Understanding how polymers such as PLLA degrade in vivo will enhance biodegradable stent design. This study examined the effect of static and dynamic loads on PLLA stent fibers in vitro. The stent fibers (generously provided by TissueGen, Inc.) were loaded axially with 0 N, 0.5 N, 1 N, or 0.125–0.25 N (dynamic group, 1 Hz) and degraded in PBS at 45 °C for an equivalent degradation time of 15 months. Degradation was quantified through changes in tensile mechanical properties. The mechanical behavior was characterized using the Knowles strain energy function and a degradation model. A nonsignificant increase in fiber stiffness was observed between 0 and 6 months followed by fiber softening thereafter. A marker of fiber softening, β, increased between 9 and 15 months in all groups. At 15 months, the β values in the dynamic group were significantly higher compared to the other groups. In addition, the model indicated that the degradation rate constant was smaller in the 1-N (0.257) and dynamic (0.283) groups compared to the 0.5-N (0.516) and 0-N (0.406) groups. While the shear modulus fluctuated throughout degradation, no significant differences were observed. Our results indicate that an increase in static load increased the degradation of mechanical properties and that the application of dynamic load further accelerated this degradation.
The Effect of Static and Dynamic Loading on Degradation of PLLA Stent Fibers
Manuscript received November 14, 2013; final manuscript received April 11, 2014; accepted manuscript posted May 8, 2014; published online June 3, 2014. Assoc. Editor: Sean S. Kohles.
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Hayman, D., Bergerson, C., Miller, S., Moreno, M., and Moore, J. E. (June 3, 2014). "The Effect of Static and Dynamic Loading on Degradation of PLLA Stent Fibers." ASME. J Biomech Eng. August 2014; 136(8): 081006. https://doi.org/10.1115/1.4027614
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