Shape memory properties of 3D-printed self-expandable poly(lactic acid) vascular stents with long-chain branched structures

The shape memory properties (SMP) of long-chain branched poly(lactic acid) (b-PLA) vascular stent prepared through 3D-printed technologies are studied by comparison with PLA. SMP is expected to endow vascular stent smart properties of self-expanding stent, which could self-expand and support the stenosis after reaching the lesion. The shape recovery rate of the b-PLA samples at 60 degrees C reaches to 93%, which is much higher than that of the PLA samples with 26%. The two-cycle deformation-recovery test of dynamic mechanical analysis (DMA) shows that the shape recovery rate of b-PLA samples at 60 degrees C reaches 98% in the first and second cycle, suggesting the good SMP. Meanwhile, the 3D-printed b-PLA vascular stent could recover to initial shape within 22 s, while the PLA vascular stent could not recover to initial shape after shape deformation at 60 degrees C. Furthermore, Two-dimensional wide-angle X-ray diffraction analysis (2D-WXRD) diffraction results confirm that both PLA and b-PLA samples exhibit two bright diffraction spots of (200)/(100) plane, and 2D-SAXS scattering patterns changed from uniform scattering rings to the spindle-shaped pattern after shape deformation. After shape recovery at 60 degrees C, the 2D-WXRD diffraction and two-dimensional small-angle X-ray scattering analysis (2D-SAXS) scattering patterns of the PLA samples remain no change, while b-PLA samples recover to initial patterns and exhibit diffuse diffraction rings and uniform scattering rings, respectively, long period (L-ac) decrease and lamellae thickness (L-c) maintain constant. The above results verify the excellent SMP of b-PLA vascular stent as well as self-expandable properties, which mainly ascribing to the combined action of branched entanglement points and lamellae as stationary phase. Besides, cell counting kit-8 (CCK-8) assays, cell live/dead staining and cell nuclei/cytoskeleton staining prove the good cell compatibility of b-PLA stent before and after SMP.