A few percent of transition metals impregnated inside some biological organisms in nature remarkably improve such organisms' mechanical stability. Although the lure to emulate them for development of new biomimetic structural materials has been great, the practical advances have been rare because of the lack of proper synthetic approaches. Multiple pulsed vapor phase infiltration proved successful for the preparation of such transition metal impregnated materials with highly improved mechanical stability. The artificially infiltrated metals (Al, Ti, or Zn) from gas phase lead to around 3 times increase of toughness (in terms of breaking energy) of natural collagen in a dried state. In addition, the infiltrated metals apparently induce considerable crystallographic changes in the natural collagen structures. This infiltration approach can be used as guide for the synthesis of bioinspired structural materials related to metal infiltration.