Unlocking the secrets of bone, tooth and shell formation

Charles T. Troy, charlie.troy@laurin.com

Researchers at Eindhoven University of Technology (TU/e) have made high-resolution images of the earliest stages of bone formation using an advanced electron microscope to make three-dimensional images of the nanoparticles that are at the heart of the process. For industrial applications, this technology promises materials that are better and processes that are based on nature itself.

Led by Dr. Nico Sommerdijk, the researchers imaged clusters in a solution of calcium carbonate (the basic material of which shells are made) with a cross section of 0.7 nm. They showed for the first time that these clusters, each consisting of only about 10 ions, are the beginning of the growth process through which the crystalline biomineral is ultimately formed.

Shown is a three-dimensional electron microscopy image of the calcium carbonate crystals that grow to the organic surface. The flat part of the crystals is in contact with the organic layer. The width of the crystals is approximately 400 nm.

The team used a very high resolution electron microscope, the cryoTitan from FEI Co. of Hillsboro, Ore., USA, which enabled them to make three-dimensional images of rapidly frozen samples. The images showed how the clusters in the solution nucleate into larger, unstructured nanoparticles with an average diameter of around 30 nm.

An organic surface applied by the researchers ensured that these particles could grow into larger ones in which crystalline regions can later form by ordering of the ions. The researchers also demonstrated a second function of the organic layer: It controls with great precision the direction in which the mineral can grow into a fully fledged biomineral. They now hope to show that the mechanism they have identified also applies to the formation of other crystalline biominerals and perhaps even to some inorganic materials.

Understanding mineral formation is important for research into bone growth and bone replacement materials. In addition, it could be used in nanotechnology to control the growth of nanoparticles in the same way as seems to be the case in nature – through subtle interactions between organic and inorganic materials.

Biomineralization

Biomineralization is the formation of inorganic materials in a biological environment, as found in bones, teeth and shells. During the process, the growth of the mineral is controlled by specialized organic biomolecules such as sugars and proteins. Although the underlying mechanisms have been studied for some time, they still are not fully understood.

A strategy widely employed is the use of so-called biomimetic studies, which simulate and simplify the biomineralization process in a laboratory, allowing parts of the mineralization process to be studied individually.

With this approach and the microscope referred to above, members of Sommerdijk’s group from the chemical engineering and chemistry departments at TU/e have been able to image the earliest stages of such a biomimetically controlled mineralization reaction.