Degree of bioresorbable vascular scaffold expansion modulates loss of essential function

An integrated mechanical degradation model to explore the mechanical response of a bioresorbable polymeric scaffold

Simulation of bioresorbable medical devices is hindered by the limitations of current material models. Useful simulations require that both the short- and long-term response must be considered; existing models are not physically-based and provide limited insight to guide performance improvements. This study presents an integrated degradation framework which couples a physically-based degradation model, which predicts changes in both crystallinity (Xc) and molecular weight (Mn), with the results of a micromechanical model, which predicts the effective properties of the semicrystalline polymer. This degradation framework is used to simulate the deployment of a bioresorbable PLLA (Poly (L-lactide) stent into a mock vessel and the subsequent mechanical response during degradation under different diffusion boundary conditions representing neointimal growth. A workflow is established in a commercial finite element code that couples both the immediate and long-term responses. Clinically relevant lumen loss is reported and used to compare different responses and the effect of neo-intimal tissue regrowth post-implantation on degradation and on the mechanical response is assessed. In addition, the effects of possible changes in Xc, which could occur during processing and stent deployment, are explored.

Investigation of 3D Printed Bioresorbable Vascular Scaffold Crimping Behavior

The rise in additive manufacturing (AM) offers myriad opportunities for 3D-printed polymeric vascular scaffolds, such as customization and on-the-spot manufacturing, in vivo biodegradation, incorporation of drugs to prevent restenosis, and visibility under X-ray. To maximize these benefits, informed scaffold design is critical. Polymeric bioresorbable vascular scaffolds (BVS) must undergo significant deformation prior to implantation in a diameter-reduction process known as crimping which enables minimally invasive surgery. Understanding the behavior of vascular scaffolds in this step provides twofold benefits: first, it ensures the BVS is able to accommodate stresses occurring during this process to prevent failure, and further, it provides information on the radial strength of the BVS, a key metric to understanding its post-implant performance in the artery. To capitalize on the fast manufacturing speed AM provides, a low time cost solution for understanding scaffold performance during this step is necessary. Through simulation of the BVS crimping process in ABAQUS using experimentally obtained bulk material properties, we have developed a qualitative analysis tool which is capable of accurately comparing relative performance trends of varying BVS designs during crimping in a fraction of the time of experimental testing, thereby assisting in the integration of informed design into the additive manufacturing process.

Development of finasteride/PHBV@polyvinyl alcohol/chitosan reservoir-type microspheres as a potential embolic agent: from in vitro evaluation to animal study

Benign prostatic hyperplasia (BPH) is a prevalent urological disease affecting elders. Currently, the prostatic artery embolization (PAE) is considered as a minimally invasive and safe technique to treat BPH. However, various drug-loaded embolic agents have not been thoroughly investigated in BPH therapy. In this study, finasteride/poly(3-hydroxybutyrate-3-hydroxyvalerate)@polyvinyl alcohol/chitosan (FNS/PHBV@PVA/CS) reservoir-type microspheres were prepared via the solid-in-water-in-oil (S/W/O) emulsion crosslinking method with the aim to reduce the burst effect and control localized drug delivery. The structure and properties of the drug and resultant microspheres were characterized via field emission scanning electron microscopy (FESEM), Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The results showed that the drug-loaded hybrid microspheres were well-dispersed and spherical with a mean diameter of 238.1 ± 27.3 μm. All samples exhibited excellent thermal stability. The FNS/PHBV microspheres were successfully encapsulated inside the PVA/CS polymeric matrix, which effectively suppressed the burst effect and prolonged the drug release up to 51 days. In vitro biocompatibility assessment indicated that the microspheres possessed excellent cytocompatibility and hemocompatibility. Furthermore, in vivo studies performed in the rabbit ear embolization model showed the formation of progressive ischemic necrosis after treatment for various periods. Histopathological studies revealed that the microspheres completely occluded the blood vessels with minimal foreign body response and formed the fibrotic area at the periphery of embolized arteries. Furthermore, the auricular vascular endothelial cells showed acute ultrastructural changes, associated with the ischemic necrosis induced by the embolization procedures. All these findings suggest that the FNS/PHBV@PVA/CS hybrid microspheres could be used as a promising drug delivery system for potential applications in BPH therapy.

Bioresorbable Vascular Scaffolds-Dead End or Still a Rough Diamond?

Percutaneous coronary interventions with stent-based restorations of vessel patency have become the gold standard in the treatment of acute coronary states. Bioresorbable vascular scaffolds (BVS) have been designed to combine the efficiency of drug-eluting stents (DES) at the time of implantation and the advantages of a lack of foreign body afterwards. Complete resolution of the scaffold was intended to enable the restoration of vasomotor function and reduce the risk of device thrombosis. While early reports demonstrated superiority of BVS over DES, larger-scale application and longer observation exposed major concerns about their use, including lower radial strength and higher risk of thrombosis resulting in higher rate of major adverse cardiac events. Further focus on procedural details and research on the second generation of BVS with novel properties did not allow to unequivocally challenge position of DES. Nevertheless, BVS still have a chance to present superiority in distinctive indications. This review presents an outlook on the available first and second generation BVS and a summary of results of clinical trials on their use. It discusses explanations for unfavorable outcomes, proposed enhancement techniques and a potential niche for the use of BVS.

