By Ian Hayman

You’re sitting in lab, fiddling with the newest duct tape/wire/clamp/tubing/ring stand amalgamation you jury-rigged to support your experimental apparatus. Everything looks good (or as good as it can look), so you start your experiment and head to lunch. Calamity strikes. Upon returning to lab, your monstrosity has fallen apart and your precious sample is all over the floor. Sound familiar? If only there was a way to rapidly produce custom durable parts and equipment tailored to your specific need, you could avoid problems like your spilled sample in the future. If only B’elanna, Trip, or Geordi La Forge could swoop in and save the day with their complex engineering skills and fanciful Star Trek replicators, then maybe you could get your experiment done and that next lab meeting wouldn’t be so awkward.

The technology for rapid prototyping and custom designed parts is already here; 24^th century not included. 3D printing, a type of additive manufacturing, allows users to develop and create functional prototypes and custom parts¹. All forms of 3D printing take a digital 3D model and use specialized (and frequently free) software to tell a 3D printer how to use the digital file to generate a physical printed object. There are many flavors of 3D printing that use various methods of converting a base material, such as plastic filament, photopolymer resin, or metal powder, into the desired object¹.

3D printing was first invented in 1986 by Chuck Hull². He developed a 3D printing method called stereolithography (SLA), a term coined by Mr. Hull to describe a process of curing ultraviolet (UV) activated photopolymer (basically chemical Legos that click together when hit with UV light) in successive layers to make a 3D object^{1, 2}. SLA printing uses a UV laser, while the closely related Digital Light Processing (DLP) method uses a UV screen to more rapidly print items¹. Most SLA and DLP printers operate using a large vat of liquid photopolymer that is set on top of a glass screen¹. A metal stage is lowered into the vat, and directed UV light solidifies the photopolymer resin in a specific shape onto the metal stage¹. The stage is then lifted slightly, photopolymer floods in to fill the gap between the stage and screen, and the UV light source solidifies the next layer onto the previous layer¹. The stage is slowly raised as subsequent layers are ‘printed’ by solidifying the photopolymer (Movie 1).

SLA and DLP printing can be used to generate solid objects with dimensional accuracy as precise as 10 micrometers, meaning details as small as 10 micrometers in size (about the size of a human red blood cell) can be faithfully produced ^{1, 3, 4}. DLP printing is relatively fast; a small object about 5 inches tall could be printed by a household machine in just a few hours. SLA printing is slightly slower as entire print layers aren’t cured at one time. SLA and DLP printing is used in a wide variety of manufacturing industries, including medical fields such as dentistry for custom printed crowns or implants^{3, 5}.

However, SLA and DLP printing is more difficult for hobbyists of 3D printing to use. Photopolymer resins are fairly dangerous irritants that are also extremely damaging to aquatic wildlife when they are liquids⁶. Fully cured solid SLA and DLP printed items are completely safe, but liquid resin waste can be difficult for hobbyists to deal with⁶. Newly printed objects also require an alcohol wash to remove excess resin and a final UV curing step. SLA and DLP printing is gaining popularity as a hobbyist printer system, although a safer and easier printing method called Fused Deposition Modeling (FDM) is more popular⁷.

FDM is by far the most popular at-home 3D printing method, and is used by the library at the Hershey College of Medicine⁷. FDM printing differs from SLA and DLP printing in just about every way, but there are two major differences worth highlighting¹. First, FDM printing uses solid plastic filament rolls instead of liquid photopolymer resin. Polyactic acid, also known as PLA, is the most popular plastic filament used for FDM printing¹. PLA is derived from corn, and is fully biodegradable and safe to use¹. PLA or any plastic filament used in FDM printers is melted by the ‘hot-end’, a metal nozzle heated to over 200°C, and laid down while molten.  The plastic cools rapidly, and hardens to build a solid object¹. The second way FDM printing differs from DLP printing is how the object is generated. Where DLP uses a UV panel to cure a whole object layer at once, FDM printers instead move a hot-end that is extruding molten plastic in a thin ribbon that slowly generates each layer (Movie 2)¹. SLA printing is actually more similar to FDM printing instead of DLP printing in this regard as the laser cures resin in a piecewise manner just like a FDM printer laying down molten plastic.

FDM printing is generally faster than SLA printing but slower than DLP printing ⁸. An object that a DLP printer can make in a couple hours can take several hours or even days for an FDM printer to make⁸. FDM printing is also generally less accurate, with most objects having a dimensional accuracy of 100-200 micrometers (about the thickness of a piece of paper) ^{1, 4}. The final object printed by an FDM printer is typically ready to use as soon as printing completes, but some models require simple post-printing processing methods like sanding with sandpaper to clean up. FDM printing is used by hobbyists for everything from making models for Dungeons and Dragons, special cosplay parts for complex costumes, custom household objects like soap dishes and battery organizers, or prototype parts for cars and other machines^{1, 5, 9}. Researchers also use FDM printing to make specialized apparatuses for experiments or autoclavable parts for custom tissue culture needs ⁵.

3D printing technology has rapidly advanced since 1986. 3D printing houses has recently caught the attention of social media and uses printers that are massive in size and function like FDM printers, but instead of molten plastic they lay down lines of concrete that then harden into walls (Movie 3)¹. While specialized construction crews are still needed for internal components like plumbing and electrical systems, as well as external parts like windows, the ability to print the walls can decrease building costs by 20-40% and building time by weeks or even months^{10, 11}. 3D printed houses could effectively provide lower cost homes for people priced out of the current market¹¹. Furthermore, charitable organizations are designing special concrete compounds that can be made from local soils, allowing for 3D printing of housing in refuge situations where building materials are normally prohibitively expensive^{1, 12}. 3D printing structures is also likely to be used on any future missions to the Moon or Mars, as they would allow extraterrestrial soil to be used for structure construction in place of shipping materials into space¹.

The printers described in this article are popular for hobbyists, home users, small companies, and research labs. Many people incorrectly think that buying and using a 3D printer is expensive and requires engineering technical know-how. Entry level 3D printers can be found for $300 or less for both DLP and FDM printing, and entry-level printers are extremely capable. The vast majority of people use entry-level printers, and only upgrade when they want multiple printers or printers with larger build areas to print more objects at one time. Many public libraries, including the library at the Penn State College of Medicine, offer 3D printing services at or near cost for the raw materials. Digital files used to print a huge variety of objects can be readily found online for free, and the most common software program used to translate digital files for 3D printers is also free. Programs to make your own digital models from scratch are also free, and cater to beginners, experienced users, and experts. It may be some time before we have Star Trek replicators in every home, but it is already feasible for anyone with a little time and patience to make custom designed objects with the help of some molten plastic or the flash of a UV laser.

TL:DR

• 3D printing can make prototypes, household objects, custom lab products, and hobby items
• There are multiple types of 3D printing
• 3D printing is relatively cheap and easy to do!

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References

1. Shahrubudin, N.; Lee, T.; Ramlan, R. An Overview on 3D Printing Technology: Technological, Materials, and Applications. Procedia Manufacturing 2019, 35, 1286-1296. DOI: 10.1016/j.promfg.2019.06.089.
2. Hickey, S. