American scientists have demonstrated three-dimensional imaging of damaged bone tissue using functionalised gold nanoparticles that could be used in vivo. 

Repetitive stress to bone tissue causes tiny cracks or scratches, known as microdamage, which increases the risk of fractures and can be a major concern for the physically active and elderly. Research into how this condition relates to bone fragility is critical for the early diagnosis of fractures. 

Current imaging techniques are limited to thin sections of bone and are invasive and destructive explains Ryan Roeder at the University of Notre Dame. By attaching glutamic acid to gold nanoparticles, Roeder's team synthesised an X-ray contrast agent that could be used to accurately image microdamage non-destructively in vivo. 

The amine group anchors the amino acid to the gold, leaving the carboxylate free to attach to the bone mineral that becomes exposed when the surface is damaged, explains Roeder. This allows the damage to be detected using X-ray techniques, such as CT scans. The particle's nanoscale size also means that it can be transported via blood capillaries into micro-sized cracks.

'There isn't an alternative known system to do non-destructive three dimensional imaging of damage,' says Roeder. 

Thorfinnur Gunnlaugsson, an expert in medicinal chemistry at the University of Dublin, Ireland recognises the merits of Roeder's achievements. 'This is a real step forward. I'm delighted to see this work,' he enthuses. 

'The beauty of the nanoparticles is they have a very large surface area, so you can populate them very highly [with amino acid], which means you can get higher concentrations and to a more targeted area,' he adds. 

Having demonstrated the effectiveness of the nanoparticle system, Roeder and his team are now looking at its deliverability through tissue, further increasing its potential for use in vivo. 

Yuandi Li 

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