Indirect Actuation of Thermally-Induced Shape-Memory Effect

3 Indirect Actuation of Thermally-Induced Shape-Memory Effect 

Indirect triggering of the thermally-induced SME has broadened the application spectrum of SMPs and has been explored following two different strategies. The first strategy was indirect heating, e.g., by exposure to IR-radiation. In the second 

Strategy SME was triggered by lowering Ttrans, the sample temperature remaining constant. The decrease of Ttrans could be achieved by diffusion of a low molecular 

In a laser-activated medical device based on SMPU the indirect acmation of SME was induced by irradiation with IR-light [98, 99], Although the required energy is quite high, the principle could be extended to laser activated shape-memory vascular stents and SMP foams for aneurysm treatment [100, 101] both requiring a light diffuser for the uniform application of light [102]. 

A reduction of the required energy could be reached by the incorporation of conductive fillers such as heat conductive ceramics, carbon black and carbon nanotubes [103-105] as these materials allowed a better heat distribution between the heat source and the shape-memory devices. At the same time the incorporation of particles influenced the mechanical properties increased stiffness and recoverable strain levels could be reached by the incorporation of microscale particles [106, 107], while the usage of nanoscale particles enhanced stiffness and recoverable strain levels even more [108, 109]. When nanoscale particles are used to improve the photothermal effect and to enhance the mechanical properties, the molecular structure of the particles has to be considered. An inconsistent behavior in mechanical properties was observed by the reinforcement of polyesterurethanes with carbon nanotubes or carbon black or silicon carbide of similar size [3, 110]. While carbon black reinforced materials showed limited Ri around 25-30%, in carbon-nanotube reinforced polymers shape-recovery stresses increased and R s of almost 100% could be determined [110]. A synergism between the anisotropic carbon nanotubes and the crystallizing polyurethane switching segments was proposed as a possible 

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