Speaker 1: Welcome to tex Stuff, a production of I Heart Radios,
Speaker 1: How Stuff Works. Hey there, and welcome to tex Stuff.
Speaker 1: I'm your host, Jonathan Strickland. I'm an executive producer with
Speaker 1: I Heart Radio and a love of all things tech. Now,
Speaker 1: before I jump into this episode, I want to address
Speaker 1: an error I made multiple times in a recent episode,
Speaker 1: and it's a very Jonathan kind of mistake. So in
Speaker 1: the episode I did about smoke detectors, I talked about
Speaker 1: the radioactive element ama sirium to forty one. Here's the problem.
Speaker 1: I inserted an extra syllable there, and even in my
Speaker 1: notes I had it spelled correctly. It's a marasium to
Speaker 1: forty one. So in other words, I I kind of
Speaker 1: pulled a classic Homer Simpson goof, like a Saxoma phone uh,
Speaker 1: several times in one episode. So thanks to Twitter user
Speaker 1: Ken Waldrop for pointing it out. It is incredibly embarrassing.
Speaker 1: It is all my mistake. It's totally me. It's kind
Speaker 1: of an insight into how Jonathan's brain works, which is
Speaker 1: not all that great sometimes. I don't know why I
Speaker 1: inserted an extra syllable multiple times throughout that episode, but
Speaker 1: thank you Ken for letting me know, so that I
Speaker 1: could correct that error in this episode. Let's move on
Speaker 1: to another episode where I'm sure I will mispronounce multiple things.
Speaker 1: But it's a fascinating topic, or at least I find
Speaker 1: it fascinating. So I was looking through tech news recently
Speaker 1: and I saw a really interesting article. It was covered
Speaker 1: in a lot of places. The first place I saw
Speaker 1: it was engadget, but I read about it elsewhere as well,
Speaker 1: and on engadget it has the title Researchers find a
Speaker 1: way to three D print whole objects in seconds. Now
Speaker 1: that immediately got my attention because typically three D printing
Speaker 1: takes a while, sometimes a long while to create an object,
Speaker 1: because it typically does it layer by layer. The answer
Speaker 1: in this case lies in the technique called tomography. So
Speaker 1: this episode is going to cover a few different topics
Speaker 1: so that I can explain as best I can how
Speaker 1: this methodology works. So let's start talking first about just
Speaker 1: three D printing in general. It's a type of additive manufacturing,
Speaker 1: which means you're making something by adding to it rather
Speaker 1: than taking unwanted stuff away. So with traditional sculpture, the
Speaker 1: sculptor might take a block of some material like marble
Speaker 1: and then carve it and cut away tons of it.
Speaker 1: There's an undoubtedly apocryphal quote attributed to Michaelangelo who allegedly
Speaker 1: described his process as you just chip away the stone
Speaker 1: that doesn't look like David. Now, Mikey probably never said that,
Speaker 1: but you get the point of the quote. You're removing
Speaker 1: material and whatever is left after you're done is the
Speaker 1: finished piece. Additive manufacturing goes the opposite way. You add
Speaker 1: material bit by bit until you have the thing you
Speaker 1: wanted to make. So it's kind of like how potters work,
Speaker 1: you know, you add clay until you've got enough mass
Speaker 1: to shape it into whatever final form they have in mind.
Speaker 1: And three D printers work in a similar way. They
Speaker 1: lay down thin layers of material one after another until
Speaker 1: layer by layer they have completed a print job, and
Speaker 1: typically the bottom surface would be whichever one is the
Speaker 1: largest of the finished three D object, So it might
Speaker 1: not necessarily be the bottom of the three D object,
Speaker 1: but the bottom of the print job, because a larger
Speaker 1: surface area means it's going to support the rest of
Speaker 1: that physical structure much more easily. There are three D printers.
Speaker 1: They can work with all sorts of materials. The kind
Speaker 1: of average person would have access to. Uses plastic, one
Speaker 1: of two types, and a typical three D printer uses
Speaker 1: spools of plastic cable as printing material. So the cable
Speaker 1: gets pulled into a piece called the extruder, which heats
Speaker 1: the plastic to make it sort of a semi liquid
Speaker 1: before depositing layers of this plastic, usually mixed with some
Speaker 1: sort of binding agent, onto the printing surface, or after
Speaker 1: the first layer, onto the last layer that was laid down.
