Microfabrication and nanotechnology in stent design

Abstract

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 to 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.

A Survey of Surface Modification Techniques for Next-Generation Shape Memory Polymer Stent Devices

“…These categories are surface roughening, surface patterning, chemical modification of the surface, surface coatings and films, attachment of pharmaceuticals or biopharmaceuticals to the surface, and the formation of porous surfaces to facilitate drug delivery, many of which are represented in Figure 1. Multiple techniques may be used to achieve the desired properties [1]. …”

“…This absorbable coating served to encourage endothelialization through a directed drug release profile and reduced inflammatory response during polymer degradation. While these improved DESs did decrease the occurrence of restenosis through release of anti-proliferative agents, late stage thrombosis still occurred [1,11,[15][16][17][18]. Late stage or late stent thrombosis (LST) can result from a variety of issues, ranging from the stenting procedure itself to early termination of antiproliferative drugs loaded in the stent; these issues may cause increased local fibrin deposition and delayed healing [15,16].…”

“…Despite the variety of materials and designs currently available for stents, there is still a need for a single material that has the desired mechanical properties while simultaneously achieving optimal biocompatibility [1,21]. Biocompatibility refers to the reaction elicited by a material when it is inserted into the body; ideally, this reaction should be favorable and should not provoke a negative response such as an attack by the immune system on the foreign material [27][28][29][30].…”

“…Since shape memory is not a surface property, surface modifications should enhance biocompatibility without interfering with the shape memory capabilities of SMPs. Surface modifications that allow for improved blood contact (minimal thrombogenicity) while encouraging vascular wall healing via endothelial cell migration, anchorage and proliferation, are the focus of research goals in this area [1,6,27,32,33]. In addition, surface modifications for drug release in an effort to eliminate the polymer coating are also being explored [1].…”

“…These diseases, collectively grouped under the term cardiovascular disease, are some of the main causes of death in the Western World as well as worldwide [1][2][3]. Atherosclerosis, or hardening of the arteries, occurs due to plaque formation and is often a result of inflammatory signals emitted by local cells and subsequent inflammatory response.…”