Bioresorbable Scaffolds: A Complex Journey to the "Promised Land"

Drug loaded implantable devices to treat cardiovascular disease

INTRODUCTION

It is widely acknowledged that cardiovascular diseases (CVDs) continue to be the leading cause of death globally. Furthermore, CVDs are the leading cause of diminished quality of life for patients, frequently as a result of their progressive deterioration. Medical implants that release drugs into the body are active implants that do more than just provide mechanical support; they also have a therapeutic role. Primarily, this is achieved through the controlled release of active pharmaceutical ingredients (API) at the implementation site.

AREAS COVERED

In this review, the authors discuss drug-eluting stents, drug-eluting vascular grafts, and drug-eluting cardiac patches with the aim of providing a broad overview of the three most common types of cardiac implant.

EXPERT OPINION

Drug eluting implants are an ideal alternative to traditional drug delivery because they allow for accurate drug release, local drug delivery to the target tissue, and minimise the adverse side effects associated with systemic administration. Despite the fact that there are still challenges that need to be addressed, the ever-evolving new technologies are making the fabrication of drug eluting implants a rewarding therapeutic endeavour with the possibility for even greater advances.

A Biodegradable Metal-Polymer Composite Stent Safe and Effective on Physiological and Serum-Containing Biomimetic Conditions

The new-generation coronary stents are expected to be biodegradable, and then the biocompatibility along with biodegradation becomes more challenging. It is a critical issue to choose appropriate biomimetic conditions to evaluate biocompatibility. Compared with other candidates for biodegradable stents, iron-based materials are of high mechanical strength, yet have raised more concerns about biodegradability and biocompatibility. Herein, a metal-polymer composite strategy is applied to accelerate the degradation of iron-based stents in vitro and in a porcine model. Furthermore, it is found that serum, the main environment of vascular stents, ensured the safety of iron corrosion through its antioxidants. This work highlights the importance of serum, particularly albumin, for an in vitro condition mimicking blood-related physiological condition, when reactive oxygen species, inflammatory response, and neointimal hyperplasia are concerned. The resultant metal-polymer composite stent is implanted into a patient in clinical research via interventional treatment, and the follow-up confirms its safety, efficacy, and appropriate biodegradability.

In vivo degradation and endothelialization of an iron bioresorbable scaffold

Detection of in vivo biodegradation is critical for development of next-generation medical devices such as bioresorbable stents or scaffolds (BRSs). In particular, it is urgent to establish a nondestructive approach to examine in vivo degradation of a new-generation coronary stent for interventional treatment based on mammal experiments; otherwise it is not available to semi-quantitatively monitor biodegradation in any clinical trial. Herein, we put forward a semi-quantitative approach to measure degradation of a sirolimus-eluting iron bioresorbable scaffold (IBS) based on optical coherence tomography (OCT) images; this approach was confirmed to be consistent with the present weight-loss measurements, which is, however, a destructive approach. The IBS was fabricated by a metal-polymer composite technique with a polylactide coating on an iron stent. The efficacy as a coronary stent of this new bioresorbable scaffold was compared with that of a permanent metal stent with the name of trade mark Xience, which has been widely used in clinic. The endothelial coverage on IBS was found to be greater than on Xience after implantation in a rabbit model; and our well-designed ultrathin stent exhibited less individual variation. We further examined degradation of the IBSs in both minipig coronary artery and rabbit abdominal aorta models. The present result indicated much faster iron degradation of IBS in the rabbit model than in the porcine model. The semi-quantitative approach to detect biodegradation of IBS and the finding of the species difference might be stimulating for fundamental investigation of biodegradable implants and clinical translation of the next-generation coronary stents.

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A semi-quantitative OCT method was suggested to evaluate in vivo biodegradation of an iron based coronary stent IBS in a nondestructive manner.

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The in vivo biodegradation of IBS exhibited dependence on animal species.

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The endothelial coverage on the biodegradable stent IBS was better than on the commercialized nonbiodegradable stent Xience in rabbits.