Soft shape memory

In this chapter, we focus on recent efforts to design and fabricate soft shape-memory materials, including both polymeric and supramolecular systems. We first classify these materials based on their micro- and nanostructure (Section 5.2.2). We then highlight how soft shape-memory materials have been applied to biomedical applications as implantables (Section 5.2.3.1), drug delivery devices (Section 5.2.3.2), and tissue engineering scaffolds (Section 5.2.3.3). In addition, we briefly discuss future trends for utilizing soft shape-memory materials for biomedical applications (Section 5.2.4). 

FIGURE 5.2.3 Classification of soft shape-memory materials from the viewpoint of nanoaivhitectonics. (a-c) Structures and (d) molecular mechanism, (a) Chemically cross-linked polymer network, (b) supramolecular network with clay nanosheets [29], and (c) inorganic/polymer composite network system, and their shape-memory profiles [30]. (d) The nanoscale molecular mechanism for one-way and two-way SME of a cross-linked semicrystalline polymer system. 

So far, we have discussed the properties of soft shape-memory materials as a function of their nanoarchitectonics. At the same time, material microarchitectonics, also known as material forms, should be tailored to specific applications as SME in material was generally treated with bulk phenomenon. As such, designing an SMP object at the submicron to microscale is challenging. In particular, the synthesis of well-regulated nanoscale structures built up as meso- or macroscopic materials remains challenging. Recent rapid evolution in SMPs has been developed in efforts to meet various requirements in diverse potential applications. As a result, not only traditional film, tube, and sponge (foam) forms, but also microparticles, surface as well as micro/nanofiber that exhibit SMEs at mesoscopic to microscopic scales, have attracted much attention (Fig. 5.2.4). 

Although these forms have different object scales from nano- (nm) to centimeter (cm) and various dimensions from one-dimensional (ID) fiber to three-dimensional (3D) sponge, it is possible to fabricate these material forms with excellent shape-memory properties [37,38]. Despite unique material textures and forms with multiscale, the underlying molecular principle of SMEs is largely equivalent to that of bulk systems, suggesting similar design criteria and principles. Structural flexibility and diversity originated from material microarchitectonics may certainly promote soft shape memory for many new applications. 

FIGURE 5.2.4 Classification of soft shape-memory materials fiom the viewpoint of macroarchitectonics (forms). 

Burke, K.A. and P.T. Mather (2010), Soft shape memory in main-chain liquid crystal-hne elastomers./oMrnu/ of Materials Chemistry,pp. 3449-3457. 

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