Biodegradation

Problem Statement

Evaluate biodegradation of the PCL polymer in the stent format. The stent is designed with the goal that it will be replaced as it degrades and the patient ages and grows, requiring a new stent. The degradation profile in physiological conditions should be well understood to inform clinicians of when a new stent needs to be implanted.

We want to evaluate degradation profile over time and observe differences in surface treatment times.

PCL has long biodegradation times in-vivo (around 2-3 years), but according to the literature, it is possible to speed up the process by pre-treating the PCL with NaOH at a given time point. Potentially, the NaOH treatment allowed us to explore the possibility of greater control over the degradation of the stents.

Experimental Workflow

Immerse Stents in NaOH Solution

As an attempt to accelerate biodegradation time, stents were immersed in a 5M solution of NaOH. Various immersion times were considered: 30 min, 15min, and 5 min. A group of stents will remain untreated with NaOH. Each type of stent (baby and rabbit) will have 3 of each type of group totaling in 24 stents.

Immerse Stents in PBS

Test tubes were filled with PBS to simulate the in-vivo environment. Each stent from the 24, are placed into the test tubes filled with PBS and left alone in a fume hood in the Christman Lab.

Measure Mass over 20 weeks

Dry stents by patting them down with paper towels. After drying, mass and elasticity are measured at 4-week intervals for all 8 experimental groups. This is to be done for a 20-week time period.

Results

Baby Stents

Baby-sized stents and NaOH treatments at 0, 5, 15, and 30 minute time intervals. Negative slope magnitude trends with NaOH treatment duration. The stents that had no treatment of NaOH, or the 0 min. treatment, exhibited a slope of -0.006876. The stents that were treated with NaOH for 5, 15, and 30 minutes all have negative slopes with values of -0.09828, -0.1085, and -0.1779 respectively. At this rate, it is expected that the stents are losing about 1 mg of material every 10 weeks.

Rabbit Stents

Rabbit sized stents and NaOH treatments at 0, 5, 15, and 30 min time intervals. The rabbit sized stents did not show any general trends across all treatment times of NaOH. The 0 min NaOH treatment has a slope of 0.08386, 5 min NaOH treatment has a slope of -0.07186, 10 min NaOH treatment has a slope of 0.06342, and the 30 min NaOH treatment has a slope of -0.1224. While the rabbit sized stent with the 30 min NaOH exhibited a similar slope to the baby sized stent with 30 min NaOH treatment, it was not large enough to be deemed a statistically significant slope.

Baby Stents: 0 vs 30 min

Comparison of the 0 min and 30 minute NaOH treatment for the baby sized stent to highlight the statistical significance of the 30 minute treatment group in being non-zero. The stents treated with 30min NaOH have a significant non-zero slope (p = 0.0001)

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