Planck Wrap Up III: Results

Feeling my way through the article:

Regards our friends the Type I Bone Collagen Fibrils--and this site will be sans illustrations until eviction of some extremely pesky computer viruses--might we be interested, per Planck, in the "elastic stiffness" tensor? Thinking this may have something to do with fracture resistance (FR)???

Hypothesis from earlier research (2005): strength and toughness depend on size/arrangement pattern of mineral platelets. Patterns?

The initial growth of platelets along the naked fibril skin first "thickens" and then grows into reinforcing rings around the fibril. Pattern!

Growth of these "rings", i.e resulting from deposition of additional extrafibrillar shells on its surface, the fibril becomes considerably stiffer in directions perpendicular its axis. (Reconsider that last. This seems highly important. A "force" blows by perpendicular to the axis of the fibril--i.e. at 90 degree angle. The fibril is "stiffer" due to reinforcing rings.) Furthermore: due to the geometric design of this growth the fibril's flexibility is preserved! And so, we a have a stronger, flexible fibril resulting from the extrafibrillar mineral rings.

But, more tests necessary.

Enter Planck which looks at these hypothesis from the smallest levels in the materials hierarchy on up. Planck decides to test this at the levels of the hierarchy smallest to larger, by modeling and calculating. "Different mineralization scenarios are tested." And, Planck uses 3D (3 dimensional) calculations whereas earlier research was 1D.

Elastic properties of bone is calculated at each hierarchy level. They calculate by methods of materials science the "elastic stiffness tensor" of each level.

Results:
1. A single collagen fibril: elastic properties of a single fibril strongly depend on shape and volume fraction of the fibril. i.e. shape of the HA mineral platelets and percentage of the fibril which is mineralized.

And, of equal importance, when the volume fraction of mineral platelets is lower the interaction (reinforcement) between neighboring mineral platelets is greatly reduced compared to a volume fraction that is optimized!!!

2. Mineralized collagen fibril reinforced with extrafibrillar minerals (i.e. maximum mineralization on the interior, and mineral coated on the exterior):

Note that the outside mineral coating attached to the "skin" of the fibril is composed of platelets of different shapes and sizes. The HA mineral platelets "strongly adhere" to this skin(recall the Hansma images!).

3. Fibril Arrays: Space between collagen fibrils is only 1-2n: the HA mineral platelet is initially deposited in the extrafibrillar space and these platelets prevent the collagen fibrils from merging.

Fibrils arrange themselves in parallel bundles.

What is the spacing between the mineral blobs on the fibril surface?Roughly the same as the spacing between HA platelets within the fibrils, about 40 nm. They conclude that the growth of exterior platelets is an extension of the intrafibrillar platelet growth. Remember that mineral platelet growth occurs simultaneous and at the same rate inside and outside the fibril! I guess those collagen molecules are literally farting minerals from the moment of birth.

Continue next post.

Training:
still off. busy week, frozen ground. trainer needing to get in training mode. but, lost shoe has been reapplied. Theoretically, we're ready to go. Fairmount back in business!