Performance Advantages of IonGuard® Ion Implantation Treatment for Titanium-based Orthopedic Implants

Titanium is generally recognized as one of the most biocompatible materials with many properties that make it ideal for bone and joint replacement applications, such as a low modulus of elasticity, excellent fatigue and tensile strength, and low weight/density.

Untreated titanium, however, has lower wear resistance compared to other metallic alloys such as CoCr 1,2 and should not be used untreated for loadbearing applications. For over 30 years titanium implants have been improved using IonGuard® ion implantation surface treatment to increase the hardness, lower friction, improve fretting resistance, and increase wettability of orthopedic implants.

In the IonGuard® process, the surface of the titanium implant is exposed to an energetic beam of nitrogen ions. The nitrogen ions penetrate the titanium substrate, changing the chemical structure, smoothing the surface profile and imparting compressive stresses at the surface. These changes result in a three-fold increase in surface hardness and up to a 97% reduction in metal particulate release.

The penetrating ions induce changes in the chemical structure of the surface by creating a hard titanium nitride phase which significantly increases surface hardness as well as enhances wear and fretting resistance. At the same time, the impinging ions dislodge the titanium atoms from their lattice sites, resulting in a highly homogenized surface structure.

Figure 1: Surfaces of Ti-6Al-4V, without ion implantation (left) and with ion implantation (right) show the two-phase transformation into a highly homogenized surface structure.

Figure 1 compares the etched microstructure of an untreated Ti-6AI-4V alloy surface to that of the sample treated with ion implantation. As shown, the ion implantation treatment results in a complete transformation of the two-phase alloy microstructure at the surface of the material. The result reduces friction and improves surface energetics and wettability.3

In addition, the ion implantation process imparts compressive stress to the surface of titanium. The induced compressive stress, coupled with a higher degree of surface homogeneity, is responsible for an increase in fatigue strength of the titanium material.4

The ion implantation process is a highly controlled, precise, and repeatable process used to fabricate semiconductors, photovoltaic cells and to treat orthopedic, cardiovascular, neurovascular and active implantable implants.

IonGuard® is a low temperature vacuum process suitable for metals and many medical polymers and silicones. The controlled penetration depth of the impinging ions and the low temperature improves surface properties with no deleterious effects on the bulk properties of the substrate material. Finally, the built-in quality control associated with the ion implantation technology provides a high degree of quality assurance, with nearly 100% yield for the processing of titanium alloy components.

The combined effects of increased hardness, lower friction, improved fretting resistance, and increased wettability translate to superior performance of IonGuard® treated implants.

Look for more information on improving hardness and wear resistance in our next article or download our white paper here.

N2 Biomedical’s proprietary Ion Implantation Surface Treatment and IBAD Nano-Engineered Coating technologies transforms the surfaces of titanium medical implants and devices to last longer, fight infection, improve biocompatibility and have durable aesthetics.

 

References

  1. Agins HJ, Albock NW, Bansal M, et al: Metallic wear in failed titanium-alloy total hip replacement. J Bone Joint Surg. 1988;70A:347.
  2. Lombardi AV Jr, Mallory TH, Vaughn BK, Drouillard P: Aseptic loosening in total hip arthroplasty secondary to osteolysis induced by wear debris from titanium-alloy modular femoral heads. J Bone Joint Surg. 1989;71A:1337-1342.
  3. Piran Sioshansi, “Ion Implantation improves wear resistance of titanium,” Orthopedics Today, 10(6) 24- 26, June 1990.
  4. I. C. Clarke, H. A. McKellop, P. McGuire, R. Okuda, and A. Sarmiento, “Wear of Ti-6Al-4V implant alloy and ultrahigh molecular weight poly-ethylene combinations,” in Titanium Alloys in Surgical Implants, ASTM STP 796, H. A. Luckey and Fred Kubli, Jr. (eds.), ASTM, Philadelphia, 1983, pp. 136-147.