Science Friday - The Science Of Replacing Body Parts, From Hair To Hearts

Episode Date: October 15, 2025

It seems like every week, there’s a new headline about some kind of sci-fi-esque organ transplant. Think eyeballs, 3D-printed kidneys, pig hearts.In her new book, Replaceable You: Adventures in Human Anatomy, science writer Mary Roach chronicles the effort to fabricate human body parts—and where that effort sometimes breaks down. Host Flora Lichtman speaks with Roach about everything from hair transplants to 3D-printed hearts, and why our anatomy is so hard to replicate in the first place.Guest: Mary Roach is a science writer and the author of Replaceable You: Adventures in Human Anatomy.Transcripts for each episode are available within 1-3 days at sciencefriday.com. Subscribe to this podcast. Plus, to stay updated on all things science, sign up for Science Friday's newsletters.

Hey, it's Flora Lichten, and you're listening to Science Friday. On today's episode, The Science of Replacing Body Parts, from hearts to hair. If you take armpit hair and put it on the head, this is a quote from some clinic in L.A. It is difficult to style. It seems like every week there is a new headline about some kind of sci-fi-sounding organ transplant. Eyeballs, 3D-printed kidneys, pig hearts. In the new book, Replaceable You, Adventures in Human Anatomy, science writer Mary Roach chronicles this effort to fabricate human body parts

and why it can be so monumentally difficult. The book does not skimp on the details, and neither do we. So if you want to hear the nitty-gritty on hair transplants or vaginoplasties, today is your day. And if you don't, don't say we didn't warn you. Mary, welcome to Science Friday. Thank you, Flora. This is your fifth book on the human body.

I think, if I'm counting right. It's a characteristically wild ride. What keeps you curious about our bodies? Well, they're just endlessly amazing and weird, I think, is the answer. I mean, because I didn't study biology or physiology in any formal way every time I step into a new system of the body, whether it's the elementary canal, you know, the gut or sexual physiology or whatever it is, I'm just kind of gobsmacked by the stuff that's kind of going on behind the scenes, behind the curtain. It's kind of miraculous and weird. Behind the skin drapes. Yeah.

Yeah, the skin drapes. Exactly. Mary, let's start with a transplant that weirdly is dominating my social feeds right now. Hair transplants. What is the state of hair transplant science? Yeah, hair transplants are interesting. The principle by which they work is something called donor dominance. So if you take follicles from the sides or the back of the head where they're not sensitive to testosterone, they're not going to fall out. You put those on the top of the head. Now they're going to stay permanent. They're going to fall out because they retain the characteristics of the back of the head, side and back of the head hair. They've got that back of the head hair identity. Yeah, exactly. Yeah. Exactly. So that's kind of the principle of it. But over time, of course, if your hairline recedes and it continues behind where the new transplants were, now you're going to have a bear patch

there. So it's kind of an ongoing relationship between the surgeon and the patient. And I looked into the history of hair transplants. It began with a surgeon named Okuda, Japanese surgeon. And I found the Okuda Papers, and he was going crazy with the donor dominance. He was like, you can take chest hair, you can take armpit hair, put it on the head. You can take head hair and use it for pubic alopecia, which I had never heard of, but apparently it is something that can happen. That's such a you book thing, Mary. I know, the Okuda papers. I was like, wow, he did that. He was like putting armpit hair on the mustache. Anyway, but it works. It all works. The issue,

Again, with donor dominance, say you had head hair in the pubic region, now you need to trim it. If you take armpit hair and put it on the head, this is a quote from some clinic in L.A. It is difficult to style. You did some self-experimentation for this book on this. Yes, I did. When I went out on book tour, I wanted to be able to demonstrate donor dominance. So I was at a hair transplant clinic in Southern California, and I asked if they would transplant a follicular unit from my head to my calf so that during the book tour I could roll up my

pant leg and just show them this long, luxurian hair that was growing on my leg. A leg pony. Yeah. Yeah, exactly. You know, and then it had, I think it had two hair, two follicles in it. So it would have been like, it would have been two hairs, long flowing hairs. Unfortunately, it didn't take. But they did it.

Like, were they like, oh, sure, we'll do it on our lunch break? Yeah, well, what happened? I was donating a dozen follicles to science. So they were studying just the process by which follicles grow, you know, from the basic cells, you know, keratinocytes and dermal papilla cells. How do they grow into a follicle so they could try to match that? So I said, sure, I will donate a dozen hairs to you and your effort. I have now a little tiny bald spot. Itty-bitty. Yeah, at the top of my head. And I said, well, while you're doing this, would you mind putting a few in my leg? I mean, I explained I really want to be able to demonstrate donor dominance. You know, this is educational. It's for.

