Novel Bioresorbable Stent Design and Fabrication: Congenital Heart Disease Applications

The design and development of bioresorbable stents tailored for treatment of pediatric patients with congenital heart disease is described. First, we examined the mechanical properties of thermally annealed PL-32 and PL-18 PLLA fibers using an Instron 5565 tensiometer. Stent designs ranging from 3 to 6 mm diameter and up to 15 mm length were examined. We adapted a winding jig to enable fabrication of coiled stents consisting of double-opposed helices. Double-opposed helical stents were thermally annealed for strength and flexibility. Following winding, stents were crimped on appropriately sized balloon catheters, and then expanded in a 37 °C water bath. Mechanical characteristics were measured as a function of stent size and design. PL-32 fiber has stronger mechanical properties with a 33% increase in stiffness. The opposing coil design improves stent expansion for larger stent designs. In addition, the stiffness of small diameter double-opposed helical stents was higher than values for the larger diameter stents hence having higher collapse pressure 1.07 ± 0.02 atm and the resistance to external pressure-induced collapse for larger diameter stents was lower decreasing to 0.63 ± 0.02 atm. The larger deformations at larger diameters were experienced since mechanical strain in the stent fibers is increased under these conditions. This led to increased twisting of the coils and higher striation angle measurements ranging from 17.5° to 26.7° from smaller to larger stents. The large diameter double opposed helix stents showed larger axial shortening of 3–3.5% and higher elastic recoil increase of 1.12%. The PL-32 stents also showed a slower degradation of 5% over 6 months. Modulating the number of coils within the double helical stent design and winding in opposing directions favorably affects stent mechanical properties.