Speaker 1: This process tends to take a while, and you have
Speaker 1: to get the temperature and speed just right, or you
Speaker 1: get problems with layers not adhering to each other properly,
Speaker 1: or peeling away or sticking to the extruder as it
Speaker 1: moves through its path. I say this from experience. We
Speaker 1: have a three D printer in the office. We have
Speaker 1: successfully printed on it perhaps four times. We have run
Speaker 1: it many more times than that. But however, it does
Speaker 1: me you can actually make whatever the object is relatively
Speaker 1: quickly compared to more traditional forms of manufacturing, and there
Speaker 1: are lots of benefits with three D printing. One is
Speaker 1: that it makes the prototyping process much faster. So let's
Speaker 1: say you got an idea for the body shape of
Speaker 1: a car. You could build a three D model of
Speaker 1: the shape. Then you could use a three D printer
Speaker 1: to create a small physical model of what you had
Speaker 1: in mind, and you could test that and say a
Speaker 1: wind tunnel, to make sure it would work the way
Speaker 1: you planned before you moved further into the process. But
Speaker 1: maybe you discover that your design has some unexpected quality,
Speaker 1: like increased air resistance, so the extra drag would mean
Speaker 1: the car would not be as fuel efficient, so you
Speaker 1: need to go back to the drawing board. You could
Speaker 1: go make some quick adjustments to your model and then
Speaker 1: send that to the printer again and print up a
Speaker 1: new prototype and would go pretty quickly. You don't have
Speaker 1: to carve away its stuff over and over, and another
Speaker 1: big benefit is that you have less waste overall. You're
Speaker 1: taking material and then only using a small part of
Speaker 1: the overall mass and throwing the rest away. So lots
Speaker 1: of companies that manufacture physical goods use three D printing
Speaker 1: for the prototyping phase, and several are using three D
Speaker 1: printing in the actual manufacturing process for finished items, whether
Speaker 1: it's for a small component that goes into a bigger
Speaker 1: product or a complete product from top to bottom. And
Speaker 1: while we've heard predictions that three D printing would bring
Speaker 1: about the end two mass manufacturing as we know it,
Speaker 1: the future in which everyone either has a three D
Speaker 1: printer or has easy access to a business that owns
Speaker 1: a three D printer. Thus far, that has not happened.
Speaker 1: We have not seen a world where we all just
Speaker 1: print whatever we need on demand, where I sit there
Speaker 1: and think, oh, I need a new chair, so I'm
Speaker 1: gonna go down to the three D printers down the
Speaker 1: block and get one printed out. That has not yet happened.
Speaker 1: Maybe one day that will change, but for now the
Speaker 1: process isn't quite as convenient or as reliable as more
Speaker 1: traditional manufacturing methods. But that's traditional three D printers, and
Speaker 1: I've done episodes to go further into detail about their
Speaker 1: history and how they work. So you can go and
Speaker 1: listen to those classic episodes if you want to hear
Speaker 1: more about that. But that's not what we're going to
Speaker 1: focus on for the rest of this episode. Now it's
Speaker 1: time to switch over to tomography, which is not the
Speaker 1: science of how tom works. It's that has nothing to
Speaker 1: do with tom and my space. Now, this relates to
Speaker 1: radiography and the use of stuff like X rays. Those
Speaker 1: we'll learn. It's not exclusively limited to X rays. And
Speaker 1: I know I've talked a lot about X rays in
Speaker 1: recent episodes, but bear with me here. So early on,
Speaker 1: physicists learned about how X rays could penetrate solid material
Speaker 1: much more effectively than visible light could, and that if
Speaker 1: these X rays hit a sheet of photoreactive material, it
Speaker 1: would cause that material to react, so it reacted as
Speaker 1: if visible light had hit it. So if you put
Speaker 1: something like, I don't know your wife's hand between an
Speaker 1: X ray emitter and a sheet of photographic paper, you
Speaker 1: would end up with an image of your wife's skeletal
Speaker 1: hand on that paper. I say wife because runt Jen
Speaker 1: Vilham run Jen, who discovered X rays, used his wife
Speaker 1: as a photographic subject for a lot of early X
Speaker 1: ray photographs, exposing her two ridiculous amounts of radiation in
Speaker 1: the process. At the time, he didn't know any better.
Speaker 1: But that's why I use that specific example. Now, why
Speaker 1: do you get the skeleton hand in the finished image. Well,
Speaker 1: it's because X rays can pass through different materials with
Speaker 1: different levels of ease, so they can pass through less
Speaker 1: dense material more easily than the denser stuff, and that
Speaker 1: follows common logic. That just makes sense, right. So X
Speaker 1: rays can pass through muscle tissue far more readily than
Speaker 1: they can pass through bone, and bone is just much
Speaker 1: more dense. They can pass even less easily through something
Speaker 1: like metal. So if you were to take an X
Speaker 1: ray photo of a typical person's hand, the bone would
Speaker 1: block more X rays from hitting the paper than the
Speaker 1: soft tissues would. The soft tissues would allow more X
Speaker 1: rays to come through. So the result is that the
Speaker 1: image on the photographic paper would be kind of like
Speaker 1: a negative. The skeletal hand would show the spots on
Speaker 1: the paper where X rays were blocked from hitting it,
Speaker 1: and that meant that it would be relatively unexposed to light,
Speaker 1: and the softer tissues would allow it to go through,
Speaker 1: and thus you would have a greater exposure. So you
Speaker 1: can see that skeletal hand because the contrast between these
Speaker 1: two sections where the rays were blocked versus where they
Speaker 1: passed through. Now, the discovery of X rays came at
Speaker 1: the very end of the nineteenth century. The medical establishment
Speaker 1: quickly saw the potential for this technology. They saw that
Speaker 1: this could be really valuable. You can see stuff like
Speaker 1: broken bones very easily. They immediately recognized its usefulness. They
Speaker 1: also over time recognized some of the dangers of X rays,
Speaker 1: such as radiation exposure, which was really more of a
Speaker 1: problem for doctors than it was for patients. Patients would
Speaker 1: get small exposures whenever they would get an X ray
Speaker 1: done on them, but the doctors who were performing the
Speaker 1: X rays, we're getting exposures time and time again, and
Speaker 1: they were the ones who were really sorry to develop
Speaker 1: serious problems because X rays are a form of ionizing radiation,
Speaker 1: which means they can do cellular damage, and that in
Speaker 1: turn can manifest in different ways from radiation poisoning to
Speaker 1: higher risk of contracting cancer. So uh, they also saw
Speaker 1: a limitation of this technology, namely that X ray photos
Speaker 1: have the same problem as any traditional photo has. They
Speaker 1: produced two dimensional images of three dimensional objects. So in
Speaker 1: medical schools, it was pretty standard practice for students to
Speaker 1: work with or even produce cross sections of organs. Essentially
Speaker 1: involves cutting organs into thin slices like a loaf of bread,
Speaker 1: and then examining each of those slices carefully, and it's
Speaker 1: an effective way to teach medical students about anatomy and
Speaker 1: organ structures as well as learning what is and isn't typical,
Speaker 1: so that if one were to encounter an atypical scenario,
Speaker 1: the doctor would be able to recognize that as such. Now,
Speaker 1: if you put all the slices together, it looks like
Speaker 1: the original organ. Of course, the big problem with this
Speaker 1: method is that it usually requires the original owner of
Speaker 1: that organ to be, you know, not alive anymore, making
Speaker 1: it a little difficult to apply medical knowledge to their case.
