1 00:00:04,240 --> 00:00:07,240 Speaker 1: Welcome to tex Stuff, a production of I Heart Radios, 2 00:00:07,320 --> 00:00:14,040 Speaker 1: How Stuff Works. Hey there, and welcome to tex Stuff. 3 00:00:14,120 --> 00:00:17,480 Speaker 1: I'm your host, Jonathan Strickland. I'm an executive producer with 4 00:00:17,560 --> 00:00:20,360 Speaker 1: I Heart Radio and a love of all things tech. Now, 5 00:00:20,360 --> 00:00:23,680 Speaker 1: before I jump into this episode, I want to address 6 00:00:23,800 --> 00:00:28,800 Speaker 1: an error I made multiple times in a recent episode, 7 00:00:29,440 --> 00:00:34,479 Speaker 1: and it's a very Jonathan kind of mistake. So in 8 00:00:34,520 --> 00:00:38,640 Speaker 1: the episode I did about smoke detectors, I talked about 9 00:00:38,640 --> 00:00:44,000 Speaker 1: the radioactive element ama sirium to forty one. Here's the problem. 10 00:00:44,040 --> 00:00:47,239 Speaker 1: I inserted an extra syllable there, and even in my 11 00:00:47,280 --> 00:00:51,120 Speaker 1: notes I had it spelled correctly. It's a marasium to 12 00:00:51,360 --> 00:00:54,280 Speaker 1: forty one. So in other words, I I kind of 13 00:00:54,320 --> 00:00:59,600 Speaker 1: pulled a classic Homer Simpson goof, like a Saxoma phone uh, 14 00:00:59,680 --> 00:01:02,720 Speaker 1: several times in one episode. So thanks to Twitter user 15 00:01:02,840 --> 00:01:06,800 Speaker 1: Ken Waldrop for pointing it out. It is incredibly embarrassing. 16 00:01:07,120 --> 00:01:11,240 Speaker 1: It is all my mistake. It's totally me. It's kind 17 00:01:11,240 --> 00:01:15,520 Speaker 1: of an insight into how Jonathan's brain works, which is 18 00:01:15,520 --> 00:01:19,679 Speaker 1: not all that great sometimes. I don't know why I 19 00:01:19,760 --> 00:01:24,280 Speaker 1: inserted an extra syllable multiple times throughout that episode, but 20 00:01:24,720 --> 00:01:27,160 Speaker 1: thank you Ken for letting me know, so that I 21 00:01:27,200 --> 00:01:30,560 Speaker 1: could correct that error in this episode. Let's move on 22 00:01:30,600 --> 00:01:34,520 Speaker 1: to another episode where I'm sure I will mispronounce multiple things. 23 00:01:35,680 --> 00:01:38,520 Speaker 1: But it's a fascinating topic, or at least I find 24 00:01:38,520 --> 00:01:42,360 Speaker 1: it fascinating. So I was looking through tech news recently 25 00:01:42,800 --> 00:01:45,440 Speaker 1: and I saw a really interesting article. It was covered 26 00:01:45,440 --> 00:01:47,320 Speaker 1: in a lot of places. The first place I saw 27 00:01:47,319 --> 00:01:50,480 Speaker 1: it was engadget, but I read about it elsewhere as well, 28 00:01:50,880 --> 00:01:54,680 Speaker 1: and on engadget it has the title Researchers find a 29 00:01:54,720 --> 00:01:59,240 Speaker 1: way to three D print whole objects in seconds. Now 30 00:01:59,280 --> 00:02:02,880 Speaker 1: that immediately got my attention because typically three D printing 31 00:02:02,880 --> 00:02:06,440 Speaker 1: takes a while, sometimes a long while to create an object, 32 00:02:06,440 --> 00:02:10,640 Speaker 1: because it typically does it layer by layer. The answer 33 00:02:10,680 --> 00:02:14,160 Speaker 1: in this case lies in the technique called tomography. So 34 00:02:14,200 --> 00:02:16,560 Speaker 1: this episode is going to cover a few different topics 35 00:02:16,840 --> 00:02:19,520 Speaker 1: so that I can explain as best I can how 36 00:02:19,560 --> 00:02:24,240 Speaker 1: this methodology works. So let's start talking first about just 37 00:02:24,400 --> 00:02:28,639 Speaker 1: three D printing in general. It's a type of additive manufacturing, 38 00:02:28,880 --> 00:02:32,639 Speaker 1: which means you're making something by adding to it rather 39 00:02:32,720 --> 00:02:37,440 Speaker 1: than taking unwanted stuff away. So with traditional sculpture, the 40 00:02:37,480 --> 00:02:40,960 Speaker 1: sculptor might take a block of some material like marble 41 00:02:41,200 --> 00:02:44,320 Speaker 1: and then carve it and cut away tons of it. 42 00:02:44,520 --> 00:02:51,279 Speaker 1: There's an undoubtedly apocryphal quote attributed to Michaelangelo who allegedly 43 00:02:51,320 --> 00:02:54,800 Speaker 1: described his process as you just chip away the stone 44 00:02:54,800 --> 00:03:00,400 Speaker 1: that doesn't look like David. Now, Mikey probably never said that, 45 00:03:01,040 --> 00:03:03,560 Speaker 1: but you get the point of the quote. You're removing 46 00:03:03,720 --> 00:03:07,720 Speaker 1: material and whatever is left after you're done is the 47 00:03:07,760 --> 00:03:12,959 Speaker 1: finished piece. Additive manufacturing goes the opposite way. You add 48 00:03:13,000 --> 00:03:16,360 Speaker 1: material bit by bit until you have the thing you 49 00:03:16,400 --> 00:03:19,360 Speaker 1: wanted to make. So it's kind of like how potters work, 50 00:03:19,480 --> 00:03:22,560 Speaker 1: you know, you add clay until you've got enough mass 51 00:03:22,600 --> 00:03:26,880 Speaker 1: to shape it into whatever final form they have in mind. 52 00:03:27,400 --> 00:03:30,000 Speaker 1: And three D printers work in a similar way. They 53 00:03:30,080 --> 00:03:35,200 Speaker 1: lay down thin layers of material one after another until 54 00:03:35,320 --> 00:03:38,200 Speaker 1: layer by layer they have completed a print job, and 55 00:03:38,240 --> 00:03:42,400 Speaker 1: typically the bottom surface would be whichever one is the 56 00:03:42,520 --> 00:03:46,000 Speaker 1: largest of the finished three D object, So it might 57 00:03:46,000 --> 00:03:48,680 Speaker 1: not necessarily be the bottom of the three D object, 58 00:03:49,040 --> 00:03:51,880 Speaker 1: but the bottom of the print job, because a larger 59 00:03:51,920 --> 00:03:54,200 Speaker 1: surface area means it's going to support the rest of 60 00:03:54,200 --> 00:03:58,440 Speaker 1: that physical structure much more easily. There are three D printers. 61 00:03:58,640 --> 00:04:01,560 Speaker 1: They can work with all sorts of materials. The kind 62 00:04:01,600 --> 00:04:05,320 Speaker 1: of average person would have access to. Uses plastic, one 63 00:04:05,360 --> 00:04:08,800 Speaker 1: of two types, and a typical three D printer uses 64 00:04:08,920 --> 00:04:12,760 Speaker 1: spools of plastic cable as printing material. So the cable 65 00:04:12,840 --> 00:04:16,760 Speaker 1: gets pulled into a piece called the extruder, which heats 66 00:04:16,800 --> 00:04:20,120 Speaker 1: the plastic to make it sort of a semi liquid 67 00:04:20,200 --> 00:04:23,800 Speaker 1: before depositing layers of this plastic, usually mixed with some 68 00:04:23,880 --> 00:04:28,640 Speaker 1: sort of binding agent, onto the printing surface, or after 69 00:04:28,839 --> 00:04:32,839 Speaker 1: the first layer, onto the last layer that was laid down. 70 00:04:33,160 --> 00:04:35,520 Speaker 1: This process tends to take a while, and you have 71 00:04:35,600 --> 00:04:38,919 Speaker 1: to get the temperature and speed just right, or you 72 00:04:38,960 --> 00:04:42,120 Speaker 1: get problems with layers not adhering to each other properly, 73 00:04:42,360 --> 00:04:45,680 Speaker 1: or peeling away or sticking to the extruder as it 74 00:04:45,680 --> 00:04:48,520 Speaker 1: moves through its path. I say this from experience. We 75 00:04:48,600 --> 00:04:51,000 Speaker 1: have a three D printer in the office. We have 76 00:04:51,440 --> 00:04:55,839 Speaker 1: successfully printed on it perhaps four times. We have run 77 00:04:55,880 --> 00:04:59,800 Speaker 1: it many more times than that. But however, it does 78 00:04:59,839 --> 00:05:03,200 Speaker 1: me you can actually make whatever the object is relatively 79 00:05:03,279 --> 00:05:08,360 Speaker 1: quickly compared to more traditional forms of manufacturing, and there 80 00:05:08,400 --> 00:05:10,560 Speaker 1: are lots of benefits with three D printing. One is 81 00:05:10,640 --> 00:05:14,320 Speaker 1: that it makes the prototyping process much faster. So let's 82 00:05:14,320 --> 00:05:16,320 Speaker 1: say you got an idea for the body shape of 83 00:05:16,360 --> 00:05:19,160 Speaker 1: a car. You could build a three D model of 84 00:05:19,200 --> 00:05:21,520 Speaker 1: the shape. Then you could use a three D printer 85 00:05:21,720 --> 00:05:24,800 Speaker 1: to create a small physical model of what you had 86 00:05:24,800 --> 00:05:27,279 Speaker 1: in mind, and you could test that and say a 87 00:05:27,279 --> 00:05:29,719 Speaker 1: wind tunnel, to make sure it would work the way 88 00:05:29,760 --> 00:05:33,120 Speaker 1: you planned before you moved further into the process. But 89 00:05:33,279 --> 00:05:36,560 Speaker 1: maybe you discover that your design has some unexpected quality, 90 00:05:36,600 --> 00:05:40,360 Speaker 1: like increased air resistance, so the extra drag would mean 91 00:05:40,400 --> 00:05:42,640 Speaker 1: the car would not be as fuel efficient, so you 92 00:05:42,680 --> 00:05:44,440 Speaker 1: need to go back to the drawing board. You could 93 00:05:44,440 --> 00:05:47,480 Speaker 1: go make some quick adjustments to your model and then 94 00:05:47,600 --> 00:05:49,760 Speaker 1: send that to the printer again and print up a 95 00:05:49,760 --> 00:05:53,359 Speaker 1: new prototype and would go pretty quickly. You don't have 96 00:05:53,400 --> 00:05:56,159 Speaker 1: to carve away its stuff over and over, and another 97 00:05:56,200 --> 00:05:59,880 Speaker 1: big benefit is that you have less waste overall. You're 98 00:06:00,160 --> 00:06:02,640 Speaker 1: taking material and then only using a small part of 99 00:06:02,680 --> 00:06:05,400 Speaker 1: the overall mass and throwing the rest away. So lots 100 00:06:05,440 --> 00:06:08,839 Speaker 1: of companies that manufacture physical goods use three D printing 101 00:06:09,160 --> 00:06:12,279 Speaker 1: for the prototyping phase, and several are using three D 102 00:06:12,360 --> 00:06:16,400 Speaker 1: printing in the actual manufacturing process for finished items, whether 103 00:06:16,440 --> 00:06:19,719 Speaker 1: it's for a small component that goes into a bigger 104 00:06:19,760 --> 00:06:23,560 Speaker 1: product or a complete product from top to bottom. And 105 00:06:23,680 --> 00:06:26,360 Speaker 1: while we've heard predictions that three D printing would bring 106 00:06:26,360 --> 00:06:29,960 Speaker 1: about the end two mass manufacturing as we know it, 107 00:06:30,520 --> 00:06:33,000 Speaker 1: the future in which everyone either has a three D 108 00:06:33,080 --> 00:06:36,360 Speaker 1: printer or has easy access to a business that owns 109 00:06:36,360 --> 00:06:40,239 Speaker 1: a three D printer. Thus far, that has not happened. 110 00:06:40,279 --> 00:06:41,880 Speaker 1: We have not seen a world where we all just 111 00:06:42,000 --> 00:06:44,200 Speaker 1: print whatever we need on demand, where I sit there 112 00:06:44,200 --> 00:06:46,160 Speaker 1: and think, oh, I need a new chair, so I'm 113 00:06:46,160 --> 00:06:47,880 Speaker 1: gonna go down to the three D printers down the 114 00:06:47,880 --> 00:06:50,640 Speaker 1: block and get one printed out. That has not yet happened. 115 00:06:51,120 --> 00:06:53,560 Speaker 1: Maybe one day that will change, but for now the 116 00:06:53,600 --> 00:06:58,039 Speaker 1: process isn't quite as convenient or as reliable as more 117 00:06:58,040 --> 00:07:03,080 Speaker 1: traditional manufacturing methods. But that's traditional three D printers, and 118 00:07:03,120 --> 00:07:06,039 Speaker 1: I've done episodes to go further into detail about their 119 00:07:06,080 --> 00:07:08,560 Speaker 1: history and how they work. So you can go and 120 00:07:08,600 --> 00:07:10,920 Speaker 1: listen to those classic episodes if you want to hear 121 00:07:10,960 --> 00:07:12,920 Speaker 1: more about that. But that's not what we're going to 122 00:07:12,920 --> 00:07:15,200 Speaker 1: focus on for the rest of this episode. Now it's 123 00:07:15,240 --> 00:07:18,880 Speaker 1: time to switch over to tomography, which is not the 124 00:07:18,920 --> 00:07:22,920 Speaker 1: science of how tom works. It's that has nothing to 125 00:07:22,960 --> 00:07:25,880 Speaker 1: do with tom and my space. Now, this relates to 126 00:07:26,000 --> 00:07:28,960 Speaker 1: radiography and the use of stuff like X rays. Those 127 00:07:29,000 --> 00:07:32,040 Speaker 1: we'll learn. It's not exclusively limited to X rays. And 128 00:07:32,080 --> 00:07:33,800 Speaker 1: I know I've talked a lot about X rays in 129 00:07:33,800 --> 00:07:36,680 Speaker 1: recent episodes, but bear with me here. So early on, 130 00:07:37,280 --> 00:07:41,760 Speaker 1: physicists learned about how X rays could penetrate solid material 131 00:07:42,280 --> 00:07:45,480 Speaker 1: much more effectively than visible light could, and that if 132 00:07:45,480 --> 00:07:48,960 Speaker 1: these X rays hit a sheet of photoreactive material, it 133 00:07:49,000 --> 00:07:51,840 Speaker 1: would cause that material to react, so it reacted as 134 00:07:51,880 --> 00:07:54,840 Speaker 1: if visible light had hit it. So if you put 135 00:07:54,880 --> 00:07:59,000 Speaker 1: something like, I don't know your wife's hand between an 136 00:07:59,160 --> 00:08:02,680 Speaker 1: X ray emitter and a sheet of photographic paper, you 137 00:08:02,720 --> 00:08:06,840 Speaker 1: would end up with an image of your wife's skeletal 138 00:08:06,880 --> 00:08:10,160 Speaker 1: hand on that paper. I say wife because runt Jen 139 00:08:10,320 --> 00:08:14,240 Speaker 1: Vilham run Jen, who discovered X rays, used his wife 140 00:08:14,240 --> 00:08:16,800 Speaker 1: as a photographic subject for a lot of early X 141 00:08:16,880 --> 00:08:21,080 Speaker 1: ray photographs, exposing her two ridiculous amounts of radiation in 142 00:08:21,120 --> 00:08:24,200 Speaker 1: the process. At the time, he didn't know any better. 143 00:08:24,800 --> 00:08:28,000 Speaker 1: But that's why I use that specific example. Now, why 144 00:08:28,360 --> 00:08:32,760 Speaker 1: do you get the skeleton hand in the finished image. Well, 145 00:08:32,800 --> 00:08:36,880 Speaker 1: it's because X rays can pass through different materials with 146 00:08:36,960 --> 00:08:39,959 Speaker 1: different levels of ease, so they can pass through less 147 00:08:40,000 --> 00:08:44,040 Speaker 1: dense material more easily than the denser stuff, and that 148 00:08:44,080 --> 00:08:47,320 Speaker 1: follows common logic. That just makes sense, right. So X 149 00:08:47,400 --> 00:08:51,319 Speaker 1: rays can pass through muscle tissue far more readily than 150 00:08:51,360 --> 00:08:54,920 Speaker 1: they can pass through bone, and bone is just much 151 00:08:54,960 --> 00:08:58,520 Speaker 1: more dense. They can pass even less easily through something 152 00:08:58,559 --> 00:09:02,000 Speaker 1: like metal. So if you were to take an X 153 00:09:02,120 --> 00:09:06,520 Speaker 1: ray photo of a typical person's hand, the bone would 154 00:09:06,520 --> 00:09:10,239 Speaker 1: block more X rays from hitting the paper than the 155 00:09:10,280 --> 00:09:13,280 Speaker 1: soft tissues would. The soft tissues would allow more X 156 00:09:13,360 --> 00:09:15,680 Speaker 1: rays to come through. So the result is that the 157 00:09:15,720 --> 00:09:17,680 Speaker 1: image on the photographic paper would be kind of like 158 00:09:17,720 --> 00:09:20,680 Speaker 1: a negative. The skeletal hand would show the spots on 159 00:09:20,720 --> 00:09:23,160 Speaker 1: the paper where X rays were blocked from hitting it, 160 00:09:23,800 --> 00:09:27,880 Speaker 1: and that meant that it would be relatively unexposed to light, 161 00:09:28,600 --> 00:09:31,160 Speaker 1: and the softer tissues would allow it to go through, 162 00:09:31,200 --> 00:09:33,600 Speaker 1: and thus you would have a greater exposure. So you 163 00:09:33,600 --> 00:09:36,559 Speaker 1: can see that skeletal hand because the contrast between these 164 00:09:36,559 --> 00:09:40,360 Speaker 1: two sections where the rays were blocked versus where they 165 00:09:40,400 --> 00:09:43,600 Speaker 1: passed through. Now, the discovery of X rays came at 166 00:09:43,640 --> 00:09:47,840 Speaker 1: the very end of the nineteenth century. The medical establishment 167 00:09:48,080 --> 00:09:51,240 Speaker 1: quickly saw the potential for this technology. They saw that 168 00:09:51,440 --> 00:09:54,319 Speaker 1: this could be really valuable. You can see stuff like 169 00:09:54,360 --> 00:09:59,520 Speaker 1: broken bones very easily. They immediately recognized its usefulness. They 170 00:09:59,600 --> 00:10:04,720 Speaker 1: also over time recognized some of the dangers of X rays, 171 00:10:04,760 --> 00:10:07,400 Speaker 1: such as radiation exposure, which was really more of a 172 00:10:07,400 --> 00:10:10,680 Speaker 1: problem for doctors than it was for patients. Patients would 173 00:10:10,720 --> 00:10:13,880 Speaker 1: get small exposures whenever they would get an X ray 174 00:10:14,679 --> 00:10:17,160 Speaker 1: done on them, but the doctors who were performing the 175 00:10:17,280 --> 00:10:20,320 Speaker 1: X rays, we're getting exposures time and time again, and 176 00:10:20,360 --> 00:10:22,559 Speaker 1: they were the ones who were really sorry to develop 177 00:10:22,880 --> 00:10:27,160 Speaker 1: serious problems because X rays are a form of ionizing radiation, 178 00:10:27,400 --> 00:10:29,920 Speaker 1: which means they can do cellular damage, and that in 179 