Computer-aided design of degradable Mg-based metallic glasses for safe medical implantation

As human life expectancy continues to lengthen, there will be an increased number of implants in human bodies. The growing biomaterials field can already produce artificial teeth and skin, cochlear implants, artificial corneas, coronary stents and artificial hips, among others. As our need for implants grows, there is a continuing drive to improve the materials from which they are made.

Magnesium-based metals and alloys are often used for orthopaedic implants, because they have similar mechanical properties to human bone, and they dissolve to components already present in the body. In the past, they have caused problems because they release hydrogen gas when placed in the body, which can be harmful and needs to be removed. Certain compositions of Mg-based metallic glass containing zinc and calcium, do not release hydrogen, and so, providing they retain the appropriate mechanical properties, they are much more suitable for use as biomedical implants than existing materials. The aim of this project is to use computer modelling to design and optimise these Mg-based metallic glasses for safe implantation into the human body.

Advances in computer simulation mean that it is now possible to investigate the structure of complex materials such as these ternary metallic glasses. The molecular dynamics (MD) simulations we will use will reveal the atomic structure and the nature of the chemical bonds which exist in the glass. In the glass compositions which do not release hydrogen, a passivating layer is known to form on the surface of the glass when it is implanted in the body, but only for certain compositions of the glass.

We will construct accurate models of the bulk and surface properties of these glasses, as well as those of related compositions. MD simulations will provide atomic-level resolution of the structure of the glass, and we will use this to identify the features which control the formation of the surface layer, and the release of hydrogen, and understand how these can be controlled. We will also model the interaction of the glass surface with the physiological environment, to gain a full understanding of the reactions which occur in the body. Through the simulation of a wide range of glass compositions, and full analysis of the compositional dependence of the surface layer, we will be able to deduce what reactions cause the formation of the passivating layer, and inhibit the release of hydrogen.

Once we understand the features which control the formation of the surface layer, we will optimise Mg-based metallic glasses for use in biomedical implantation, by computational design of suitable glass compositions which have the appropriate mechanical properties but also do not release hydrogen. This will lead to the design of improved and safe implants for biomedicine, especially in orthopaedic applications.

The ability to design and optimise metallic glasses for safe medical implantation will have impact in a variety of areas, from academics and industry to the general public. I anticipate specific impact as follows:

Orthopaedic implants are increasingly common as life expectancy increases. They offer a return to increased mobility for patients with bone diseases. Therefore, by designing and optimising a new and safer class of materials used for these implants, this project will lay the groundwork for substantial improvement in patients' quality of life. In particular, replacement or repair of an implant often carries significant health risks to the patient, not least because it is typically carried out at an advanced age. Development of this technology will help to mitigate this risk.

This project will also develop new scientific techniques and methodologies which will be relevant beyond the immediate scope of the project. Despite the exciting potential applications, not even the atomic structure of Mg-Zn-Ca glasses has been characterised, which we will do during this project. In addition to this study, this project will offer an advance in the study of metallic glass surfaces, which is not as well developed as the study of oxide glass surfaces. We will also make advances in the characterisation of interactions between the metal and the body, which will be relevant for future work in medical implants. Although widely applicable, the force-matching method for the development of accurate classical interatomic force fields is more widely used in oxide systems, and so its application to metallic glasses will represent a very useful advance as well.

Because this is a computational study performed on a relatively new class of materials, I do not envisage commercial exploitation during the lifetime of this project. However, there is the possibility that in the future, work building on this project will lead to the development of a commercially viable product, and I will be alert to opportunities to facilitate this during the project.

The development of technical expertise during the project will impact on scientists in a variety of fields, as well as benefit the PI's career development. The project will offer a new route to the development of materials for medical implantation, which is traditionally an experimental science. The development of these technologies, and in particular, the study of the implant-body interactions, could represent an entirely new way of developing such materials.