Long-term assessment of a novel biodegradable paclitaxel-eluting coronary polylactide stent

Efficacy and Safety of Absorb Everolimus-Eluting Bioresorbable Vascular Scaffold in Peripheral Artery Disease: A Single-Arm Meta-Analysis

PURPOSE

This study aimed to evaluate the benefits and risks of patients with peripheral artery disease (PAD) treated with Absorb everolimus-eluting bioresorbable vascular scaffold (BVS) by analyzing all the published studies on the clinical characteristics of patients with PAD.

MATERIALS AND METHODS

PubMed, Embase, and the Cochrane Library were searched for relevant studies. Efficacy, safety, and basic characteristics were analyzed.

RESULTS

Four studies were included in meta-analysis, including a total number of 155 patients with PAD. The pooled overall primary patency, freedom from target lesion revascularization (TLR), symptom resolution, and wound healing were 90%, 96%, 94%, and 86%, respectively. The pooled perioperative complication and all-cause mortality were 4% and 9%, respectively. Preoperative total occlusion was detected in 43 of 192 lesions (22%). The mean lesion length was 27.26 mm. In terms of comorbidities, the pooled percentage of hypertension, hyperlipidemia, diabetes mellitus, coronary artery disease, chronic kidney disease history, and smoking were 65%, 74%, 49%, 43%, 20%, and 57%, respectively.

CONCLUSION

Among these studies, hypertension, hyperlipidemia, and diabetes mellitus were the most common comorbidities in patients with PAD. The Absorb everolimus-eluting BVS was safe and showed the favorable clinical outcomes in both patency and TLR, especially in infrapopliteal disease with heavy calcification. The conclusions of this meta-analysis still needed to be verified by more relevant studies with more careful design, more rigorous execution, and larger sample size.

An exploratory research on antitumor effect of drug-eluting slow-releasing electrospinning membranes

Objective

To evaluate the long-term inhibition of malignant biliary tumor growth using paclitaxel (PTX)-covered polycaprolactone (PCL) electrospun membranes.

Methods

A mixture of PCL, a material used to fabricate polymer stents, and PTX, a widely used chemotherapeutic agent, was synthesized by electrospinning. After preparing the drug-eluting membrane, drug release and fiber degradation were assessed in vitro under different pH conditions. The QBC939 cholangiocarcinoma cell line was cultured to establish a xenograft nude mouse model. Finally, the drug-eluting membrane was implanted into the mouse model, and the relative tumor inhibition rate was evaluated.

Results

A new PTX-loaded PCL electrospun fiber membrane was developed. The drug release rate was about 20-40% in the 32-day release cycle, and the release quantity was between 20 and 170 mg. As pH decreased, the release rate increased significantly. The degradation rate of the fiber membranes in vitro was approximately 20-48%, and was positively correlated with the drug loading rate. In animal experiments, the growth of tumors in mice was suppressed using drug-eluting membranes.

Conclusion

The PTX-loaded PCL electrospun fiber membrane enhanced the long-term drug release and exhibited excellent antitumor effects in vivo.

Coronary artery aneurysm formation after paclitaxel-coated balloon-only intervention for de novo coronary chronic total occlusion

Background

Although coronary artery aneurysm (CAA) is an uncommon complication of drug-coated balloon (DCB) treatment, the incidence and mechanisms CAA formation after DCB intervention for chronic total occlusion (CTO) remains to be clarified. The aim of this study was to investigate the incidence of CAA after DCB intervention for the treatment of CTO of coronary arteries.

Materials and methods

This was a retrospective analysis of 82 patients, contributing 88 vessels, who underwent successful DCB-only treatment for de novo CTO lesions. Follow-up angiography was performed in all cases, at a mean 208.5 (interquartile range [IQR]: 174.8 to 337.5) days after the index procedure.

Results

CAA was identified in seven vessels, in seven patients, at the site of previous successful DCB-only treatment. Of these, six were fusiform in shape and one saccular, with a mean diameter of 4.2 ± 1.0 mm and length of 6.7 ± 2.6 mm. Six CAAs developed at the CTO inlet site, and all CAAs occurred at the lesions following dissection immediately after DCB treatment. CAAs were not associated with an increased risk of major clinical events over the median follow-up of 676.5 (IQR: 393.8 to 1,304.8) days.

Conclusion

The incidence of CAA after DCB-only treatment for CTO lesions was 8.0% in this study. Further research is warranted, using intravascular imaging, to clarify the mechanism of DCB-related CAA formation and prognosis.

Computational Pressure-Fluid Dynamics Applied to Index of Microcirculatory Resistance, Predicting the Prognosis of Drug-Coated Balloons Compared With Drug-Eluting Stents in STEMI Patients

Background: The impairment of microvascular injury on prognosis has increasingly drawn extensive awareness along with the high morbidity and mortality of ST-segment elevation myocardial infarction (STEMI) over recent years. The prognostic significance of computational pressure-fluid dynamics applied to index of microcirculatory resistance, derived from coronary angiography (CPFD-caIMR) in microvascular injury evaluation of STEMI patients remained inconclusive.