00:10:29,960 --> 00:10:33,960 Speaker 1: turn can manifest in different ways from radiation poisoning to 180 00:10:34,920 --> 00:10:40,679 Speaker 1: higher risk of contracting cancer. So uh, they also saw 181 00:10:41,000 --> 00:10:45,800 Speaker 1: a limitation of this technology, namely that X ray photos 182 00:10:45,840 --> 00:10:49,800 Speaker 1: have the same problem as any traditional photo has. They 183 00:10:49,840 --> 00:10:54,360 Speaker 1: produced two dimensional images of three dimensional objects. So in 184 00:10:54,400 --> 00:10:57,839 Speaker 1: medical schools, it was pretty standard practice for students to 185 00:10:57,880 --> 00:11:03,240 Speaker 1: work with or even produce cross sections of organs. Essentially 186 00:11:03,280 --> 00:11:06,880 Speaker 1: involves cutting organs into thin slices like a loaf of bread, 187 00:11:07,320 --> 00:11:10,439 Speaker 1: and then examining each of those slices carefully, and it's 188 00:11:10,440 --> 00:11:13,600 Speaker 1: an effective way to teach medical students about anatomy and 189 00:11:13,840 --> 00:11:17,360 Speaker 1: organ structures as well as learning what is and isn't typical, 190 00:11:17,679 --> 00:11:20,679 Speaker 1: so that if one were to encounter an atypical scenario, 191 00:11:21,360 --> 00:11:24,440 Speaker 1: the doctor would be able to recognize that as such. Now, 192 00:11:24,480 --> 00:11:26,200 Speaker 1: if you put all the slices together, it looks like 193 00:11:26,240 --> 00:11:28,720 Speaker 1: the original organ. Of course, the big problem with this 194 00:11:28,800 --> 00:11:31,679 Speaker 1: method is that it usually requires the original owner of 195 00:11:31,679 --> 00:11:37,720 Speaker 1: that organ to be, you know, not alive anymore, making 196 00:11:37,720 --> 00:11:41,600 Speaker 1: it a little difficult to apply medical knowledge to their case. 197 00:11:42,040 --> 00:11:45,280 Speaker 1: So it's a useful educational tool, but not great for 198 00:11:45,360 --> 00:11:49,160 Speaker 1: diagnosing a patient, at least not in a timely manner. 199 00:11:49,559 --> 00:11:51,800 Speaker 1: So doctors at the time were hopeful that there would 200 00:11:51,800 --> 00:11:54,160 Speaker 1: be a new technology that would make it possible to 201 00:11:54,240 --> 00:11:58,320 Speaker 1: create images of three dimensional objects in an accurate way, 202 00:11:58,400 --> 00:12:02,880 Speaker 1: specifically organs showing their volume metric property, so that you 203 00:12:02,920 --> 00:12:05,400 Speaker 1: could do things like look at them in perspective, as 204 00:12:05,400 --> 00:12:08,040 Speaker 1: opposed to looking at what amounted to a series of 205 00:12:08,040 --> 00:12:10,560 Speaker 1: silhouettes of organs and bones. If you took an X 206 00:12:10,640 --> 00:12:13,800 Speaker 1: ray of someone's torso the rib cage would obscure a 207 00:12:13,800 --> 00:12:17,240 Speaker 1: lot of your your view. And then your lungs in 208 00:12:17,280 --> 00:12:21,280 Speaker 1: your heart are located in an area where it's hard 209 00:12:21,320 --> 00:12:25,800 Speaker 1: to see them individually because they're overlapping each other, so 210 00:12:25,840 --> 00:12:27,640 Speaker 1: they wanted to find a way to create a three 211 00:12:27,640 --> 00:12:31,920 Speaker 1: dimensional representation of this. Doctors at the time, we're hopeful 212 00:12:32,000 --> 00:12:34,800 Speaker 1: that they could come up with a way of doing 213 00:12:34,800 --> 00:12:37,720 Speaker 1: this in a practical manner, but they weren't really sure 214 00:12:37,920 --> 00:12:41,440 Speaker 1: how that would happen now. One person whose work would 215 00:12:41,520 --> 00:12:45,640 Speaker 1: contribute to achieving this goal, though that was not his 216 00:12:45,880 --> 00:12:49,120 Speaker 1: particular aim at the time, was a mathematician in the 217 00:12:49,120 --> 00:12:55,280 Speaker 1: early twentieth century named Johann Raydon. In nineteen seventeen, Raydon 218 00:12:55,440 --> 00:13:00,240 Speaker 1: produced a mathematical transform, a specifically an integral trans form, 219 00:13:00,360 --> 00:13:03,960 Speaker 1: which means you add up basic elements until you get 220 00:13:04,040 --> 00:13:07,480 Speaker 1: the full thing you're looking for. There are a lot 221 00:13:07,480 --> 00:13:10,800 Speaker 1: of different versions of integral transforms, and he also discovered 222 00:13:10,840 --> 00:13:14,920 Speaker 1: its inverse. So this transform described mathematically a process that 223 00:13:14,960 --> 00:13:18,079 Speaker 1: could be realized in a practical setting, namely that one 224 00:13:18,120 --> 00:13:22,280 Speaker 1: could take the result of projections of an object and 225 00:13:22,400 --> 00:13:26,520 Speaker 1: reconstruct an image in real space based on those projections. 226 00:13:26,559 --> 00:13:28,840 Speaker 1: It all has to do with geometry, and again into 227 00:13:28,840 --> 00:13:32,880 Speaker 1: further detail would require someone far more educated in mathematics 228 00:13:32,880 --> 00:13:36,000 Speaker 1: than i am, but there are some great videos online 229 00:13:36,240 --> 00:13:39,000 Speaker 1: about the Radon transform that give it a good explanation 230 00:13:39,040 --> 00:13:42,760 Speaker 1: of it, including one from Rich rad k It's titled 231 00:13:42,960 --> 00:13:47,560 Speaker 1: d I P Lecture eighteen Reconstruction from Parallel Projections and 232 00:13:47,600 --> 00:13:50,319 Speaker 1: the Radon transform. You can find that on YouTube if 233 00:13:50,360 --> 00:13:54,120 Speaker 1: you want to see a really detailed mathematical explanation of 234 00:13:54,160 --> 00:13:56,520 Speaker 1: this that is far beyond what I can give you. 235 00:13:57,080 --> 00:13:59,400 Speaker 1: Radon's work was interesting, but at the time there wasn't 236 00:13:59,440 --> 00:14:02,280 Speaker 1: really any practical way to put it into actual use. 237 00:14:03,120 --> 00:14:06,040 Speaker 1: One early step in getting to the goal was the 238 00:14:06,080 --> 00:14:11,160 Speaker 1: development of linear tomography, or the ability to take radiographic 239 00:14:11,240 --> 00:14:15,360 Speaker 1: images of a specific plane or cross section in a 240 00:14:15,440 --> 00:14:19,200 Speaker 1: solid object like a human being. So, in other words, 241 00:14:19,200 --> 00:14:21,160 Speaker 1: you could create a cross section of a human being 242 00:14:21,400 --> 00:14:24,680 Speaker 1: without having to cut the human being open. It was 243 00:14:24,720 --> 00:14:28,800 Speaker 1: a miracle. So this relates to that mathematical transform I 244 00:14:28,880 --> 00:14:32,320 Speaker 1: just mentioned, and interestingly, in the early days of tomography 245 00:14:32,520 --> 00:14:36,680 Speaker 1: they that actually would predate Radon's transformers. Physicists were thinking 246 00:14:36,680 --> 00:14:39,840 Speaker 1: about how to take X ray images from multiple angles 247 00:14:39,880 --> 00:14:43,200 Speaker 1: to get a more complete picture of a specific internal 248 00:14:43,360 --> 00:14:48,120 Speaker 1: organ as early as nineteen fourteen. For actual implementations, there 249 00:14:48,160 --> 00:14:50,920 Speaker 1: was a period from around nineteen twenty one to nineteen 250 00:14:50,960 --> 00:14:55,400 Speaker 1: thirty four in which multiple people all working independently, all 251 00:14:55,440 --> 00:14:59,360 Speaker 1: not knowing about each other, started to build systems capable 252 00:14:59,360 --> 00:15:04,560 Speaker 1: of producing what would be called tomographic images. They didn't 253 00:15:04,600 --> 00:15:08,040 Speaker 1: know about the other's work for a very long time, 254 00:15:08,080 --> 00:15:10,480 Speaker 1: and when they found out. Can you guess what happened? 255 00:15:11,160 --> 00:15:14,200 Speaker 1: If your guess was, I bet they all rushed to 256 00:15:14,240 --> 00:15:17,280 Speaker 1: be the one to claim credit for it, you'd be right, 257 00:15:17,360 --> 00:15:20,600 Speaker 1: because that was a very human reaction to say I'm 258 00:15:20,640 --> 00:15:23,600 Speaker 1: the reason why this works. But that was put on 259 00:15:23,640 --> 00:15:27,240 Speaker 1: hold because a little thing called World War two happened. 