A team of California researchers discovered that they could create blood cells by layering hemoglobin and other proteins on top of a microscopic, donut-shaped polymer mold. When the proteins had a stable structure, they removed the polymer mold and presto - they had a classic blood-cell shaped hollow vessel. The cells are also biodegradable, so you wouldn't have synth-cells roaming your body forever. Here are typical red blood cells, below.

One synth-cell could carry oxygen through the blood just like a typical red blood cell, its unique shape allowing it to squeeze through tiny capillaries. But it could also carry drugs like anti-coagulant heparin, releasing it gradually. This could prove a boon for doctors trying to administer drugs to highly-targeted areas fed by the circulatory system. And of course it could prove a perfect system for hiding data or other sensitive substances in your bloodstream. One injection of synth-cells and you're carrying secret plans around in your blood that can't be detected by anyone.

via PNAS

Cameron has promised us that Avatar represents a huge technological advancement, a blending of real-world performances and imagination that will transport us to the foreign world of Pandora in an immersive, visceral way. But developers of medical technologies are looking to achieve the same sort of experience with the world we have, and the entertainment industry's advances in image capture and graphics processing are paving the way.

Certainly medicine is no stranger to computer animation, something they have long used to explain concepts and train personnel. And motion capture has been used for years in gait analysis. Physiotherapists often film patients wearing reflective motion capture markers to analyze their gait, in much the way that filmmakers use motion capture markers on their actors.

But the demand for improved computer graphics technology graphics from the entertainment industry means more sophisticated applications in medicine as well. Just this fall, Nvidia, which develops graphics processing technology for, among other things, gaming systems, demonstrated how the technology used to create immersive 3D experiences for games can also create immersive experiences of the human body. Along with Siemens Healthcare, Nvidia has developed an ultrasound viewing experience that sounds like it was scripted by Cameron: parents and healthcare workers can put on a pair of stereoscopic glasses and examine a fetus as if they were looking directly inside the womb. The demonstration comes just months after Nvida released its GeForce 3D Vision system, with a pair of stereoscopic glasses to improve the immersive experience of playing video games and watching 3D movies.

For filmmakers like Cameron, the goal is to capture the detail of the human experience, down to the most minute muscle movements and to create worlds that are so detailed as to appear real. If he's successful in creating an experience with Avatar that gives audiences both a fully immersive experience of a world that's completely invented and manages to translate the twitches of the human face onto an animated alien, imagine what his technology could accomplish when simply reflecting a world that actually exists. Perhaps the legacy of Cameron, Zemeckis, and other filmmakers working in these fields will include advances in virtual surgery, diagnosis, and other innovations in the medical field.

One set of researchers from the Max Planck Institute for Extraterrestrial Physics are trialling a device for quickly disinfecting human skin using low-temperature plasma, which would save a significant amount of time, compared to traditional hospital scrubbing.

The second is an "argon plasma torch", developed with ADTEC Plasma Technology Ltd in Japan, for disinfecting chronic non-healing wounds. This terrifying sounding device can specifically target bacteria but is harmless to human cells.

MRSA (Methicillin-resistant Staphylococcus aureus) arose as such a threat because it is mutation that is resistant all but the most powerful antibiotics. It can prove lethal if it spreads to your heart or other key organs. But finding stronger treatments against MRSA may not be the best long-term solution — by attacking the bugs with plasma, we may ensure that the mutations that survive will be even tougher. We're effectively breeding Fremen bacteria.

[via the Institute of Physics]

We've written about this kind of work before, specifically the research into optogenetics, which allows scientists to genetically-engineer light-sensitive reactions in animals or plants. What's different about this nematode experiment, however, is that no genetic engineering was involved - the little worm just ate a small amount of a chemical (basically the equivalent of popping a pill).

According to National Geographic:

After feeding a light-sensitive chemical to transparent, microscopic worms called nematodes, scientists at Simon Fraser University in British Columbia were able to paralyze the tiny creatures by exposing them to UV light. The paralysis works because UV light changes the structure of the ingested chemical, called dithienylethene.

Upon UV exposure, the normally clear chemical turns blue, and it shuts down the worms' metabolism, said study co-author Neil R. Branda. A shot of visible light restored the worms to normal, and the animals slowly began to wiggle around "as if they had never been paralyzed," the study authors say.