Methods: A total of 213 patients who met the inclusion criteria were selected retrospectively from 1003 STEMI patients from February 2018 to February 2020. Propensity score matching (PSM) was thereafter finished. CPFD-caIMR of all patients was obtained off-line using the software (FlashAngio, Rainmed Ltd., Suzhou, China) after PPCI. The primary endpoint was to compare the CPFD-caIMR and the incidence of major adverse cardiovascular events (MACEs) between drug-coated balloons (DCB) and drug-eluting stents (DES) groups. The correlation between CPFD-caIMR and MACEs was analyzed, and the prognosis of patients with STEMI was evaluated by CPFD-caIMR by multivariate regression analysis.

Results: Totally 213 STEMI patients with successful primary percutaneous coronary intervention (PPCI) were included, of whom 84 patients accepted DCB and 129 patients accepted DES respectively. Baseline characteristics and CPFD-caIMR were comparable between DCB and DES groups after PSM (62 patients in each group). CPFD-caIMR was not significantly different between two groups (DES vs. DCB: mean difference: 2.26, 95% CI -4.05 to 8.57, p = 0.45), and so was it when re-grouped by whether CPFD-caIMR > 40U or not (DES vs. DCB: 34.17% vs. 27.16%, p = 0.29). After a follow-up of 1 year, more MACEs occurred in DES group than DCB group (relative risk: 2.50, 95% CI 1.04 to 6.02, p = 0.04). The predictors of MACEs by multi-variate analysis found that, only time from symptom to balloon (p = 0.03) and time from door to balloon (p < 0.01) were independent predictors of MACEs, independent of treatment with DCB or DES intervention. Furthermore, CPFD-caIMR > 40U became an independent predictor of the combined events including cardiovascular deaths or heart failure readmission irrespective of PSM (odds ratio: 4.07, 95% CI: 1.06 to 7.66, p = 0.04).

Conclusion: CPFD-caIMR was a promising method for prognosis, which can predict CV death or heart failure readmission in STEMI patients. DCB was a possible strategy in PPCI of STEMI patients, not inferior to DES based on microvascular injury evaluated by CPFD-caIMR.

Influence of parameters on mechanical properties of poly (L-lactic acid) helical stents

With better biocompatibility, bioresorbable poly (L-lactic acid) (PLLA) helical stents are expected to replace the commonly used metallic stents. However, due to the great difference between the material properties of PLLA and those of metals, the current research results on mechanical properties of stents will not be applicative. In this article, the effects of i on the radial compression performance and bending stiffness of PLLA helical stents were systematically studied, and the effect of temperature on the radial compression performance of the helical stent was investigated. The findings obtained indicate that the reduction of initial pitch angle and initial diameter can enhance the radial compression performance. The reduction of initial pitch angle and the increase of initial diameter can weaken the bending stiffness of the helical stent. Moreover, the increase of temperature will reduce the radial stiffness and peak compression force of the helical stent. A favorable agreement between the theoretical and experimental results of radial compression properties was found in stents with the initial pitch angle between 14° and 21° and all initial diameters. This work can provide suggestions for the use of the theoretical formula in structure design of the helical stent.

Biodegradable phosphorylcholine copolymer for cardiovascular stent coating

Phosphorylcholine (PC) based polymer coatings with excellent biocompatibility have shown successful commercialization in drug-eluting stents. However, poor degradability represents a challenge in the application of biodegradable stents. Herein, a biodegradable phosphorylcholine copolymer is developed based on one-step radical ring-opening polymerization (RROP). This copolymer was synthesized by copolymerization of a PC unit, degradable ester (2-methylene-1,3-dioxepane, MDO) unit and non-degradable butyl methacrylate (BMA) unit, which showed ratio controllability by changing the monomer ratio during polymerization. We demonstrated that the copolymer with the ratio of 34% MDO, 19% MPC and 47% BMA could form a stable coating by ultrasonic spray, and showed good blood compatibility, anti-adhesion properties, biodegradability, and rapamycin eluting capacity. In vivo study revealed its promising application as a biodegradable stent coating. This work provides a facile path to add biodegradability into PC based polymers for further bio-applications.

On the Size Effect of Additives in Amorphous Shape Memory Polymers

Small additive molecules often enhance structural relaxation in polymers. We explore this effect in a thermoplastic shape memory polymer via molecular dynamics simulations. The additive-to-monomer size ratio is shown to play a key role here. While the effect of additive-concentration on the rate of shape recovery is found to be monotonic in the investigated range, a non-monotonic dependence on the size-ratio emerges at temperatures close to the glass transition. This work thus identifies the additives' size to be a qualitatively novel parameter for controlling the recovery process in polymer-based shape memory materials.

Intelligent H2S release coating for regulating vascular remodeling

Coronary atherosclerotic lesions exhibit a low-pH chronic inflammatory response. Due to insufficient drug release control, drug-eluting stent intervention can lead to delayed endothelialization, advanced thrombosis, and unprecise treatment. In this study, hyaluronic acid and chitosan were used to prepare pH-responsive self-assembling films. The hydrogen sulfide (H₂S) releasing aspirin derivative ACS14 was used as drug in the film. The film regulates the release of the drug adjusted to the microenvironment of the lesion, and the drug balances the vascular function by releasing the regulating gas H₂S, which comparably to NO promotes the self-healing capacity of blood vessels. Drug releasing profiles of the films at different pH, and other biological effects on blood vessels were evaluated through blood compatibility, cellular, and implantation experiments. This novel method of self-assembled films which H₂S in an amount, which is adjusted to the condition of the lesion provides a new concept for the treatment of cardiovascular diseases.

