Hydrogels made from 2D materials could replace traditional inorganic (ceramic) scaffolds in tissue engineering applications. Indeed, synthetic clays made from these materials have already been employed in many advanced technological applications, such as hydrogel nanocomposites with self-healing properties, injectable haemostatic biomaterials and bioactive materials for bone tissue engineering. However, the problem is that many of these materials are not completely biocompatible.

Magnesium is the fourth most common metal in the human body and is important for metabolizing minerals. It promotes calcification and the formation of hydroxyapatite crystals, and increases adhesion between bone cells and how they proliferate and differentiate. Not surprisingly, half of the body’s magnesium is stored in bone.

Magnesium phosphates are biocompatible

Magnesium phosphates, for their part, are biocompatible and resorbable in vivo, and thus interesting for biomedical applications. However, until now, there was no biomaterial made from magnesium phosphate that could be injected into the body.

Researchers at McGill University in Canada, Massachusetts General Hospital and Harvard Medial School have now developed a new nanocrystalline material by tuning the crystallization of a sodium-magnesium-phosphate system (Mg-Na-(HPO4)-(PO4). Sodium ions can control how magnesium phosphate precipitates by interacting with the crystal’s surface, which leads to crystal growth in a certain direction and thus a 2D morphology.

Biocompatible and thixotropic

The researchers found that their material has several interesting and unique biological properties. It is not only biocompatible with human fibroblasts but it also accelerates bone healing because it enhances the formation of collagen. What is more, in vitro experiments, it appears to “up-regulate” the mRNA expression of several genes involved in osteogenesis (bone formation). These include runt related transcription factor 2 (RunX2) and alkaline phosphatase (ALP), and also the genes responsible for the formation of the extracellular matrix such as osteocalcin (OCN), osteopontin (OPN) and collagen type I alpha1 (COL1A1).

The material is extremely thixotropic too, which means that it can be injected through high gauge needles into bone fractures to speed up the rate at which they heal. “Being able to inject the material through needles as thin as those used for injecting insulin means that it could be used in minimally invasive medical procedures,” team leader Faleh Tamimi at the faculty of Dentistry at McGill tells nanotechweb.org.

The researchers, reporting their work in Nano Letters DOI: 10.1021/acs.nanolett.6b00636 have already tested their material on rat tibias (see figure).