylacrylamide) 

PNIPAAm is a widely studied thermoresponsive polymer that exhibits a lower critical solution temperature (LCST) [51, 52]. Below the LCST, the polymer is expanded and hydrophihc and is thus soluble in water. Above this critical temperature, there is an abrupt phase transition leading to a collapsed and hydrophobic polymeric structure, which renders the polymer insoluble in water [53-55]. The LCST of 

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In addition to electric potential, light can also be used to trigger switching properties of surfaces and polymers. Application of ultraviolet (UV) light to these materials may result in reversible changes in characteristics such as hydrophilic-ity/hydrophobicity, structural arrangement, and shape. Commonly utilized photoresponsive materials include azobenzene molecules, spiropyran molecules, and shape-memory polymers. 

White TJ (2012) Light to work transduction and shape memory in glassy, photoresponsive macromolecular systems trends and opportunities. J Polym Sci B50 877... 

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