Fabrication and Testing of Planar Stent Mesh Designs Using Carbon-Infiltrated Carbon Nanotubes

Abstract

This paper explores and demonstrates the potential of using pyrolytic carbon as a material for coronary stents. Stents are commonly fabricated from metal, which has worse biocompatibilty than many polymers and ceramics. Pyrolytic carbon, a ceramic, is currently used in medical implant devices due to its preferable biocompatibility properties. Micropatterned pyrolytic carbon implants can be created by growing carbon nanotubes (CNTs), and then filling the space between with amorphous carbon via chemical vapor deposition (CVD). We prepared multiple samples of two different stent-like flexible mesh designs and smaller cubic structures out of carbon-infiltrated carbon nanotubes (CI-CNT). Tension loads were applied to expand the mesh samples and we recorded the forces at brittle failure. The cubic structures were used for separate compression tests. These data were then used in conjunction with a nonlinear finite element analysis (FEA) model of the stent geometry to determine Young's modulus and maximum fracture strain in tension and compression for each sample. Additionally, images were recorded of the mesh samples before, during, and at failure. These images were used to measure an overall percent elongation for each sample. The highest fracture strain observed was 1.4% and Young's modulus values confirmed that the material was similar to that used in previous carbon-infiltrated carbon nanotube work. The average percent elongation was 86% with a maximum of 145%. This exceeds a typical target of 66%. The material properties found from compression testing show less stiffness than the mesh samples; however, specimen evaluation reveals poorly infiltrated samples.

Using non-destructive testing to predict bending modulus of carbon infiltrated-carbon nanotubes

“…If the polyenes are the results of deformities or damage to the CNTs from oxidation as in the study by [17], then smaller polyenes would suggest less damage. The first explanation has some support from [5] who suggested that sp 2 sites in amorphous carbon prefer olefinic ordering. This is also supported by [10] who found that amorphous carbon is more likely to form polyene like structures as sp 2 sites increase.…”

“…The process to grow the CI-CNTs is based upon the process used by Jones et al [5]. The summary of the procedure is summarized in seven steps as follows and portrayed in figure 1.…”

“…Pyrolitic carbon and other similar carbon structures to CI-CNTs have been found biocompatible with animal cells. As a result CI-CNTs can be made as a stent that is more biocompatible then typical metals [5]. Micro-electro-mechanical-systems (MEMS) devices that actuate with much less input force than their silicon counter parts have also been demonstrated [6].…”

Curvature-induced defects on carbon-infiltrated carbon nanotube forests

“…CICNT in quartz tubes were manufactured using a process that has been reported previously for at, silicon substrates. 27,28 The tubes were cut roughly 2 inches long and then in half lengthwise (Fig. 2a) to expose the inside curvature to thin lm deposition processes.…”