Fracture Process At The Molecular Level

For our horse there is actually a physical observable process of fracture that we would like to avoid. But, to avoid, do we first have to understand the process?

Above left an illustration of "cross linking". Solid materials at the molecular level hold together by certain mechanisms. Spider web molecules (fromHansma website, ) hold together both by a successive looping of molecules in terms of their arrangement and molecular cross linking as in the illustration, i.e. an assembly of molecules of some sort.

As force applies to this spider web material Hansma (through Atomic Force Microscope Imaging) notes the material contains sacrificial bonds and hidden length that reform quickly if the protein is allowed to relax after it is extended.

As force increases to rupture Hansma uses such terms as "rupture peaks" and "successive rupture peaks" along the molecular matrix. The cross linking springs and molecular loops give way molecule by molecule breaking the sacrificial bonds.

In bone collagen the process is similar. From Hansma: "We found that collagen molecules can rupture sacrificial bonds at constant values of the distances they are stretched. We observed two patterns of rupture: After applying forces greater than 500pN, several ruptures would occur for every 78+3nm the molecule was stretched. (IT TAKES FORCES OF OVER 1000pN TO BREAK A COLLAGEN BACKBONE)" Note that the number of ruptures is related to the distance the molecules are stretched + force applied.

The two patterns of rupture Hansma observed here involved, merely, different degrees of force, one much greater than the other. With application of weaker force, increasing it slowly as you go, they note the breaking of the bonds still occurs as force continues to increase but the breaking process is barely detectable.

The conclusion is logically exactly what you'd expect. The individual subunits rupture sequentially AND less and less peak force is necessary to continue the rupture process because the backone of the collagen begins to break and so less force is needed to rupture the remaining molecules.

One may imagine for our breezing/racing horse the various degrees of force that may apply depending on circumstance. As in Hansma's example we might have weaker forces working on already damaged bone, stronger forces rupturing healthy bone or any sort of combo.

Our interest of course is in making sure the bone is healthy before our next breeze. We need to understand precisely what's happened, and what will occur before we breeze again.

Training:
Thurs 7/17 tack work after yesterday's speed work. Rod walked 10 min and Art trotted the pasture course 1.4 miles.
Fri. 7/18 Rain again. 1/2 inch. unbelievable. Off.
Sat. 7/19 RR getting disgusted with the weather. What's new? Unable to gallop due to wet conditions so we settle on riderless fast work. The horses went 4 x 2f as fast as the muddy conditions allowed. Nice work by the 3 yr. old, less so by Rod who we're declining to press due to the state of his physical development at the moment.