Will we be seeing the equivalent kinds of experiments taking place with humans? Yes indeed, though not for paralyzing people. Researchers are interested in light-activated medicines, which only get activated when exposed to light. This would allow doctors to activate drugs in very precise places in your body.

via NatGeo (thanks to Marilyn Terrell)

When he was 20 years old, Rom Houben was involved in a car accident that left him completely paralyzed. The accident didn't place him in a coma, however, and he tried desperately to communicate with those around him, but to no avail. Dr. House may have recognized "locked-in" syndrome in a few minutes, but Houben's doctors spent 23 years believing their patient was a vegetable, leaving Houben to experience nothing outside the hospital soap operas playing out in his room (apparently, his nurses were frequent gossips).

How did this happen? Houben's doctors determined that he was in a coma using the Glasgow Coma Scale, a widely used system that evaluates eye movement and motor responses. The trouble is that while Houben's body was functioning like a coma patient, his cerebral cortex was still chugging along. It took a brain scan to reveal that Houben was still fully conscious, and he is currently able to communicate thanks to a keyboard that responds to the barest tremors he can coax from his right hand.

While one would hope Houben was the unlucky winner of a terrifying medical lottery, situations like his may not be rare. Neurologist Steven Laureys, who performed the revealing brain scan on Houben, says that in 40 percent of supposedly vegetative patients he examined, brain scans revealed some level of consciousness. Both Houben and Laureys are advocating that doctors lean less on the Glasgow Scale and look more toward brain scans.

Brain scan finds man was not in a coma—23 years later [CNET]

The Rectenna:
Rectennas are like solar panels, but rely on light acting as a wave rather than a particle. Imagine a rooftop antenna, that would create DC power from visible light waves. The waves influence electrons in the antenna, driving them back and forth, and potentially inducing a current. Right now, this technology only works with microwaves, but researchers are working on new materials to make this possible.

Nanopolymers mimic gecko feet and insect wings:
Polymers can be created to mimic the properties of gecko feet and insect wings by forming structures with approximately 40,000,000 aligned nanocolumns per square millimeter, which could be tuned to adjust hydrophobicity, porosity, electrochemistry, chemical reactivity, surface energy and crystallinity. The material was developed by researchers at Penn State, and they plan to use it for targeted drug delivery.

Bioink:
3D bio-constructions, comprised of scaffolding, living cells, and drugs if needed. Cell printing allows for cells to be precisely positioned, and to create microvasculature. Layer by layer, a construction of human endothelial cells and fibrin would be created, the latter as a scaffold. This would provoke the further grown of endothelial cells, and the formation of microvasculature.

Programmable Matter:
This one's so off the wall and hard to summarize, I'm just going to quote the abstract. This is from David Erickson at Cornell:

A dichotomy exists between the bottom-up self-assembly paradigm used to create regular structures at the nanoscale, and top-down approaches used to fabricate arbitrary structures serially at larger scales. The former of these enables rapid, highly parallel assembly but lacks critically important features of the latter such as the ability to arbitrarily direct the assembly location and perform error correction. We and our collaborators have recently proposed an alternative approach which combines these two based on dynamically programmable self-assembling materials, or programmable matter. The uniqueness of our approach is that it uses dynamically-switchable affinities between assembling components faci litating the assembly of irregular structures. In this talk I present an overview of our approach and detail some of the analytical and experimental ad vances towards a programmable matter system we have recently made. These include: the development of a multi-chamber microfluidic chip for improved far-field assembly, the demonstration of near-field inter-tile affinity switching using a thermorheological assembly fluid and the ability to enhance assembly in three dimensions using unique fluid-structure interactions.

Surfboard Nanoparticles:
It turns out the ideal shape for nanoparticles is that of a surfboard, the same as platelets. It turns out cells of this shape stay close to the walls of vessels, which makes them better for targeting the blood supply of tumors.

Nanoboxes

Researchers at Washington University in St Louis have developed tiny gold cubes called nanoboxes which could deliver drugs to precisely targeted areas of the body. How? These boxes only open up and spill their drug contents when exposed to light.

