A stitch whose time has come
Oct 29th 2008
A protein extracted from cows’ blood may provide the best answer yet to the question of how to sew up wounds
FIFTY years ago a soldier injured on the battlefield would be sewn up by medics using sheep’s gut. A hundred years earlier they would have used silk. Before that, metal wire. Today, surgeons often prefer plastics such as polypropylene. Sutures have a long and bizarre history, dating back to ancient Egypt where everything from tree bark to hair was used to stitch torn human flesh back together again.
The latest suggestion, though, is probably the most bizarre of the lot: bovine serum albumin, a protein found in cows’ blood. The reasons for picking it are that it is already produced on a commercial scale (it has many applications in biochemistry) and that it is sufficiently similar to human serum albumin, one of the most abundant proteins in the human body, for the immune system not to notice the difference. That reduces the risk of a wound becoming inflamed. But there is a problem. Bovine serum albumin does not come in thread form.
Eyal Zussman and his colleagues at the Technion-Israel Institute of Technology in Haifa think, however, that they have found a solution to this problem. They propose to use a technique called electrospinning to turn the stuff into threads that a surgeon can use.
Electrospinning works by connecting a needlelike spinneret to a high-voltage power source and releasing a charged liquid from it towards an earthed collector plate. Like a spark between a cloud and a lightning conductor, the liquid stretches out to the collector. If the molecules within it hold together while this is happening, a solid thread may form.
Some materials, however, are easier to spin in this way than others, for if the molecules do not stick together, the liquid stream will break up. And, until now, that has been true of bovine serum albumin. The molecules of this protein are more or less globular, and are held in that shape by internal cross-links between different parts of the amino-acid chain of which the protein is composed. That discourages them from forming fibres. Though electrospun bovine serum albumin does not actually break up into droplets, the resulting threads have been so short and irregular as to be useless.
What Dr Zussman and his colleagues have managed to do is break the internal bonds in the protein molecules by mixing them with a chemical called beta-mercaptoethanol. The result, as they report in Biomacromolecules, is that they can spin bovine serum albumin into long, even fibres that are perfect for creating both suture threads and thick mats similar to conventional wound dressings, but on a small scale. Not only are these threads and mats readily accepted by the body, but the albumin of which they are composed has glue-like properties, which helps to stick torn tissues together.
The consequence is that sutures made with these new threads are expected to reduce the scarring left when the stitches are removed. More significantly, that they do not provoke inflammation means they might be used to repair the wounds of patients with conditions such as diabetes, in which chronic skin infections often get in the way of healing when normal stitches are used. And that would be a real advance on polypropylene and sheep’s gut.