I, personally, have a lot of hope for CLARITY style brain preservation and clarification. After formaldehyde fixation, or congruent with it, a plastic gel monomer is introduced. Once the tissue is fully saturated with the fixative and the gel monomers, the gel monomers are ‘activated’ and link up to form a robust plastic matrix. Then the fats can be dissolved with a gentle soap mixture and washed away. What remains is a foggy haze of crosslinked proteins suspended in clear gel. Very robust, more so than just formaldehyde fixation alone.
The proteins can now be temporarily labeled with removable fluorescent tags, and laser microscopy used to image through thick slices of the gel. Great for 3D reconstruction of the positions of many different proteins.
We discuss the possibility of fluid preservation after tissue clearing in our article:
An alternative option is to perform tissue clearing prior to long-term preservation (118). This would remove the lipids in the brain, but offer several advantages, including repeated non-invasive imaging, and potentially reduced oxidative damage over time (119).
I’m not sure why this option is much more robust that formaldehyde fixation alone. I haven’t seen any strong evidence for that. I do agree that it is potentially very useful for 3D reconstruction, but reconstruction is a much different problem than preservation.
Ah, I mean, robust as in physically robust. The plastic gel that results is quite sturdy. The embedded clarified tissue is relatively easily handled without damaging it. Just my impression from having worked with fresh human brain tissue (delicate), cryopreserved-only (also delicate, in some ways even more so since the cold causes it to stick to tools and surfaces when handling it. In other ways, such as the glassy ice/preservative mixture being firm, not so delicate), formaldehyde or paraformaldehyde fixed (sturdier, relatively firm instead of mooshy, relatively easy to slice cleanly and deliberately), gel embedded (quite sturdy), hard resin embedded (extremely sturdy, appropriate for super thin slicing for electron microscopy).
I realize that reconstruction is a different problem from preservation, but if your goal (like mine is) is to preserve in such a way that you facilitate reconstruction, this seems like a big win.
Imagine, for instance, you must evaluate whether the reconstruction technology is sufficiently advanced to attempt to do a reconstruction for a particular brain. The threshold for ‘good enough tech to make an attempt’ is much lower if the brain is already prepared in a way (e.g. 1 cm thick slices of clarified stabilized tissue) such that it can easily be non-destructively imaged now, and then imaged again later if need be. A cryopreserved brain, on the other hand, needs to wait until you are very sure that the tech is good enough to handle it. Subjectively, I would feel quite reassured by my chosen method of brain preservation being: 1) stable at room temperature, and relatively robust to less-than-exquisitely-careful handling 2) ready to be non-destructively and relatively cheaply imaged, such that it would be an easy call to make a first attempt 3) preserved in a form that would facilitate reconstruction and multi-protein labeling
You are in good company in thinking that clearing and embedding the tissue in a hydrogel is the best approach. Others with expertise in the area have suggested the same thing to me. I’m just not convinced, so I think that more research is required to tell whether that is the best approach.
ETA: Sorry, just saw your edit. Interesting thoughts on the interaction between preservation and reconstruction. Your perspective and goals make sense to me, although it is not exactly what we are pursuing at Oregon Brain Preservation. We are agnostic as to the potential method of revival and expect this to be relatively further away in the future, if it ever becomes possible.
Yes, more research definitely seems like the best answer to me too.
I’m hopeful that some of these open questions about the relative efficacy of various techniques, and about how to image and then process the data, will be resolved before I’m on my deathbed and need to make a final will / living will.
I, personally, have a lot of hope for CLARITY style brain preservation and clarification. After formaldehyde fixation, or congruent with it, a plastic gel monomer is introduced. Once the tissue is fully saturated with the fixative and the gel monomers, the gel monomers are ‘activated’ and link up to form a robust plastic matrix. Then the fats can be dissolved with a gentle soap mixture and washed away. What remains is a foggy haze of crosslinked proteins suspended in clear gel. Very robust, more so than just formaldehyde fixation alone.
The proteins can now be temporarily labeled with removable fluorescent tags, and laser microscopy used to image through thick slices of the gel. Great for 3D reconstruction of the positions of many different proteins.
We discuss the possibility of fluid preservation after tissue clearing in our article:
And also in our fluid preservation article we have a whole section on it. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11058410/#S7
I’m not sure why this option is much more robust that formaldehyde fixation alone. I haven’t seen any strong evidence for that. I do agree that it is potentially very useful for 3D reconstruction, but reconstruction is a much different problem than preservation.
Ah, I mean, robust as in physically robust. The plastic gel that results is quite sturdy. The embedded clarified tissue is relatively easily handled without damaging it. Just my impression from having worked with fresh human brain tissue (delicate), cryopreserved-only (also delicate, in some ways even more so since the cold causes it to stick to tools and surfaces when handling it. In other ways, such as the glassy ice/preservative mixture being firm, not so delicate), formaldehyde or paraformaldehyde fixed (sturdier, relatively firm instead of mooshy, relatively easy to slice cleanly and deliberately), gel embedded (quite sturdy), hard resin embedded (extremely sturdy, appropriate for super thin slicing for electron microscopy).
I realize that reconstruction is a different problem from preservation, but if your goal (like mine is) is to preserve in such a way that you facilitate reconstruction, this seems like a big win.
Imagine, for instance, you must evaluate whether the reconstruction technology is sufficiently advanced to attempt to do a reconstruction for a particular brain. The threshold for ‘good enough tech to make an attempt’ is much lower if the brain is already prepared in a way (e.g. 1 cm thick slices of clarified stabilized tissue) such that it can easily be non-destructively imaged now, and then imaged again later if need be. A cryopreserved brain, on the other hand, needs to wait until you are very sure that the tech is good enough to handle it. Subjectively, I would feel quite reassured by my chosen method of brain preservation being:
1) stable at room temperature, and relatively robust to less-than-exquisitely-careful handling
2) ready to be non-destructively and relatively cheaply imaged, such that it would be an easy call to make a first attempt
3) preserved in a form that would facilitate reconstruction and multi-protein labeling
Thanks for the clarification and your thoughts. In my view, the question is to what extent the polymer gel embedding is helpful from the perspective of maintaining morphomolecular structure, so that it is worth the trade-off of removing the lipids, which could potentially also have information content. https://brainpreservation.github.io/Biomolecules#how-lipid-biomolecules-in-cell-membranes-could-affect-ion-flow
You are in good company in thinking that clearing and embedding the tissue in a hydrogel is the best approach. Others with expertise in the area have suggested the same thing to me. I’m just not convinced, so I think that more research is required to tell whether that is the best approach.
ETA: Sorry, just saw your edit. Interesting thoughts on the interaction between preservation and reconstruction. Your perspective and goals make sense to me, although it is not exactly what we are pursuing at Oregon Brain Preservation. We are agnostic as to the potential method of revival and expect this to be relatively further away in the future, if it ever becomes possible.
Yes, more research definitely seems like the best answer to me too.
I’m hopeful that some of these open questions about the relative efficacy of various techniques, and about how to image and then process the data, will be resolved before I’m on my deathbed and need to make a final will / living will.