Light-induced temperature transitions in biodegradable polymer and nanorod composites.

Shape-memory materials (including polymers, metals, and ceramics) are those that are processed into a temporary shape and respond to some external stimuli (e.g., temperature) to undergo a transition back to a permanent shape. Shape memory polymers are finding use in a range of applications from aerospace to fabrics, to biomedical devices and microsystem components. For many applications, it would be beneficial to initiate heating with an external trigger (e.g., transdermal light exposure). In this work, we formulated composites of gold nanorods (<1% by volume) and biodegradable networks, where exposure to IR light induced heating and consequently, shape transitions. The heating is repeatable and tunable based on nanorod concentration and light intensity and the nanorods did not alter the cytotoxicity or in vivo tissue response to the networks. The temperature at which shape transitions occur in polymers can be controlled through properties such as the glass transition temperature (Tg) or the melting temperature (e.g., through crystallization). In polymer networks the permanent shape is typically governed by covalent bonds, whereas the temporary shape is controlled by the thermal transition. For many implantable biodevices, the Tg of the material is defined to be slightly below body temperature so that implantation in vivo induces the desired shape change. These materials are being applied in applications such as