TOTAL HIP REPLACEMENT IS ONE OF THE MOST SUCCESSFUL ORTHOPEDIC OPERATIONS IN MODERN TIMES. OSTEOLYSIS OF THE FEMUR BONE RESULTS IN IMPLANT LOOSENING AND FAILURE DUE TO IMPROPER LOADING. TO REDUCE INDUCED STRESS, ENHANCE LOAD TRANSFER, AND MINIMIZE STRESS, THE USE OF TI-6AL-4V ALLOY IN BONE IMPLANTS WAS INVESTIGATED. THE OBJECTIVE OF THIS STUDY WAS TO PERFORM A THREE-DIMENSIONAL FINITE ELEMENT ANALYSIS (FEA) OF THE FEMORAL STEM TO OPTIMIZE ITS SHAPE AND ANALYZE THE DEVELOPED DEFORMATIONS AND STRESSES UNDER OPERATIONAL LOADS. IN ADDITION, THE CHALLENGES ASSOCIATED WITH THE MANUFACTURING OPTIMIZATION OF THE FEMORAL STEM USING LARGE STRAIN-BASED FINITE ELEMENT MODELING WERE ADDRESSED. THE NUMERICAL FINDINGS SHOWED THAT THE OPTIMIZED FEMORAL STEM USING TI-6AL-4V ALLOY UNDER THE NORMAL DAILY ACTIVITIES OF A PERSON PRESENTED A STRAINS DISTRIBUTION THAT PROMOTE UNIFORM LOAD TRANSFER FROM THE PROXIMAL TO THE DISTAL AREA, AND PROVIDED A MASS REDUCTION OF 26%. THE STRESS DISTRIBUTION WAS FOUND TO RANGE FROM 700 TO 0.2 MPA IN THE CRITICAL NECK AREA OF THE IMPLANT. THE DEVELOPED COMPUTATIONAL TOOL ALLOWS FOR IMPROVED CUSTOMIZED DESIGNS THAT LOWER THE RISK OF PROSTHESIS LOSS DUE TO STRESS SHIELDING.

IN THIS RESEARCH, A THREE-DIMENSIONAL AUXETIC CONFIGURATION BASED ON A KNOWN RE-ENTRANT CELL IS PROPOSED. THE 3D AUXETIC CELL IS CONFIGURED FROM A NEW DESIGN PARAMETER THAT PRODUCES AN INTERNAL ROTATION ANGLE TO ITS RE-ENTRANT ELEMENTS TO STUDY ELASTIC PROPERTIES IN ITS THREE ORTHOGONAL DIRECTIONS. THROUGH A TOPOLOGICAL ANALYSIS USING TIMOSHENKO BEAM THEORY, THE BENDING OF ITS RE-ENTRANT STRUTS IS MODELED AS A FUNCTION OF THE NEW DESIGN PARAMETER TO MANIPULATE POISSON?S RATIO AND YOUNG?S MODULUS. EXPERIMENTAL SAMPLES WERE FABRICATED USING A FUSED FILAMENT FABRICATION SYSTEM USING ABS AND SUBSEQUENTLY TESTED UNDER QUASI-STATIC COMPRESSION AND BENDING TESTS. ADDITIONALLY, AN ORTHOTROPY FACTOR IS APPLIED THAT ALLOWS FOR MEASURING THE DEVIATION BETWEEN THE MECHANICAL PROPERTIES OF EACH STRUCTURE. THE EXPERIMENTAL RESULTS VALIDATE THE THEORETICAL DESIGN AND SHOW THAT THIS NEW UNIT CELL CAN TRANSMIT AN ORTHOTROPIC MECHANICAL BEHAVIOR TO THE MACROSTRUCTURE. IN ADDITION, THE PROPOSED STRUCTURE CAN PROVIDE A DIFFERENT BENDING STIFFNESS BEHAVIOR IN UP TO THREE WORKING DIRECTIONS, WHICH ALLOWS THE APPLICATION UNDER DIFFERENT CONDITIONS OF EXTERNAL FORCES, SUCH AS A PROSTHETIC ANKLE.