Shape memory polymers with magnetic nanoparticles

Shape memory polymers and composites have received great attention in recent years due to potential applications in biomedical field such as drug delivery systems, vascular surgery and implant devices. Their properties such as biocompatibility, ease in manufacturing and affordable prices make them a convenient option for the fabrication of biomedical devices. Shape memory polymers (SMPs) are stimuli responsive materials and they belong to the class of actively moving polymers, which can be actuated by light, electricity, magnetism, external heating or inductive heating by electromagnetic field. Typical procedure for thermally stimulated SMPs consists of four steps which are; heating the sample above Tg, applying force when sample's temperature is above Tg (softening and free deformation), cooling the sample below Tg (shape keeping) and finally heating the sample above Tg (shape recovery). In this study, shape memory nanocomposite is obtained with conventional heating where magnetic nanoparticles are used as nanofillers to obtain this nanocomposite from poly (DL lactide – co – glycolide) (PLGA) which does not exhibit shape memory behavior when neat. Exploring the mechanical properties it was found that addition of Fe3O4 NPs improves the mechanical properties of the PLGA. However, the increase of stiffness and durability of the polymer remains constant after a threshold concentration which is attributed to the nanoparticle aggregation in the matrix. Also, thermal properties of these nanomaterials were analyzed and shape memory property was shown above a threshold Fe3O4 concentration with conventional heating-cooling cycles. Also, by adding gold NPs to this nanomaterial, photothermal effect was used to stimulate the shape memory property. Green laser was applied to this nanocomposite which was heated conventionally to a certain temperature. Local heating of gold NPs in PLGA matrix due to photothermal heating is followed by using fluorescence probe. Upon further heating with green laser, the nanocomposite is shown to exhibit shape memory property. The obtained nanocomposite with the both Fe3O4 and gold NPs can be triggered to exhibit shape memory by conventional heating and laser induction, as well as by the application of magnetic field which lend these particles for a wide range of biomedical applications.