In material selection for an implanted device, one needs to consider the effects

Question

In material selection for an implanted device, one needs to consider the effects of similarity and differences of mechanical properties between the device material and the surrounding tissue. In the case of a hip implant, let's consider using metal as the femoral stem and head. The figure below show perpendicular and parallel load configurations of metal and bone in contact with each other. Given that the table below (Table 1) of the material properties of bone and common metals used in a hip implant, answer the following questions. a. For the perpendicular load configuration, the metal and bone compartments will be subject to the same amount of load. What can you say about the amount of deformation in the two compartments? b. For the parallel load configuration, the metal and bone compartments will deform the same length. What can you say about the amount of stress in the two compartments? c. What may be the consequences of having dissimilar mechanical properties between bone and metal in load bearing?

Explanation / Answer

a. For perpendicular load configuration, both, bone and metal would have same load on them
   so, they will have different compression depending on their elastic properties, but the length change will be in the direction of the force and dimension changte in other directions will be different too depending on the poissons ratio of the two objects
b. For parallel configuration, both have same deformation, so same strain, and for differnt elastic modulus, different stress. SO both materials will be under different stress in parallel        configuration
c. In case 1, when there are different compressive strains in both objects, the net deformation for any biuo mechanical system would be a sum of these deformations and mus tbe taken care of
   In case 2 though, for same length change both materials are under different stress and it has to be taken care that none of them crosses the stress limit or else we could observe structural faliure

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