Surface Modification of Bio-metals Based on Plasma Technologies

Surface modification plays an important role in improving the biocompatibility of biometals for clinical applications. Plasma-based techniques such as plasma immersion ion implantation have already been utilized to modify their biocompatibility in recent years. In this invited talk, our recent work on plasma surface modification related to titanium, nickeltitanium, and magnesium biomaterials is reviewed. Titanium and its alloys are suitable hard tissue replacements due to their excellent fatigue strength, good formability and superior corrosion resistance. However, they are generally bioinert because they cannot bond directly to bone tissues readily in the human body. OUf experiments indicate the biocompatibility of titanium alloys can be improved by calcium plasma immersion ion implantation. This treatment forms bioactive hydroxyapatite on the surface in the physiological environment.
NiTi shape memory alloys (SMA) have attracted the attention of the orthopedics community due to their potential applications to bone implants. However, release of nickel ions is one of the most common causes of allergic contact dermatitis. Oxygen plasma immersion ion implantation can be used to modify the surface of NiTi alloys. By forming titanium oxide on the surface, nickel ion leaching can be impeded successfully. We have further made the treated NiTi alloys into medical devices to automatically correct spinal problems such as scoliosis. It
has in fact gone into clinical trials with a number of patients having been implanted with the correction devices surgically. Magnesium-based materials are considered revolutionary metallic biomaterials due to their unique biodegradability and Young's modulus similar to that of human bones. Their proper use in securing bone fracture can obviate the need for a second surgery to remove the implant after the tissues have healed sufficiently. However, the degradation rate ofmagnesium alloys is normally too high in the initial healing stage. Surface alloying with AI (or Cr or Ti) is recommended prior to oxygen plasma ion implantation for magnesium alloys. After the dual surface treatment, degradation of magnesium alloys is effectively mitigated due to the formation ofAI (or Cr or Ti)-containing oxide on the surface.