Biodegradable vascular stents with high tensile and compressive strength: a novel strategy for applying monofilaments via solid-state drawing and shaped-annealing processes

Biomater Sci. 2017 Feb 28;5(3):422-431. doi: 10.1039/c7bm00011a.

Abstract

Monofilaments such as those consisting of polyamide (PA), polydioxanone (PDS), and poly(vinylidene fluoride) (PVDF), have been commonly used in various industries. However, most are non-biodegradable, which is unfavorable for many biomedical applications. Although biodegradable polymers offer significant benefits, they are still limited by their weak mechanical properties, which is an obstacle for use as a biomaterial that requires high strength. To overcome the current limitations of biodegradable monofilaments, a novel solid-state drawing (SSD) process was designed to significantly improve the mechanical properties of both PA and poly(l-lactic acid) (PLLA) monofilaments in this study. Both PA and PLLA monofilaments exhibited more than two-fold increased tensile strength and a highly reduced thickness using SSD. In X-ray diffraction and scanning electron microscopy analyses, it was determined that SSD could not only promote the α-crystal phase, but also smoothen the surface of PLLA monofilaments. To apply SSD-monofilaments with superior properties to cardiovascular stents, a shaped-annealing (SA) process was designed as the follow-up process after SSD. Using this process, three types of vascular stents could be fabricated, composed of SSD-monofilaments: double-helix, single-spring and double-spring shaped stents. The annealing temperature was optimized at 80 °C to minimize the loss of mechanical and physical properties of SSD-monofilaments for secondary processing. All three types of vascular stents were tested according to ISO 25539-2. Consequently, it was confirmed that spring-shaped stents had good recovery rate values and a high compressive modulus. In conclusion, this study showed significantly improved mechanical properties of both tensile and compressive strength simultaneously and extended the potential for biomedical applications of monofilaments.

MeSH terms

  • Biocompatible Materials / adverse effects
  • Biocompatible Materials / chemistry*
  • Compressive Strength
  • Hemolysis
  • Human Umbilical Vein Endothelial Cells
  • Humans
  • Materials Testing
  • Nylons / adverse effects
  • Nylons / chemistry*
  • Polyesters / adverse effects
  • Polyesters / chemistry*
  • Prosthesis Design
  • Stents* / adverse effects
  • Tensile Strength

Substances

  • Biocompatible Materials
  • Nylons
  • Polyesters
  • poly(lactide)