How long is HA paste moldable?

[Tiny]

Could you elaborate a bit more on how that makes it more brittle?

Collagen is an alpha-helix.  As such, at the molecular level, it is able to twist, bend, stretch and compress.  The secondary structure is held in place by hydrogen bonds, which are weak and can stretch, break and reform easily (and even covalent bonds can stretch/bend somewhat)   The collagen in bone is lined up in sheets and bundles, which gives bones a degree of spring and flexibility.

Also, the HA crystals in natural bone are very small - nanocrystals.  Means they're less likely to shatter simply because of their size; they're also less organised so have a less strict 'crystal plane'.  Meaning they're softer, but less brittle.

Compare that to HA pastes - the collagen fibres are more randomly distributed so cannot bend or stretch en masse to absorb a shock.  The inorganic part, the HA, is probably made up of much larger crystals that are more organised than 'native' HA.  Held together primarily by ionic bonds, the material cannot absorb any of the force on a molecular level so it will just snap...it's related to electrostatic repulsions caused by a shift in the crystal plane.  Ionic solids are brittle by nature; ionic crystal structures are more rigid (ie. less flexible) than covalently bonded materials (even though the bonds themselves are somewhat weaker)

Just how much more brittle?  What kind of force would be required to shatter it?

I'm a chemist, not a physicist     But it's really impossible to say without experimentation and it would also depend on the 'mix' of the HA used

Incidentally, young bones have more collagen than older ones, which is one of the reason why older bones are more brittle



The most exciting current research is stuff like this -

http://www.nbcnews.com/id/5832265/ns/health-cloning_and_stem_cells/t/new-jaw-bone-grown-mans-back-muscle/

Of course, stem cells are key.  You want to grow real bone, you're going to need osteoblasts, a framework, and time. (of course, in the meantime, it would definitely be possible to get bacteria to produce the kind of dense collagen than you get in bone)

[Optimistic]

Thank you for taking the time to write that. I always enjoy learning about that stuff.

You mentioned about getting a bacteria to grow the kind of dense collagen that is present in bone. Did you mean to grow that inside the hydroxyapatite?

It's an interesting thought but given that I've never seen it mentioned before I doubt anyone actually offers it.


My main concern now is that if I were to get HA paste applied on the infraorbital rim there would be a risk of shattering it. So how easily it shatters is of huge importance. I'd hate to take a knock and literally have part of my face break off.

[Tiny]

You mentioned about getting a bacteria to grow the kind of dense collagen that is present in bone. Did you mean to grow that inside the hydroxyapatite?

No no no I meant in the lab.  It's a lot easier to get bacteria to grow you pure proteins than eukaryotic cells.  That said, a good approximation of bone will be impossible without stem cell. It's osteoblasts that lay down the collagen fibres in the right way i.e. in organised bundles

My main concern now is that if I were to get HA paste applied on the infraorbital rim there would be a risk of shattering it. So how easily it shatters is of huge importance. I'd hate to take a knock and literally have part of my face break off.

Hmmm, good point.  I was considering getting HA to my cheekbones when I got my revision rhino.  I must have mentioned to the surgeon that I did MMA but he never said that would be an issue.  Glad you brought it up though, maybe I shouldn't be getting HA on my cheekbones!

I think orbital rim though would probably be fine...it's not exactly as exposed an area as the jaw or cheekbones.  Are you into boxing or other contact sports?

[Gregor Samsa]

HA is not that hard. The paranasal area where I had HA injected isn't exactly soft but it's definitely not super hard either. I'm not sure I would recomend taking punches in the face either way.

[Optimistic]

No no no I meant in the lab.  It's a lot easier to get bacteria to grow you pure proteins than eukaryotic cells.  That said, a good approximation of bone will be impossible without stem cell. It's osteoblasts that lay down the collagen fibres in the right way i.e. in organised bundles


Hmmm, good point.  I was considering getting HA to my cheekbones when I got my revision rhino.  I must have mentioned to the surgeon that I did MMA but he never said that would be an issue.  Glad you brought it up though, maybe I shouldn't be getting HA on my cheekbones!

I think orbital rim though would probably be fine...it's not exactly as exposed an area as the jaw or cheekbones.  Are you into boxing or other contact sports?

Hold on, I was thinking about this in the shower... shower thoughts...

Does bone grafting resolve these issues? Wouldn't it have the collagen in it already needed to make it less brittle?