260 00:15:27,920 --> 00:15:31,720 Speaker 1: The basic idea was the same from one instance to 261 00:15:31,760 --> 00:15:34,120 Speaker 1: another instance that all these people were coming up with, 262 00:15:34,160 --> 00:15:37,200 Speaker 1: but the actual details were different, such as the angles 263 00:15:37,240 --> 00:15:40,360 Speaker 1: of motion for the X ray emitter and the detectors 264 00:15:40,360 --> 00:15:42,920 Speaker 1: which would be on the opposite side of the patient, 265 00:15:43,480 --> 00:15:46,520 Speaker 1: or the speed at which these components should move with 266 00:15:46,560 --> 00:15:49,960 Speaker 1: each other. Also, the word tomography itself was coined around 267 00:15:50,040 --> 00:15:53,400 Speaker 1: nineteen thirty five and comes from the Greek word thomas, 268 00:15:53,920 --> 00:15:58,480 Speaker 1: meaning section, and the suffix graphy from the Latin word 269 00:15:58,880 --> 00:16:02,800 Speaker 1: graphia mean study of So it's the study of sections 270 00:16:02,840 --> 00:16:05,480 Speaker 1: and it combines Greek and Latin. So I have friends 271 00:16:05,520 --> 00:16:10,040 Speaker 1: who hate this word. They would say, stick with one 272 00:16:10,240 --> 00:16:14,160 Speaker 1: or the other, um, one of them sitting right across 273 00:16:14,200 --> 00:16:17,840 Speaker 1: from me, but never mind that anyway. So imagine you've 274 00:16:17,880 --> 00:16:22,040 Speaker 1: got a person standing in front of you, and you 275 00:16:22,080 --> 00:16:26,080 Speaker 1: are somehow able to produce an image of a slice 276 00:16:26,400 --> 00:16:30,200 Speaker 1: of that person from head to toe, and their shoulders 277 00:16:30,200 --> 00:16:32,000 Speaker 1: are facing you. So it's like it's like you just 278 00:16:32,280 --> 00:16:34,760 Speaker 1: are able to look at a slice of them right 279 00:16:34,840 --> 00:16:38,080 Speaker 1: from the middle of that person, but you're able to 280 00:16:38,080 --> 00:16:40,360 Speaker 1: do it without, you know, actually physically slicing them. So 281 00:16:40,360 --> 00:16:42,640 Speaker 1: how does it work. Well, I'm gonna do my best 282 00:16:42,640 --> 00:16:45,040 Speaker 1: to try and explain this process. So this is gonna 283 00:16:45,080 --> 00:16:47,920 Speaker 1: be an example. They don't all have to look this way, 284 00:16:47,920 --> 00:16:50,400 Speaker 1: but this is a way for me to explain how 285 00:16:50,440 --> 00:16:53,800 Speaker 1: this could happen. Imagine that we've got a patient laying 286 00:16:53,840 --> 00:16:57,520 Speaker 1: down on an X ray table, and above this patient 287 00:16:57,680 --> 00:17:00,880 Speaker 1: there is a track that's in an kind of like 288 00:17:00,920 --> 00:17:04,920 Speaker 1: a rainbow above the patient, starting from around the head 289 00:17:05,000 --> 00:17:09,639 Speaker 1: and ending somewhere around let's say the knees. Uh On 290 00:17:09,800 --> 00:17:13,840 Speaker 1: this arc is mounted an X ray emitter, So this 291 00:17:13,920 --> 00:17:16,960 Speaker 1: is the tube that will shoot out X rays at 292 00:17:16,960 --> 00:17:20,960 Speaker 1: the patient. On the opposite side are X ray detectors. 293 00:17:20,960 --> 00:17:23,920 Speaker 1: This is underneath the table and the two can move 294 00:17:23,960 --> 00:17:29,119 Speaker 1: with each other, So you start UH make moving the 295 00:17:29,119 --> 00:17:33,399 Speaker 1: the emitter along this track. It moves gets in motion 296 00:17:34,080 --> 00:17:37,080 Speaker 1: once it starts. Shortly after it started to move, it 297 00:17:37,119 --> 00:17:41,120 Speaker 1: begins to emit X rays, and then it nears the 298 00:17:41,240 --> 00:17:43,879 Speaker 1: end of its arc, it stops emitting X rays and 299 00:17:43,920 --> 00:17:47,320 Speaker 1: then it comes to a physical stop. And you're aiming 300 00:17:47,359 --> 00:17:49,760 Speaker 1: this at a specific point on the patient. Perhaps you 301 00:17:49,800 --> 00:17:53,400 Speaker 1: want to image this patient's liver, so you've aimed the 302 00:17:53,440 --> 00:17:56,400 Speaker 1: emitter at the patient's liver, and as it goes through 303 00:17:56,400 --> 00:18:00,360 Speaker 1: this entire arc, it still stays focused on a liver, 304 00:18:00,840 --> 00:18:03,359 Speaker 1: so that point of focus does not change as it 305 00:18:03,400 --> 00:18:08,679 Speaker 1: goes through this arc. UH. That liver will then become 306 00:18:08,880 --> 00:18:14,240 Speaker 1: the pivot point for this particular scan. The ends of 307 00:18:14,320 --> 00:18:17,920 Speaker 1: the seesaw of this pivot point would be the X 308 00:18:18,040 --> 00:18:20,600 Speaker 1: ray tube on one side and the X ray receptors 309 00:18:20,640 --> 00:18:22,920 Speaker 1: on the other side. So if you think of a 310 00:18:22,960 --> 00:18:25,359 Speaker 1: seesaw going up and down, in this case, it's not 311 00:18:25,400 --> 00:18:27,440 Speaker 1: really going up and down, it's just going through an arc. 312 00:18:27,880 --> 00:18:30,280 Speaker 1: Then one end of the seesaw is the emitter, the 313 00:18:30,280 --> 00:18:33,119 Speaker 1: other end of the seesaw is the receiver, and the 314 00:18:33,160 --> 00:18:39,120 Speaker 1: middle is the liver. The pivot point the The angle 315 00:18:40,000 --> 00:18:42,960 Speaker 1: from the top of the arc to the bottom of 316 00:18:43,000 --> 00:18:47,040 Speaker 1: the arc is called the tomographic angle. The angle at 317 00:18:47,040 --> 00:18:50,360 Speaker 1: which the X ray emitter starts to admit X rays, 318 00:18:50,480 --> 00:18:52,840 Speaker 1: and the angle at which are and when it stops 319 00:18:53,480 --> 00:18:56,159 Speaker 1: is called the exposure angles. There are two different angles 320 00:18:56,160 --> 00:18:58,560 Speaker 1: in here. The exposure angle is always going to be 321 00:18:58,600 --> 00:19:03,760 Speaker 1: smaller than the tomographic angle because of that. So how 322 00:19:05,200 --> 00:19:08,119 Speaker 1: why why would you go through all this? What? What's 323 00:19:08,160 --> 00:19:20,240 Speaker 1: the end result? I'll explain after we take a quick break. Okay, 324 00:19:20,280 --> 00:19:23,840 Speaker 1: I just described this weird process of an X ray 325 00:19:23,840 --> 00:19:27,160 Speaker 1: emitter going across an arc aimed at a patient. Why 326 00:19:27,200 --> 00:19:30,520 Speaker 1: would you do that? Well, it's because the image produced 327 00:19:30,560 --> 00:19:33,560 Speaker 1: at the end of this process creates a very sharp 328 00:19:33,680 --> 00:19:38,640 Speaker 1: picture of everything within the exposure angle along the focal 329 00:19:38,760 --> 00:19:42,960 Speaker 1: plane of the pivot point. So let's say you're looking 330 00:19:43,000 --> 00:19:45,080 Speaker 1: at this patient from the side the patient's laying on 331 00:19:45,119 --> 00:19:48,080 Speaker 1: the table, you're off to an observation area off to 332 00:19:48,119 --> 00:19:52,520 Speaker 1: the side. The focal plane is the horizontal slice of 333 00:19:52,560 --> 00:19:55,960 Speaker 1: that patient that runs through the pivot point. So let's 334 00:19:55,960 --> 00:19:58,479 Speaker 1: say that you've determined that you wanted to aim at 335 00:19:58,480 --> 00:20:01,320 Speaker 1: a point that's about eight centim ter's up from the 336 00:20:01,320 --> 00:20:04,480 Speaker 1: surface of the table. That means that at that eight 337 00:20:04,520 --> 00:20:08,919 Speaker 1: centimeters height along that entire horizontal slice of the patient, 338 00:20:09,400 --> 00:20:13,879 Speaker 1: you're gonna get a very clear X ray image. The 339 00:20:14,000 --> 00:20:16,560 Speaker 1: further out you are from the focal plane, so the 340 00:20:16,600 --> 00:20:21,920 Speaker 1: further towards the patient's front or anterior and back or posterior, 341 00:20:22,359 --> 00:20:25,400 Speaker 1: then the fuzzier the image is going to be. Now, 342 00:20:25,400 --> 00:20:28,119 Speaker 1: in this way, a radiologist could produce a sharp image 343 00:20:28,119 --> 00:20:31,240 Speaker 1: of a specific slice inside a person. You would get 344 00:20:31,280 --> 00:20:34,240 Speaker 1: that cross section, but you still have to deal with 345 00:20:34,240 --> 00:20:36,280 Speaker 1: other issues, such as the fact that bone is more 346 00:20:36,280 --> 00:20:39,080 Speaker 1: effective in blocking X rays than soft tissues or water. 347 00:20:39,480 --> 00:20:41,439 Speaker 1: So if the area you wanted to look at was 348 00:20:41,760 --> 00:20:44,560 Speaker 1: below bone, such as within the rib cage, the bones 349 00:20:44,560 --> 00:20:47,280 Speaker 1: would still present something of a problem, but you would 350 00:20:47,280 --> 00:20:50,399 Speaker 1: still get a better look within a specific depth of 351 00:20:50,440 --> 00:20:52,960 Speaker 1: a person, if that makes sense. So it was definitely 352 00:20:53,040 --> 00:20:56,320 Speaker 1: an evolution of the science of radiology. Now you can 353 00:20:56,400 --> 00:20:59,360 Speaker 1: repeat this process, and you could adjust the pivot location 354 00:21:00,160 --> 00:21:03,520 Speaker 1: further up or further down to get sharp images along 355 00:21:03,600 --> 00:21:06,800 Speaker 1: different depths. But that also means you're also exposing the 356 00:21:06,840 --> 00:21:10,880 Speaker 1: patient to multiple, you know, exposures of X ray radiation. 