Anything for psychoms, as we say. Exactly. Let's talk about Judy. Tell us about Judy. Oh, sure. Yeah. Judy is, she's kind of the starting point. for this book. She's a reader who wrote to me, going back almost four years now, and said,

I love your books, and would you write one about professional football referees? I don't know why. She thought that that was a good fit for me. I don't watch football. I don't know anything about football. But anyway, in the course of emailing back and forth with her, she mentioned that she's an amputee, specifically elective amputee. It was an elective. amputation. She had had spina bifida, her, because of the tumor on her spinal cord, her foot was twisted. She wasn't able to walk on it the way she wanted to be able to walk on it. She'd had numerous surgeries that weren't really resolving the problem, and she would see people with a prosthetic lower limb who were hiking and running and doing the things she couldn't really do. And she

tried, she was trying to find a surgeon to cut off her foot. trying to find a surgeon because it was hard to find a surgeon. It was hard to find somebody because they'd say to her, well, this is a healthy foot. It has a blood supply. It's not gangrenous. You could just get more surgeries. And it took her years to find someone to do the amputation. And it's an interesting issue.

I mean, there are reasons why surgeons don't want to do that. Such as. Such as what if there's phantom limb pain? What if the patient sues me? I can't put this foot back on. You know, it's just safer to say, let's try one more surgery. You know, safer in the sense of, am I going to help this patient or make things worse? Because there's a certain finality to cutting off a foot. It's also, you know, you need the insurance to cover it unless the patient wants to pay for the surgery out of pocket. So you need to make the case that this is necessary, medically necessary. And now if the food, you is not dying, that may be hard to do. Right. You know, in this chapter, you write about this bias that we seem to have towards wholeness, you know, that like the whole body is better than some incomplete body. And as I was reading it, I was thinking that culturally, like in other ways, we do accept body modification all the time, Botox, collagen, rhinoplasty.

And then sometimes we don't at all. And I wondered what you made of that. Well, I think we accepted if it's making us, quote, unquote, more attractive or more cutting edge or trendy. I think we don't accept it as much when it's perceived as a disability. There are studies that look at limb salvage surgery. And otherwise, let's keep the foot, but let's just do surgery after surgery after surgery and try and get it to the point. where it's almost as good as new versus let's be realistic. This is unlikely to get to 100% let's amputate now and the person will ultimately be better off in terms of discomfort and function. And time and again, things land on the side of amputation. But I think because it feels

drastic, you know, no matter how problematic that foot has been, it's you. It's you. And now it's gone. And I think particularly as an outsider imagining that when you're not dealing with the discomfort and the pain of this foot that doesn't really work well, you can't imagine that. You know, you put yourself in that position. The book is filled with stories. What was your favorite replacement from the book? My favorite replacement? Well, I found fascinating the ones in which some part of the human body is asked to become a different part. And there were a number of those. The body is very flexible, agreeable, you might almost say. I had dinner with a surgeon at Cedar Sinai, Center for Transgender Health and Surgery. And one of the techniques that is sometimes used is not a common first approach,

but to create a neo-vigina for a trans woman, you can take a section of the ascending, want to think it was, and you can keep it attached to a blood supply and kind of use it as a vagina, and then also do vulvoplasty. So, you know, you have all the other, the sort of outside components, but that's something dating from the 1800s or patients who'd had cancer, and there were a couple of surgeons who had tried that, and it does work. Another one that was fascinating to me is that you could kind of, you could use the rectum as kind of a third lung. If in certain situations, not recreationally, but if you, if you have an infant born very, very premature, so their lungs haven't developed to the point where they're really working,

you know, that means that you're going to have to go on the neonatal intensive care unit and to use a ventilator, a positive pressure ventilator on an infant that young can be, can damage the lungs. So if you could augment with material through the rectum, which you can, the body, the mucosa will absorb oxygen that way, then, you know, you get a boost. You can breathe through your butt. You can breathe through your butt is what I'm saying. That is an aha, I would say.

You can. Yeah, you can be somebody totally. me about that. And I'm like, so it's going all the way through. That's this like constant copious farting then. Like that, it's not, that doesn't, that doesn't. On babies, it's cute. It's cute. Exactly. Exactly. You know? They get away with it. That's right. Hey, don't go away because coming up after the break, just how close are we with 3D printed organs? We're kind of in the Wright Brothers era if you compare it to flight. Let's talk about lab grown organs. Where are we that? Well, bioprinted organs, I asked that exact question. I was at Carnegie Mellon,

the Feinberg Lab, where they're doing some very cool stuff printing, printing muscle in particular, and it's so much more complicated than you would think. It's not like printing a four-color brochure. And I said to Dr. Feinberg, how long before we're at the point where we can print an organ that can be installed. And he said, we're kind of in the Wright brothers era, if you compare it to flight. But that's a big era, you know? Yeah. And things happened fast between Wright brothers and plane flights, right?