The nanoscale boxes will come packed with a drug, and then release it when hit by a laser. To do this, nanoscale gold boxes are created, and then coated with a polymer called poly(N-isopropylacrylamide). The polymers cling to the outer walls of the cube like hairs on a muppet, and seal the pores on the cube, thus preventing any of the payload from leaking. When the gold is hit by light of a resonant frequency, it absorbs it and converts it to heat, and when the polymer is warmed, it shrinks and collapses, releasing the medicine. Once the light is turned off, the polymers stand on end again, re-sealing the boxes.

According to Dr. Jingyi Chen, one of the principal investigators on the technology, the opening and closing is nearly instantaneous. The nanocubes heat up "from a nanosecond to a femtosecond, [the drugs] are released a little bit slower, that takes around a millisecond." They cool down at the same rate, which allows for extremely fine targeting of dosage. The really cool part is that both the gold and polymer can be fine tuned to work under specific conditions. By thickening the gold walls, the wavelength of light that it can absorb shifts. In this case, they're aiming for the 750-900 nanometer range. Why this wavelength? Because at this point it can penetrate the human body very easily, and can travel inches into the body, as the muscle and blood doesn't easily absorb this wavelength of light. The polymer is then tuned to react to a level of heat that won't kill any cells, but is still above the normal temperature of the body. In trials, the boxes were exposed to a laser of the correct frequency, releasing their dose, and then closing up once the light was turned off. Researchers used the boxes as a way of delivering targeted chemotherapy drugs and antibiotics to a controlled area.

Synthetic Skin

If you're dealing with open wounds, once you flush out any possible bacteria, you need to deal with the realities of closing the flesh. In situations where an injury is over a certain size, it can't be relied on to close normally. Through the use of collagen extracted from skin, doctors can induce new skin to grow by giving it a framework over which to expand. The collagen can be extracted and grown from a variety of sources, such as donated skin, baby's foreskins (apparently up to four football fields worth, which is an utterly disturbing mental image), or from non-human sources, such as mammal organs or reptile skin. The collagen can also be impregnated with other ingredients, such as silver, which is naturally antibiotic. For anything from burns to bedsores, this skin scaffolding can lead to impressive regrowth and healing.

Nerve Regeneration

With spinal injuries, on the other hand, growth is a major problem. The creation of scar tissue around damaged areas of the central nervous system can prevent nerves from healing and regaining function. Previously, the enzyme chrondroitinase ABC (chABC) was used to reduce the scar tissue, but it functioned poorly at body temperature. Within an hour of being injected, it loses half of its potency, and the rest within a few days. Due to this a catheter or pump has to be installed, so that the enzymes can be repeatedly delivered over the two weeks required for it to be effective. Researchers at Georgia Tech have discovered away to reduce the thermal sensitivity of the enzyme, so it can stay in your body effectively for weeks, by bonding the chABC with the sugar trehalose. They also developed a new way to deliver the drug, via an injection of hydrogel filled with microtubes, which allowed deeper penetration than catheters, and slowly releases the drugs over a two week period. This means that the spinal scar tissue can be effectively reduced by a single injection, rather than weeks of constant exposure, and without requiring invasive implants.

To boost sales of a product called OP-1 Implant with a bone-setting filler called Calstrux. The mixture was not approved by the FDA, and in fact OP-1 was only supposed to be used on a rare bone disease, not on people who simply needed to have their bones knit together fast. Surgeons were urged by Stryker to shape the OP-1/Calstrux paste into a "tootsie roll" or "vienna sausage" shape and implant it. Unfortunately, the substance often broke down and drifted through patients' bodies. Bids of sprouting bone that looked like "oatmeal" or "white sesame seeds" would appear far from the site of injury where the substance had been implanted.

According to NPR:

When those wayward bits bit landed in places they shouldn't have, bone sprouted and, in some patients, had to be surgically removed. According to the papers, then-president of the company, Mark Philip, touted the combination at sales meetings as "perfect" even while knowing it wasn't FDA approved and that the company was receiving complaints about nasty side effects.

The indictment say the president and sales team continued to promote the illegal mixture for two more years, until Feb. 2008, without informing surgeons of the side effects to keep sales rolling.

Stryker and some of its partners have been indicted on several counts of wire fraud and conspiracy.

via NPR (thanks, Kle!)

