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

Abstract

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.

Characterization and modelling the mechanical behaviour of poly(l-lactic acid) for the manufacture of bioresorbable vascular scaffolds by stretch blow moulding

“…These scaffolds have the potential to replace metal scaffolds (stents) since they have the advantage of supporting the artery for 6 months and of being completely resorbed into the body within 2 years, thus preventing late stent thrombosis and in stent restenosis [1,2]. Un-oriented PLLA in its natural format is typically a brittle material that does not have the desired mechanical properties to resist the forces experienced during crimping and deployment [3][4][5]. To further enhance its mechanical performance, a change of molecular orientation and crystallinity can be induced by performing biaxial stretching at temperatures above the glass transition temperature (T g ).…”

Effect of working environment and procedural strategies on mechanical performance of bioresorbable vascular scaffolds

“…Rigorous benchtop experiments are thus enforced to provide thorough mechanical characterizations on these devices [13–15]. In addition, the irregular and complex structural design of stents relies increasingly on finite element (FE) analysis drawing on material mechanical responses characterized from benchtop stress-strain tests [16–19]. Yet, the accuracy of FE analysis highly depends on benchtop mechanical characterization.…”

Drug-Eluting Stents and Balloons—Materials, Structure Designs, and Coating Techniques: A Review

“…Since it was recognized that nonbiodegradable polymers could initiate an inflammatory response contributing to in-stent restenosis (ISR), polymeric materials with increased biocompatibility and biodegradability were proposed for stent skeleton construction. These much safer stents with thinner struts are known as second-generation DES [ 41 ].…”

“…Besides, BRSs show a better capacity to restore natural vascular function and higher flexibility in comparison to metal backbones. All of these bright sides can represent a significant advance in interventional surgery for cardiovascular diseases [ 41 ].…”

“…Despite the predominance of polymers as a stent material, there are still uncertainties related to their use that require analysis: (1) understanding the mechanical behavior during and after implantation at the site of the injury and during its degradation and (2) comparing the efficacy of polymer-based and metal-based stents [ 41 ].…”