Marc Yap -- Purdue Graduate Student
Titanium Powder Metallurgy for Spinal Implants
In the human spine there are 23 articulating vertebrae and 9 fused. When a disc requires repair the current practice is to encourage interbody fusion between the adjacent vertebrae. The design criteria for such repair is replacement of the damaged disc with new bone growth, and to restore the interspace.Early fusion methods called packing relocated bone between the vertebrae. Complications of this method included pain, collapse, and settling. This was followed by using rigid interbody spacers and posterior rods. These, however, frequently failed from fatigue loading. Next came the bone dowel (which was more rigid than the packed bone) and then the concept of the threaded diffusion cage (a porous metal dowel packed with bone).
The emphasis of this research is material development for a new surgical mesh (in a trapezoidal [wedge] shape) which will be an improvement on the threaded cage. The porous wedge holds position better than the dowel but is much more expensive and difficult to manufacture.
Titanium and specifically powder formed titanium alloys offer great potential for the trapezoidal surgical wedge because of their low elastic modulus, biocompatability, and ease of manufacturing to near net shape. A potential improvement to the technology is the development of a "dual density" wedge. This is easily accomplished by multiple sintering operations of the formed powder, and offers the advantage of a fairly dense and strong outer load bearing shell, with a much more porous inner ring. (The added inner porosity can be optimized for ingrowth of new living bone while providing high strength and a low modulus). At this time the demonstration has been restricted to simple geometric shapes, but the dual density titanium P/M technology should easily transfer to the more complex surgical wedge. This work is in need of sponsorship. If interested, please contact Dr. Matthew Krane, School of Materials Engineering, Purdue University.