4D printing is a technology that makes the 3D printed structure deformed by responding the environmental stimuli such as water, temperature or UV. Especially, 4D printing has been actively studied for applications in medical devices such as a stent or a scaffold, which can be deformed under body fluid conditions to the intended shape. Even though the 4D structures transform properly under temperature or water, one may wait for longer duration to achieve its final configuration, which is not desired in medical level application.
In this presentation, we introduce a multi-structured 4D stent with large deformation and faster response to the small temperature change. A multi-structure 3D printing scheme is presented by printing a raster line in curved or coiled configuration by using a fused deposition modeling (FDM) type 3D printer with a shape memory polymer (SMP). The printed configurations in several curved shapes such as wavy or coiling shape were achieved by setting two main parameters of the interval between the printer bed and the nozzle as well as the filament flow rate. As increased the interval from 0.2~0.3 mm to 1~2 mm and the flow speed of 3 times faster than the normal printing conditions, the extruded raster line patterns were changed from straight to wavy or coiled. Since the thermoplastic SMP has a viscoelastic property, the configuration of the printed patterns was formed by a liquid rope-coiling effect that is a phenomenon based on buckling instability of viscoelastic material. It was also found that by tuning the deformation temperature below or above the glassy temperature, Tg, of the SMP, the curved line was deformed 1.5 times more than the straight line with much faster recovery rate. By alternating stacking layers printed with the curved line pattern over the straight line pattern, we fabricated a 4D stent structure with larger and faster response to warm temperature of our body fluid. It is expected that this 4D stent can alleviate the problem of blood vessel scarring during the insertion of the stent.