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PH-responsive self-assembling films were used to intelligently release the drugs at atherosclerotic lesions.

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As a gaseous signaling molecule, H₂S donor ACS14 was loaded into the films used in the field of cardiovascular disease treatment.

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H₂S can help to regulate vascular remodeling and balance the vascular function.

Numerical analysis of paclitaxel-eluting coronary stents: Mechanics and drug release properties

Since theoretical models provide data that cannot be otherwise gathered, numerical methods applied to medical devices analysis have emerged as fundamental tool in preclinical development. Large efforts were done to study mechanical and drug-eluting properties in stents but often the coating modelling is neglected. This work presents a finite element framework to calculate mechanical loads and drug distribution in three commercial drug-eluting stents (Palmaz-Schatz, Palmaz Genesis and Multi Link Vision), to check coatings strength and drug distribution maps in biological tissues. The promising copolymer poly(methylmethacrylate-co-n-butylmethacrylate), loaded with paclitaxel, is analyzed. Results demonstrated that the coating undergoes localized plastic phenomena, and calculated stresses are lower than the ultimate stress, ensuring coating integrity. Computed drug concentration depends on stent geometry and its values are in all cases lower than the toxicity level for this drug.

Apolipoprotein E deficient rats generated via zinc-finger nucleases exhibit pronounced in-stent restenosis

The long-term success of coronary stent implantation is limited by in-stent restenosis (ISR). In spite of a broad variety of animal models available, an ideal high-throughput model of ISR has been lacking. Apolipoprotein E (apoE) deficient rats enable the evaluation of human-sized coronary stents while at the same time providing an atherogenic phenotype. Whereas apoE deficient rats have been proposed as animal model of atherosclerosis, to date it is unknown whether they also develop pronounced ISR. We sought to assess ISR after abdominal aorta stent implantation in apoE deficient rats. A total of 42 rats (16 wildtype, 13 homozygous apoE^−/− and 13 heterozygous apoE^+/− rats) underwent abdominal aorta stent implantation. After 28 days blood samples were analyzed to characterize lipid profiles. ISR was assessed by histomorphometric means. Homozygous apoE^−/− rats exhibited significantly higher total cholesterol and low-density cholesterol levels than wildtype apoE^+/+ and heterozygous apoE^+/− rats. ISR was significantly pronounced in homozygous apoE^−/− rats as compared to wildtype apoE^+/+ (p = <0.0001) and heterozygous apoE^+/− rats (p = 0.0102) on western diet. Abdominal aorta stenting of apoE^−/− rats is a reliable model to investigate ISR after stent implantation and thus can be used for the evaluation of novel stent concepts. Apolipoprotein E (apoE) deficient rats have been proposed as animal model of atherosclerosis. We investigated the development of restenosis 28 days after stent implantation into the abdominal aorta of wildtype apoE^+/+, homozygous apoE^−/− and heterozygous apoE^+/− rats, respectively. Homozygous apoE^−/− rats exhibited significantly higher LDL and significantly lower HDL cholesterol levels compared to wildtype apoE^+/+ and heterozygous apoE^+/− rats. Restenosis after stent implantation was significantly pronounced in western-diet-fed homozygous apoE^−/− rats, accompanied by a significantly increased neointimal thickness. Thus, apoE knockout rats exhibit elevated restenosis and might provide a novel tool for testing of innovative stent concepts.

Comparison of endothelial cell attachment on surfaces of biodegradable polymer-coated magnesium alloys in a microfluidic environment

Polymeric coatings can provide temporary stability to bioresorbable metallic stents at the initial stage of deployment by alleviating rapid degradation and providing better interaction with surrounding vasculature. To understand this interfacing biocompatibility, this study explored the endothelial-cytocompatibility of polymer-coated magnesium (Mg) alloys under static and dynamic conditions compared to that of non-coated Mg alloy surfaces. Poly (carbonate urethane) urea (PCUU) and poly (lactic-co-glycolic acid) (PLGA) were coated on Mg alloys (WE43, AZ31, ZWEKL, ZWEKC) and 316L stainless steel (316L SS, control sample), which were embedded into a microfluidic device to simulate a vascular environment with dynamic flow. The results from attachment and viability tests showed that more cells were attached on the polymer-coated Mg alloys than on non-coated Mg alloys in both static and dynamic conditions. In particular, the attachment and viability on PCUU-coated surfaces were significantly higher than that of PLGA-coated surfaces of WE43 and ZWEKC in both static and dynamic conditions, and of AZ31 in dynamic conditions (P<0.05). The elementary distribution map showed that there were relatively higher Carbon weight percentages and lower Mg weight percentages on PCUU-coated alloys than PLGA-coated alloys. Various levels of pittings were observed underneath the polymer coatings, and the pittings were more severe on the surface of Mg alloys that corroded rapidly. Polymer coatings are recommended to be applied on Mg alloys with relatively low corrosion rates, or after pre-stabilizing the substrate. PCUU-coating has more selective potential to enhance the biocompatibility and mitigate the endothelium damage of Mg alloy stenting.

