Planck Wrap Up IV

Black regions (above) HA extrafibrillar mineral reinfocements, white regions--underlying collagen fibril.

Extra (outside)fibrillar mineralization enhances FR (fracture resistance). That's a bare statement for us, but becomes established fact in Planck. Why?

Note the fibrils and mineral patterns in the illustration..

With extrafibrillar mineralization research finds a decrease in spacing between fibrils Those weaker spaces have filled with stronger extrafibrillar mineral rings.

BUT, there's more. Due to the pattern or periodicity of the mineral arrangement (above) the fibril maintains its flexibility. Hence this conclusion: extrafibrillar mineralization (mineral growth outside the fibril) increases strength while maintaining flexibility. The conclusion as stated in Planck:

"As a result of this process and the deposition of additional extrafibrillar shells on the surface, the fibril would become considerably stiffer in directions perpendicular to the fibril axis while the increase in its bending rigidity would be less pronounced, thus preserving the fibril's flexibility."

For us its simply: extrafibrallar mineralization enhances FR!!!

But, you're cleverly asking, that mineral pattern in their illustration hardly looks anything like the muck in those Hansma images of the fibrils? How can they know extrafibrillar minerals pattern in this manner? See last post--they discern these patterns because the rate of growth of extrafibrillar minerals is exactly the same as intrafibrillar growth. The cellular mineral growth inside and outside occurs simultaneously, and so, the staggered pattern of HA platelets inside the fibril is the same on the outside. Intrafibrillar platelets, per last post, maintain a spacing of 40nm between themselves, and they Planck can assume, for purpose of calculations, that the pattern of growth outside the fibril and inside are exactly the same! By measuring one aspect of the structure they're able to arrive at additional valid calculations, such as this one:


They go on. As a result of these considerations we can find the mechanical properties of a collagen fibril coated with minerals. AND we can find those mechanical properties in various stages of the mineralization process for various mineral fractions!

They calculate strength for the initial naked stage, and on to various mineral fractions, and they come up with a set of numbers. We can look at these numbers and see various strengths depending on the degree of extrafibrillar mineralization. One measurement leads to the next, and finally we come up with strength calculations for these:
a fibril bundle.

Interestingly, they note, by looking at their numbers, that strength appears to increase geometrically as mineralization increases. Increasing strength brings into play additional strength increasing properties, e.g. as the spaces between the fibrils fill with platelets interactions between neighboring fibrils also increases. To accurately calculate thereafter they need consider the numbers produced by these additional interactions, and so on.

And, as they consider the mineral bundle they must commence calculations of the effect of the bone glue proteins that aid in holding the bundle together! The glue is referred in the article as NCPs (non-collageneous proteins).

Then: "with the above considerations in mind, we can express the effective stiffness tensor of a bundle of aligned fibrils."

Again, the result is various numbers depending on all the material variables of the ever changing structure.

The article concludes with them making calculations for fibril arrays aligned in different manners: parallel, perpendicular, chaotic, patterned, unpatterned, and so on. "Once the stiffness tensor (of one type of array) is known, we can model other types of fibril arrays corresponding to differences in known orientations."

I am now, I think, ready for the grand finale, next post.

Training: We're off due to weather and other things, and hopefully can get going tomorrow as a warm up starts. Noticed the Blood Horse video of Street Cry. What a beaut.! Then there's Double Honor, sire of Jet Propulsion, winner of the Sunshine Millions Turf today, looking even better and standing in Florida for less than $4000.00. Double Honor, quite a horse:

http://www.thoroughbredtimes.com/stallion-directory/stallion.aspx?stallion_no=4008760