Speaker 1: So it's a useful educational tool, but not great for
Speaker 1: diagnosing a patient, at least not in a timely manner.
Speaker 1: So doctors at the time were hopeful that there would
Speaker 1: be a new technology that would make it possible to
Speaker 1: create images of three dimensional objects in an accurate way,
Speaker 1: specifically organs showing their volume metric property, so that you
Speaker 1: could do things like look at them in perspective, as
Speaker 1: opposed to looking at what amounted to a series of
Speaker 1: silhouettes of organs and bones. If you took an X
Speaker 1: ray of someone's torso the rib cage would obscure a
Speaker 1: lot of your your view. And then your lungs in
Speaker 1: your heart are located in an area where it's hard
Speaker 1: to see them individually because they're overlapping each other, so
Speaker 1: they wanted to find a way to create a three
Speaker 1: dimensional representation of this. Doctors at the time, we're hopeful
Speaker 1: that they could come up with a way of doing
Speaker 1: this in a practical manner, but they weren't really sure
Speaker 1: how that would happen now. One person whose work would
Speaker 1: contribute to achieving this goal, though that was not his
Speaker 1: particular aim at the time, was a mathematician in the
Speaker 1: early twentieth century named Johann Raydon. In nineteen seventeen, Raydon
Speaker 1: produced a mathematical transform, a specifically an integral trans form,
Speaker 1: which means you add up basic elements until you get
Speaker 1: the full thing you're looking for. There are a lot
Speaker 1: of different versions of integral transforms, and he also discovered
Speaker 1: its inverse. So this transform described mathematically a process that
Speaker 1: could be realized in a practical setting, namely that one
Speaker 1: could take the result of projections of an object and
Speaker 1: reconstruct an image in real space based on those projections.
Speaker 1: It all has to do with geometry, and again into
Speaker 1: further detail would require someone far more educated in mathematics
Speaker 1: than i am, but there are some great videos online
Speaker 1: about the Radon transform that give it a good explanation
Speaker 1: of it, including one from Rich rad k It's titled
Speaker 1: d I P Lecture eighteen Reconstruction from Parallel Projections and
Speaker 1: the Radon transform. You can find that on YouTube if
Speaker 1: you want to see a really detailed mathematical explanation of
Speaker 1: this that is far beyond what I can give you.
Speaker 1: Radon's work was interesting, but at the time there wasn't
Speaker 1: really any practical way to put it into actual use.
Speaker 1: One early step in getting to the goal was the
Speaker 1: development of linear tomography, or the ability to take radiographic
Speaker 1: images of a specific plane or cross section in a
Speaker 1: solid object like a human being. So, in other words,
Speaker 1: you could create a cross section of a human being
Speaker 1: without having to cut the human being open. It was
Speaker 1: a miracle. So this relates to that mathematical transform I
Speaker 1: just mentioned, and interestingly, in the early days of tomography
Speaker 1: they that actually would predate Radon's transformers. Physicists were thinking
Speaker 1: about how to take X ray images from multiple angles
Speaker 1: to get a more complete picture of a specific internal
Speaker 1: organ as early as nineteen fourteen. For actual implementations, there
Speaker 1: was a period from around nineteen twenty one to nineteen
Speaker 1: thirty four in which multiple people all working independently, all
Speaker 1: not knowing about each other, started to build systems capable
Speaker 1: of producing what would be called tomographic images. They didn't
Speaker 1: know about the other's work for a very long time,
Speaker 1: and when they found out. Can you guess what happened?
Speaker 1: If your guess was, I bet they all rushed to
Speaker 1: be the one to claim credit for it, you'd be right,
Speaker 1: because that was a very human reaction to say I'm
Speaker 1: the reason why this works. But that was put on
Speaker 1: hold because a little thing called World War two happened.
