Spotlight on polymerisation to repair damaged faces

Scarred facial tissue can be difficult to repair and even harder to live with. To tackle this problem, US scientists have developed a minimally invasive repair method combining natural and synthetic materials to form a tissue scaffold to help the body heal itself. And the construction of the scaffold is directed and controlled using light.

Doctors need a way to reconstruct soft tissue that mimics the patient’s normal tissue. The material needs to be biocompatible, and it should also stretch and behave in a similar way to native tissue, as well as lasting as long as needed. However, it is also important that the implant can be easily reshaped or removed when no longer required, preferably without further surgery. Biological and synthetic materials have been used to date, but biological materials can be easily degraded by the body and synthetic compounds may not integrate or degrade properly and can cause immune responses. 

Jennifer Elisseeff and colleagues at Johns Hopkins University, US, have solved some of these challenges using their new composite biomaterial that combines biological activity with mechanical strength and durability. The composite is made from synthetic poly(ethylene glycol) (PEG), mixed with a radical polymerisation initiator and naturally occurring hyaluronic acid (HA). This mix can then be injected at the site of tissue damage and shaped to fit the injury. Shining a specially designed array of green light-emitting diodes (LEDs) on the skin causes free-radical polymerisation of PEG, which results in crosslinking that traps the HA in a polymer network. Cells can grow and heal the injury while supported by the implant, although it did provoke some inflammation but this was not too serious in most cases. After the HA-PEG composite has done its job it can be easily removed by injecting an enzyme that degrades it.

The scientists tested several combinations of HA and PEG in rats and have started human trials. Elisseeff notes that ’these materials can respond differently depending on where they are in the body’, so having different functional combinations is important. The team hope to help those with traumatic injuries, such as soldiers.

’A key issue in the use of various soft tissue replacements is that, in many cases, the replacement is either quickly degraded and/or loses its shape,’ says Ali Khademhosseini, a tissue engineering expert at Harvard Medical School, US. ’This work demonstrates that photocrosslinkable polymers can be used to generate an approach that can replace large sections of soft tissue for extensive periods of time.’ He adds that the ’process is easy to perform, cheap and rapid’.

Carol Stanier