357 00:21:11,359 --> 00:21:15,840 Speaker 1: A little exposure presents relatively low risk, but the more 358 00:21:15,960 --> 00:21:18,040 Speaker 1: you're exposed to X rays, the greater the risk of 359 00:21:18,080 --> 00:21:21,520 Speaker 1: adverse effects like damage to yourselves, right, so you want 360 00:21:21,520 --> 00:21:25,040 Speaker 1: to be careful with this. Over time, advances in technology 361 00:21:25,160 --> 00:21:29,480 Speaker 1: created the possibility of axial tomography, which was introduced in 362 00:21:29,480 --> 00:21:32,280 Speaker 1: the nineteen seventies. So in this version, instead of having 363 00:21:32,320 --> 00:21:36,359 Speaker 1: an arc above the patient, the X ray emitter and 364 00:21:36,480 --> 00:21:40,439 Speaker 1: receivers are mounted on a ring that goes around a table. 365 00:21:40,760 --> 00:21:43,760 Speaker 1: So think of a table that passes through a ring 366 00:21:43,880 --> 00:21:46,680 Speaker 1: and the patient lays on the table. The emitter and 367 00:21:46,720 --> 00:21:48,920 Speaker 1: the receivers are mounted on opposite sides of this ring, 368 00:21:49,359 --> 00:21:51,280 Speaker 1: and the patient and table are at the center of it. 369 00:21:51,680 --> 00:21:55,040 Speaker 1: And with axial tomography, you take a series of images 370 00:21:55,119 --> 00:21:58,240 Speaker 1: with the X ray tube along different points of the ring, 371 00:21:58,320 --> 00:22:00,320 Speaker 1: moving in a full circle around the patient it on 372 00:22:00,359 --> 00:22:03,080 Speaker 1: the table, So you get above, below, and on either 373 00:22:03,160 --> 00:22:06,159 Speaker 1: side and every angle you can really imagine, and the 374 00:22:06,200 --> 00:22:09,560 Speaker 1: machines typically take a ton of quick images as the 375 00:22:09,600 --> 00:22:12,760 Speaker 1: machine rotates around the table very very fast. You can 376 00:22:12,800 --> 00:22:17,199 Speaker 1: actually find videos of a cat scan because this is 377 00:22:17,440 --> 00:22:21,640 Speaker 1: what this is a computer axial tomography scan. You can 378 00:22:21,640 --> 00:22:25,840 Speaker 1: find videos of this equipment rotating where the cover is 379 00:22:25,880 --> 00:22:28,760 Speaker 1: off so you can see how the internal structure rotates 380 00:22:28,800 --> 00:22:33,480 Speaker 1: within this this machine. It's amazing how fast it goes. 381 00:22:33,960 --> 00:22:36,760 Speaker 1: Uh I found it almost alarming how fast it goes, 382 00:22:36,840 --> 00:22:39,240 Speaker 1: because these machines also are very big, and to think 383 00:22:39,240 --> 00:22:42,000 Speaker 1: that something is spinning that fast around you is a 384 00:22:42,040 --> 00:22:44,960 Speaker 1: little unsettling. But the result of all this fuss is 385 00:22:45,000 --> 00:22:48,000 Speaker 1: you get a cross section image of the subject, and 386 00:22:48,000 --> 00:22:50,800 Speaker 1: the table can be moved further in or out of 387 00:22:50,800 --> 00:22:53,480 Speaker 1: the ring, and another series of images can be taken, 388 00:22:53,680 --> 00:22:55,760 Speaker 1: and that gives you another cross section, and you could 389 00:22:55,800 --> 00:22:58,600 Speaker 1: do it again and take another cross section. You do 390 00:22:58,680 --> 00:23:01,280 Speaker 1: this no off and you eventually end up with images, 391 00:23:01,440 --> 00:23:04,440 Speaker 1: three dimensional images of the stuff you want to take 392 00:23:04,480 --> 00:23:08,520 Speaker 1: pictures of, and you're able to put that together through 393 00:23:08,560 --> 00:23:12,920 Speaker 1: the help of computers. Engineers would call these CATS scans, 394 00:23:12,920 --> 00:23:16,080 Speaker 1: and later just CT scans. A bit later, in the 395 00:23:16,160 --> 00:23:19,800 Speaker 1: nineteen seventies, you had Dr Raymond Damedian who created a 396 00:23:19,840 --> 00:23:24,320 Speaker 1: device capable of imaging internal body scans using magnetic resonance 397 00:23:24,600 --> 00:23:27,359 Speaker 1: rather than X rays. The major benefit of this technology 398 00:23:27,400 --> 00:23:30,040 Speaker 1: is that, unlike X rays, m r I machines do 399 00:23:30,119 --> 00:23:34,879 Speaker 1: not emit ionizing radiation, so you don't get that radiation 400 00:23:35,119 --> 00:23:38,320 Speaker 1: damage to yourselves with an MRI machine. There are other 401 00:23:38,400 --> 00:23:41,520 Speaker 1: damages if you are other dangers I should say, if 402 00:23:41,520 --> 00:23:44,120 Speaker 1: you happen to have, you know, magnetic material on you, 403 00:23:44,600 --> 00:23:47,159 Speaker 1: that's bad to be anywhere close to an m r 404 00:23:47,240 --> 00:23:51,320 Speaker 1: I when it goes off, because you could stand to 405 00:23:52,119 --> 00:23:55,560 Speaker 1: injure yourself or somebody else seriously, if they are in 406 00:23:55,640 --> 00:23:58,600 Speaker 1: between the m r I machine and whatever it is 407 00:23:58,680 --> 00:24:00,800 Speaker 1: you have on your body that is my metic or 408 00:24:01,000 --> 00:24:05,680 Speaker 1: you know, is ferromagnetic. Today, though, hospitals typically have both 409 00:24:05,800 --> 00:24:09,240 Speaker 1: mr I machines and CT scanners because they're actually different 410 00:24:09,720 --> 00:24:13,240 Speaker 1: reasons to use either one, like they're each good for 411 00:24:13,359 --> 00:24:17,240 Speaker 1: different things. Uh. Over time, scientists and doctors have really 412 00:24:17,240 --> 00:24:19,720 Speaker 1: refined the tech of CT scanners to really minimize the 413 00:24:19,720 --> 00:24:23,160 Speaker 1: amount of ionizing radiation that patients will absorb, so they're 414 00:24:23,240 --> 00:24:26,280 Speaker 1: they're pretty darn safe. So what does all this have 415 00:24:26,359 --> 00:24:29,320 Speaker 1: to do with three D printing? Well, in this case, 416 00:24:29,560 --> 00:24:32,479 Speaker 1: tomography is all about creating a three dimensional object in 417 00:24:32,520 --> 00:24:37,840 Speaker 1: real space using light and special photoreactive resins. It's super 418 00:24:37,920 --> 00:24:42,320 Speaker 1: fascinating stuff which you probably can't tell just based on 419 00:24:42,480 --> 00:24:45,879 Speaker 1: the words I'm using. So this reson I'm talking about 420 00:24:45,920 --> 00:24:50,440 Speaker 1: is a type of photo polymer polymers are long chain molecules. 421 00:24:50,760 --> 00:24:54,360 Speaker 1: A typical polymer is a chain of similar building blocks 422 00:24:54,400 --> 00:24:57,720 Speaker 1: linked together, and by building blocks, I mean monomers, and 423 00:24:57,760 --> 00:25:00,960 Speaker 1: a monomer can either be a single atom or more frequently, 424 00:25:00,960 --> 00:25:04,120 Speaker 1: it's a small group of atoms that form a molecule, 425 00:25:04,680 --> 00:25:08,639 Speaker 1: so that's a monomer. A polymer is a chain of 426 00:25:08,680 --> 00:25:12,280 Speaker 1: these monomers that are all chemically bound together in some way. 427 00:25:12,560 --> 00:25:16,199 Speaker 1: So you can think of the chemical bindings as the 428 00:25:16,359 --> 00:25:21,920 Speaker 1: link holding two elements together, and you get long, long, 429 00:25:21,960 --> 00:25:25,440 Speaker 1: long chains of these monomers to create polymers. A lot 430 00:25:25,480 --> 00:25:29,520 Speaker 1: of polymers are artificial, including plastics. It's a common polymer 431 00:25:29,560 --> 00:25:31,240 Speaker 1: we encounter in our day to day lines. But you 432 00:25:31,280 --> 00:25:36,360 Speaker 1: can also find some natural polymers cotton, silk, cellulose, which 433 00:25:36,440 --> 00:25:39,920 Speaker 1: is the stuff that woody plants are made out of, starches. 434 00:25:40,040 --> 00:25:43,840 Speaker 1: These are all polymers, and proteins are polymers, right. Proteins 435 00:25:43,880 --> 00:25:47,240 Speaker 1: are polymers that are created by chaining together amino acids. 436 00:25:47,920 --> 00:25:52,720 Speaker 1: Larger polymers are naturally heavier than smaller polymers. Makes sense. 