Speaker 1: The basic idea was the same from one instance to
Speaker 1: another instance that all these people were coming up with,
Speaker 1: but the actual details were different, such as the angles
Speaker 1: of motion for the X ray emitter and the detectors
Speaker 1: which would be on the opposite side of the patient,
Speaker 1: or the speed at which these components should move with
Speaker 1: each other. Also, the word tomography itself was coined around
Speaker 1: nineteen thirty five and comes from the Greek word thomas,
Speaker 1: meaning section, and the suffix graphy from the Latin word
Speaker 1: graphia mean study of So it's the study of sections
Speaker 1: and it combines Greek and Latin. So I have friends
Speaker 1: who hate this word. They would say, stick with one
Speaker 1: or the other, um, one of them sitting right across
Speaker 1: from me, but never mind that anyway. So imagine you've
Speaker 1: got a person standing in front of you, and you
Speaker 1: are somehow able to produce an image of a slice
Speaker 1: of that person from head to toe, and their shoulders
Speaker 1: are facing you. So it's like it's like you just
Speaker 1: are able to look at a slice of them right
Speaker 1: from the middle of that person, but you're able to
Speaker 1: do it without, you know, actually physically slicing them. So
Speaker 1: how does it work. Well, I'm gonna do my best
Speaker 1: to try and explain this process. So this is gonna
Speaker 1: be an example. They don't all have to look this way,
Speaker 1: but this is a way for me to explain how
Speaker 1: this could happen. Imagine that we've got a patient laying
Speaker 1: down on an X ray table, and above this patient
Speaker 1: there is a track that's in an kind of like
Speaker 1: a rainbow above the patient, starting from around the head
Speaker 1: and ending somewhere around let's say the knees. Uh On
Speaker 1: this arc is mounted an X ray emitter, So this
Speaker 1: is the tube that will shoot out X rays at
Speaker 1: the patient. On the opposite side are X ray detectors.
Speaker 1: This is underneath the table and the two can move
Speaker 1: with each other, So you start UH make moving the
Speaker 1: the emitter along this track. It moves gets in motion
Speaker 1: once it starts. Shortly after it started to move, it
Speaker 1: begins to emit X rays, and then it nears the
Speaker 1: end of its arc, it stops emitting X rays and
Speaker 1: then it comes to a physical stop. And you're aiming
Speaker 1: this at a specific point on the patient. Perhaps you
Speaker 1: want to image this patient's liver, so you've aimed the
Speaker 1: emitter at the patient's liver, and as it goes through
Speaker 1: this entire arc, it still stays focused on a liver,
Speaker 1: so that point of focus does not change as it
Speaker 1: goes through this arc. UH. That liver will then become
Speaker 1: the pivot point for this particular scan. The ends of
Speaker 1: the seesaw of this pivot point would be the X
Speaker 1: ray tube on one side and the X ray receptors
Speaker 1: on the other side. So if you think of a
Speaker 1: seesaw going up and down, in this case, it's not
Speaker 1: really going up and down, it's just going through an arc.
Speaker 1: Then one end of the seesaw is the emitter, the
Speaker 1: other end of the seesaw is the receiver, and the
Speaker 1: middle is the liver. The pivot point the The angle
Speaker 1: from the top of the arc to the bottom of
Speaker 1: the arc is called the tomographic angle. The angle at
Speaker 1: which the X ray emitter starts to admit X rays,
Speaker 1: and the angle at which are and when it stops
Speaker 1: is called the exposure angles. There are two different angles
Speaker 1: in here. The exposure angle is always going to be
Speaker 1: smaller than the tomographic angle because of that. So how
Speaker 1: why why would you go through all this? What? What's
Speaker 1: the end result? I'll explain after we take a quick break. Okay,
Speaker 1: I just described this weird process of an X ray
Speaker 1: emitter going across an arc aimed at a patient. Why
Speaker 1: would you do that? Well, it's because the image produced
Speaker 1: at the end of this process creates a very sharp
Speaker 1: picture of everything within the exposure angle along the focal
Speaker 1: plane of the pivot point. So let's say you're looking
Speaker 1: at this patient from the side the patient's laying on
Speaker 1: the table, you're off to an observation area off to
Speaker 1: the side. The focal plane is the horizontal slice of
Speaker 1: that patient that runs through the pivot point. So let's
Speaker 1: say that you've determined that you wanted to aim at
Speaker 1: a point that's about eight centim ter's up from the
Speaker 1: surface of the table. That means that at that eight
Speaker 1: centimeters height along that entire horizontal slice of the patient,
Speaker 1: you're gonna get a very clear X ray image. The
Speaker 1: further out you are from the focal plane, so the
Speaker 1: further towards the patient's front or anterior and back or posterior,
Speaker 1: then the fuzzier the image is going to be. Now,
Speaker 1: in this way, a radiologist could produce a sharp image
Speaker 1: of a specific slice inside a person. You would get
Speaker 1: that cross section, but you still have to deal with
Speaker 1: other issues, such as the fact that bone is more
Speaker 1: effective in blocking X rays than soft tissues or water.
Speaker 1: So if the area you wanted to look at was
Speaker 1: below bone, such as within the rib cage, the bones
Speaker 1: would still present something of a problem, but you would
Speaker 1: still get a better look within a specific depth of
Speaker 1: a person, if that makes sense. So it was definitely
Speaker 1: an evolution of the science of radiology. Now you can
Speaker 1: repeat this process, and you could adjust the pivot location
Speaker 1: further up or further down to get sharp images along
Speaker 1: different depths. But that also means you're also exposing the
Speaker 1: patient to multiple, you know, exposures of X ray radiation.
