Natural structural materials are capable to adapt their properties to external environmental loads. For example, bone is capable of self-stiffening by regulating the mineral quantity. It becomes stronger only in locations subjected to the highest mechanical loads. This process enables our skeleton to become sufficiently strong and to minimize the energy cost associated with walking by mass optimization.

The absence of engineering materials that self-adapt their properties (e.g. stiffness) to a specific loading environment is a limiting factor in some strategic fields, such as biomedical, defense and transportation. For example, in structural applications advanced materials are required to have sufficient load bearing capacity and minimum weight to reduce energy cost. In the biomedical field, implants and dental restorations are required to have matching mechanical properties with their counterpart to prevent debonding and consequent failure.

In my current research we found a mechanism to control mineral deposition (same as bone) onto a fiber-matrix in response to external loading. 

 

As presented in the figure, the stiffness of the composite was increased over time due to the continuous deposition of minerals and activated by cyclic loading.

 

Thus, the material becomes actively stronger in mechanically stressed areas. 

Comparing the SEM images, one can see the structure differences before and after cyclic loading. Minerals attach to the fibers resulting in the increase of mechanical properties.

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