The development of bioresorbable composite polymeric implants with high mechanical strength

Implants for the treatment of tissue defects should mimic the mechanical properties of the native tissue of interest and should be resorbable as well as biocompatible. In this work, we developed a scaffold from variants of poly(glycolic) acid which were braided and coated with an elastomer of poly(glycolide-co-caprolactone) and crosslinked. The coating of the scaffold with the elastomer led to higher mechanical strength in terms of compression, expansion and elasticity compared to braids without the elastomer coating. These composite scaffolds were found to have expansion properties similar to metallic stents, utilizing materials which are typically much weaker than metal. We optimized the mechanical properties of the implant by tuning the elastomer branching structure, crosslink density, and molecular weight. The scaffolds were shown to be highly resorbable following implantation in a porcine femoral artery. Biocompatibility was studied in vivo in an ovine model by implanting the scaffolds into femoral arteries. The scaffolds were able to support an expanded open lumen over 12 months in vivo and also fully resorbed by 18 months in the ovine model.

Treatment of the femoropopliteal artery with the bioresorbable REMEDY stent

OBJECTIVE

Bioresorbable stents are an emerging technology in the endovascular treatment of femoropopliteal lesions. They address the issue of leaving permanent stents in the treated arterial segment that are only temporarily needed to treat dissection or recoil. The REMEDY stent (Kyoto Medical Planning Co, Kyoto, Japan) was the first commercially available biodegradable scaffold for peripheral use. We evaluated its performance and safety in the treatment of short femoropopliteal stenosis or occlusion.

METHODS

A prospective, multicenter, observational registry was set up of patients in Rutherford-Becker categories 2 to 5 with femoropopliteal lesions that could be treated with one REMEDY stent. Clinical examination and duplex ultrasound imaging were performed at 1, 6, and 12 months. The primary end point was absence of clinically driven target lesion revascularization at 12 months. Secondary end points were technical and clinical success, primary and secondary patency rate, clinically driven target vessel revascularization, major complications, and Rutherford-Becker classification at 6 and 12 months.

RESULTS

The registry enrolled 99 patients between January 2011 and July 2013 in 12 centers in Belgium. Most lesions were determined as TransAtlantic Inter-Society Consensus for the Management of Peripheral Arterial Disease (TASC II) A (n = 80) and located in the superficial femoral artery (n = 91). There were 19 total occlusions (mean length, 41.3 mm) and 80 stenoses (mean length, 37.5 mm). Technical success was achieved in 96 patients, and clinical success was obtained in 95. Target lesion revascularization, which equalled target vessel revascularization, was 19% at 6 months and rose to 33% at 12 months. Primary patency was 68% at 6 months and 58% at 12 months. Secondary patency was 85% at 6 months and 86% at 12 months. After 12 months, two patients had undergone an amputation.

CONCLUSIONS

The 1-year follow-up results of the REMEDY stent do not meet current standards set by nitinol stents. Given the significant issues concerning bioresorbable stents in femoropopliteal arteries, their use outside clinical trials should be withheld until improvements are made and better data are available.

Fractional flow reserve-guided coronary angioplasty using paclitaxel-coated balloons without stent implantation: feasibility, safety and 6-month results by angiography and optical coherence tomography

Background

Percutaneous coronary interventions (PCI) with drug-coated balloons (DCB) might be a promising trade-off between balloon angioplasty and drug-eluting stents, since DCB inhibit neointimal proliferation and limit duration of dual antiplatelet therapy. We investigated the safety, feasibility, and 6-month results of fractional flow reserve (FFR)-guided use of the paclitaxel-coated SeQuent Please^® balloon without stenting for elective PCI of de novo lesions.

Methods and results

In 46 patients (54 lesions) with stable symptomatic coronary artery disease (CAD), a FFR-guided POBA (plain old balloon angioplasty) was performed. In case of a sufficient POBA result with residual stenosis < 40 %, FFR > 0.8 and no severe dissection, the target lesion was finally dilated using the DCB. Quantitative coronary angiography (QCA) was performed before and after the index procedure and at 6-month follow-up (f/u) to calculate late lumen loss (LLL) and net luminal gain (NLG). Optical coherence tomography (OCT) was performed at f/u to assess vascular remodeling. DCB-only treatment was applied to 43 patients (51 lesions), while 3 patients (3 lesions) needed provisional stenting. Invasive f/u was completed in 39 patients (47 lesions). At the stenotic site, the lumen diameter showed a trend toward progressive increase at f/u (LLL: −0.13 ± 0.44 mm, n.s.; NLG: 1.10 ± 0.53 mm, p < 0.001) without aneurysm formation or restenosis after DCB-only treatment.

Conclusions

FFR-guided DCB-only PCI of de novo lesions appeared feasible and safe in stable CAD with clopidogrel discontinuation after 4 weeks, showing a trend toward positive vessel remodeling without lumen loss at 6 months.

Clinical trial registration http://www.clinicaltrials.gov. Unique identifier: NCT02120859

Electronic supplementary material

The online version of this article (doi:10.1007/s00392-016-1019-4) contains supplementary material, which is available to authorized users.