Speaker 1: A little exposure presents relatively low risk, but the more
Speaker 1: you're exposed to X rays, the greater the risk of
Speaker 1: adverse effects like damage to yourselves, right, so you want
Speaker 1: to be careful with this. Over time, advances in technology
Speaker 1: created the possibility of axial tomography, which was introduced in
Speaker 1: the nineteen seventies. So in this version, instead of having
Speaker 1: an arc above the patient, the X ray emitter and
Speaker 1: receivers are mounted on a ring that goes around a table.
Speaker 1: So think of a table that passes through a ring
Speaker 1: and the patient lays on the table. The emitter and
Speaker 1: the receivers are mounted on opposite sides of this ring,
Speaker 1: and the patient and table are at the center of it.
Speaker 1: And with axial tomography, you take a series of images
Speaker 1: with the X ray tube along different points of the ring,
Speaker 1: moving in a full circle around the patient it on
Speaker 1: the table, So you get above, below, and on either
Speaker 1: side and every angle you can really imagine, and the
Speaker 1: machines typically take a ton of quick images as the
Speaker 1: machine rotates around the table very very fast. You can
Speaker 1: actually find videos of a cat scan because this is
Speaker 1: what this is a computer axial tomography scan. You can
Speaker 1: find videos of this equipment rotating where the cover is
Speaker 1: off so you can see how the internal structure rotates
Speaker 1: within this this machine. It's amazing how fast it goes.
Speaker 1: Uh I found it almost alarming how fast it goes,
Speaker 1: because these machines also are very big, and to think
Speaker 1: that something is spinning that fast around you is a
Speaker 1: little unsettling. But the result of all this fuss is
Speaker 1: you get a cross section image of the subject, and
Speaker 1: the table can be moved further in or out of
Speaker 1: the ring, and another series of images can be taken,
Speaker 1: and that gives you another cross section, and you could
Speaker 1: do it again and take another cross section. You do
Speaker 1: this no off and you eventually end up with images,
Speaker 1: three dimensional images of the stuff you want to take
Speaker 1: pictures of, and you're able to put that together through
Speaker 1: the help of computers. Engineers would call these CATS scans,
Speaker 1: and later just CT scans. A bit later, in the
Speaker 1: nineteen seventies, you had Dr Raymond Damedian who created a
Speaker 1: device capable of imaging internal body scans using magnetic resonance
Speaker 1: rather than X rays. The major benefit of this technology
Speaker 1: is that, unlike X rays, m r I machines do
Speaker 1: not emit ionizing radiation, so you don't get that radiation
Speaker 1: damage to yourselves with an MRI machine. There are other
Speaker 1: damages if you are other dangers I should say, if
Speaker 1: you happen to have, you know, magnetic material on you,
Speaker 1: that's bad to be anywhere close to an m r
Speaker 1: I when it goes off, because you could stand to
Speaker 1: injure yourself or somebody else seriously, if they are in
Speaker 1: between the m r I machine and whatever it is
Speaker 1: you have on your body that is my metic or
Speaker 1: you know, is ferromagnetic. Today, though, hospitals typically have both
Speaker 1: mr I machines and CT scanners because they're actually different
Speaker 1: reasons to use either one, like they're each good for
Speaker 1: different things. Uh. Over time, scientists and doctors have really
Speaker 1: refined the tech of CT scanners to really minimize the
Speaker 1: amount of ionizing radiation that patients will absorb, so they're
Speaker 1: they're pretty darn safe. So what does all this have
Speaker 1: to do with three D printing? Well, in this case,
Speaker 1: tomography is all about creating a three dimensional object in
Speaker 1: real space using light and special photoreactive resins. It's super
Speaker 1: fascinating stuff which you probably can't tell just based on
Speaker 1: the words I'm using. So this reson I'm talking about
Speaker 1: is a type of photo polymer polymers are long chain molecules.
Speaker 1: A typical polymer is a chain of similar building blocks
Speaker 1: linked together, and by building blocks, I mean monomers, and
Speaker 1: a monomer can either be a single atom or more frequently,
Speaker 1: it's a small group of atoms that form a molecule,
Speaker 1: so that's a monomer. A polymer is a chain of
Speaker 1: these monomers that are all chemically bound together in some way.
Speaker 1: So you can think of the chemical bindings as the
Speaker 1: link holding two elements together, and you get long, long,
Speaker 1: long chains of these monomers to create polymers. A lot
Speaker 1: of polymers are artificial, including plastics. It's a common polymer
Speaker 1: we encounter in our day to day lines. But you
Speaker 1: can also find some natural polymers cotton, silk, cellulose, which
Speaker 1: is the stuff that woody plants are made out of, starches.
Speaker 1: These are all polymers, and proteins are polymers, right. Proteins
Speaker 1: are polymers that are created by chaining together amino acids.
Speaker 1: Larger polymers are naturally heavier than smaller polymers. Makes sense.
Speaker 1: You've got more stuff, it's gonna have more weight. They
Speaker 1: also have higher viscosity, which means they resist flow as
Speaker 1: a liquid, So think of something like ketchup how it
Speaker 1: will resist flow. That's a high viscosty. Not that I'm
Speaker 1: saying that ketchups a polymer, but rather that it demonstrates
Speaker 1: high viscosity. Larger polymers also tend to have higher melting
Speaker 1: points and higher boiling points than shorter polymers they tend to.
