Chemical Nanotomography of Ultrahard Tooth Mineral

Derk Joester, Northwestern University, DMR 0805313

Chitons, a kind of “rock-munching” marine mollusk, have the teeth that are ~4 times harder than ours. The teeth are composed of both nano-crystalline magnetite (Fe3O4) and and organic fibers. The resulting composite is not only strong and tough, but also exhibits self-sharpening. Understanding the structure and the chemistry of the fiber-magnetite interface is critical, yet very challenging.

L. Gordon and D. Joester, Nature 2011

We have pioneered the use of atom probe tomography (APT), a technique with unrivaled spatial resolution and chemical sensitivity, to investigate this interface. We found that two kinds of nano-scale fibers decorated with either magnesium or sodium ions are present in the tooth. This has implications for the biological design strategy of the Chiton tooth and informs bio-inspired approaches to better materials.

Chiton teeth are arrangedin rows on the radula.

Cross section of a tooth showing outer, ultrahard layer.

Very thin organic fibers (3-5 nm, black) inside the magnetite give the tooth give it

the necessary toughness to chew on rock.

Cross section of fiber showing individual sodium

(Na+) ions detected by APT.

200 µm 20 µm

Bioengineering Single Crystal Growth

Derk Joester, Northwestern University, DMR 0805313

In biology, there are ample examples for sophisticated synthesis and use of materials, in particular the biominerals that make shells, bones and teeth, or gravity and magnetic field receptors. Many hallmarks of biological crystal synthesis, in particular the control of crystal shape, polymorph, and generation of nano-composites are extremely challenging to reproduce in the laboratory. We are biotechnological approaches to grow materials rather than synthesize them.

C.-H. Wu, A. Park, and D. Joester, JACS 2011

We have learned that we can control the growth of single crystals of calcium carbonate by engineering PMC cells from the sea urchin embryo (A). We use micro-patterned surfaces with sticky and non-stick patches to control location/orientation of crystals (cf. B and C). In a breakthrough discovery, we have furthermore learned how to switch from linear to branching single crystals using a recombinant growth factor (a protein) from the sea urchin embryo (cf. D and E). We anticipate that this will allow us to grow much more complex structures in the future.

A

B C

D E

Bioengineering Single Crystal Growth

Derk Joester, Northwestern University, DMR 0805313

UG students in the Discovery Lab reverse-engineer a “competitor’s”

CdSe quantum dot synthesis.

Curriculum Development:Discovery Labs

High School Junior Rhiannon Flanagan-Rosario (left) and her mentor Ching-Hsuan “Ann” Wu

working on a Hitachi S4800 HR-FESEM.

Engaging Women and MinoritiesIn Science and Engineering

Haven Middle School students discover science using our mobile lab. Here, they set up an experiment with live sea urchin embryos.

Mobile Lab forK-12 Outreach

Janesh Lakhoo, Piotr Maniak, Steve Fitzgerald, Alexander Park, Laura Mueller, Rose Gruenhagen, Fangzheng Quian, Kellen Mobilia,

Wisaruth Maethasith, Fei Yin Luk, Lawrence Tran

Sea urchin tank farm designed and built by Janesh Lakhoo and

Piotr Maniak (BME)

Stirrers for sea urchin embryo culture designed / built by

Alexander Park (MSE)

Undergraduate Participation in Research and Engineering

Live cell fluorescence microscopy of PMCs by Kellen Mobilia (CBE)

MBP-GFP fusion protein immobilized on amylose beads by

Wisaruth Maethasith (MSE)