Effects of annealing temperature on both radial supporting performance and axial flexibility of poly(L‐lactic acid) braided stents

Abstract

In this paper, the effects of annealing temperature on both radial supporting performance and axial flexibility of poly(L‐lactic acid) (PLLA) braided stents are studied. Stents are annealed at a series of temperatures ranging from 80 to 160°C for 1 h, then indicators of shaping effect, radial supporting performance, and axial flexibility are compared. Stents not annealed and annealed at 80°C cannot be completely shaped. In contrast, stents annealed at 100 to 160°C are well shaped showing radial shrinkage rate of 1.0 ± 0.2% and almost no axial elongation. The radial compressive force and axial force are gradually increased by 51.2% and 89.2%, respectively with the annealing temperature gradually increasing from 80 to 160°C, indicating that the radial supporting performance is improved but axial flexibility is weakened by a higher annealing temperature. Taken together, PLLA braided stents can be annealed at 100 to 120°C to obtain sufficient radial force and lower axial force simultaneously for clinical applications. Moreover, tensile test, X‐ray diffraction, and differential scanning calorimetry are performed for monofilaments annealed at different temperatures to further explore the effect mechanism of annealing temperature on the mechanical properties of stents. This study may provide helpful suggestions for the manufacture of biodegradable braided stents.

A poly(l‐lactic acid) braided stent with high mechanical properties during in vitro degradation in bile

“…The bending stiffness (EI) is the product of the slope ( k ) of the linear fitting line of the bending force‐bending stiffness curve and a constant (L 3 /3) related to the cantilever beam length according to Equation (), and the axial force can be directly read from the bending force‐bending displacement curve. A higher bending stiffness or a higher axial force means a worse bending performance of PLLA braided stents 11 …”

“…A higher bending stiffness or a higher axial force means a worse bending performance of PLLA braided stents. 11 As shown in Figure 4(b), the bending stiffness and axial force of PLLA braided stents range from 3.05 to 3.66 N mm 2 and 53.93-65.33 mN, respectively during degradation, both of which are slightly increased. These results indicate that there is no risk of kinking or damaging the bile duct for PLLA braided stents during 270 days of degradation.…”

“…The bending performance of stents is measured using a homemade device based on the cantilever beam theory. 11 A stent is installed with one end fixed and the other end free. The cantilever beam length is 9.5 mm.…”

“…Moreover, BBS must have good bending performance to be adapted to the physiological motion of the bile duct. If not, BBS will be easily twisted even fractured, which may cause injuries to the bile duct 11 . Taken together, it is imperative to prepare BBS that can keep sufficient radial force and good bending performance during a longer‐term degradation in the bile duct.…”

A study of the radial and bending performance for poly (L‐lactic acid) braided stents with innovative runners

“…10 Recently developed bioresorbable braided stent (BBS) is believed to solve this problem since BBS can provide early support and then degrade completely, freeing the lumen from permanent foreign bodies and avoiding subsequent removal. 11 Therefore, BBS is expected to treat lumen stenosis in clinic. Meanwhile, bioabsorbable polymers with their appropriate absorption rate, biocompatibility and minimal inflammatory response have been extensively used in BBS prototypes.…”