The use of intelligent surfaces as interfaces to control the behavior of biomolecules is an increasingly popular strategy. Intelligent surfaces are surfaces that
have one or more properties being controlled by external stimuli. The most
common way to obtain an intelligent surface is to introduce a smart polymer
onto the surface of a material. Our laboratory focuses on the use of poly(Nisopropylacrylamide) (PIPAAm) as a smart polymer for creating thermoresponsive surfaces. In aqueous solutions, PIPAAm has a reversible phase
transition temperature of 32°C. This property allows the hydrophilic/hydrophobic character of the polymer to be controlled by changing the temperature of the surrounding medium. This can be used as an “on-off” switch
for modulating the interactions between the polymer and various biomolecules. Therefore, PIPAAm has been used to produce intelligent surfaces for diverse applications. By modulating temperature, the separation of biomolecules can be controlled by using PIPAAm-modified chromatographic matrices. The alterations of the hydrophobicity of PIPAAm provoked by temperature changes allow the affinity of PIPAAm-grafted surfaces to be modulated for separating solutes, resulting in a temperature-responsive chromatographic system. Temperature alterations also result in changes of the PIPAAm chain conformation. This property is used to produce temperatureresponsive polymeric micelles with thermoresponsive cores or coronas for drug delivery purposes. The expansion and shrinking of the coronas can be controlled by changing temperature, and thus the capture or release of a drug can be regulated. PIPAAm-grafted cell culture substrates for producing cell sheets are, however, the most addressed subject in our laboratory.These culture substrate surfaces are cell adhesive when temperature is above the phase transition temperature, also called “lower critical solution temperature (LCST),” but the substrates become nonadhesive for cells when the temperature is lower than LCST. Our concept of “cell sheet engineering” is based on this very property of thermoresponsive culture dishes. Cells can be cultured on the dishes until they are confluent and then harvested as a single contiguous cell sheet composed of cells and their intact extracellular matrix (ECM) capable of being transplanted, just by lowering the temperature below LCST. Our laboratory has successfully applied this concept to the regeneration of a variety of tissues. The following sections of this chapter will present in more detail the applications of thermoresponsive surfaces for chromatographic purposes, for the production of drug delivery nanoparticles, and for cell sheet engineering.
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