User:Anthony Salvagno/Notebook/Research/2010/03/01/Catching up on class work

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I have a bunch of class work to work on and I am going to try and get as much done today as possible. Of course if something pressing research wise comes up, I will work on that as well.

I need to read a review article and I'm going to take notes below.

Mechanical Properties of Biological Nanocomposites

by Baohua Ji and Huajian Gao
DOI: 10.1146/annurev-matsci-070909-104424

Abstract:

Biological nanocomposites, such as bone, tooth, shell, and wood, exhibit exceptional mechanical properties. Much recent effort has been directed at exploring the basic mechanical principles behind the microstructures of these natural materials to provide guidelines for the development of novel man-made nanocomposites. This article reviews some of the recent studies on mechanical properties of biological nanocomposites, including their stiffness, strength, toughness, interface properties, and elastic stability. The discussion is focused on the mechanical principles of biological nanocomposites, including the generic nanostructure of hard-mineral crystals embedded in a soft protein matrix, the flaw-tolerant design of the hard phase, the role of the soft matrix, the hybrid interface between protein and mineral, and the structural hierarchy. The review concludes with some discussion of and outlook on the development of biomimicking synthetic materials guided by the principles found in biological nanocomposites.

Theory

This section begins talking about the TSC model (Tension-Shear Chain model) which I have almost no interest in. It is sad and strange to see how my upbringing in Math and Physics has pretty much excluded me from the field while my side learnings in Biology has welcomed me to the field with open arms.

I'm going to glaze over this section and take no notes, but I will read a little just to get an idea of what they are talking about. There are some useful subsections though.

Role of Protein Matrix

Protein can:

  • Template mineralization - controls nucleation and deposition of minerals
  • governs size and assembly of mineral crystals
  • transfers load through shear
  • traps cracks through soft matrix
  • dissipates energy through deformation and viscoelastic properties (similar to load transfer)
  • act as sources of microcrack nucleation to redistribute stress

They provide several examples of how proteins do this and one description is due to the unfolding of proteins since there are numerous ways this can happen. Interestingly there have been force spectroscopy studies on Collagen (as an example) to understand its force bearing nature.

Protein-Mineral Interface

Through a lot of technical jargon, which is really annoying and only further fails to convey information to the reader, I gathered that there is a large protein-mineral interface and that as one looks at smaller and smaller scales this region increases largely. An example they provide is that in the volume of a raindrop, the interfacial area can be as large as a football field. They didn't clarify if it was American or not. Strength of the interface depends on the size and geometry of the minerals although I guess that's self explanatory. They do a bunch of MD study analysis and for some reason seeing the letters M-D makes me shut my brain off.

Role of Hierarchical Structures

Hierarchy is important and it is shown that biocomposites are structured in this way which provides greater stability and strength. "...The extraordinary toughness of bone is due to the combined action of structural elements at both nanometer and micrometer levels." (From the paper.) There is a lot of model analysis and I can't think about that clearly right now, plus I don't really care.

Biomimicking

This section talks about designing synthetic polymers designed to mimic structures found naturally in biocomposite materials. It seems as though many experiments have taken great strides in this regards being able to mimic:

  • layer-by-layer construction brick and mortar style
  • design of a montmorillonite clay platelet–poly(vinyl alcohol) matrix nacre-mimetic nanocomposite, whatever that means
  • multistructure design to mimic seashell structure (which is highly strong and coveted)
  • complex hierarchical structures
  • developed a zinc oxide and poly(amino acid) system to synthesize a nacre-mimic nanocomposite

Conclusion

I grow bored of this paper, although there is a nice summary at the end that discuss key points in the paper.

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