Effects of fatigue on the chemical and mechanical degradation of model stent sub-units

Dreher, Maureen L.; Nagaraja, Srinidhi; Batchelor, Benjamin L.

doi:10.1016/j.jmbbm.2015.12.020

Cited by 20 publications

(18 citation statements)

References 18 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This could even be construed as negligible, as weight loss remained below 2% of the sample’s initial weight. These results agree with multiple studies, 21–24 where no significant weight changes were found for solid PLLA with in vitro degradation during a substantial portion of the time scale expected for full resorption of the device within the body.…”

Section: Resultssupporting

confidence: 91%

“…Basically, the amorphous regions are the first to succumb to attack by hydrolytic degradation, thereby increasing the sample crystallinity with degradation time. 23,24 Based on the continual increase in sample crystallinity over the two-year period, it can be said that degradation was in the mid-phase for these in vitro samples, as its decline in crystallinity would be expected after the peak when the shorter polymer chains start to move out of the sample. Overall, the results from DSC, GPC and weight loss analyses agree with one another.…”

Section: Resultsmentioning

confidence: 99%

“…As seen in Table 3, from the beginning to the end of the degradation period (2 years), the sample crystallinity increased by 25.9%, which corresponds to the bulk degradation mechanism for aliphatic polyesters such as PLLA. Basically, the amorphous regions are the first to succumb to attack by hydrolytic degradation, thereby increasing the sample crystallinity with degradation time [23,24]. Based on the continual increase in sample crystallinity over the 2-year period, it can be said that degradation was in the mid-phase for these in vitro samples, as its decline in crystallinity would be expected after the peak when the shorter polymer chains start to move out of the sample.…”

Section: Crystallinity Variationmentioning

confidence: 99%

See 2 more Smart Citations

Mechanical and chemical characterisation of bioresorbable polymeric stent over two-year in vitro degradation

et al. 2019

View full text Add to dashboard Cite

Polymeric stent is a temporary cardiovascular scaffold, made of biodegradable poly (l-lactic) acid, to treat coronary artery stenosis, with expected resorption by the human body over two to three years. In this paper, the mechanical properties of a polymeric stent over two-year in vitro degradation were studied and characterised using atomic force microscopy and nanoindentation techniques, complemented with analyses of weight loss, gel permeation chromatography and differential scanning calorimetry. Atomic force microscopy assessed stent degradation at the surface, whilst nanoindentation was able to investigate the property at a greater depth into the material. No significant changes to the Young's modulus were observed with the atomic force microscopy due to bulk degradation nature of the polymer. Chemical analyses demonstrated a reduction of molecular weight and an increase of crystallinity, indicating degradation of the stents.Berkovich nanoindentation showed a trend of reduction in modulus over in vitro degradation, which was, however, not continuous due to the variations of measurements associated with the pyramidal indenter tip and the semi-crystalline structure of the polymer.

show abstract

Section: Resultssupporting

confidence: 91%

Section: Resultsmentioning

confidence: 99%

Section: Crystallinity Variationmentioning

confidence: 99%

See 1 more Smart Citation

Mechanical and chemical characterisation of bioresorbable polymeric stent over two-year in vitro degradation

et al. 2019

View full text Add to dashboard Cite

show abstract

“…In addition, fatigue analyses presented in this study are in good agreement with the work of Li et al 19 , confirming the risk of strut U-bends to fatigue failure for both metallic and polymeric stents. For fatigue, Dreher et al 42 tested the fatigue life (up to 1.210 7 cycles) for a PLLA stent subunit (U-bend) subjected to displacement-controlled cyclic loading. The work confirmed the fatigue failure of U-bend unit, exhibiting a decreased life with increasing loading amplitude.…”

Section: Validationmentioning

confidence: 99%

A Computational Study of Mechanical Performance of Bioresorbable Polymeric Stents with Design Variations

