Bioinspired Material Can “Shape-Shift” to External Forces

Inspired by how human bone and colorful coral reefs adjust mineral deposits in response to their surrounding environments, Johns Hopkins researchers have created a self-adapting material that can change its stiffness in response to the applied force.

According to the researchers, the development could lead to materials that can self-reinforce to prepare for increased force or to stop further damage in dental and other applications beyond healthcare.

“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,” said Sung Hoon Kang, PhD, an assistant professor in the Department of Mechanical Engineering, Hopkins Extreme Materials Institute, and Institute for NanoBioTechnology at the Johns Hopkins University and the study’s senior author.

Other researchers have tried to create similar synthetic materials, though it has been challenging because they are difficult and expensive to create. Or, they require active maintenance when they are created and are limited in how much stress they can bear. Materials with adaptable properties like wood and bone can provide safer structures, save money and resources, and reduce harmful environmental impact, the researchers said.

Natural materials can self-regulate by using resources in the surrounding environment. For example, the researchers said, bones use cell signals to control the addition or removal of minerals taken from blood around them. With these natural materials in mind, the researchers sought to create a materials system that could add minerals in response to applied stress.

The researchers began by using materials that can convert mechanical forces into electrical charges as scaffolds, or support structures, that can create charges proportional to external force placed on it. Their hope was that these charges could serve as signals for the materials to start mineralization from mineral ions in the environment.

Next, the researchers immersed polymer films of these minerals in a simulated body fluid mimicking ionic concentrations of human blood plasma. After the materials incubated in the simulated body fluid, minerals started forming on the surfaces. The researchers also discovered that they could control the types of minerals formed by controlling the fluid’s ion composition.

Then, the researchers set up a bean anchored on one end to gradually increase stress from one end of the materials to the other and found that regions with more stress had more mineral buildup. The mineral height was proportional to the square root of stress applied.

Their methods, the researchers said, are simple and low-cost, and they 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,” said Kang, who hopes that these materials can someday be used as scaffolds to accelerate treatment of bone-related disease or fracture, smart resins for dental treatments, or similar applications.

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