Composite Material Stent Comprising Metallic Wire and Polylactic Acid Fibers, and its Mechanical Strength and Retrievability
Abstract
Background: Although metallic stents are characterized by strong expanse of force, thin walls, and easy stent deployment, their removal from the body is usually difficult or impossible due to the difficulty of unraveling their mesh structure. A stent built of a composite material comprising a metallic wire and a polylactic acid (PLA) fiber, in which the metallic wire component could be unraveled after PLA fiber degradation in the body, should allow easy stent removal. Purpose: To evaluate the mechanical strength and retrievability of a composite material stent comprising a metallic wire and a PLA fiber. Material and Methods: We produced a composite material stent comprising a metallic wire and a biodegradable fiber (hybrid stent). As the metallic wire is not cross-linked with itself, but with the PLA fibers only, the hybrid stent can be easily unraveled after PLA fiber degradation. This stent was built with a 0.2-mm stainless-steel wire and a 0.23-mm PLA fiber knitted in the same textile as an Ultraflex stent. For comparison, an identical stent was built using PLA fiber only (PLA stent). The mechanical strength of these stents was tested by the radial expansive force response against circumferential shrinkage stress load. Change in radial force due to PLA fiber degradation was estimated by adding an artificial PLA degeneration process, by immersing each stent in a water bath at 80°C for 48 hours. Retrievability of the hybrid stent after PLA degeneration was examined by hooking and pulling out the residual stainless-steel wire from a silicon tube. Results: The hybrid stent exhibited a linear response in radial expansive force within the range of 15% diameter reduction. The PLA stent did not exhibit linear response at over 15% diameter reduction. Decrease of radial expansive force after PLA degradation was within 5% of the original force in the hybrid stent, but the PLA stent did not create effective radial expansive force. Hybrid stents, even after PLA degradation, exhibited a linear response in radial expansive force, within the range of 15% diameter reduction. The metallic component of the heat-processed hybrid stent was easily unraveled by pulling out the wire. Conclusion: The hybrid stent comprising a stainless-steel wire and a PLA fiber appears to provide effective radial expansive force and retrievability.