I mean, I don't have the timeline, but it's pretty quick. And so stuff is movie. I mean, he said a couple of decades. And to me, that sounds slow because, you know, to me, that's, well, that was like three or four books. Whoa, that's not fast, but he's like, things are moving very quickly, two to three decades. No. So with printing muscle, it's fascinating. You have to align the cells so that they will perform the function for which that muscle is intended.

For example, the heart, and I didn't know this, when the heart squeezes blood out, it twists slightly, kind of like ringing out a sweater. you get the maximum amount of blood expelled from the, you know, via the musculature contraction. So if you're printing a heart, say, or a ventric, you print them in like a helix form, as opposed to, say, a hamstring muscle where they're kind of parallel. So, you know, you don't really think about that. Plus, you know, you got to feed that muscle. So are you going to print the vascular? You're going to, they're at the point where they're trying to figure out, okay, how much can we let the body do?

Because the body will grow in capillary. So some of it you can get the body to do, but at a certain point, you're going to have to print those. Nobody's printing nerves quite yet. So. And should I be imagining a 3D printer, or is this more like a chia pet where you have some kind of scaffolding and you sprinkle the? No, it's a, what I saw is it's a printer with like four extruder heads that can be printing different material like cellular material and one extracellular, like collagen material. and another one. So it is, it's, it's laying down one layer at a time. So it's a, it's a, printer. Findberg teaches a course where you can take like a office depot printer and you can kind of like rejigger it to make a 3D printer. So obviously, you know, for simpler things than hearts, but it is a, it's a, it's a printer. I'm assuming the best option for transplants is

there's still organ donors, though. Yeah, yes, the best option is right now still a human donor's organ. One of the things going on that I found kind of exciting because it's a little bit simpler than printing something or growing it from scratch at the University of Michigan extracorporeal life support laboratory, extracorporeal, meaning outside the body. It's a great name for a lab. It is, totally. So one of the things they're trying to do is extend the shelf life of a donated organ, like a heart say, okay, the traditional method where you put it on ice and you ship it out. You've got four to six hours to get it where it needs to go. But they're looking at tweaking that so that they can extend it to a few days or more, which would be very cool because you could now bring in a echocardiogram machine and take a look at the heart, see how it's pumping, how well is it, how healthy is that heart? And you could, and if there's an issue that could be fixed, you could fix it. So right now, you know, there's an age cutoff because it's, you don't have

time to take a look and see how well it's working. You basically say, well, these are too old, so we're not going to take them. But if you could do it based on quality, that'd be helpful. And if you could repair them, that would also be helpful. The title of the book is Replaceable You. Do you feel like we are replaceable or our parts anyway? No, the title really should be irreplaceable you, but it doesn't sound as good because it's a play on this song

that of course nobody who's younger than 40 is going to know Embraceable You. It's some old kind of standard from way back when that I happened to have heard of. But yeah, it should technically, the book should be called irreplaceable You

because I don't, you know, I tried to find just what's a simple bit of the body that we, what is, is there anything simple that we can replace so that it's 100% as good as what you were born with? And I thought about, okay, tears, that seems pretty straightforward, like salt water, a little bit of oil to keep it from evaporating, how hard could that be? And I contacted this researcher who has studied tiers for decades. And, you know, we went on for two of the free zooms because I'm too cheap to be. We went on for two 45-minute zooms about the tear film. And I said, so artificial tiers that you buy, he goes, well, yeah, those will buy you, you know, a couple of hours. But they kind of wash away the good stuff.

So, no, they're not. a replacement. Yeah, I mean, we as a species have gotten pretty good at coming up with substitutes when things go wrong. But in terms of plugging in something that is as good as what you started out with, I don't, I can't name one. Mary Roach is a science writer and author of the new book, Replacable You, Adventures in Human Anatomy. Thanks for coming on, Mary. Oh, thank you so much. That was really fun. Really fun. As always. Yeah. Yay. Okay. Thanks, Laura.

Thanks for listening. Don't forget to rate and review us if you like the show. And you can always leave us a comment on this segment on Spotify. We'd love to hear from you. Today's episode was produced by Rasha Aredi. I'm Flora Lickman. Thanks for listening.