Biodegradable Metals for Cardiovascular Stents: from Clinical Concerns to Recent Zn-Alloys

Metallic stents are used to promote revascularization and maintain patency of plaqued or damaged arteries following balloon angioplasty. To mitigate the long-term side effects associated with corrosion-resistant stents (i.e., chronic inflammation and late stage thrombosis), a new generation of so-called "bioabsorbable" stents is currently being developed. The bioabsorbable coronary stents will corrode and be absorbed by the artery after completing their task as vascular scaffolding. Research spanning the last two decades has focused on biodegradable polymeric, iron-based, and magnesium-based stent materials. The inherent mechanical and surface properties of metals make them more attractive stent material candidates than their polymeric counterparts. A third class of metallic bioabsorbable materials that are based on zinc has been introduced in the last few years. This new zinc-based class of materials demonstrates the potential for an absorbable metallic stent with the mechanical and biodegradation characteristics required for optimal stent performance. This review compares bioabsorbable materials and summarizes progress towards bioabsorbable stents. It emphasizes the current understanding of physiological and biological benefits of zinc and its biocompatibility. Finally, the review provides an outlook on challenges in designing zinc-based stents of optimal mechanical properties and biodegradation rate.

Polymeric Biodegradable Stent Insertion in the Esophagus

Esophageal stent insertion has been used as a well-accepted and effective alternative to manage and improve the quality of life for patients diagnosed with esophageal diseases and disorders. Current stents are either permanent or temporary and are fabricated from either metal or plastic. The partially covered self-expanding metal stent (SEMS) has a firm anchoring effect and prevent stent migration, however, the hyperplastic tissue reaction cause stent restenosis and make it difficult to remove. A fully covered SEMS and self-expanding plastic stent (SEPS) reduced reactive hyperplasia but has a high migration rate. The main advantage that polymeric biodegradable stents (BDSs) have over metal or plastic stents is that removal is not require and reduce the need for repeated stent insertion. But the slightly lower radial force of BDS may be its main shortcoming and a post-implant problem. Thus, strengthening support of BDS is a content of the research in the future. BDSs are often temporarily effective in esophageal stricture to relieve dysphagia. In the future, it can be expect that biodegradable drug-eluting stents (DES) will be available to treat benign esophageal stricture, perforations or leaks with additional use as palliative modalities for treating malignant esophageal stricture, as the bridge to surgery or to maintain luminal patency during neoadjuvant chemoradiation.

The development of carotid stent material

Endovascular angioplasty with stenting is a promising option for treating carotid artery stenosis. There exist a rapidly increasing number of different stent types with different materials. The bare-metal stent is the most commonly used stent with acceptable results, but it leaves us with the problems of thrombosis and restenosis. The drug-eluting stent is a breakthrough as it has the ability to reduce the restenosis rate, but the problem of late thrombosis still has to be addressed. The biodegradable stent disappears after having served its function. However, restenosis and degradation rates remain to be studied. In this article, we review every stent material with its characteristics, clinical results and complications and point out the standards of an ideal carotid stent.

Progress in interventional cardiology: challenges for the future

Cardiovascular disease is the leading cause of death in the western and developing countries. Percutaneous transluminal coronary interventions have become the most prevalent treatment option for coronary artery disease; however, due to serious complications, such as stent thrombosis and in-stent restenosis (ISR), the efficacy and safety of the procedure remain important issues to address. Strategies to overcome these aspects are under extensive investigation. In this review, we summarise relevant milestones during the time to overcome these limitations of coronary stents, such as the development of polymer-free drug-eluting stents (DES) to avoid pro-inflammatory response due to the polymer coating or the developement of stents with cell-directing drugs to, simultaneously, improve re-endothelialisation and inhibit ISR amongst other techniques most recently developed, which have not fully entered the clinical stage. Also the novel concept of fully biodegradable DES featured by the lack of a permanent foreign body promises to be a beneficial and applicable tool to restore a natural vessel with maintained vasomotion and to enable optional subsequent surgical revascularisation.

A poly(lactide) stereocomplex structure with modified magnesium oxide and its effects in enhancing the mechanical properties and suppressing inflammation

Biodegradable polymers such as poly(L-lactide) (PLLA) have been widely utilized as materials for biomedical applications. However, the relatively poor mechanical properties of PLLA and its acid-induced cell inflammation brought about by the acidic byproducts during biodegradation pose severe problems. In this study, these drawbacks of PLLA are addressed using a stereocomplex structure, where oligo-D-lactide-grafted magnesium hydroxide (MgO-ODLA) is synthesized by grafting d-lactide onto the surface of magnesium hydroxide, which is then blended with a PLLA film. The structure, morphology, pH change, thermal and mechanical properties, in-vitro cytotoxicity, and inflammation effect of the MgO-ODLAs and their PLLA composites are evaluated through various analyses. The PLLA/MgO70-ODLA30 (0-20 wt%) composite with a stereocomplex structure shows a 20% increase in its tensile strength and an improvement in the modulus compared to its oligo-L-lactide (PLLA/MgO70-OLLA30) counterpart. The interfacial interaction parameter of PLLA/MgO70-ODLA30 (5.459) has superior properties to those of PLLA/MgO70-OLLA30 (4.013) and PLLA/Mg(OH)2 (1.774). The cell cytotoxicity and acid-induced inflammatory response are suppressed by the neutralizing effect of the MgO-ODLAs. In addition, the inflammatory problem caused by the rapid acidification of the stereocomplex structure is also addressed. As a result, the stereocomplex structure of the MgO-ODLA/PLLA composite can be used to overcome the problems associated with the biomedical applications of PLLA films.

