• Ellis, Amanda V.
• Cole, Martin
• Vasani, Roshan

Abstract

Stimulus-responsive polymers (SRPs) are synthetic macromolecules that undergo changes in their properties in response to a defined external stimulus. A range of responsive polymers exist that are sensitive to different stimuli (triggers) such as light, temperature, electric field, magnetic field, pH, and chemicals. The types of response associated with the stimuli also vary greatly, including structural changes, sol – gel transitions, changes to optical properties, solubility changes, and micelle formation. The most widely studied stimuli are changes in pH, temperature, light intensity or wavelength, ionic strength and electric field strength [1, 2]. Additionally, SRPs can be designed that exhibit responses to more than one type of stimulus, such as temperature - and pH - responsive systems [3] or light - and temperature - responsive polymers [4] . The responsiveness of SRPs is somewhat comparable to the behavior of certain biomacromolecules (proteins, DNA, RNA) in natural systems. This biomimicry, combined with the additional properties of synthetic (abiotic) macromolecules, is being exploited for manifold applications in the life sciences, such as controlled drug release [5 – 7] , cell and tissue culture [1,8] , actuators [9] , and sensing [10]. With regards to biological applications, it is important to be aware that the physiologically relevant window of pH, temperature or ionic strength is limited [11] , and that any polymer responsive to these environmental factors must be carefully matched to the biological application in mind.Interfacing SRPs with other, non-stimulus-responsive materials conveys extra advantages, and expands the repertoire of the SRPs. The combination with nanostructured materials such as nanoparticles, nanotubes or nanoporous materials, allows the construction of novel functional materials. For example, liposomes functionalized with poly( N - isopropylacrylamide) ( PNIPAAm ) chains combine the thermoresponsive nature of the polymer with the drug - carrying capacity of the liposome [12] . Likewise, iron oxide nanoparticles combined with PNIPAAm allow for the in vivo targeting of the coated nanoparticles by using an externally applied magnetic field. Such targeting can employed for targeted drug delivery [13]. Coating materials with SRPs, for example in the form of polymer brushes, sets the stage for the development of advanced biosensors, scaffolds for tissue engineering, cell culture materials and textiles, as well as microfl uidic and microelectromechanical devices [10, 14 – 17] . SRPs can form nanointerfaces with fl at and porous surfaces, and also with different types of inorganic and organic nanoparticles. Some of the key types of SRP nanointerfaces are depicted in Figure 3.1, and these will be the subject of this chapter. In addition to the generation of stimulus - responsive nanointerfaces, recent developments in terms of applying these nanointerfaces to drug delivery, microfluidics, molecular separation, and tissue culture will be highlighted.

Topics

• nanoparticle
• porous
• impedance spectroscopy
• surface
• polymer
• nanotube
• strength
• iron
• micelle formation