Qiu

Zhao

Song

2018

Cardiovasc Eng Tech

View full text Add to dashboard Cite

The study compared the mechanical behavior of bioresorbable polymeric stents with various designs during deployment, and investigated their fatigue performance under pulsatile blood pressure loading. Methods: Finite element simulations have been carried out to compare the mechanical performance of four bioresorbable polymeric stents, i.e., Absorb, Elixir, Igaki-Tamai and RevaMedical, during deployment in diseased artery. Tri-folded balloon was modelled to expand the crimped stent onto the three-layered arterial wall with plaque. Cyclic diastolic-systolic pressure loading was applied to both stent and arterial wall to study fatigue behavior. Results: Stents with larger U-bend and longer axial strut demonstrate more flexibility but suffer from severe dogboning and recoiling effects. Stress concentrations in the stent, as well as in the plaque and artery, are higher for stents designed with increased rigidity such as 2 those with smaller U-bends and shorter axial struts. Simulations of fatigue deformation for Elixir stent demonstrate that the U-bends, with high stress concentrations, have a potential risk of fatigue failure under pulsatile systolic-diastolic blood pressure as opposed to the counter metallic stents which are normally free of fatigue failure. Conclusion: The structural behaviour of bioresorbable polymeric stent is strongly affected by its design, in terms of expansion, dogboing, recoiling and stress distribution during the deployment process.

show abstract

“…The study demonstrated the necessity to obtain baseline properties of a material and that the copolymeric blend in fact had lower mechanical properties and a higher, less stable degradation rate. The effect of fatigue on chemical and mechanical degradation of model stent sub units was analysed by Dreher et al (2016) since this factor can impact greatly on a stent's performance and was studied insufficiently. Subunits composed of PLLA were exposed to fatigue and degradation conditions simultaneously, amounting to one year of implantation within the body.…”

Section: Mechanical Performance Of Scaffolds With Degradationmentioning

confidence: 99%

Experimental and computational studies of poly-L-lactic acid for cardiovascular applications: recent progress

Naseem

Zhao

Liu

et al. 2017

Mech Adv Mater Mod Process

View full text Add to dashboard Cite

Stents are commonly used in medical procedures to alleviate the symptoms of coronary heart disease, a prevalent modern society disease. These structures are employed to maintain vessel patency and restore blood flow. Traditionally stents are made of metals such as stainless steel or cobalt chromium; however, these scaffolds have known disadvantages. An emergence of transient scaffolds is gaining popularity, with the structure engaged for a required period whilst healing of the diseased arterial wall occurs. Polymers dominate a medical device sector, with incorporation in sutures, scaffolds and screws. Thanks to their good mechanical and biological properties and their ability to degrade naturally. Polylactic acid is an extremely versatile polymer, with its properties easily tailored to applications. Its dominance in the stenting field increases continually, with the first polymer scaffold gaining FDA approval in 2016. Still some challenges with PLLA bioresorbable materials remain, especially with regard to understanding their mechanical response, assessment of its changes with degradation and comparison of their performance with that of metallic drug-eluting stent. Currently, there is still a lack of works on evaluating both the pre-degradation properties and degradation performance of these scaffolds. Additionally, there are no established material models incorporating non-linear viscoelastic behaviour of PLLA and its evolution with in-service degradation. Assessing these features through experimental analysis accompanied by analytical and numerical studies will provide powerful tools for design and optimisation of these structures endorsing their broader use in stenting. This overview assesses the recent studies investigating mechanical and computational performance of poly(l-lactic) acid and its use in stenting applications.

show abstract

Effects of fatigue on the chemical and mechanical degradation of model stent sub-units

Cited by 20 publications

References 18 publications

Mechanical and chemical characterisation of bioresorbable polymeric stent over two-year in vitro degradation

Mechanical and chemical characterisation of bioresorbable polymeric stent over two-year in vitro degradation

A Computational Study of Mechanical Performance of Bioresorbable Polymeric Stents with Design Variations

Experimental and computational studies of poly-L-lactic acid for cardiovascular applications: recent progress

Contact Info

Product

Resources

About