Tuesday, October 16, 2007

Stemcell cyborgs

Yesterday morning I thought about the fact that I hadn't been doing exercises at all consistently since going to Greece for my eldest son's wedding in July. July? Ulp. So I did my forty pushups and forty situps and walked steadily (instead of trotted) up and down the front stairs for half an hour and did twenty pullups and weighed myself, at 180.8 pounds. Not good, not terrible. But while I walked, I thought about Aubrey de Grey's Ending Aging which I'd just read over the weekend. Hmmm...

Suppose that my exercise and not-too-terrible diet and ordinary medical care manage to keep me going into my mid-eighties, thirty years from now; all four grandparents lasted that long, although my parents did not. de Grey thinks that by then, we'll have found therapies for each of the major categories of aging-damage, so that I may feel no older than I do now... He concedes that some problems will be harder than others, and that we will still be headed downhill, but he thinks that the early treatments are likely to give us enough extra years of (active healthy) life that we can afford to wait for the solutions to the harder problems; lasting another thirty years may thus be good enough for "eternal youth."

Okay, I can see the pattern, and I can see some plausibility in each of his SENS solutions, but yesterday as I walked, I was thinking about alternatives.

de Grey's view of what I should be, several decades from now, seems to involve switching off all cell replication (as the one sure way to stop cancer) and then to introduce controlled cell replacement via embryonic stem cells every ten years or so, plus when you want to generate a baby; he goes on a bit about the inferiority of adult stem cells for the general problem. I think this is a bit of a problem in that the current embryonic cells naturally have the DNA of the embryo:

After receiving umbilical cord stem cells to replace bone marrow as treatment for non-Hodgkin's lymphoma, Greg Graves temporarily had three different sets of DNA.
I'm skeptical about gradually replacing my cells with all kinds of DNA. de Grey has possible solutions, but I don't think they're necessary: as of last June,
Three teams of scientists said yesterday they had coaxed ordinary mouse skin cells to become what are effectively embryonic stem cells without creating or destroying embryos in the process.
So it ought to be possible to generate stem cells for me that are really my stem cells, and stem cells for you that are really yours. How (and when) to replace bad cells with good ones? de Grey's program is not impossible, but I would rather think of four levels of replacement: cell-at-a-time, tissue, organ, and whole-body.

The whole-body replacement is what you see in Scalzi's science-fiction novel Old Man's War: you grow a new body and "upload" your consciousness to it. (This is also seen in some science fiction of the 60's or earlier; see Ben Bova's "Call Me Joe.) It's not impossible, and if we upload to higher-speed processing we may find lots of amusing changes, as in Accelerating Future's claim:

Mind uploading will make space travel useless. If my mind is running at a million times human speed, then the Moon, Mars, and Proxima Centauri look far more distant than they were previously. It becomes pointless to visit them.
Well, I think that I think that that's an implausible view of what uploading will amount to, based on an essentialist view of what a mind is, but in any case it's not an issue here: if we get that kind of uploading, then aging is irrelevant.

Organ replacement is possible for everything except the brain; cell-at-a-time or tissue replacement is possible for any tissue (with the caveat that cell-at-a-time replacement may need extension to handle intercellular connections and debris). If you replace old bad stuff with new good stuff, and find/destroy cancers as well as bacteria and virus invasions, then you can last indefinitely. I believe Current stem-cell treatments are of the cell-at-a-time variety, but tissues and organs can be grown on spider-silk scaffolding or, eventually, simply printed in 3D.

My belief is that continuous maintenance will work better than occasional updates, because a continuous-maintenance system can also help handle infections and injury repair. Imagine a microbot, about the size of a cell, with a few fixed functions. It carries a squished stem cell to the targeted tissue, through your circulatory system (or through tubes made of spider-silk or woven nanotube fibers which run alongside your circulatory system, forming a scaffolding through your whole body which turns you into a sort of a cyborg, though perhaps not very --how cyborgy you are depends on whether that scaffolding is dynamic, and how much information it carries, and what wavelengths it picks up wifi on, and so forth). The microbot drops its cargo as it collects a cell for disposal, and goes on back for more -- I'd propose that the stem-cell center for cyborg operations should be right around the heart, for obvious reasons. Selection is pretty random: about a tenth of one percent of your cells get replaced each day, giving each cell about a 693-day half-life. If a cancer starts to grow, or if an infection goes beyond the capacities of your regular immune system, or even if you get a bruise... then there will be a whole lot of bad or damaged cells in one place: some microbot will detect them very early, and you'll know what and where they are; cyborg healing should be pretty quick.

Or then again, maybe not.

upd: fixed half-life to be ln(2)/0.001 days; 1.001^693 =approx 2.


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