Thread lightly

Fractures and broken bones are no fun and the worst are those that require surgical screws. Sure, it’s a chance for some twisted braggadocio – “I’ve got precision-machined, surgical-grade titanium inside me!” – but these injuries are almost always very serious, painful and long-to- heal. The screws may be essential to holding things together in the right places during the healing process, but they present particular problems of their own.

To wit: They eventually must be removed, requiring more surgery and leaving behind a hole in bone that also must heal.

Much better would be a surgical screw strong enough to do its job and then go away. In a recent Nature Communications paper, scientists described just such a candidate. The screws are made of silk fibers. In experiments with rats, the screws successfully pinned bones together for eight weeks but behaved more like bone than metal. They are less stiff (reducing stress problems with surrounding bone), less sensitive to temperature changes, produce minimal inflammatory response and promote bone healing as they biodegrade.

The silk screws aren’t the first on the market. There are already screws made from polylactic acid, which is derived from corn starch, tapioca root and sugarcane. In 2010, a German company debuted a biodegradable screw made of polylactic acid and hydroxylapatite, a naturally occurring mineral that is also a primary component of natural bone and used in prosthetic devices. These screws are hollow to further encourage bone growth into them and reportedly completely disappear in two years.

And there is fracture putty, which in some cases could theoretically do away with screws altogether. It’s an experimental compound being developed by DARPA that is packed in and around compound bone fractures, where it quickly hardens to provide loadbearing capabilities while the bone heals. The putty is resorbed as the bone regenerates and grows into it.