Shape-memory hydrogels

Fig. 3 Image frames captured from a video of an EGC hydrogel scaffold (a) prior to, (b) during, and (c) immediately following compression, illustrating its elastic shape-memory properties...

Degradable implants, shape-memory polymers in, 22 355 Degradable-pendant-chain hydrogels, 13 741... 

Also, PVA hydrogels evidenced a very good behaviour in contact with skin and other tissues, mucosa, or blood. PVA exhibits a bioadhesive nature, shape-memory properties, avoid the protein adsorption onto the gel surface and is biocompatible. 

Hydrogels are another class of polymers with shape memory properties. They are cross-linked polymers with a hydrophilic portion that has high affinity for water and a hydrophobic part that can be controlled by temperature variations. The cross-linked part is responsible for setting the permanent shape at an elevated temperature, whilst the hydrophobic part assumes a secondary shape at a specific or critical temperature. Heating above these temperatures completes the recovery (Liu et al., 2007). 

Hron, R, and Slechtova, J. 1999. Shape memory of composites based on silicone rubber and polyacrylamide hydrogel. Die Angewandte Makromolekulare Chemie 268 29-35. 

Hydrogels with hydrophobic, crystallizable side chains formed by copolymerization of acrylic acid and stearyl acrylate crosslinked with methylenebisacrylamide (BIS) showed a strong temperature dependence in their mechanical properties [91-93]. Such shape-memory gels having Tians = 7m displayed a reversible order-disorder transition associated with the interactions between the alkyl side chains. While behaving like hard plastic below 25 °C, softening above 50 °C enabled the materials... 

Han Y et al (2012) Zinc ion uniquely induced triple shape memory effect of dipole-dipole reinforced ultra-high stiraigth hydrogels. Maruomol Rapid Commun 33(3) 225-231... 

Water swollen hydrogels are generally amorphous without any particularly ordered structure at molecular level. For many years, polymer gels have been studied for the development of low-voltage soft actuators [187-193]. As an example, they can be used to construct thermo-responsive diaphragms capable of automatically opening and closing a valve [194]. They can also show shape memory effects. For instance, a thermal activation of a shape memory gel is shown in Fig. 6.96. 

Nochel, U., Reddy, C.S., Uttamchand, N.K., Kratz, K., Behl, M., Lendlein, A., 2013. Shape-memory properties of hydrogels having a poly(epsilon-caprolactone) crosslinker and switching segment in an aqueous environment European Polymer Journal 49, 2457-2466. 

Osada Y and Matsuda A, Shape memory in hydrogels . Nature, 1995, 376, 219. 

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