The Effect of Static and Dynamic Loading on Degradation of PLLA Stent Fibers

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.

Finite element methods to analyze helical stent expansion

Helical polymeric stents have been proposed as a suitable geometry for biodegradable drug-eluting polymer-based stents. However, helical stents often experience nonuniform local expansion (dog boning), which can prohibit full stent expansion using conventional methods. The development of stents and deployment methods is challenging and can be supported by numerical analysis; however, this complex problem is often approached with simplified boundary conditions that may not be appropriate for helical stents. The finite element method (explicit and implicit) was used to investigate three common stent expansion approaches with a focus on helical stent geometry, which differs from traditional wire mesh stent expansion. Although each of the three methods considered provided some insight into the expansion characteristics, common displacement controlled, and uniform expansion methods were not able to demonstrate the characteristic local deformations observed in expansion. A coupled stent-balloon model, although computationally expensive, was able to demonstrate the expected nonuniform deformation. To address nonuniform expansion, a progressive expansion approach has been investigated and verified numerically. This method may also provide a suitable solution for nonuniform expansion in other stent designs by minimizing loading and potential damage to the artery that can occur during stent deployment.

New stent surface materials: the impact of polymer-dependent interactions of human endothelial cells, smooth muscle cells, and platelets

Despite the development of new coronary stent technologies, in-stent restenosis and stent thrombosis are still clinically relevant. Interactions of blood and tissue cells with the implanted material may represent an important cause of these side effects. We hypothesize material-dependent interaction of blood and tissue cells. The aim of this study is accordingly to investigate the impact of vascular endothelial cells, smooth muscle cells and platelets with various biodegradable polymers to identify a stent coating or platform material that demonstrates excellent endothelial-cell-supportive and non-thrombogenic properties. Human umbilical venous endothelial cells, human coronary arterial endothelial cells and human coronary arterial smooth muscle cells were cultivated on the surfaces of two established biostable polymers used for drug-eluting stents, namely poly(ethylene-co-vinylacetate) (PEVA) and poly(butyl methacrylate) (PBMA). We compared these polymers to new biodegradable polyesters poly(l-lactide) (PLLA), poly(3-hydroxybutyrate) (P(3HB)), poly(4-hydroxybutyrate) (P(4HB)) and a polymeric blend of PLLA/P(4HB) in a ratio of 78/22% (w/w). Biocompatibility tests were performed under static and dynamic conditions. Measurement of cell proliferation, viability, glycocalix width, eNOS and PECAM-1 mRNA expression revealed strong material dependency among the six polymer samples investigated. Only the polymeric blend of PLLA/P(4HB) achieved excellent endothelial markers of biocompatibility. Data show that PLLA and P(4HB) tend to a more thrombotic response, whereas the polymer blend is characterized by a lower thrombotic potential. These data demonstrate material-dependent endothelialization, smooth muscle cell growth and thrombogenicity. Although polymers such as PEVA and PBMA are already commonly used for vascular implants, they did not sufficiently meet the criteria for biocompatibility. The investigated biodegradable polymeric blend PLLA/P(4HB) evidently represents a promising material for vascular stents and stent coatings.

No indication for an unexpected high rate of coronary artery aneurysms after angioplasty with drug-coated balloons

AIMS

Coronary artery aneurysms (CAA) are a rare complication after percutaneous coronary intervention (PCI) and are reported with an incidence of 0.6% to 3.9%. While in recent years the use of paclitaxel drug-coated balloons (DCB) has increased, so far no CAA formation after DCB intervention has been reported.

METHODS AND RESULTS

During the years 2010 and 2011 we used DCBs in 704 PCIs. Follow-up angiography was scheduled at four months in all patients and has so far been achieved in 380 PCIs. In three patients we found development of a CAA at the former PCI site within four months of observation. Aneurysm length varied between 8.4 mm and 13 mm and lumina increased 58% to 131%. Retrospectively all patients with CAA development showed small intimal dissection partially with tiny persisting contrast bands parallel to the lumen according to type B and type C of the NHLBI classification after PCI.

CONCLUSIONS

CAA formation after DCB intervention was found in three out of 380 PCIs with DCB, consistent with an incidence of 0.8%. Thus, PCI with DCB does not cause an unexpectedly high rate of coronary artery aneurysms.

Development and characterization of a coronary polylactic acid stent prototype generated by selective laser melting

In-stent restenosis is still an important issue and stent thrombosis is an unresolved risk after coronary intervention. Biodegradable stents would provide initial scaffolding of the stenosed segment and disappear subsequently. The additive manufacturing technology Selective Laser Melting (SLM) enables rapid, parallel, and raw material saving generation of complex 3- dimensional structures with extensive geometric freedom and is currently in use in orthopedic or dental applications. Here, SLM process parameters were adapted for poly-L-lactid acid (PLLA) and PLLA-co-poly-ε-caprolactone (PCL) powders to generate degradable coronary stent prototypes. Biocompatibility of both polymers was evidenced by assessment of cell morphology and of metabolic and adhesive activity at direct and indirect contact with human coronary artery smooth muscle cells, umbilical vein endothelial cells, and endothelial progenitor cells. γ-sterilization was demonstrated to guarantee safety of SLM-processed parts. From PLLA and PCL, stent prototypes were successfully generated and post-processing by spray- and dip-coating proved to thoroughly smoothen stent surfaces. In conclusion, for the first time, biodegradable polymers and the SLM technique were combined for the manufacturing of customized biodegradable coronary artery stent prototypes. SLM is advocated for the development of biodegradable coronary PLLA and PCL stents, potentially optimized for future bifurcation applications.

