Protein Structure and Silk Screws - An Alternative Surgical Tool

As an alternative to using metal for craniofacial fracture repair, screws have been developed from the silk of the Bombyx mori caterpillar.

(By Ash Bowie (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons)

They offer advantages to metal screws by remaining fixed in bone for 4-8 weeks, allowing for biocompatibility, bone remodeling, and reduced inflammation. Silk fibroin is a polymeric arrangement of 3 amino acids that can form beta-pleated sheets, a secondary structure of proteins.

BC Learning Network - Levels of Protein Structure

 

Left photo: Finished silk screws. Right photo: Silk screw in a bone after 4 weeks.

Article: The use of silk-based devices for fracture fixation by G.S. Perrone, G.G. Leisk, T.J. Lo, J.E. Moreau, D.S. Haas, B.J. Papenburg, E.B. Golden, B.P. Partlow, S.E. Fox, A.M.S. Ibrahim, S.J. Lin & D.L. Kaplan; Nature Communications 5, Article number: 3385 doi:10.1038/ncomms4385

Chitin and Hydroxyapatite - Chemicals for a Phenomenal Hammer

The peacock shrimp (Odontodactylus scyllarus) is an odd-looking creature with the amazing ability to use its extremely strong hammer claws and penetrate the shells of crabs and clams. How is it able to do this without injury? A lot of the claws' tough exterior is based on what it is made of - chitin and hydroxyapatite.

structure of chitin
("Chitin" by Dschanz - own work (drawn with BKchem). Licensed under Public Domain via Wikimedia Commons)

If you look closely at the bonds linking the two 6-membered rings, you see that they are connected by a 1,4-beta linkage (where C#1 of one ring is connected to C#4 of the other ring). The groups attached to the N atoms are acetyl groups, so these are known as N-acetyl groups.

With lots of O and N atoms around the polymer, there are many opportunities for hydrogen bonding, which lend to the strength of chitin.

 

structure of hydroxyapatite          Ca₅(PO₄)₃OH

Electrostatic forces of attraction between the ions of hydroxyapatite contribute to its hardness and is commonly found in tooth enamel.

For a cool video on how the peacock shrimp smashes with its hammer claws and a more detailed explanation, I highly recommend Destin Sandlin at Smarter Everyday.

 (By Jens Petersen (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html), CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/) or CC BY 2.5 (http://creativecommons.org/licenses/by/2.5)], via Wikimedia Commons)

 

For more on the analysis and engineering of the hammer claw, here is a paper by James Weaver and co-authors:

The Stomatopod Dactyl Club: A Formidable Damage-Tolerant Biological Hammer

ChemCrafter for the iPad - A Virtual Chemistry Set

Chemistry sets have changed so much since we were kids (back in the 70's). Here is a safer version where you can virtually make vigorous reactions while learning about precipitations, gases, acids, and bases. Earn points with more complex, explosive reactions and watch some retro videos. Appropriate for high school students starting to learn about chemical reactivity as well as college students in their first semester of college chemistry. Free app for the iPad. Compliments of the Chemical Heritage Foundation.