Chemical shape-responsive polymers

Muscles contract and expand in response to electrical, thermal, and chemical stimuli. Certain polymers, such as synthetic polypeptides, are known to change shape on application of electric current, temperature, and chemical environment. For instance, selected bioelastic smart materials expand in salt solutions and may be used in desalination efforts and as salt concentration sensors. Polypeptides and other polymeric materials are being studied in tissue reconstruction, as adhesive barriers to prevent adhesion growth between surgically operated tissues, and in controlled drug release, where the material is designed to behave in a predetermined matter according to a specific chemical environment. 

Presently, the study of shape memory polyurethane (SMPU) has been widely conducted. For common elastic fibers, the elasticity should be defined as the instant recoverability of the length on release of the deforming stress. The recovery in shape memory fibers is the ability of deformed fibers to recover under external stimulus such as heat or chemicals. In this case, the external stimulus is a must. Figure 3.1 shows the net-points and switches which response to the stimulus (Hu et al., 2012). The elongation of shape memory polymer fiber are a little less than spandex, but mechanical... 

Shape memory polymers make up another class of injectable biomaterials for vascular applications, yet are relatively new in the field of endovascular embolization. Shape memory polymers are chemically structured so that they are able to reversibly take on a different physical shape in response to some stimuli (Small et al, 2007). Usually these different shapes include a compact form and an expanded form of the polymer. In the case of endovascular embolization, the expanded polymer can be pre-formed to fit specific contours of an individual aneurysm (Ortega et al, 2007). Upon interacting with some type of stimuli, such as heat or cold, the material is compacted into a shape that can be delivered through a microcatheter. The process of using shape memory polymers to embolize an aneurysm is shown in Fig. 7.5, along with samples of expanded SMPs (Ortega et al, 2007). 

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