Adjusting a polymer formulation for an optimal bioresorbable stent: a 6-month follow-up study

AIMS

To assess the impact of the composition in L- and D- of lactic acid stereo copolymers without drug elution on the in situ behaviour of prototype stents in terms of biomechanics and biocompatibility.

METHODS AND RESULTS

PLA50, 75, and 92 stereo-copolymer stents (L/D lactic acid ratio from 1 to 11.5) were processed using the injection moulding facilities of Arterial Remodeling Technologies (Noisy le Roi, France). The resulting 3 mm outer diameter tubes having a diameter at the desired nominal size were laser-cut and crimped on regular angioplasty balloons and chemically sterilised prior to implantation in iliac rabbit arteries. Acute recoil was higher in PLA50 and PLA75 stent-treated arteries than in those with PLA92 stents (17.4 ± 11.4 vs. 13.5 ± 7.6 vs. 4.1 ± 3.8 %, respectively, p=0.001). At one month, in-stent area was higher in PLA92 than in PLA50 and PLA75 stented arteries (5.9 ± 0.6 vs. 1.6 ± 1.6 vs. 2.6 ± 3.2 mm², respectively, p<0.001). Re-endothelialisation was complete, and inflammation was mild around the struts, similar among the three stents. Late lumen loss and neointimal area were low and similar in PLA92 stent-treated arteries one and six months after angioplasty (0.2 ± 0.2 vs. 0.3 ± 0.2 mm, p=0.60; 0.5 ± 0.5 vs. 0.5 ± 0.8 mm², p=0.72, respectively). At six months, inflammation decreased compared to one-month follow-up (1.4 ± 0.5 vs. 0.6 ± 0.5, p=0.006).

CONCLUSIONS

A stereo-copolymer composition strongly influences biomechanical properties of PLA bioresorbable stents in agreement with what has been known for a long time from other applications, but not biocompatibility. PLA92 stents appeared as presenting acceptable acute deployment and 6-month favourable outcome in the rabbit model despite the absence of drugs.

Introduction of a high-throughput double-stent animal model for the evaluation of biodegradable vascular stents

Current stent system efficacy for the treatment of coronary artery disease is hampered by in-stent restenosis (ISR) rates of up to 20% in certain high-risk settings and by the risk of stent thrombosis, which is characterized by a high mortality rate. In theory, biodegradable vascular devices exhibit crucial advantages. Most absorbable implant materials are based on poly-L-lactic acid (PLLA) owing to its mechanical properties; however, PLLA might induce an inflammatory reaction in the vessel wall. Evaluation of biodegradable implant efficacy includes a long-term examination of tissue response; therefore, a simple in vivo tool for thorough biocompatibility and biodegradation evaluation would facilitate future stent system development. Rats have been used for the study of in vivo degradation processes, and stent implantation into the abdominal aorta of rats is a proven model for stent evaluation. Here, we report the transformation of the porcine double-stent animal model into the high-throughput rat abdominal aorta model. As genetic manipulation of rats was introduced recently, this novel method presents a powerful tool for future in vivo biodegradable candidate stent biocompatibility and biodegradation characterization in a reliable simple model of coronary ISR.

Uniform Expansion of a Polymeric Helical Stent

Helical coil polymeric stents provide an alternative method of stenting compared to traditional metallic stents, but require additional investigation to understand deployment, expansion, and fixation. A bilayer helical coil stent consisting of PLLA and PLGA was investigated using the finite element model to evaluate performance by uniform expansion and subsequent recoiling. In vitro material characterization studies showed that a preinsertion water-soaking step to mimic body implantation conditions provided the required ductility level expansion. In this case, the mechanical contribution of the outer PLGA layer was negligible since it softened significantly under environmental conditions. The viscoelastic response was not considered in this study since the strain rate during expansion was relatively slow and the material response was primarily plastic. The numerical model was validated with available experimental expansion and recoiling data. A parametric study was then undertaken to investigate the effect of stent geometry and coefficient of friction at the stent-cylinder interface on the expansion and recoiling characteristics. The model showed that helical stents exhibit a uniform stress distribution after expansion, which is important for controlled degradation when using biodegradable materials. The results indicated that increasing stent width, pitch value, and coil thickness resulted in a larger diameter after recoiling, which would improve fixation in the artery. It was also noted that a helical stent should have more than five coils to be stable after recoiling. This work is part of a larger research study focused on the performance of a balloon-inflated polymeric helical stent for artery applications.

Novel fully bioabsorbable salicylate-based sirolimus-eluting stent

AIMS

The concept of fully biodegradable stents has emerged as an attractive alternative to current permanent metallic stents, mainly as a potential solution to avoid late stent thrombotic events. We sought to evaluate a novel, fully bioabsorbable sirolimus-eluting stent (SES) synthesised entirely from a unique salicylic-acid polymer, in a clinically relevant animal model.