Mechanical properties and degradation of drug eluted bioresorbable vascular scaffolds prepared by three-dimensional printing technology

Bioresorbable vascular scaffolds are expected to replace the traditional metal stent, avoiding the long-term complications of metal stents. However, it is hard for the traditional scaffold manufacturing process to meet the requirements of individualized treatment for vascular lesions, which requires different morphologies. Here, we used a new method of scaffold manufacturing, three-dimensional printing technology, to prepare bioresorbable vascular scaffolds. The fabricated scaffold was loaded with sirolimus mixed with scaffold preparation material for slow drug release. The engineered, drug- loaded, bioresorbable vascular scaffold (BVS) was analyzed and tested in vivo. The scaffolds produced by three-dimensional printing technology exhibited good mechanical properties and in vitro degradation performance. The results also suggested that these scaffolds could maintain effective radial strength after long-term degradation and sustained release of the drug. As a new scaffold preparation method, it may provide a promising idea for developing bioresorbable vascular scaffold technology.

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

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.

Visualizing polymeric bioresorbable scaffolds with three-dimensional image reconstruction using contrast-enhanced micro-computed tomography

There are no previous studies showing how to visualize polymeric bioresorbable scaffolds (BRSs) by micro-computed tomography (mCT). There are no previous studies showing how to visualize polymeric bioresorbable scaffolds (BRSs) by micro-computed tomography (mCT). This study aimed to explore the feasibility of detecting polymeric BRS with 3-dimensional reconstruction of BRS images by contrast-enhanced mCT and to determine the optimal imaging settings. BRSs, made of poly-L-lactic acid (PLLA), were implanted in coronary bifurcation models. Five treatments were conducted to examine an optimal condition for imaging BRSs: Baseline treatment, samples were filled with normal saline and scanned with mCT immediately; Treatment-1, -2, -3 and -4, samples were filled with contrast medium and scanned with mCT immediately and 1, 2 and 3 h thereafter, corresponding to soaking time of contrast medium of 0, 1, 2 and 3 h. Compared to Baseline, mCT scanning completely discriminate the scaffold struts from the vascular lumen immediately after filling the samples with contrast agent but not from the vascular wall until the contrast agent soaking time was more than 2 h (Treatment-3 and -4). By setting 10-15 HU as a cut-point of CT values, the scaffold strut detectable rate at Baseline and Teatment-1, -2, -3 and -4 were 1.23 ± 0.31%, 1.65 ± 0.26%, 58.14 ± 12.84%, 97.97 ± 1.43% and 98.90 ± 0.38%, respectively (Treatment-3 vs. Treatment-2, p < 0.01); meanwhile, the success rate of 3D BRS reconstruction with high quality images at Baseline and Teatment-1, -2, -3 and -4 were 1.23%, 1.65%, 58.14%, 97.97% and 98.90%, respectively (Treatment-3 vs. Treatment-2, p < 0.01). In conclusions, reconstruction of 3D BRS images is technically feasible by contrast-enhanced mCT and soaking time of contrast agent for more than 2 h is necessary for complete separation of scaffold struts from the surrounding structures in the phantom samples.

Bioresorbable vascular scaffolds - basic concepts and clinical outcome

The introduction of percutaneous treatment of coronary artery stenosis with balloon angioplasty was the first revolution in interventional cardiology; the advent of metallic coronary stents (bare and drug-eluting) marked the second and third revolutions. However, the latest generation of drug-eluting stents is limited by several factors. Permanent vessel caging impairs arterial physiology, and the incidence of very late stent thrombosis - although lower with the second generation than with the first generation of drug-eluting stents - remains a major concern. This complication is mainly related to the presence of permanent metallic implants, chronic degeneration triggered by an inflammatory response to the coating polymer, and/or adverse effects of antiproliferative drugs on endothelial regeneration. In 2011, self-degrading coronary stents - the bioresorbable vascular scaffolds (BVS) - were introduced into clinical practice, showing good short-term results owing to their adequate strength. The advantage of these devices is the transient nature of vascular scaffolding, which avoids permanent vessel caging. In this Review, we summarize the latest research on BVS, with a particular emphasis on the implantation technique (which is different from that used with metallic stents) to outline the concept that BVS deployment methods have a major effect on procedural success and prognosis of patients with coronary artery stenosis. Furthermore, the clinical outcome of BVS in randomized clinical trials and in phase IV studies are discussed in different pathophysiological settings, such as stable or acute coronary disease. Finally, all the available data on the safety profile of BVS regarding scaffold thrombosis are discussed.

The Systems Biocompatibility of Coronary Stenting

The coronary stent has propelled our understanding of the term "biocompatibility." Stents are expanded at sites of arterial blockage and mechanically reestablish blood flow. This simplicity belies the complex reactions that occur when a stent contacts living substrates. Biocompatible seek to elicit the intended response; stents should perform rather than merely exist. Because performance is assessed in the patient, stent biocompatibility is the multiscale examination of material and cell, and of material, structure, and device in the context of cell, tissue, and organism. This review tracks major biomaterial advances in coronary stent design and discusses biocompatibility clinical performance.