Porous Nitinol for Load Bearing Implants Using Rapid Prototyping

Washington State University, Pullman WA

Investigators

Abstract

The research objective of this award is to apply Laser Engineered Net Shaping (LENS(TM)), a rapid prototyping based advanced manufacturing technology, to create porous structures of nitinol. The physical, mechanical and biological properties of nitinol structures of varying porosity will be measured. Use of porous materials in load bearing implants can reduce the stiffness mismatches due to porosity and solve long-standing problems like stress shielding. Designed porosity will also achieve stable long-term biological fixation due to bone-tissue in-growth into interconnected porosity from the surface to the inside. Nitinol is a shape memory alloy that shows up to 8 percent recoverable strain, similar to bone in which about 1 percent recoverable strain is observed. This similarity in the deformation behavior between Nitinol and bone contribute to identical performance of load bearing implants under loading-unloading conditions in the body ensuring excellent biomechanical compatibility. Nitinol is also a biocompatible material and currently in use in several biomedical devices. The approach is to use flexible LENS(TM) parameters to fabricate porous nitinol implants with designed macro and micro porous structures to achieve desired performance. Process-property relationships, for both mechanical and biological properties, for LENS(TM) fabricated nitinol will then be established. If successful, results from this program will offer design and manufacturing flexibility of simple and complex shaped implants with novel shape memory alloy, nitinol, that can match mechanical properties of bone. Novel porous implants can potentially double or triple the lifetime of load bearing implants. Being a computer-aided, design-based process, LENS(TM) can also be used to fabricate patient-specific implants from computed tomography and magnetic resonance imaging data. The project will also educate and train graduate and undergraduate students in mechanical engineering, materials science and engineering and bioengineering.