The cells, discovered in 2005, are called Th17; they're thought to trigger inflammation and tissue injury associated with autoimmune diseases, but scientists at Houston's MD Anderson Cancer Center testing an assumed link between Th17 and cancer discovered exactly the opposite of what they expected. Instead of promoting the growth of cancer within a body - as inflammation tends to do - Th17 appeared to restrict it. This discovery opens the door to a potential new treatment for cancer victims, according to MD Anderson's Chen Dong:

While there is much work to be done, these findings imply the possibility of taking a patient's Th17 cells, expanding them in the lab and then reinfusing them as a treatment.

Autoimmune disease cells harnessed to fight cancer [New Scientist]

The Nobel Prize for Medicine was awarded to Elizabeth Blackburn, an Australian-American, with the Physics Prize being awarded to Canadian-American Willard Boyle and British-American Charles Kao. The Chemistry Prize was shared between Americans Venkatraman Ramakrishnan and Thomas A. Steitz and Israel's Ada E. Yonath.

Since 1985, Americans have dominated the science prizes, winning the Chemistry prize all but two years, the Medicine prize all but five years, and the Physics prize all but seven. Scientists are arguing that such results prove the need of government funding for long-term projects that may not show immediate return on investment; the National Institute of General Medical Sciences' Dr. Jeremy Berg cited Yonath's research as a good example of the kind of thing the government should be involved in:

I remember at the time being just completely stunned that she was somewhere between brave enough and crazy enough and because it was way, way, way beyond the technology available at that point... But it was seen as certainly completely unique and something potentially so important that it should be funded.

Nobel prize shows need for funding - scientists [Reuters]

Don't break out the face masks just yet. Right now, the research is not mature enough to say one way or the other whether you can infect your friends and family with chronic fatigue. But scientists have discovered that two-thirds of people suffering chronic fatigue are also infected with the retrovirus XMRV, which is related to mouse leukemia.

Chronic fatigue is a disease which affects human organs, resulting in feelings of exhaustion, and it affects about 1 million Americans.

According to Science:

Vincent Lombardi and colleagues uncovered the human retrovirus XMRV, which bears a genetic resemblance to a mouse leukemia virus, in 68 of 101 blood samples taken from patients with CFS, while identifying the retrovirus in only eight samples from 218 healthy patients. The researchers show that the XMRV is infectious and can provoke an immune response.

The researchers caution that XMRV does occur commonly in humans, and that there is currently no evidence that there is a causal link between the retrovirus and chronic fatigue. There is, however, enough evidence to merit further investigation.

via Science Express

The woman suffered from damaged corneas, and she seemed to have no options if she wanted to regain her sight. Luckily, one of her doctors had heard of a surgery developed in the 1960s in Italy, and in widespread use in Japan. The patient's tooth becomes the scaffold for an artificial cornea.

According to the Miami Herald:

A tooth is used, [lead surgeon Victor] Perez said, because it provides a stable, living platform of tooth, bone and cartilage that can remain alive, get nutrition from the eye and grow into a single piece with the cornea . . . The multistage procedure began in March when Dr. Yoh Sawatari, a dental surgeon at the University of Miami Medical School, extracted the tooth — coincidentally, it was Thornton's eyetooth, also called the canine tooth — shaved it flat horizontally, drilled a hole in it and inserted an acrylic lens. He implanted the tooth/lens prosthesis under the skin inside her cheek, intending to leave it there for three months so the combination could heal together. Unfortunately, she developed a sinus infection, so he had to remove it and re-implant it under a pouch of skin in her upper chest.

Meanwhile, an eye surgeon removed scar tissue lining her damaged cornea.

A month later, surgeons removed a patch of skin from the inside of her cheek and laid it over her cornea to replace the moist tissue lost to the disease.

Two months after that, Perez extracted the tooth-lens combination from her chest, cut a flap out of the skin over the center of her cornea, cut a hole down into the eye and inserted the tooth-lens. He sewed the flap shut to hold in the tooth-lens and cut a tiny hole so the lens can protrude a couple of millimeters out of the eye.

via Miami-Herald

This week in the Proceedings of the National Academy of Sciences, a group of researchers announced that they've figured out how to turn human fat cells into stem cells. According to a release about their work:

The researchers isolated adipose [fat] cells from adults between the ages of 45 and 60 and attempted to reprogram the cells into stem cells using an established genetic targeting method. At the same time, the authors began the same procedure with adult skin cells. The adipose cells produced adult stem cells nearly twice as fast and approximately 20 times more efficiently than skin cells.

