By George Wigmore of Nature magazine

Injectable, light-activated implants could help to reconstruct soft tissue. The implants offer a less invasive alternative to current techniques for rebuilding tissue lost as a result of trauma or disease; they will be especially useful for facial tissue, which is difficult to reconstruct without scarring or loss of function.

Jennifer Elisseeff, a biomedical engineer at Johns Hopkins University in Baltimore, Maryland, and her colleagues developed the implants from a combination of naturally occurring hyaluronic acid and the synthetic polymer polyethylene glycol (PEG). The team publishes its results in Science Translational Medicine today.

The implant is injected under the skin as a liquid, then massaged into shape. Light-emitting diodes are then shone onto the skin, triggering a photoinitiator system. This causes links to form between the PEG molecules, creating a solid hydrogel that traps and entangles the particles of hyaluronic acid, fixing the implant into place.

The proportions of hyaluronic acid and PEG used can affect the characteristics of the implant. "We created composite materials that had a synthetic component, which allowed us to control implantation and physical properties," says Elisseeff.

Tailored approach

Currently, soft-tissue implants fall into two general categories, she says. "You can either inject something and once it's in the body do nothing about it, or you can create an external implant which is then surgically implanted."

The latest implants offer a different approach. "By tuning the properties for the material we can match the surrounding mechanical properties, whether you're in more of a fatty area, a muscle area or a skin area," says Elisseeff. This will enable doctors to tailor the implant to the needs of each patient.

"Injecting a hydrogel and fixing the shape in situ is just like a dream," says Zhanfeng Cui, director of the Oxford Centre for Tissue Engineering and Bioprocessing at the University of Oxford, UK. "This team has made the breakthrough by choosing the right photoinitiator and the right wavelength of light."

The implants have better longevity than injectables already in use. The team found that, depending on the mixture of hyaluronic acid and PEG used, their implants kept their volume for at least twice as long as standard implants in rodent models.

But there are still issues to iron out, says Cui. For example, the implants caused more inflammation than was expected in human trials. But despite these obstacles, with the right financial backing the implants could be available within a year, says Elisseeff.

The main focus of the technique is on clinical reconstruction, says Cui, but "it will not be a surprise to see that a much higher number of applications are actually in plastic surgery".

This article is reproduced with permission from the magazine Nature. The article was first published on July 27, 2011.