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Mussel-protein coating keeps implants safe from infections

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Mussel-protein coating keeps implants safe from infections

A protein obtained from mussels could one day keep infections from occurring at the site of bone implants such as artificial hips. And while the protein does kill the microbes, it should still limit the development of antibiotic-resistant “superbacteria.”

Bacterial infections at the sites of recently installed implants can be very serious, potentially leading to complications such as a weakening of the bond between the implant and the bone. When this happens, subsequent surgeries are often required in order to keep the implant from prematurely failing.

A number of groups have already developed antibiotic coatings for implants – to get them past the initial infection-prone state – although some of those substances continuously release their antibiotic payload, regardless of the state of the site. This indiscriminate use of the drugs can cause bacteria to build up a resistance to them, thus making the antibiotics less effective.

Seeking a more selective and longer-lasting alternative, a team of Korean scientists looked to the proteins that mussels use to adhere themselves to rocks.

The researchers created a bioengineered MAP (mussel adhesive protein) that expressed large quantities of a naturally occurring amino acid known as DOPA. Additionally, the engineered MAP was boosted with a combination of gentamicin (a commonly used antibiotic) and iron ions.

Under healthy implant-site conditions, DOPA forms a strong bond with the ions, keeping them and the gentamicin securely contained within a durable hydrogel-type coating made from the MAP.

When harmful bacteria move in, however, they increase the acidity of the site. In response to this lowered pH, the bond between the DOPA and iron ions weakens, causing the ions and gentamicin to be released. The antibiotic is then freed up to kill all the bacteria in the area. Importantly, though, the coating only releases the gentamicin in proportion to the level of infection – as indicated by the pH level.

A diagram illustrating how the MAP coating works


In animal tests, the coating released 70% of its antibiotic payload within eight hours of infection by Staphylococcus aureus bacteria, effectively eliminating all of the microbes. It also stayed securely adhered to titanium implants even when subjected to mechanical stress, and remained effective throughout the bone regeneration phase (about four weeks).

“The immediate and sustained antimicrobial effect of the adhesive implant coating material has the potential to significantly enhance the success rate of implant procedures,” said lead scientist Prof. Hyung Joon Cha of Pohang University of Science and Technology (POSTECH).

A paper on the research, which also involved scientists from Kyungpook National University, was recently published in the journal Biomaterials.


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