Screws with a Twist
● Secrets of the Silkworm: Did you know that the silkworm was domesticated in China over 5,000 years ago? Legend has it that the Empress Lei Zhu was drinking tea under a tree when a cocoon fell into the hot beverage, unraveling silken threads to reveal the Bombyx caterpillar within. Silk making was a deeply guarded secret until 550 AD, until Christian monks successfully smuggled silkworms out of China in a hollow stick and introduced them to the rest of the world. Today, there are thousands of genetically inbred and engineered strains, all completely dependent on humans for survival!
● From Steel to Silk: Fractured bones are often held in place by metal screws and plates until they heal. Removing the metal carries unnecessary risks, which can be averted using biocompatible materials that are naturally absorbed into the body over time. Silk is strong, stable to high heat of sterilization and can be fashioned into “self-tapping” surgical screws that have been successfully tested in rats. The silk screws are “radiolucent” or invisible to x-rays, allowing the fracture to be monitored post-operation, without the impedance of metal. Best of all, silk protein is digested by natural enzymes and resorbed into the body within 4-8 weeks. Researchers hope to use silk screws in facial fractures, which number in several hundred thousand each year.
● Bench to Body: (1) Fill test tube with silk solution then freeze dry. (2) Use scissors or a blender to cut into small pieces. (3) Dissolve pieces in 1,1,1,3,3,3 hexafluoro-2-propanol (HFIP) in a syringe. (4) Inject dissolved silk into bone plate or screw blank moulds. (5) Place molds in methanol for 3–4 days (to convert silk protein into β-sheets). (6) Remove and allow to dry (fume hood for 1 week then 60 °C oven for 5 days), then autoclave for stability. (8) Machine using a mill, lathe or die to obtain desired geometry. Almost DIY, right? 🙂
REF: Perrone et al., 2014 Nature Communications http://goo.gl/uYKM3N
● Gary Ray R describes a different kind of biodegradable screw made of an iron alloy-ceramic composite. This material could be used for shoulder surgeries and degrades at a slower rate over 1-2 years. http://goo.gl/eWmcDV