437 00:25:52,760 --> 00:25:55,320 Speaker 1: You've got more stuff, it's gonna have more weight. They 438 00:25:55,320 --> 00:25:58,880 Speaker 1: also have higher viscosity, which means they resist flow as 439 00:25:58,880 --> 00:26:02,600 Speaker 1: a liquid, So think of something like ketchup how it 440 00:26:02,680 --> 00:26:05,439 Speaker 1: will resist flow. That's a high viscosty. Not that I'm 441 00:26:05,440 --> 00:26:08,600 Speaker 1: saying that ketchups a polymer, but rather that it demonstrates 442 00:26:08,680 --> 00:26:12,880 Speaker 1: high viscosity. Larger polymers also tend to have higher melting 443 00:26:12,920 --> 00:26:16,800 Speaker 1: points and higher boiling points than shorter polymers they tend to. 444 00:26:17,480 --> 00:26:22,760 Speaker 1: Polymers can have all sorts of different manifestations and traits. So, 445 00:26:22,840 --> 00:26:27,240 Speaker 1: for example, take starch and cellulose. Both of these natural 446 00:26:27,280 --> 00:26:31,840 Speaker 1: polymers are made up of chains of glucose monomers, so 447 00:26:32,280 --> 00:26:34,760 Speaker 1: at their core they're made of the same stuff. However, 448 00:26:35,640 --> 00:26:42,000 Speaker 1: those chemical bonds between monitors are different between starches and cellulose, 449 00:26:42,480 --> 00:26:48,840 Speaker 1: and that means that they have different h traits. Those 450 00:26:48,840 --> 00:26:54,280 Speaker 1: differences are significant. So, for example, cellulose does not dissolve 451 00:26:54,280 --> 00:26:58,560 Speaker 1: in water. It's not digestible by human beings. Starch is 452 00:26:58,600 --> 00:27:02,160 Speaker 1: dissolvable in water, and it is digestible by human beings. 453 00:27:02,200 --> 00:27:04,959 Speaker 1: So even though they're both made of the same basic 454 00:27:05,000 --> 00:27:07,680 Speaker 1: building blocks, the way those building blocks connect to each 455 00:27:07,680 --> 00:27:11,760 Speaker 1: other changes there the way they manifest, the way they 456 00:27:11,800 --> 00:27:16,040 Speaker 1: behave if you prefer so. All polymers have a chain 457 00:27:16,080 --> 00:27:20,040 Speaker 1: of chemically bonded links, but some polymers have additional structures 458 00:27:20,080 --> 00:27:23,919 Speaker 1: attached to the links between those chain units. If those 459 00:27:23,960 --> 00:27:27,720 Speaker 1: structures are complex, they're called pendant groups, kind of like 460 00:27:27,760 --> 00:27:31,119 Speaker 1: a charm bracelet. Those pendant groups can affect how the 461 00:27:31,160 --> 00:27:33,840 Speaker 1: polymer interacts with other stuff, and one of the things 462 00:27:33,960 --> 00:27:37,640 Speaker 1: some pendent groups can do is link to pendent groups 463 00:27:37,680 --> 00:27:42,000 Speaker 1: and other chains, so it can connect chains to each other. 464 00:27:42,800 --> 00:27:46,560 Speaker 1: This is called cross linking, and cross linking makes polymers 465 00:27:46,720 --> 00:27:51,679 Speaker 1: harder or more solid. Longer cross links are flexible, and 466 00:27:51,840 --> 00:27:55,360 Speaker 1: shorter cross links create a more stiff material. So they're 467 00:27:55,400 --> 00:27:58,560 Speaker 1: all different types of polymers, and humans have made tons 468 00:27:58,640 --> 00:28:02,520 Speaker 1: of different kinds and labs by changing different monomers together 469 00:28:02,560 --> 00:28:06,040 Speaker 1: in different ways. And photopolymers are material that, as the 470 00:28:06,160 --> 00:28:10,040 Speaker 1: name implies, react with light. The light changes the polymer's 471 00:28:10,080 --> 00:28:13,439 Speaker 1: properties in some way, typically by causing it to go 472 00:28:13,560 --> 00:28:17,280 Speaker 1: from liquid to solid, and sometimes it requires a specific 473 00:28:17,320 --> 00:28:20,320 Speaker 1: frequency of light, like ultra violet light in order to 474 00:28:20,440 --> 00:28:23,040 Speaker 1: create this change. Sometimes it's not a frequency of light, 475 00:28:23,080 --> 00:28:27,840 Speaker 1: it's a proper light intensity or absorption, but in any case, 476 00:28:28,200 --> 00:28:32,080 Speaker 1: exposure to light causes the polymers to cross link, locking 477 00:28:32,119 --> 00:28:35,040 Speaker 1: them together, solidifying them so you quickly go from a 478 00:28:35,080 --> 00:28:38,880 Speaker 1: liquid material to a solid one. How quickly. Well, in 479 00:28:38,920 --> 00:28:43,000 Speaker 1: the case of photopolymers developed by researchers at the Ecole 480 00:28:43,240 --> 00:28:48,400 Speaker 1: Polytechnique Federal de Lausanne, and I know I butchered the pronunciation, 481 00:28:49,120 --> 00:28:52,760 Speaker 1: it only takes a few seconds, and that's really darn fast. 482 00:28:52,920 --> 00:28:56,120 Speaker 1: And once the polymer's cross link they're locked in. They 483 00:28:56,160 --> 00:28:59,480 Speaker 1: are not going to spontaneously let loose those links, so 484 00:28:59,640 --> 00:29:02,640 Speaker 1: there's no danger of a solid object suddenly going curse 485 00:29:02,680 --> 00:29:06,960 Speaker 1: bluche and turning into a liquid that's a technical term, 486 00:29:07,120 --> 00:29:11,560 Speaker 1: curse bluche. Now, three D printing with photopolymers isn't a 487 00:29:11,600 --> 00:29:15,240 Speaker 1: brand new thing. Some groups have been using processes involving 488 00:29:15,360 --> 00:29:18,680 Speaker 1: light and photopolymers for a while, but most of those 489 00:29:18,720 --> 00:29:21,880 Speaker 1: have had limited resolution. Now, when we're talking about three 490 00:29:21,920 --> 00:29:25,080 Speaker 1: D printing with resolution, we're talking about how fine you 491 00:29:25,120 --> 00:29:28,360 Speaker 1: can get the details on a finished three D piece. 492 00:29:28,960 --> 00:29:31,720 Speaker 1: A low resolution means you're not gonna have really any 493 00:29:31,800 --> 00:29:35,600 Speaker 1: smooth edges or curved surfaces. It's kind of like building 494 00:29:35,600 --> 00:29:39,200 Speaker 1: stuff out of standard lego bricks, so you can't make 495 00:29:39,360 --> 00:29:41,520 Speaker 1: a smooth curve surface with those. You get this sort 496 00:29:41,520 --> 00:29:45,680 Speaker 1: of stair step effect instead. Earlier work, such as a 497 00:29:45,760 --> 00:29:49,760 Speaker 1: project from the Lawrence Livermore National Laboratory, in collaboration with 498 00:29:49,880 --> 00:29:52,840 Speaker 1: researchers from m I T, the University of Rochester, and 499 00:29:52,920 --> 00:29:57,520 Speaker 1: UC Berkeley, would use multiple overlapping lasers projecting a holographic 500 00:29:57,600 --> 00:30:01,000 Speaker 1: image into a vat of photopolymer us in. The three 501 00:30:01,080 --> 00:30:05,760 Speaker 1: lasers would each project into the vat from different angles. Collectively, 502 00:30:06,040 --> 00:30:08,880 Speaker 1: they would create a three dimensional representation of the object, 503 00:30:09,160 --> 00:30:12,680 Speaker 1: which would then take shape within the resin as it 504 00:30:12,720 --> 00:30:15,680 Speaker 1: would start to harden into a solid. Now, the version 505 00:30:15,720 --> 00:30:18,240 Speaker 1: I want to talk about is a little more advanced 506 00:30:18,280 --> 00:30:20,800 Speaker 1: than that. I'll explain more in just a moment, but 507 00:30:20,840 --> 00:30:31,040 Speaker 1: first let's take another quick break. So, with a new 508 00:30:31,080 --> 00:30:34,760 Speaker 1: approach out of Switzerland, the team wanted to create a 509 00:30:34,840 --> 00:30:37,560 Speaker 1: virtual three D model of a small object and then 510 00:30:37,600 --> 00:30:40,520 Speaker 1: turn that into a physical one. The system they built 511 00:30:40,560 --> 00:30:43,280 Speaker 1: is capable of printing objects that are just a couple 512 00:30:43,320 --> 00:30:47,080 Speaker 1: of centimeters in size, So they project an image of 513 00:30:47,080 --> 00:30:51,400 Speaker 1: this object using a laser projector. The container that's holding 514 00:30:51,440 --> 00:30:56,880 Speaker 1: the resin rotates at a pretty fast rate. Synchronized with 515 00:30:57,040 --> 00:31:01,520 Speaker 1: that rotation is the perspective of the three to mentional projection. So, 516 00:31:01,680 --> 00:31:05,960 Speaker 1: in other words, imagine a rotating virtual representation of an object. 517 00:31:06,360 --> 00:31:09,920 Speaker 1: Like a chess piece. So imagine like a night on 518 00:31:09,960 --> 00:31:12,960 Speaker 1: a chessboard, and the night is rotating. It's it's a 519 00:31:13,080 --> 00:31:16,240 Speaker 1: laser projection of it. That laser projection is rotating pretty quickly. 520 00:31:16,720 --> 00:31:19,880 Speaker 1: It's rotating at the same rotational speed as a vat 521 00:31:19,960 --> 00:31:23,239 Speaker 1: of liquid photo polymers, so that they're synchronized up with 522 00:31:23,280 --> 00:31:26,240 Speaker 1: each other. Now, all of this is supremely cool and 523 00:31:26,280 --> 00:31:28,440 Speaker 1: awesome on its own, but here's the part that I 524 00:31:28,480 --> 00:31:32,040 Speaker 1: think is truly astounding. The team has designed this process 525 00:31:32,440 --> 00:31:36,640 Speaker 1: so that the resin doesn't receive enough light to solidify 526 00:31:36,840 --> 00:31:40,920 Speaker 1: until the entire sequence of images and rotations is complete. 