Silk protein implants help mend broken bones

The development, from Tufts University School of Engineering and Beth Israel Deaconess Medical Center (BIDMC), is claimed to overcome disadvantages experienced when fixing broken bones with metal screws and plates.

These include stiffness that can cause stress to underlying bone, increased risk of infection and poor wound healing, plus surgery to remove implants.

Resorbable fixation devices, made of synthetic polymers, avoid some of these problems but may pose a risk of inflammatory reactions and are difficult to implant.

It is claimed the surgical plates and screws from BIDMC and Tufts have the potential to offer improved bone remodelling following injury and can be absorbed by the body over time, eliminating the need for surgical removal of the devices.

The findings, demonstrated in vitro and in a rodent model, are described in Nature Communications.

‘Unlike metal, the composition of silk protein may be similar to bone composition,’ said co-senior author Samuel Lin, MD, of the Division of Plastic and Reconstructive Surgery at BIDMC and Associate Professor of Surgery at Harvard Medical School. ‘Silk materials are extremely robust. They maintain structural stability under very high temperatures and withstand other extreme conditions, and they can be readily sterilised.’

Collaborating with Lin were co-senior author and Tufts chair of biomedical engineering David Kaplan, PhD, and a team of biomedical and mechanical engineers.

‘One of the other big advantages of silk is that it can stabilise and deliver bioactive components, so that plates and screws made of silk could actually deliver antibiotics to prevent infection, pharmaceuticals to enhance bone regrowth and other therapeutics to support healing,’ Kaplan said in a statement.

Kaplan and his team have previously developed silk-based sponges, fibres and foams for use in the operating room and in clinical settings but until now, silk hadn’t been used in the development of a solid medical device for fracture fixation.

The Tufts researchers used silk protein obtained from Bombyx mori (B. mori) silkworm cocoons to form the surgical plates and screws. Produced from the glands of the silkworm, the silk protein is folded in complex ways that give it exceptional strength and versatility.

To test the new devices, the investigators implanted 28 silk-based screws in six laboratory rats. Insertion of screws was said to be straightforward and assessments were then conducted at four weeks and eight weeks, post-implantation.

‘No screws failed during implantation,’ said Kaplan.

Furthermore, because silk is slow to swell, the new devices maintained their mechanical integrity, even when coming into contact with fluids and surrounding tissue during surgery, he said.

The outcomes suggest that the use of silk plates and screws can spare patients the complications that can develop when metal or synthetic polymer devices come into contact with fluids.

‘Having a resorbable, long-lasting plate and screw system has potentially huge applications,’ said Lin. While the initial aim is to use silk-based screws to treat facial injuries, which occur at a rate of several hundred thousand each year, the devices have the potential for the treatment of a variety of different types of bone fractures.