Speaker 1: Polymers can have all sorts of different manifestations and traits. So,
Speaker 1: for example, take starch and cellulose. Both of these natural
Speaker 1: polymers are made up of chains of glucose monomers, so
Speaker 1: at their core they're made of the same stuff. However,
Speaker 1: those chemical bonds between monitors are different between starches and cellulose,
Speaker 1: and that means that they have different h traits. Those
Speaker 1: differences are significant. So, for example, cellulose does not dissolve
Speaker 1: in water. It's not digestible by human beings. Starch is
Speaker 1: dissolvable in water, and it is digestible by human beings.
Speaker 1: So even though they're both made of the same basic
Speaker 1: building blocks, the way those building blocks connect to each
Speaker 1: other changes there the way they manifest, the way they
Speaker 1: behave if you prefer so. All polymers have a chain
Speaker 1: of chemically bonded links, but some polymers have additional structures
Speaker 1: attached to the links between those chain units. If those
Speaker 1: structures are complex, they're called pendant groups, kind of like
Speaker 1: a charm bracelet. Those pendant groups can affect how the
Speaker 1: polymer interacts with other stuff, and one of the things
Speaker 1: some pendent groups can do is link to pendent groups
Speaker 1: and other chains, so it can connect chains to each other.
Speaker 1: This is called cross linking, and cross linking makes polymers
Speaker 1: harder or more solid. Longer cross links are flexible, and
Speaker 1: shorter cross links create a more stiff material. So they're
Speaker 1: all different types of polymers, and humans have made tons
Speaker 1: of different kinds and labs by changing different monomers together
Speaker 1: in different ways. And photopolymers are material that, as the
Speaker 1: name implies, react with light. The light changes the polymer's
Speaker 1: properties in some way, typically by causing it to go
Speaker 1: from liquid to solid, and sometimes it requires a specific
Speaker 1: frequency of light, like ultra violet light in order to
Speaker 1: create this change. Sometimes it's not a frequency of light,
Speaker 1: it's a proper light intensity or absorption, but in any case,
Speaker 1: exposure to light causes the polymers to cross link, locking
Speaker 1: them together, solidifying them so you quickly go from a
Speaker 1: liquid material to a solid one. How quickly. Well, in
Speaker 1: the case of photopolymers developed by researchers at the Ecole
Speaker 1: Polytechnique Federal de Lausanne, and I know I butchered the pronunciation,
Speaker 1: it only takes a few seconds, and that's really darn fast.
Speaker 1: And once the polymer's cross link they're locked in. They
Speaker 1: are not going to spontaneously let loose those links, so
Speaker 1: there's no danger of a solid object suddenly going curse
Speaker 1: bluche and turning into a liquid that's a technical term,
Speaker 1: curse bluche. Now, three D printing with photopolymers isn't a
Speaker 1: brand new thing. Some groups have been using processes involving
Speaker 1: light and photopolymers for a while, but most of those
Speaker 1: have had limited resolution. Now, when we're talking about three
Speaker 1: D printing with resolution, we're talking about how fine you
Speaker 1: can get the details on a finished three D piece.
Speaker 1: A low resolution means you're not gonna have really any
Speaker 1: smooth edges or curved surfaces. It's kind of like building
Speaker 1: stuff out of standard lego bricks, so you can't make
Speaker 1: a smooth curve surface with those. You get this sort
Speaker 1: of stair step effect instead. Earlier work, such as a
Speaker 1: project from the Lawrence Livermore National Laboratory, in collaboration with
Speaker 1: researchers from m I T, the University of Rochester, and
Speaker 1: UC Berkeley, would use multiple overlapping lasers projecting a holographic
Speaker 1: image into a vat of photopolymer us in. The three
Speaker 1: lasers would each project into the vat from different angles. Collectively,
Speaker 1: they would create a three dimensional representation of the object,
Speaker 1: which would then take shape within the resin as it
Speaker 1: would start to harden into a solid. Now, the version
Speaker 1: I want to talk about is a little more advanced
Speaker 1: than that. I'll explain more in just a moment, but
Speaker 1: first let's take another quick break. So, with a new
Speaker 1: approach out of Switzerland, the team wanted to create a
Speaker 1: virtual three D model of a small object and then
Speaker 1: turn that into a physical one. The system they built
Speaker 1: is capable of printing objects that are just a couple
Speaker 1: of centimeters in size, So they project an image of
Speaker 1: this object using a laser projector. The container that's holding
Speaker 1: the resin rotates at a pretty fast rate. Synchronized with
Speaker 1: that rotation is the perspective of the three to mentional projection. So,
Speaker 1: in other words, imagine a rotating virtual representation of an object.
Speaker 1: Like a chess piece. So imagine like a night on
Speaker 1: a chessboard, and the night is rotating. It's it's a
Speaker 1: laser projection of it. That laser projection is rotating pretty quickly.
Speaker 1: It's rotating at the same rotational speed as a vat
Speaker 1: of liquid photo polymers, so that they're synchronized up with
Speaker 1: each other. Now, all of this is supremely cool and
Speaker 1: awesome on its own, but here's the part that I
Speaker 1: think is truly astounding. The team has designed this process
Speaker 1: so that the resin doesn't receive enough light to solidify
Speaker 1: until the entire sequence of images and rotations is complete.
