Shape memory materials and 4D printing in pharmaceutics.

Shape memory materials (SMMs), including alloys and polymers, can be programmed into a temporary configuration and then recover the original shape in which they were processed in response to a triggering external stimulus (e.g. change in temperature or pH, contact with water). For this behavior, SMMs are currently raising a lot of attention in the pharmaceutical field where they could bring about important innovations in the current treatments. 4D printing involves processing of SMMs by 3D printing, thus adding shape evolution over time to the already numerous customization possibilities of this new manufacturing technology. SMM-based drug delivery systems (DDSs) proposed in the scientific literature were here reviewed and classified according to the target pursued through the shape recovery process. Administration route, therapeutic goal, temporary and original shape, triggering stimulus, main innovation features and possible room for improvement of the DDSs were especially highlighted.