METHODS AND RESULTS

Fully biodegradable balloon-expandable stents (n=45) were implanted in a porcine coronary arteries using quantitative coronary angiography (QCA) and intravascular ultrasound (IVUS) to optimise stent apposition. Dose density of sirolimus was 8.3 µg/mm of stent length with in vitro studies demonstrating elution over 30 days and complete stent degradation over 12 months. Animals were terminated at 7, 14, 30, 90, and 180 days for complete histological analysis. Optical coherence tomography (OCT) was also performed for the 90- and 180-days samples. All stents were deployed successfully without notable mechanical difficulties. Angiographic diameter stenosis (DS) was 20±16%, 24±4%, and 23±17%, at one, three, and six months, respectively. In parallel, IVUS showed good stent apposition with DS of 21±9%, 25±7%, and 18±3%; and area stenosis (AS) of 35±13%, 33±7%, and 32±4% at one, three, and six months,respectively. OCT further demonstrated good stent apposition with DS of 28±7% and 20±6%, and AS of 37±10% and 33±13% at three and six months, respectively. OCT showed reduction of stent thickness by 23% from three to six months. Histologic analysis confirmed these in vivo findings and revealed a favourable healing process of absorbable stent incorporation into the arterial wall, without excessive thrombotic or inflammatory reactions.

CONCLUSIONS

This study shows favourable vascular compatibility and efficacy for a novel fully bioabsorbable salicylate-based SES. This device has good mechanical performance during deployment and stays well-apposed to the vessel wall at long-term follow-up. These initial results are highly encouraging and support progress into more extensive preclinical studies as well as early clinical testing.

Magnesium used in bioabsorbable stents controls smooth muscle cell proliferation and stimulates endothelial cells in vitro

Magnesium-based bioabsorbable cardiovascular stents have been developed to overcome limitations of permanent metallic stents, such as late stent thrombosis. During stent degradation, endothelial and smooth muscle cells will be exposed to locally high magnesium concentrations with yet unknown physiological consequences. Here, we investigated the effects of elevated magnesium concentrations on human coronary artery endothelial and smooth muscle cell (HCAEC, HCASMC) growth and gene expression. In the course of 24 h after incubation with magnesium chloride solutions (1 or 10 mM) intracellular magnesium level in HCASMC raised from 0.55 ± 0.25 mM (1 mM) to 1.38 ± 0.95 mM (10 mM), while no increase was detected in HCAEC. Accordingly, a DNA microarray-based study identified 69 magnesium regulated transcripts in HCAEC, but 2172 magnesium regulated transcripts in HCASMC. Notably, a significant regulation of various growth factors and extracellular matrix components was observed. In contrast, viability and proliferation of HCAEC were increased at concentrations of up to 25 mM magnesium chloride, while in HCASMC viability and proliferation appeared to be unaffected. Taken together, our data indicate that magnesium halts smooth muscle cell proliferation and stimulates endothelial cell proliferation, which might translate into a beneficial effect in the setting of stent associated vascular injury.

Mechanical properties and in vivo performance of a novel sliding-lock bioabsorbable poly-p-dioxanone stent

A bioabsorbable poly-p-dioxanone (PPDO) stent with a novel sliding-lock structure was fabricated to treat stenotic peripheral vessels. The sliding-lock PPDO stents have greater radial strength (107 kPa) than PPDO stents with conventional net-tube structure (32 kPa). The sliding-lock PPDO stents were implanted into the iliac arteries of pigs, and implantation success rate was 90% indicating the feasibility of this design. Additionally, we found that sliding-lock PPDO stents kept vessels patent, although by 3 and 6 months post implantation, luminal diameter decreased slightly due to intimal hyperplasia. At 1 month post implantation, the stents were sparsely covered with endothelial cells, and by 6 months, the stents were mostly absorbed and inflammatory reaction gradually decreased as the stents were absorbed. This study shows favorable mechanical strength, degradability and efficacy for the sliding-lock PPDO stents, and supports further research and development of this unique design of polymer stents for applications in vascular devices.

Microfabrication and nanotechnology in stent design

Intravascular stents were first introduced in the 1980s as an adjunct to primary angioplasty for management of early complications, including arterial dissection, or treatment of an inadequate technical outcome due to early elastic recoil of the atherosclerotic lesion. Despite the beneficial effects of stenting, persistent high rates of restenosis motivated the design of drug-eluting stents for delivery of agents to limit the proliferative and other inflammatory responses within the vascular wall that contribute to the development of a restenotic lesion. These strategies have yielded a significant reduction in the incidence of restenosis, but challenges remain, including incomplete repair of the endothelium at the site of vascular wall injury that may be associated with a late risk of thrombosis. A failure of vessel wall healing has been attributed primarily to the use of polymeric stent coatings, but the effects of the eluted drug and other material properties or design features of the stent cannot be excluded. Improvements in stent microfabrication, as well as the introduction of alternative materials may help to address those limitations that inhibit stent performance. This review describes the application of novel microfabrication processes and the evolution of new nanotechnologies that hold significant promise in eliminating existing shortcomings of current stent platforms.