Composite shows promise in restoring damaged soft tissue

Biomedical engineers at Johns Hopkins University have developed a liquid material that in early experiments in rats and humans shows promise in restoring damaged soft tissue relatively safely and durably.

The material, said to be a composite of biological and synthetic molecules, is injected under the skin, then ‘set’ using light to form a more solid structure. The researchers said the product could one day be used to reconstruct soldiers’ faces marred by blast injuries.

The Hopkins researchers caution that the material, described in a report in the 27 July issue of Science Translational Medicine, is promising but not ready for widespread clinical use.

‘Implanted biological materials can mimic the texture of soft tissue but are usually broken down by the body too fast, while synthetic materials tend to be more permanent but can be rejected by the immune system and typically don’t meld well with surrounding natural tissue,’ said Jennifer Elisseeff, Jules Stein professor of ophthalmology and director of the Translational Tissue Engineering Center at the Johns Hopkins University School of Medicine. ‘Our composite material has the best of both worlds, with the biological component enhancing compatibility with the body and the synthetic component contributing to durability.’

The researchers created their composite material from hyaluronic acid (HA), a natural component in the skin of young people that confers elasticity, and polyethylene glycol (PEG), a synthetic molecule used successfully as surgical glue in operations and known not to cause severe immune reactions.

The PEG can be made to form strong chemical bonds between many individual molecules using energy from light, which traps the HA molecules with it. Such cross linking makes the implant hold its shape and not ooze away from the injection site, said Elisseeff.

To develop the best PEG-HA composite with the highest long-term stability, the researchers injected different concentrations of PEG and HA under the skin and into the back muscle of rats, shone a green LED light on them to gel the material and used magnetic resonance imaging (MRI) to monitor the persistence of the implant over time.

The implants were examined at 47 and 110 days with MRIs and removed. Direct measurements and MRIs of the implants showed that the ones created from HA and the highest tested concentration of PEG with HA stayed put and were the same size over time compared with injections of only HA, which shrank over time.

The researchers evaluated the safety and persistence of the PEG-HA implants with a 12-week experiment in three volunteers already undergoing abdominoplasty.

The participants said they sensed heat and pain during the gel-setting process. Twelve weeks after implantation, MRI revealed no loss of implant size in patients. Removal of the implants and inspection of the surrounding tissue revealed mild to moderate inflammation owing to the presence of certain types of white blood cells.

‘We still have to evaluate the persistence and safety of our material in other types of human tissues, such as muscle or less fatty regions under the skin of the face, so we can optimise it for specific procedures,’ said Elisseeff.