POTENTIAL APPLICATIONS & KEY BENEFITS OPTIMAL DESIGN OF A TRAPEZO-METACARPAL PROSTHETIC IMPLANT D.Farhat Service Génie Civil et Mécanique des Structures, Faculté Polytechnique, UMONS The development of new biomaterials for orthopedic applications is one of the challenging tasks for arthroplasties today. There is an obvious need for better implants as well as for the manufacturing of artificial tissues. Ideally, a bone implant should be such that it exhibits an identical response to loading as real bone and is also biocompatible with existing tissue. A stiff stem, which is usually made of titanium, shields the proximal bone from mechanical loading (stress shielding). On the other hand, decreasing the stem stiffness increases the proximal interface shear stress and the risk of proximal interface failure. Therefore the purpose of this study is to solve these conflicting requirements in order to have more uniform interface shear stress distribution and less stress shielding through the concept of functionally graded material (FGM). OBJECTIVE Investigating the causes of the damage and progressive pathologies after an arthroplasty of the trapezium-metacarpal articulation (in the basis of the thumb) and optimizing the design of the prosthetic implant.   B/ Second Approach (using a Functionally Graded Titanium young modulus) MATERIALS & METHODS Based on Dr.Ledoux’s prosthesis as a model in this study and by developing an evolutionary 3D finite element model with ABAQUS program taking into account « the stress shielding » phenomena, the bone reformation / lysis and based on the stimulus concept and the wolf’s law, the damage has been investigated as it is due to the high difference of stiffness between Titanium material of the implant and both of cortical and trabecular bones.   FIG 5. Mathematical Optimization of The Young Modulus Distribution CONCLUSION The interest of an intelligent material with a functionally graded young modulus is now established. The possibilities to create such a material are : Powder metallurgy by mixing titanium powder and less stiff inclusion before shaping the implant. EBM process (electron beam melting) of the Arcam company and now tested by SIRIS. These two techniques seem to be very attractive but need complementary studies of feasibility. Industrial partners specially small and medium size companies should be welcome. FIG 1. Dr. Ledoux’s Prosthesis FIG 2. Finite Element Mesh FIG 3. Bone Remodeling Law RESULTS It was shown that a significant improvement of the lifetime of the implanted metacarpal bone could be obtained with a special  implant made, along its length, of different slices of hypothetic homogenous titanium material with decreasing Young modulus. Of course, the study was a first approach and additional more advanced optimizations remain necessary to improve the actual results. A/ First Approach (Homogeneous Titanium Prosthesis) FIG 6. Electron Beam Melting Technology FIG 7. Siris Prosthesis Samples POTENTIAL APPLICATIONS & KEY BENEFITS The concept of “an intelligent biocompatible material” in the form of a graded titanium young modulus allowing adaptation of local stiffness at any point of the implant ,was brought to light in the context of studying the trapezo-metacarpal implant, but this concept can be extended to different types of prosthesis (hip prosthesis,…) in order to lengthen their lifetime.   FIG 4. Temporal Evolution of Bone Density