> The team admits that larger tissue - and even whole organs - will need to have the nanoparticles injected into them, rather than just sitting around them, to achieve the same uniform heating, but it's something they want to try next.
Bad news for the already-frozen heads and bodies, but likely good news for future cryo-preservation enthusiasts. Although, I have no idea how you'd get these nanoparticles into someone's brain.
I knew that tissue damage from ice crystal formation is one of the main problems with cryopreservation, but I didn't realize that current vitrification techniques had largely solved that problem during the freezing process (implied by the article), and that the we "just" don't have a way of successfully unfreezing samples without causing ice crystal damage.
The research papers states the problem thus:
> "Unfortunately, advances in tissue and organ cooling for cryopreservation have not been matched by similar advances in rewarming. Two technological barriers have proven difficult to overcome.
>
> First, the critical warming rates to avoid devitrification, the process of crystallization during warming, are typically an order of magnitude higher than the corresponding critical cooling rates [interesting!]."
>...
> "Second, these rates need to be sufficiently uniform throughout the material to avoid large thermal gradients, which produce thermal stress that often drives fractures or cracks within the tissue if they exceed the strength of the material (the tensile strength of vitrified VS55 [the cryoprotective solution used in the study] is 3.2 MPa)."
>...
>
>"...although we can vitrify and occasionally rewarm roughly 15 g of rabbit kidneys (10), and we can physically vitrify and rewarm in 80-ml systems, we do not have the technology to reproducibly rewarm these systems at sufficiently quick and uniform rates to avoid failure by devitrification and/or cracking using convection alone."
So, true, we still can't thaw out any of those frozen heads at Alcor, but potentially they aren't totally wrecked and could be safely warmed someday in the future...
According to this article, "The effect of nanoparticle size on the probability to cross the blood-brain barrier: an in-vitro endothelial cell model"[1]:
"GNPs[gold nanoparticles] of various sizes (20, 50, 70 and 110 nm) were synthesized and coated with barbiturate, which is a molecule that can easily penetrate the BBB [34]. Therefore, coating GNPs with barbiturate molecules will facilitate their penetration through the BBB, both for therapy and imaging applications. ... The results show that GNPs of size 70 nm are optimal for the maximum amount of gold within the brain cells, and that 20 nm GNPs are the optimal size for maximum free surface area."
The nanowarming article reports using iron oxide nanoparticles with a final average diameter of 50 nm (after some chemical prep & coating operations).
So getting a bunch of iron nanoparticles into a brain isn't out of the question.
Bigger challenge is probably getting them back out!
I wonder if you could do this with a very precise microwave array, something with thousands of microwave emitters controlled by temperature monitoring feedback loop - no particles.
Bad news for the already-frozen heads and bodies, but likely good news for future cryo-preservation enthusiasts. Although, I have no idea how you'd get these nanoparticles into someone's brain.