Engineers will continue to improve designs with the goal of perfectly replicating nature. However, that might be too simple of a goal. It is entirely possible, and quite likely given enough time, that engineers will be able to create artificial limbs which offer functionality better than natural. Already there are assembly line robots favored over humans because their joints can rotate 360° and offer range of motion greater than the human body. It isn’t crazy to think that years in the future there would be a compelling reason to prefer a bionic limb, to a natural one.