Magnesium ions injected directly into compromised bone accelerate bone regeneration

Bone-regenerating treatments are in high demand due to the ageing population. Increasingly, the orthopaedic biomaterials used to support these treatments are designed to be "immunomodulatory", i.e., guide the body's inflammatory response. They do this by encouraging macrophages - a type of white blood cell that surrounds and kills microorganisms - to adopt new roles based on signals and stimuli in their microenvironment. This approach has proved effective for developing new bone and for encouraging existing bone to accept artificial implants.

Magnesium is a mineral that not only helps to maintain normal nerve and muscle function, importantly, it also supports a healthy immune system and helps bones to retain their strength. Typically, it is given to orthopaedic patients as an oral supplement.

In a recent study published in the KeAi journal Bioactive Materials, a group of researchers from Hong Kong and mainland China, trialed a new immunomodulatory approach which replaces that magnesium supplement with an injection - directly into the compromised bone - of custom-made, polymer microspheres that control the release of magnesium ions.

According to one of the study's authors, Kelvin Yeung, Professor in Orthopaedics and Traumatology at the University of Hong Kong, the team tested the hypothesis by using two different animal models. "In one, we injected the microspheres containing the magnesium (Mg) ions. In the other, we injected microspheres without the Mg loading. In the two weeks following the injections, faster bone regeneration rates were observed in the first group."

Professor Young believes that one of the benefits of magnesium is that it encourages the immune system and skeletal system to work in tandem to support in situ healing.

He explains: "The biomaterial development for bone repair usually involves the direct activation of osteoprogenitor cells - stem cells located in the bone that play a key role in bone repair and growth. However, the "conversation" that takes place between the skeletal and immune systems during the bone healing process has often been overlooked."

Professor Yeung points to the fact that the healthy functioning of immune cells significantly impacts bone regeneration and remodelling. "In this study, we have drawn on the properties of biomaterials that can tailor the plasticity of macrophages. For instance, our custom-made, magnesium-loaded microspheres created a favourable, anti-inflammatory, osteoimmune environment."

He adds: "Bioactive metal ions working as minerals has huge potential in bone or other musculoskeletal tissue regenerations. We hope our results can convince scientists to explore the potentials of these ions beyond bone healing."