Enhancing UHMWPE Antibacterial Properties Through Ion Implantation

Abstract

We propose a new technique for the surface modification of biomedical polymers in order to strongly enhance its antimicrobial quality via ion implantation, in alternative to the well known ones that use chemical reactions or films deposition. We present the experimental results of implantation of ultra high molecular weight polyethylene (UHMWPE) samples by Ag, Cu and Ti ions. As accelerator we used “Platone”, a homemade laser ion source accelerator device. The ions were extracted from the plasma generated by a KrF excimer laser operating at 248 nm. A laser beam of 12 mJ/pulse was focused on a solid target mounted in a vacuum chamber in order to obtain plasma. The laser spot was estimated to be of 0.005 cm2. This device has an accelerating system composed by two different stages. Using pure Ag, Cu and Ti disks as laser targets and applying voltages of 40 kV to the first accelerating stage and 20 kV to the second one, we produced ion beams containing about 1011 ions/cm2 per pulse. The penetration depth of ions was estimated by the Srim code and the largest depth was achieved with Ti ions. Operating 22000 laser shots we implanted our samples with doses of about 1015 ions/cm2. Next we analyzed the effects of ion implantation on the bacterial adherence to UHMWPE samples. To test their antimicrobial quality, a Staphylococcus aureus strain isolated from a catheter-related bloodstream infection was used in these assays. The results demonstrate that the adherence of bacteria is reduced of 21%, 7% and 90% for Ag, Cu and Ti ions-implanted samples with respect to the control ones, confirming the effectiveness of our approach.