Pulsed water jet treatments of the surfaces of metal alloys for biomedical applications

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Each year, over 100,000 Canadians require knee or hip replacement. Current technology uses a titanium alloy to attach the implant to the bone, but problems arise at the interface that could be solved with pulsed water jet (PWJ) technology developed at VLN Advanced Technologies Inc. The surface of the alloy is typically roughened by grit blasting with aluminum oxide particles to promote cell growth on the device. However, the particles get imbedded into the titanium surface. Once inside the patient, the particles can become dislodged and lead to cell death in the surrounding tissue and the loosening of the implant, the leading cause for revision surgery. In contrast, pulsed water jets use ultrasound to break a continuous water stream into a series of high speed pulses that create mechanical erosion by cyclic loading of the target without embedding any foreign material. Together with VLN, we will develop a cost effective way of using PWJs to eliminate the need for grit blasting and create a better biocompatible surface. For good adhesion of a titanium implant in bone, the medical implant needs to have surface features with sizes that span the micron scale down to the nano-scale in order to mimic the surrounding biological textures. Metallurgical alloys that naturally phase separate into two components create patterns in their grain structure with multi-length scale features that can imitate those of biological systems. Surgical titanium alloy separates in to a stronger and weaker component. We will design the techniques to mechanically etch away the weaker component with pulsed water jets and leave behind a rough surface with features on the micron- and nano-length scales. The physical structure, chemistry and mechanical properties of the treated surfaces will be characterized with a suite of tools at Dalhousie University to identify the optimal PWJ parameters. Finally we will explore the possibility of engineering the surface morphology by modifying the grain structure in titanium alloys currently being developed at Dalhousie.