Above, you can see a stem cell colony growing from fat cells. It's difficult to get stem cells because most of them come from embryos, which triggers both logistical and ethical problems for researchers. Scientists have had some luck reprogramming adult skin cells to become stem cells, but unfortunately (as these researchers demonstrated again) the method isn't reliable. Now the search for an endless supply of stem cells could be over. Joseph Wu, who led the study, told the Telegraph:

Not only can we start with a lot of cells, we can reprogram them much more efficiently. Fibroblasts, or skin cells, must be grown in the lab for three weeks or more before they can be reprogrammed. But these stem cells from fat are ready to go right away.

It turns out all those fattening foods may actually cure disease after all. Just liposuction your fat out, reprogram the cells to be stem cells, and grow yourself some new, unclogged arteries and a brand-new heart.

via PNAS

At the Ishikawa Komuro Lab at Tokyo University, a group working on superfast robotic motion has invented robot hands that can do things like dribble balls with alarming accuracy, twirl pencils blurringly fast, and tie knots with a flick of the wrist. This video, which has been making the rounds of the interwebs for the past couple of days, will astound you. Pay attention to the way the researcher talks about the robot motions - I think it's interesting that inventing these motions forces us to come up with ways of explaining complicated things we do with our bodies that we don't normally think about. Like "dynamic holding," which is a way of thinking about what dribbling really is.

It seems to me these would make terrific prosthetics. We already have artificial arms that are activated by neural interfaces - imagine if these were hooked into your nervous system. Essentially you would have superpowers, even if they only work on pencils and ping pong balls.

Meanwhile, Clemson University bioengineering researcher Nina Zhang has invented a biogel that you inject into somebody's brain to regrow injured brain tissues. Essentially, it's brain-in-a-tube: Zhang and her colleagues squirted this substance into rat brains, and it transformed into fully-functioning bits of gray matter. Says Zhang:

These results that we are seeing in adult lab rats are the first of its kind and show a sustained functional recovery in the animal model of TBI (traumatic brain injury). It also represents one of very few in the traumatic brain injury field that attempts structural repair of the lesion cavity using a tissue-engineering approach.

What she's saying is that basically this is a fast way to do tissue engineering on brains. And it might be ready for use in humans within three years.

Here you can see an image of some of the brain tissues that regrew after Zhang squirted the biogel into a damaged rat brain. The red indicates blood vessels, and the green shows nerve cells. Sounds like a great fix for damaged brains, but what about undamaged ones? All I'm saying is that I'd like a little extra brain to add to my current one.

via Ishikawa Komuro Lab and Clemson University

Apparently when this woman had seizures, she felt that her voice had become deeper and her arms were hairy. Once, when a female friend of hers with her as a seizure came on, she thought her friend was turning into a man too. The woman had no history of mental illness, nor did she have symptoms of gender identity disorder.

After imaging her brain, the researchers discovered that she had some damage to her amygdala, and weird electrical activity in her right temporal lobe during seizures. Had they discovered some gender identity center of the brain, which when damaged results in the feeling of changing sex? Absolutely not. In fact, there is no such center in the brain.

Instead, the researchers believe that this unusual case is simply one flavor of a more general experience of self-alienation that comes during epileptic attacks.

Reports ScienceNow:

More likely, [New York University neurologist Orrin Devinsky] says, the amygdala is one node in a network of brain regions essential for self-identity. When neural activity in this network goes haywire, a range of bizarre experiences can result, Devinsky says. The Russian novelist Fyodor Dostoyevsky wrote of feeling the presence of God in the moments preceding a seizure. More common, Devinsky says, are feelings of déjà vu or its opposite, jamais vu, the sense that a familiar environment has become unfamiliar. "In epilepsy, you can experience these intense and extreme emotions and in some cases misidentification of yourself and where you are in relation in the world," he says.

via Science Now

io9 pal Rene Najera, a public health worker with the state of Maryland, wrote in to ask if we could do an informal poll about how people prepare for flu season. This year, unlike those previous, you'll have the option to get two flu vaccines: The regular one, which includes antibodies for several anticipated flu strains; and one which can provide immunity against H1N1. So, for the sake of immunological research, give us your vaccine strategy.