527 00:31:41,240 --> 00:31:42,640 Speaker 1: So you can think of it as kind of like 528 00:31:42,680 --> 00:31:46,800 Speaker 1: a slide show. Each slide represents a slightly different angle 529 00:31:47,080 --> 00:31:51,040 Speaker 1: of this three dimensional object, and the resin only solidifies 530 00:31:51,360 --> 00:31:53,920 Speaker 1: after the slide show has gone all the way through. 531 00:31:54,200 --> 00:31:57,960 Speaker 1: Because the resident requires a certain accumulation of light before 532 00:31:58,000 --> 00:32:02,360 Speaker 1: those polymers cross link. The system actually is parceling out light. 533 00:32:02,440 --> 00:32:05,480 Speaker 1: It's only giving enough light to start the process, but 534 00:32:05,560 --> 00:32:09,560 Speaker 1: not complete it until every angle has been covered. At 535 00:32:09,600 --> 00:32:12,400 Speaker 1: that point, there has been enough light intensity to cause 536 00:32:12,440 --> 00:32:17,320 Speaker 1: the resin to solidify, which is genius. In addition, this 537 00:32:17,360 --> 00:32:21,280 Speaker 1: approach allows for much higher resolution print jobs. The process 538 00:32:21,320 --> 00:32:24,320 Speaker 1: I described earlier with the multiple lasers, the one that 539 00:32:24,480 --> 00:32:26,880 Speaker 1: was done by researchers from m I T and you 540 00:32:26,960 --> 00:32:29,920 Speaker 1: see Berkeley and such that could print objects with a 541 00:32:29,960 --> 00:32:33,920 Speaker 1: resolution of around three d microns. In articles I read 542 00:32:33,920 --> 00:32:36,520 Speaker 1: about this new process, researchers were able to print a 543 00:32:36,600 --> 00:32:41,840 Speaker 1: tiny replica two centimeter replica of Notre Dame cathedral with 544 00:32:41,920 --> 00:32:45,600 Speaker 1: a resolution of eighty microns. And just a reminder, you 545 00:32:45,640 --> 00:32:48,960 Speaker 1: want a lower number here as it describes how small 546 00:32:49,360 --> 00:32:52,920 Speaker 1: the edges are in curved surfaces. Technically it's a little 547 00:32:52,920 --> 00:32:55,880 Speaker 1: bit more complicated than that, but you that's the easiest 548 00:32:55,880 --> 00:32:59,440 Speaker 1: way to understand it. The team has created systems that 549 00:32:59,520 --> 00:33:04,080 Speaker 1: allow printing in either hard or soft plastics, and they 550 00:33:04,160 --> 00:33:07,040 Speaker 1: envisioned the process being used to print stuff for medical 551 00:33:07,040 --> 00:33:11,400 Speaker 1: applications like three D printing artificial arteries, which is super cool. 552 00:33:11,920 --> 00:33:15,720 Speaker 1: The resident can be sealed in a sterilized container, so 553 00:33:16,000 --> 00:33:20,760 Speaker 1: the finished printed product is safety use for medical applications 554 00:33:20,840 --> 00:33:24,600 Speaker 1: because it hasn't been contaminated at all. It was created 555 00:33:24,720 --> 00:33:28,600 Speaker 1: in a sterile environment. It was actually built that way. 556 00:33:29,200 --> 00:33:33,680 Speaker 1: One drawback of this approach, at least for the near future, 557 00:33:34,440 --> 00:33:37,440 Speaker 1: is the scale, because at the moment they're really limited 558 00:33:37,440 --> 00:33:39,400 Speaker 1: to printing these objects that are just a couple of 559 00:33:39,440 --> 00:33:42,680 Speaker 1: centimeters in size. The team feels confident they can create 560 00:33:42,720 --> 00:33:45,880 Speaker 1: a larger version of the system capable of printing stuff 561 00:33:45,920 --> 00:33:50,760 Speaker 1: closer to fifteen centimeters in scale, but that's still fairly small. 562 00:33:50,800 --> 00:33:53,800 Speaker 1: So you wouldn't be printing any fully formed furniture with 563 00:33:53,920 --> 00:33:57,120 Speaker 1: this stuff, unless, of course it's for a really tiny 564 00:33:57,160 --> 00:34:00,640 Speaker 1: playhouse or something. But it's still a really awesome some invention. 565 00:34:00,720 --> 00:34:02,680 Speaker 1: And while it may not be possible to build something 566 00:34:02,720 --> 00:34:07,000 Speaker 1: capable of constructing larger three dimensional objects right now, maybe 567 00:34:07,000 --> 00:34:10,359 Speaker 1: that will change down the line. If so, it would 568 00:34:10,360 --> 00:34:13,120 Speaker 1: be an incredible advance and additive manufacturing. It would be 569 00:34:14,400 --> 00:34:16,640 Speaker 1: cutting way back on the amount of time needed to 570 00:34:16,719 --> 00:34:20,839 Speaker 1: produce an object. Uh. And the resin that isn't solidified 571 00:34:20,880 --> 00:34:23,600 Speaker 1: can totally be used in future print jobs, so you 572 00:34:23,719 --> 00:34:26,160 Speaker 1: don't have it go to waste, Like if you are 573 00:34:26,200 --> 00:34:29,240 Speaker 1: making a small object and there's a lot of resin leftover, 574 00:34:29,680 --> 00:34:32,640 Speaker 1: no worries, you can still use that in future jobs. 575 00:34:32,680 --> 00:34:36,279 Speaker 1: That's pretty powerful. Now, As I said, this methodology owes 576 00:34:36,320 --> 00:34:40,640 Speaker 1: a lot tomography. It's essentially the reverse process in some ways. 577 00:34:40,680 --> 00:34:43,880 Speaker 1: So rather than using these moving elements to image a 578 00:34:43,960 --> 00:34:48,279 Speaker 1: physical object, it's using a reverse process to project a 579 00:34:48,400 --> 00:34:53,360 Speaker 1: virtual image into a three dimensional volumetric space to create 580 00:34:53,400 --> 00:34:57,279 Speaker 1: a physical object. Another area of research that relates to 581 00:34:57,360 --> 00:34:59,920 Speaker 1: this and that it's an alternate take on three D 582 00:35:00,120 --> 00:35:03,839 Speaker 1: printing is spearheaded by a guy named Adrian Bowyer, who 583 00:35:03,880 --> 00:35:06,279 Speaker 1: is the founder of a company called rep rap. Rap 584 00:35:06,400 --> 00:35:08,840 Speaker 1: Rap refers to Bowuer's work in creating what he calls 585 00:35:08,880 --> 00:35:12,440 Speaker 1: a replicating rapid prototyper, which is, in other words, a 586 00:35:12,440 --> 00:35:15,960 Speaker 1: three D printer. He's now working on a really interesting 587 00:35:15,960 --> 00:35:18,759 Speaker 1: application of science to create a new type of three 588 00:35:18,840 --> 00:35:22,600 Speaker 1: D printer, one different from the tomographic approach I just described. 589 00:35:23,040 --> 00:35:26,680 Speaker 1: So tomography is one way to scan a three dimensional object, 590 00:35:26,880 --> 00:35:29,719 Speaker 1: but Bowyer's research is looking into a different approach. He 591 00:35:29,800 --> 00:35:34,040 Speaker 1: describes a scanning technology called spectra, which already exists, and 592 00:35:34,080 --> 00:35:36,960 Speaker 1: it relies not on light or X rays as a 593 00:35:36,960 --> 00:35:41,840 Speaker 1: scanning mechanism, but electric current. And here's how it works. Okay, 594 00:35:41,840 --> 00:35:44,520 Speaker 1: you've got a three dimensional object you want to scan. 595 00:35:44,600 --> 00:35:48,399 Speaker 1: So let's say it's a little clay garden gnome, and 596 00:35:48,520 --> 00:35:51,640 Speaker 1: you put that inside a container that's already filled with 597 00:35:51,640 --> 00:35:55,760 Speaker 1: an electrically conductive fluid, so current can flow through this liquid. 598 00:35:56,040 --> 00:35:59,920 Speaker 1: The gnome is now submerged in that liquid. The container 599 00:36:00,080 --> 00:36:05,160 Speaker 1: also has little spot electrodes mounted on opposite sides of 600 00:36:05,160 --> 00:36:07,279 Speaker 1: one another on the inside of the container, so they're 601 00:36:07,280 --> 00:36:10,800 Speaker 1: pointed at each other. Uh the gnome is smack dab 602 00:36:10,880 --> 00:36:14,560 Speaker 1: in between those two electrodes. These two electrodes can apply 603 00:36:14,600 --> 00:36:17,400 Speaker 1: a difference of voltage, causing current to flow through the fluid. 604 00:36:17,680 --> 00:36:20,600 Speaker 1: The solid object inside the fluid causes the current to 605 00:36:20,680 --> 00:36:23,640 Speaker 1: move in different ways, and those fluctuations and current can 606 00:36:23,640 --> 00:36:28,400 Speaker 1: be monitored. Then you can rotate the electrodes slightly and 607 00:36:28,440 --> 00:36:31,920 Speaker 1: repeat the process again, and then you rotate it and 608 00:36:31,920 --> 00:36:34,400 Speaker 1: repeat it again. You do this many, many, many times, 609 00:36:34,840 --> 00:36:37,279 Speaker 1: and the difference in how the electric current moves through 610 00:36:37,320 --> 00:36:40,680 Speaker 1: the fluid can then be calculated and added up in 611 00:36:40,719 --> 00:36:44,360 Speaker 1: an integral function that gives you a cross section of 612 00:36:44,560 --> 00:36:46,279 Speaker 1: whatever it is you're skinning. So, in our case, the 613 00:36:46,320 --> 00:36:49,960 Speaker 1: little clay garden gnome, and it's right along the plane 614 00:36:50,120 --> 00:36:53,479 Speaker 1: of those electrodes. So however high those electrodes are within 615 00:36:53,520 --> 00:36:56,920 Speaker 1: the container, then you can move the electrodes up slightly. 