Biomineralized structures with graded and/or modulated structural properties

Hierarchical bio-mineralized composites with calcified phases (calcium carbonate and calcium phosphates) such as seashells (conch shell and mother-of-pearl) are classic examples of biomimetic research studies. Extensive studies in the past unveil that natural structures feature mechanical strength by exploiting a variety of toughening mechanisms across multiple length scales.

Recently, there's a shift in research focus on novel-intriguing structural materials made of unexpected inorganic materials (for instance Fe, Cu, Au or oxides). The materials often contain a combination of minerals, assembled in a highly controlled manner for precisely tailored functionalities. We have been investigating such systems, including the dactyl club of the mantis shrimp; the silica-based giant sponges - revealing the critical influence of lamellar architecture on abrasion damage (Advanced Functional Materials, 2008), and on the magnetite-based chiton teeth. In the latter system, we illustrated that chiton magnetite constitutes the hardest biomineral found in Nature (Materials Today, 2010), with the focus on contact mechanics studies at small scales (including indentation fracture). We have directed efforts to develop in situ mechanical testing methods (for instance under an SEM or a TEM) to reveal fundamental mechanisms of toughening, together with assessing the influence of organic-inorganic interfaces on the properties.

Mantis Shrimp Dactyl Club

The strike of the mantis shrimp dactyl club is one of the fastest movements in the animal kingdom and is used to shatter the protective shells of its prey. To duplicate the unique multi-functionality of biomineralized composites, it is imperative to learn the basic structure-properties relationships across multiple length scales. Additionally, understanding the bioprocessing pathways used by these structures to build up from bottom-up is also critical. Through our collaborative research efforts (Wyss Institute at Harvard, UC Riverside, and Purdue University), we presented the multi-scale microstructural principles responsible for the exceptional mechanical properties of the club (Science, 2012).

Further, we described that the club is made of “fluorapatite (FAP)” nano-crystals. It contains calcium sulphate, an unusual biomineral, hypothesized to facilitate the transition of amorphous to crystalline FAP, owing to the epitaxial relationships between both crystals (Nature Communications, 2014).

Subsequently, using a combination of advanced solid-state spectroscopy, nanomechanical, and finite element simulations tools, our team has unveiled the micro- and nano-scale structural designs allowing the club to deliver high-energy punches while minimizing internal self-damage. Particularly the critical role of “quasi-plasticity” of the club’s external surface in absorbing impact energy was described (Nature Materials, 2015).

We also shed light on the mechanism used by the mantis shrimp to store a remarkably high density of elastic energy within its saddle-shaped spring to achieve deadly strikes (Advanced Functional Materials, 2015).

Ultimately, we envision to distillate novel microstructural design concepts to be translated for the fabrication of impact- and abrasive-resistant biomineralized composites that can find potential applications for orthopedic implants. The investigation methods developed so far during the research can be directly applied to study wear mechanisms of hard human tissues.