Scientists at Wake Forest University injected multi-walled carbon nanotubes into tumors and then heated them up using a laser, a technique researchers have been talking about for a few years now. But what's exciting is the results of the latest study, published in the Procedings Of The National Academy Of Sciences. The mice that received the highest level of treatment saw their tumors disappear completely in 80 percent of cases.

Says Nanowerk:

Using a mouse model, the researchers injected kidney tumors with different quantities of MWCNTs and exposed the area to a 3-watt laser for 30 seconds. They found that the mice that received no treatment for their tumors died about 30 days into the study. Mice that received the nanotubes alone or laser treatment alone survived for a similar length of time. However, in the mice that received the MWCNTs followed by a 30-second laser treatment, the higher the quantity of nanotubes injected, the longer the mice lived and the less tumor regrowth was seen. In fact, in the group that received the highest dose of MWCNTs, tumors completely disappeared in 80% of the mice. Many of those mice continued to live tumor free through the completion of the study, about 9 months later.

You could actually watch the tumors shrinking, say researchers. And the mice maintained their weight and appeared healthy and normal.

A separate bit of research is also encouraging. A new method of delivering diptheria toxin-encoding DNA into ovarian tumors is at least as effective as chemotherapy — with no harmful side effects. And it could be tested in humans as soon as 18 to 24 months from now. In a nutshell, researchers injected nanoparticles into the peritoneal cavity, where ovarian cancer first starts to spread. And the nanoparticles delivered diptheria toxin that was genetically engineered to attack only ovarian cells. The toxin destroyed cells' ability to manufacture proteins.

In the past, scientists have worked on using viruses to deliver toxin-encoding DNA to a tumor, but using biodegradable nanoparticles instead is safer. And the treatment could also work in brain, lung and liver cancers.
Image from Nanotechweb.

[Nanowerk and Nanowerk]

I am at a loss for words.

Human sex from the inside out [New Scientist]

The test, as reported in the August issue of the journal Genome Research, relies on observing DNA methylation. The process involves two substances: methyl (an organic chemical group) and cytosine (the C in GATTACA). During DNA methylation, the loose methyl groups attach to the cytosine in DNA, which can lead to the suppression of important tumor-fighting proteins, and maybe eventually to cancer.

To detect this nefarious change in DNA, the newly-developed testing process essentially removes any non-methylated DNA, and dyes and measures whatever is left. This gives the tester an idea of how much methylation is happening in a patient's DNA, which also demonstrates the patient's risk for cancer.

Worth noting is the strange quantum dye that the process uses. The modified methylated DNA strands are mixed with "quantum dots," or tiny semiconductor crystals that can easily transfer energy. When light is shined on the quantum dots, now adorned with DNA strands as in the picture above, the energy is quickly put into the nearby molecules, lighting them up like a Christmas tree and making it easy for doctors to measure them.

From a practical angle, this test, as compared with current cancer screenings, is more sensitive and quicker. It would involve only a simple blood test, as opposed to an invasive biopsy. Plus, this test can specify which cancers a patient is at risk for. It's great to see chemistry nerds making life easier and safer for all of us!

New DNA test uses nanotechnology to find early signs of cancer [via EurekaAlert]

Further Reading: What's the Future of Cancer Diagnosis?

(Image: glowing methylated DNA arrayed around a quantum dot, from Yi Zhang/JHU)

Scientists have been looking at embryonic development and experimenting with organ regrowth for years. This team was working on regrowing 3D organs in place. Their experiments were a success, and they were able to regrow teeth in laboratory rats.

To make these glowing regrown teeth happen, first the team created a "germ," or a seed from which the tooth can grow. This germ was coded with the fluorescent glowing dye to track the tooth development. Then they transplanted the tooth germ into the jawbone of a rat. Finally, they tested the regrown tooth. The team found that the teeth were essentially as strong as natural teeth and were able to grow nerves throughout, making them very similar to naturally developed teeth.

In the research team's experiments, the fluorescent glowing dye was a side point, but it isn't hard to imagine bio-luminescent add-ons catching on in the future. Imagine showing off your new glowing teeth to your friends, or even growing a full head of fluorescent pink hair. It could mean a whole bio-punk movement: body modification taken to the next glowing level!

For now, though, the medical implications are as exciting as the aesthetic. The successfully regrown tooth experiment means being able to replace more complex organs more easily in the future.

Fully functional bioengineered tooth replacement as an organ replacement therapy [Proceedings of the National Academy of Sciences]