616 00:36:57,160 --> 00:36:58,680 Speaker 1: Let's say that you started at the very bottom of 617 00:36:58,680 --> 00:37:02,160 Speaker 1: the container. You can move them up a smidge. Repeat 618 00:37:02,200 --> 00:37:05,280 Speaker 1: this process and you build the next cross section layer 619 00:37:05,480 --> 00:37:09,719 Speaker 1: of this little gnome this. Now you've got a virtual representation, 620 00:37:10,120 --> 00:37:11,879 Speaker 1: and you do it again and again and again until 621 00:37:11,880 --> 00:37:15,080 Speaker 1: you had scanned the entire thing. Now, in practice, you 622 00:37:15,120 --> 00:37:18,600 Speaker 1: would likely use a container that has lots of electrodes. 623 00:37:18,600 --> 00:37:20,640 Speaker 1: You wouldn't just have to the whole thing would be 624 00:37:21,000 --> 00:37:24,080 Speaker 1: have an insight coated with a grid of fine electrodes. 625 00:37:24,320 --> 00:37:27,760 Speaker 1: You would only activate pairs of these at a time 626 00:37:28,200 --> 00:37:31,879 Speaker 1: in order to get the scan. But by having them 627 00:37:31,920 --> 00:37:34,320 Speaker 1: located around the inside of the container, you wouldn't have 628 00:37:34,400 --> 00:37:36,720 Speaker 1: to rotate anything. You wouldn't have to have any moving parts. 629 00:37:36,960 --> 00:37:40,120 Speaker 1: You would just activate pairs of electrodes to get those 630 00:37:40,160 --> 00:37:43,399 Speaker 1: measurements until you've got a full three dimensional scan. As 631 00:37:43,400 --> 00:37:48,760 Speaker 1: I said, this technology already exists. That's a scanning technology. 632 00:37:49,120 --> 00:37:51,760 Speaker 1: What Valuer wants to do is to take that model 633 00:37:52,080 --> 00:37:54,880 Speaker 1: and reverse it much in the same way that the 634 00:37:54,920 --> 00:37:58,320 Speaker 1: photopolymer resin approach I described earlier is like a reverse 635 00:37:58,400 --> 00:38:02,480 Speaker 1: tomographic scan. So Buyer's method would use a monomer solution 636 00:38:02,920 --> 00:38:06,480 Speaker 1: that polymerizes upon exposure to electric current. This is a 637 00:38:06,520 --> 00:38:11,160 Speaker 1: process called electro polymerization. It happens like there's some monomers 638 00:38:11,160 --> 00:38:15,080 Speaker 1: that if you subject them to an electric current, they 639 00:38:15,120 --> 00:38:19,759 Speaker 1: will form polymers and they'll solidify. So his ideas you 640 00:38:19,840 --> 00:38:23,440 Speaker 1: take a virtual object. You've got a model, let's say 641 00:38:23,440 --> 00:38:27,279 Speaker 1: it's a model of our little garden gnome, and you 642 00:38:27,280 --> 00:38:33,120 Speaker 1: would apply current to a container holding monomer solution, and 643 00:38:33,200 --> 00:38:35,560 Speaker 1: you would control the current in such a way so 644 00:38:35,600 --> 00:38:38,160 Speaker 1: that it would activate only the bits of resin that 645 00:38:38,200 --> 00:38:42,839 Speaker 1: would represent that garden gnome in that volumetric space. So 646 00:38:42,880 --> 00:38:46,560 Speaker 1: it's taking that scanning process completely in reverse. Now he 647 00:38:46,560 --> 00:38:49,080 Speaker 1: hasn't managed to do it yet, but he's working on 648 00:38:49,120 --> 00:38:51,840 Speaker 1: the problem. And Buyer's hope is to create a printer 649 00:38:52,200 --> 00:38:56,839 Speaker 1: based on this methodology. And not only that, he's doing 650 00:38:56,880 --> 00:39:00,120 Speaker 1: it in an open source approach. He's published all of 651 00:39:00,160 --> 00:39:03,719 Speaker 1: his work on on his research in this method and 652 00:39:03,840 --> 00:39:07,400 Speaker 1: anyone interested in contributing can do so. And moreover, he 653 00:39:07,440 --> 00:39:09,640 Speaker 1: has a goal to make sure that this process cannot 654 00:39:09,640 --> 00:39:14,480 Speaker 1: be patented, so no person, no company, no other entity 655 00:39:14,680 --> 00:39:17,400 Speaker 1: would be able to take this process and lock it 656 00:39:17,440 --> 00:39:20,359 Speaker 1: away under intellectual property rights. So, in other words, if 657 00:39:20,400 --> 00:39:23,040 Speaker 1: it works, it will work for everybody. And I think 658 00:39:23,040 --> 00:39:25,799 Speaker 1: that's pretty darn cool. Now, it may turn out that 659 00:39:25,920 --> 00:39:31,000 Speaker 1: volumetric printing has inherent limitations that we cannot overcome, and 660 00:39:32,000 --> 00:39:34,960 Speaker 1: in case that happens, it's still not a total loss 661 00:39:35,040 --> 00:39:37,600 Speaker 1: because it's going to be incredibly useful for at least 662 00:39:37,640 --> 00:39:41,000 Speaker 1: a certain number of applications, and we can still rely 663 00:39:41,080 --> 00:39:43,840 Speaker 1: on other methods to produce things that are outside of 664 00:39:43,840 --> 00:39:46,560 Speaker 1: that spectrum. That's pretty much the case with every single 665 00:39:46,600 --> 00:39:49,520 Speaker 1: process we can think of. Even with traditional three D printing, 666 00:39:50,200 --> 00:39:53,440 Speaker 1: you're limited in the size of the thing you can print, 667 00:39:53,640 --> 00:39:57,680 Speaker 1: at least in a single printing session, because you have 668 00:39:57,760 --> 00:40:01,120 Speaker 1: to keep stuff at the right temperature. Uh. If it 669 00:40:01,160 --> 00:40:03,800 Speaker 1: gets too heavy, then it can collapse in on itself. 670 00:40:04,320 --> 00:40:07,000 Speaker 1: So if you want to print a really big print job, 671 00:40:07,040 --> 00:40:09,759 Speaker 1: you typically have to do it in sections and then 672 00:40:09,840 --> 00:40:12,480 Speaker 1: glue the pieces together at the end or otherwise have 673 00:40:12,600 --> 00:40:15,160 Speaker 1: them adhere to each other at the end, because uh, 674 00:40:15,320 --> 00:40:18,799 Speaker 1: you just can't keep it structurally sound through the whole 675 00:40:18,800 --> 00:40:21,680 Speaker 1: printing process if it's a really big print job. In 676 00:40:21,719 --> 00:40:24,879 Speaker 1: the future, we could see three D volumetric printers making 677 00:40:24,920 --> 00:40:28,600 Speaker 1: all sorts of stuff, including the basic scaffolding for things 678 00:40:28,680 --> 00:40:32,240 Speaker 1: like artificial and three D printed organs. In the meantime, 679 00:40:32,560 --> 00:40:35,080 Speaker 1: I just think it's a super nifty technology to learn 680 00:40:35,120 --> 00:40:37,880 Speaker 1: more about. As for other types of three D printing, 681 00:40:37,960 --> 00:40:41,719 Speaker 1: they are still really awesome. It has not proliferated quite 682 00:40:41,760 --> 00:40:44,160 Speaker 1: to the level that people were predicting about five years ago, 683 00:40:44,200 --> 00:40:46,680 Speaker 1: but the work continues and we've seen some really cool 684 00:40:46,800 --> 00:40:50,200 Speaker 1: uses of the text so far, including enormous three D 685 00:40:50,280 --> 00:40:53,560 Speaker 1: printers that can use stuff like a concrete based resin 686 00:40:53,840 --> 00:40:57,399 Speaker 1: to build entire houses out of layer by layer, all 687 00:40:57,400 --> 00:41:00,960 Speaker 1: the way down to students using commercial three D printers 688 00:41:01,040 --> 00:41:03,759 Speaker 1: or even consumer three D printers to build stuff like 689 00:41:03,880 --> 00:41:06,439 Speaker 1: artificial limbs for people who otherwise would never be able 690 00:41:06,440 --> 00:41:10,080 Speaker 1: to afford one. So it's truly a revolutionary technology. I 691 00:41:10,120 --> 00:41:13,080 Speaker 1: can't wait to see where it goes next. And that 692 00:41:13,120 --> 00:41:16,239 Speaker 1: wraps up this episode about three D printers and tomography. 693 00:41:16,480 --> 00:41:19,200 Speaker 1: If you guys have suggestions for future topics of tech stuff, 694 00:41:19,320 --> 00:41:21,160 Speaker 1: reach out to me. You can get in touch with 695 00:41:21,200 --> 00:41:24,080 Speaker 1: me on social media on Facebook or Twitter. We use 696 00:41:24,160 --> 00:41:27,840 Speaker 1: the handle text stuff hsw at both. Look forward to 697 00:41:27,920 --> 00:41:31,160 Speaker 1: hearing from you, and I'll talk to you again really soon. 698 00:41:35,719 --> 00:41:37,920 Speaker 1: Text Stuff is a production of I Heart Radio's How 699 00:41:37,960 --> 00:41:41,359 Speaker 1: Stuff Works. For more podcasts from my heart Radio, visit 700 00:41:41,400 --> 00:41:44,480 Speaker 1: the i heart Radio app, Apple podcasts, or wherever you 701 00:41:44,520 --> 00:41:45,880 Speaker 1: listen to your favorite shows.