The influence of thermal treatment on the mechanical characteristics of a PLLA coiled stent

Abstract

We studied the effects of thermal treatment on the expansive characteristics of a coil-within-coil Poly(L-lactic acid) (PLLA) fiber stent developed at our institution to improve its mechanical performance and reproducibility. Following fabrication, furled stents were thermally treated at 62 degrees C for 25 min. The mechanical characteristics were measured compared with those of untreated stents when both were expanded via sequential balloon catheter pressure loading up to 12 atm. Treated stents reached full diameter at 3 atm and maintained that diameter despite further pressure increases. Using measurements of pressure, diameter, and axial length, we calculated the sequential mechanical work required to unfurl the stent. The mechanical work for complete unfurling of treated stents was significantly less than that required for untreated controls. Little axial dimensional change was observed for treated stents. Treated stents exhibited higher stiffness than controls at all pressure levels and also demonstrated higher resistance to external pressure-induced collapse, as measured in a special apparatus developed in our laboratory. Differential scanning calorimetry measurements indicated higher crystallinity values for fibers used in treated stents compared with controls. SEM examination of striations revealed that treated stents underwent less twist than controls following balloon-induced unfurling. The results indicate that, thermal treatment improves the reorientation and realignment of fiber crystalline structure, and favorably influences on the fiber stress-strain behavior and the expansive mechanical characteristics of the PLLA fiber stents.

Magnesium used in bioabsorbable stents controls smooth muscle cell proliferation and stimulates endothelial cells in vitro

“…[9][10][11] A promising approach to overcome the limitations of first generation DES is the application of fully bioabsorbable stents, which could be completely replaced by tissue, and may even allow for a positive vascular remodeling. 12 Apart from biodegradable polymers, such as polylactides, [13][14][15][16][17][18] stents based on the corrodible metals iron 19 and magnesium 20 have been proposed. So far, the magnesium stent is the only bioabsorbable metal stent investigated clinically as a coronary stent (PROGRESS-AMS trial).…”

Drug loaded nanoparticle coating on totally bioresorbable PLLA stents to prevent in‐stent restenosis

“…Recently, drug‐eluting stents (DES) loaded with anti‐proliferative drugs, such as sirolimus or paclitaxel, have been used extensively in percutaneous coronary interventions for the prevention of restenosis . Clinical application indicated that DES is successful in dealing with the acute vascular occlusion after PTCA and the postoperative restenosis of BMS . But DES has its own issues: these permanently existed metal implants in vessels will limit the normal movement of blood vessels and cause inflammatory reaction of vascular wall, which in turn will lead to a sequence of immunological and biochemical reactions as well as arterial wall hyperplasia and in‐stent restenosis.…”

Paraffin processing of stented arteries using a postfixation dissolution of metallic and polymeric stents

“…PLLA was melt-extruded and drawn to a final diameter of 0.065 ± 0.01 mm [11]. The drawn fibers were then wound on a specially created jig to make the double opposed coiled stent.…”