P-031 - A novel reinforcement method for the surface of gastrointestinal metal stent: gas plasma treatment

Date 04 July 2015
Event WorldGI 2015
Session Posters
Topics Palliative Care
Gastrointestinal Cancers
Surgery and/or Radiotherapy of Cancer
Presenter I.K. Yoo
Citation Annals of Oncology (2015) 26 (suppl_4): 1-100. 10.1093/annonc/mdv233
Authors I.K. Yoo1, H.S. Choi1, H.J. Chun1, J.M. Lee1, S.H. Kim1, E.S. Kim1, B. Keum1, Y.T. Jeen2, H.S. Lee1, C.D. Kim1
  • 1Korea University College of Medicine, Seoul/KR
  • 2Department of Internal Medicine, Seoul/KR

Abstract

Introduction

A gastrointestinal (GI) stent, which is made of Nickel-Titanium (NiTi) alloy coating with a silicone polymer, has been using for the relief of obstructive symptom in malignant stenosis of gastrointestinal tract. But the corrosion and fatigue failures of nitinol devices have been constant subjects of discussion. Recently, GI nitinol stent use is increasing abruptly, and fractures of GI stents have been reported. Although coating with the silicone polymer on the stent plays a key role in corroding, corrosion property may differ from along statues of surface of NiTi alloy wire. The surface modification with plasma etching technology is a way to improve the physical properties of the target. We systematically investigated a reinforcement of nitinol alloy and surface modification to stick the silicone employing gas plasma treatment.

Methods

The fifteen NiTi alloy stents were treated in a few conditions of the plasma treatment, in which vary mixture rates of Ar and O2 gas, applied voltages and duration of exposing time. We prepared three kinds of stents: normal stent (product by normal process, sample 1), slightly etched normal stent (product by plasma treatment, sample 2) and natural oxide layer-eliminated normal stent (product that removed natural oxide regions by plasma treatment, sample 3). The stents were analyzed with a transmission electron microscope (TEM) and scanning electron microscope (SEM) to examine surface topographies of the stents and the interlocking state between wire and silicone polymer. We performed a potentiodynamic test to compare corrosion state of each stent in GI state.

Results

The surface profile of the samples showed that some content of oxide layer for the normal stent was formed in thickness of about 100nm, while the others was 60 ∼ 70nm by TEM analysis. Moreover, the oxide layer for normal product and slightly etched normal stent was likely to exhibit deposition of oxygen without interlocking that enhances cohesion, whereas natural oxide layer-eliminated normal stent showed behavior of strong interlocking between oxide and nickel. SEM image showed effective modification of nitinol wire to stick the silicone polymer by plasma etching technology. In a potentiodynamic test, the sample 3 removed natural oxide regions by plasma treatment indicated the strongest corrosion resistance.

Conclusion

This result implies that an interlocking between nickel and oxide layer plays a significant role of corrosion resistance. Natural oxide layer by normal manufacture process induced micro-crack of nitinol GI stent and removing the natural oxide layer by plasma treatment improved reinforcement and surface modification of nitinol GI stent. These results revealed that the plasma treatment would be employed to improve the surface property of GI stent for malignant outlet obstruction.