Speaker 1: So you can think of it as kind of like
Speaker 1: a slide show. Each slide represents a slightly different angle
Speaker 1: of this three dimensional object, and the resin only solidifies
Speaker 1: after the slide show has gone all the way through.
Speaker 1: Because the resident requires a certain accumulation of light before
Speaker 1: those polymers cross link. The system actually is parceling out light.
Speaker 1: It's only giving enough light to start the process, but
Speaker 1: not complete it until every angle has been covered. At
Speaker 1: that point, there has been enough light intensity to cause
Speaker 1: the resin to solidify, which is genius. In addition, this
Speaker 1: approach allows for much higher resolution print jobs. The process
Speaker 1: I described earlier with the multiple lasers, the one that
Speaker 1: was done by researchers from m I T and you
Speaker 1: see Berkeley and such that could print objects with a
Speaker 1: resolution of around three d microns. In articles I read
Speaker 1: about this new process, researchers were able to print a
Speaker 1: tiny replica two centimeter replica of Notre Dame cathedral with
Speaker 1: a resolution of eighty microns. And just a reminder, you
Speaker 1: want a lower number here as it describes how small
Speaker 1: the edges are in curved surfaces. Technically it's a little
Speaker 1: bit more complicated than that, but you that's the easiest
Speaker 1: way to understand it. The team has created systems that
Speaker 1: allow printing in either hard or soft plastics, and they
Speaker 1: envisioned the process being used to print stuff for medical
Speaker 1: applications like three D printing artificial arteries, which is super cool.
Speaker 1: The resident can be sealed in a sterilized container, so
Speaker 1: the finished printed product is safety use for medical applications
Speaker 1: because it hasn't been contaminated at all. It was created
Speaker 1: in a sterile environment. It was actually built that way.
Speaker 1: One drawback of this approach, at least for the near future,
Speaker 1: is the scale, because at the moment they're really limited
Speaker 1: to printing these objects that are just a couple of
Speaker 1: centimeters in size. The team feels confident they can create
Speaker 1: a larger version of the system capable of printing stuff
Speaker 1: closer to fifteen centimeters in scale, but that's still fairly small.
Speaker 1: So you wouldn't be printing any fully formed furniture with
Speaker 1: this stuff, unless, of course it's for a really tiny
Speaker 1: playhouse or something. But it's still a really awesome some invention.
Speaker 1: And while it may not be possible to build something
Speaker 1: capable of constructing larger three dimensional objects right now, maybe
Speaker 1: that will change down the line. If so, it would
Speaker 1: be an incredible advance and additive manufacturing. It would be
Speaker 1: cutting way back on the amount of time needed to
Speaker 1: produce an object. Uh. And the resin that isn't solidified
Speaker 1: can totally be used in future print jobs, so you
Speaker 1: don't have it go to waste, Like if you are
Speaker 1: making a small object and there's a lot of resin leftover,
Speaker 1: no worries, you can still use that in future jobs.
Speaker 1: That's pretty powerful. Now, As I said, this methodology owes
Speaker 1: a lot tomography. It's essentially the reverse process in some ways.
Speaker 1: So rather than using these moving elements to image a
Speaker 1: physical object, it's using a reverse process to project a
Speaker 1: virtual image into a three dimensional volumetric space to create
Speaker 1: a physical object. Another area of research that relates to
Speaker 1: this and that it's an alternate take on three D
Speaker 1: printing is spearheaded by a guy named Adrian Bowyer, who
Speaker 1: is the founder of a company called rep rap. Rap
Speaker 1: Rap refers to Bowuer's work in creating what he calls
Speaker 1: a replicating rapid prototyper, which is, in other words, a
Speaker 1: three D printer. He's now working on a really interesting
Speaker 1: application of science to create a new type of three
Speaker 1: D printer, one different from the tomographic approach I just described.
Speaker 1: So tomography is one way to scan a three dimensional object,
Speaker 1: but Bowyer's research is looking into a different approach. He
Speaker 1: describes a scanning technology called spectra, which already exists, and
Speaker 1: it relies not on light or X rays as a
Speaker 1: scanning mechanism, but electric current. And here's how it works. Okay,
Speaker 1: you've got a three dimensional object you want to scan.
Speaker 1: So let's say it's a little clay garden gnome, and
Speaker 1: you put that inside a container that's already filled with
Speaker 1: an electrically conductive fluid, so current can flow through this liquid.
Speaker 1: The gnome is now submerged in that liquid. The container
Speaker 1: also has little spot electrodes mounted on opposite sides of
Speaker 1: one another on the inside of the container, so they're
Speaker 1: pointed at each other. Uh the gnome is smack dab
Speaker 1: in between those two electrodes. These two electrodes can apply
Speaker 1: a difference of voltage, causing current to flow through the fluid.
Speaker 1: The solid object inside the fluid causes the current to
Speaker 1: move in different ways, and those fluctuations and current can
Speaker 1: be monitored. Then you can rotate the electrodes slightly and
Speaker 1: repeat the process again, and then you rotate it and
Speaker 1: repeat it again. You do this many, many, many times,
Speaker 1: and the difference in how the electric current moves through
Speaker 1: the fluid can then be calculated and added up in
Speaker 1: an integral function that gives you a cross section of
Speaker 1: whatever it is you're skinning. So, in our case, the
Speaker 1: little clay garden gnome, and it's right along the plane
Speaker 1: of those electrodes. So however high those electrodes are within
Speaker 1: the container, then you can move the electrodes up slightly.
