NiTi Surface Modification for enhanced Biocompatibility

Stent2

Actual results by R.M.S. Martins (Instituto Tecnológico e Nuclear (ITN), Portugal) and supported by the EU-“Research Infrastructures Transnational Access” program AIM “Center for Application of Ion Beams in Materials Research” under EC contract no. 025646

PBII was used to modify and improve the surface of a NiTi alloy (» 50.2 at.% Ni) which is interesting for biomedical applications like vascular stents, vena cava filters or osteosynthetic devices. A high concentration of Ni at the surface can be the reason for allergic hazard, toxicity or carcinogenicity. The main goal has been the formation of a Ni-depleted surface, which should serve as a barrier to out-diffusion of Ni ions from the bulk material.

Ion implantation of oxygen or nitrogen was carried out.

The depth profiles of the elemental distribution in the alloy surface region, obtained by Auger electron spectroscopy (AES), confirm the formation a Ni-depleted layer.

 

 

 

 

 

Objective

  • Formation of Ni depleted surface layer
  • Creation of a barrier against the Ni release from NiTi
  • No change of bulk properties

 

Experimental setup

  • Implantation of oxygen or nitrogen
  • High voltage pulses of either 20 or 40 kV with a pulse frequency of 400Hz and a pulse length of 5µs
  • RF power 350 W
  • Pressure 0.2 Pa

 

a)REM-NiTi-O-20kV

b)REM-NiTi-O-40kV

SEM image of PBII-processed surface using O_20kV_194min (a), O_40kV_25min (b)

to a)O-NiTi-20kV-194

to b)O-NiTi-40kV-25

The depth profiles of the elemental distribution in the alloy surface region, obtained by Auger electron spectroscopy (AES), confirm the formation of a Ti-rich oxide layer.

c)REM-NiTi-N-20kV

d)REM-NiTi-N-40kV

SEM image of PBII-processed surface using N_20kV_180min (c), N_40kV_60min (d)

to c)N-NiTi-20kV-180

to d)N-NiTi-40kV-60

The AES depth profiles clearly show a Ni-depleted fraction for experiments performed with N_40 keV.

Projects:

"Nitinol" (Industry)

Publications:

1. Yankov, R. A.; Shevchenko, N.; Rogozin, A.; Maitz, M. F.; Richter, E.; Möller, W.; Donchev, A.; Schütze, M. Reactive plasma immersion ion implantation for surface passivation, Surface & Coatings Technology 201(2007), 6752-6758
2. Maitz M.F. and Shevchenko N. Plasma-immersion ion-implanted nitinol surface with depressed nickel concentration for implants in blood, Journal of Biomedical Materials Research Part A 76A (2) (2006) 356 – 365
3. Shevchenko, N., Pham, M. T., Maitz, M. F. Studies of surface modified NiTi alloy, Applied Surface Science 235 (2004) 126-131

Patents:

 Shevchenko, N.; Maitz, M.; Pham, M. T.
Verfahren zur Herstellung einer nickelarmen Oberfläche auf Nitinol.
Patent: DE 103 25 410 A1 (2004)
Patent: WO 2004/108983 A2