Stent Crimping Research Articles

Modulating the Release Kinetics of Paclitaxel from Membrane-Covered Stents Using Different Loading Strategies

Membrane-covered Express2TM Monorail® stents composed of chitosan (CH) blended with polyethylene oxide (PEO) in 70:30% wt (CH-PEO) were coated with a monolayer of hyaluronic acid (HA). This significantly improved the resistance to platelet adhesion and demonstrated excellent mechanical properties, resisting the harsh conditions during stent crimping and subsequent inflation. CH-PEO/HA membrane was then combined with a paclitaxel (Pac) delivery system via three different approaches for comparison of release profiles of Pac. The activity of Pac in these systems was confirmed since its presence in the membrane significantly decreased cell viability of U937 macrophages. Presented results are promising for applications requiring different release patterns of hydrophobic drugs.

Mechanical stability of the diamond-like carbon film on nitinol vascular stents under cyclic loading

The mechanical stability of diamond-like carbon (DLC) films coated on nitinol vascular stents was investigated under cyclic loading condition by employing a stent crimping system. DLC films were coated on the vascular stent of a three dimensional structure by using a hybrid ion beam system with rotating jig. The cracking or delamination of the DLC coating occurred dominantly near the hinge connecting the V-shaped segments of the stent where the maximum strain was induced by a cyclic loading of contraction and extension. However the failures were significantly suppressed as the amorphous Si (a-Si) buffer layer thickness increased. Interfacial adhesion strength was estimated from the spalled crack size in the DLC coating for various values of the a-Si buffer layer thickness.

Hydroxyapatite-coated cardiovascular stents.

Description and history Extensive clinical practice supported with evidence gathered during numerous animal studies has shown that in addition to its excellent biocompatibility, hydroxyapatite (HAp, a crystalline derivative of calcium phosphate) is non-toxic and does not induce allergic or inflammatory reactions. The latest research on HAp appears to confirm that HAp crystals “do not acquire a pro-inflammatory or thrombogenic phenotype, but express markers of functioning endothelium that might contribute to angiogenesis.”1 The new generation of non-polymeric drug-eluting cardiovascular stents (as compared to polymer-coated stents) is expected to offer drug delivery solutions which will be less thrombogenic and more tolerable by the body environment (less restenotic) while, at the same time, capable of delivering the desired quantity of drugs in a manner that reflects recommendations of scientists, and responding to the reallife needs and abilities of the patient. These generic observations prompted MIV Therapeutics Inc. to consider HAp as a coating suitable for drug delivery on cardiovascular stents. Such HAp coated stents are being developed within the collaborative research and development program between University of British Columbia, and MIV Therapeutics Inc., both located in Vancouver, BC, Canada. The challenge is that the brittleness of ceramic HAp coating has to withstand deformation during stent crimping and implantation, and remain undamaged and biologically inert years after the implantation into arteries of human heart. In response to this challenge, several novel coating technologies have been developed in 20032005 for deposition of HAp ceramics on stents and other implantable medical devices, by combined efforts and ingenuity of the teams of MIV Therapeutics, Inc. and University of British Columbia. Technical specifications “Wet” chemical technologies were used for deposition of ultra-thin (0.1-0.2 μm) and micro-thin (0.3-1.0 μm) HAp coatings. The ultrathin films composed of high-density non-porous hydroxyapatite are designated primarily as a biocompatible surface modification of metallic implants, whereas the micro-thin films which possess highly porous structure were developed and evaluated also as a potential vehicle for effective and highly engineerable drug delivery. The deposition of the 0.1-0.2 μm ultra-thin films of HAp ceramics used sol-gel (SG) subjected to heat treatment at 450°C which ensured their structural integrity and necessary mechanical properties. The resulting SG-HAp Class “0” ultra-thin “passive” (drug-free) coatings are very well bonded to metal substrates such as stainless steel or Co-Cr alloys, feature acceptably smooth surface (Figure 1) and survive undamaged the stent crimping-implanting-expansion proce-

New stent delivery balloon: a technical note.

This study reports the first clinical application of a new noncompliant balloon composed of a middle polyurethane layer sandwiched between an inner layer of polyethylene terephtalate and an outer membrane that provides for consistent even expansion. With this balloon design, the very low compliance and high pressure resistance of polyethylene terephthalate are associated with the high elasticity of polyurethane, preventing balloon damage from stent crimping and expansion and allowing a firm embedding of the stent struts. Palmaz-Schatz stent implantation was successful in 33/35 stents (94%), and the two stents that could not be advanced up to the lesion were successfully withdrawn. High pressure expansion of the stent was obtained during deployment with no balloon ruptures at inflation pressures equal or lower than 16 atmospheres (atm). Accurate positioning of the stent was facilitated by the two markers at the balloon ends and by the optimal visualization after contrast injection, even with 6 Fr guiding catheters. This new delivery system maintains the advantages of hand-crimped stents on noncompliant balloons, reducing the risk of stent loss.