This illustration shows how increased force (arrow pointing down) applied on the material led to more electrical charges, and thus more mineralization. Image: Pam Li/Johns Hopkins University.
This illustration shows how increased force (arrow pointing down) applied on the material led to more electrical charges, and thus more mineralization. Image: Pam Li/Johns Hopkins University.

Inspired by how human bone and colorful coral reefs can adjust mineral deposits in response to their surrounding environments, researchers at Johns Hopkins University have created a self-adapting material that can change its stiffness in response to an applied force. This advancement could someday open the doors for materials that can self-reinforce to prepare for increased force or to stop further damage. The researchers report their findings in a paper in Advanced Materials.

"Imagine a bone implant or a bridge that can self-reinforce where a high force is applied without inspection and maintenance. It will allow safer implants and bridges with minimal complication, cost and downtime," says Sung Hoon Kang, an assistant professor in the Department of Mechanical Engineering, Hopkins Extreme Materials Institute and the Institute for NanoBioTechnology at Johns Hopkins University and the paper's senior author.

While other researchers have attempted to create similar synthetic materials before, this has proved challenging because such materials are difficult and expensive to create, or require active maintenance when they are created and are limited in how much stress they can bear. Having materials with adaptable properties, like those of wood and bone, can provide safer structures, save money and resources, and reduce harmful environmental impacts.

Natural materials can self-regulate by using resources in the surrounding environment; for example, bones use cell signals to control the addition or removal of minerals taken from the blood around them. Inspired by these natural materials, Kang and his colleagues sought to create a materials system that could add minerals in response to applied stress.

The team started off by using piezoelectric materials that can convert mechanical forces into electrical charges as scaffolds, or support structures. These scaffolds can create charges proportional to the external forces placed on them. The team's hope was that these charges could serve as signals for the materials to start mineralizing using mineral ions in the environment.

Kang and his colleagues immersed polymer films of these materials in a simulated body fluid that mimicked the ionic concentrations of human blood plasma. After these materials incubated in the simulated body fluid, minerals started to form on their surfaces. The team also discovered that they could control the types of minerals formed by controlling the fluid's ion composition.

The team then set up a beam anchored at one end to gradually increase the stress from one end of the material to the other, and found that regions with more stress had more mineral build-up; the mineral height was proportional to the square root of stress applied. Their methods, the researchers say, are simple, low-cost and don't require extra energy.

"Our findings can pave the way for a new class of self-regenerating materials that can self-reinforce damaged areas," says Kang. He hopes that these materials can someday be used as scaffolds to accelerate treatment of bone-related disease or fracture, smart resins for dental treatments and other similar applications.

Additionally, these findings can contribute to scientists' understanding of dynamic materials and how mineralization works, which could shed light on ideal environments needed for bone regeneration.

This story is adapted from material from Johns Hopkins University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.