Speaker 1: Let's say that you started at the very bottom of
Speaker 1: the container. You can move them up a smidge. Repeat
Speaker 1: this process and you build the next cross section layer
Speaker 1: of this little gnome this. Now you've got a virtual representation,
Speaker 1: and you do it again and again and again until
Speaker 1: you had scanned the entire thing. Now, in practice, you
Speaker 1: would likely use a container that has lots of electrodes.
Speaker 1: You wouldn't just have to the whole thing would be
Speaker 1: have an insight coated with a grid of fine electrodes.
Speaker 1: You would only activate pairs of these at a time
Speaker 1: in order to get the scan. But by having them
Speaker 1: located around the inside of the container, you wouldn't have
Speaker 1: to rotate anything. You wouldn't have to have any moving parts.
Speaker 1: You would just activate pairs of electrodes to get those
Speaker 1: measurements until you've got a full three dimensional scan. As
Speaker 1: I said, this technology already exists. That's a scanning technology.
Speaker 1: What Valuer wants to do is to take that model
Speaker 1: and reverse it much in the same way that the
Speaker 1: photopolymer resin approach I described earlier is like a reverse
Speaker 1: tomographic scan. So Buyer's method would use a monomer solution
Speaker 1: that polymerizes upon exposure to electric current. This is a
Speaker 1: process called electro polymerization. It happens like there's some monomers
Speaker 1: that if you subject them to an electric current, they
Speaker 1: will form polymers and they'll solidify. So his ideas you
Speaker 1: take a virtual object. You've got a model, let's say
Speaker 1: it's a model of our little garden gnome, and you
Speaker 1: would apply current to a container holding monomer solution, and
Speaker 1: you would control the current in such a way so
Speaker 1: that it would activate only the bits of resin that
Speaker 1: would represent that garden gnome in that volumetric space. So
Speaker 1: it's taking that scanning process completely in reverse. Now he
Speaker 1: hasn't managed to do it yet, but he's working on
Speaker 1: the problem. And Buyer's hope is to create a printer
Speaker 1: based on this methodology. And not only that, he's doing
Speaker 1: it in an open source approach. He's published all of
Speaker 1: his work on on his research in this method and
Speaker 1: anyone interested in contributing can do so. And moreover, he
Speaker 1: has a goal to make sure that this process cannot
Speaker 1: be patented, so no person, no company, no other entity
Speaker 1: would be able to take this process and lock it
Speaker 1: away under intellectual property rights. So, in other words, if
Speaker 1: it works, it will work for everybody. And I think
Speaker 1: that's pretty darn cool. Now, it may turn out that
Speaker 1: volumetric printing has inherent limitations that we cannot overcome, and
Speaker 1: in case that happens, it's still not a total loss
Speaker 1: because it's going to be incredibly useful for at least
Speaker 1: a certain number of applications, and we can still rely
Speaker 1: on other methods to produce things that are outside of
Speaker 1: that spectrum. That's pretty much the case with every single
Speaker 1: process we can think of. Even with traditional three D printing,
Speaker 1: you're limited in the size of the thing you can print,
Speaker 1: at least in a single printing session, because you have
Speaker 1: to keep stuff at the right temperature. Uh. If it
Speaker 1: gets too heavy, then it can collapse in on itself.
Speaker 1: So if you want to print a really big print job,
Speaker 1: you typically have to do it in sections and then
Speaker 1: glue the pieces together at the end or otherwise have
Speaker 1: them adhere to each other at the end, because uh,
Speaker 1: you just can't keep it structurally sound through the whole
Speaker 1: printing process if it's a really big print job. In
Speaker 1: the future, we could see three D volumetric printers making
Speaker 1: all sorts of stuff, including the basic scaffolding for things
Speaker 1: like artificial and three D printed organs. In the meantime,
Speaker 1: I just think it's a super nifty technology to learn
Speaker 1: more about. As for other types of three D printing,
Speaker 1: they are still really awesome. It has not proliferated quite
Speaker 1: to the level that people were predicting about five years ago,
Speaker 1: but the work continues and we've seen some really cool
Speaker 1: uses of the text so far, including enormous three D
Speaker 1: printers that can use stuff like a concrete based resin
Speaker 1: to build entire houses out of layer by layer, all
Speaker 1: the way down to students using commercial three D printers
Speaker 1: or even consumer three D printers to build stuff like
Speaker 1: artificial limbs for people who otherwise would never be able
Speaker 1: to afford one. So it's truly a revolutionary technology. I
Speaker 1: can't wait to see where it goes next. And that
Speaker 1: wraps up this episode about three D printers and tomography.
Speaker 1: If you guys have suggestions for future topics of tech stuff,
Speaker 1: reach out to me. You can get in touch with
Speaker 1: me on social media on Facebook or Twitter. We use
Speaker 1: the handle text stuff hsw at both. Look forward to
Speaker 1: hearing from you, and I'll talk to you again really soon.
Speaker 1: Text Stuff is a production of I Heart Radio's How
Speaker 1: Stuff Works. For more podcasts from my heart Radio, visit
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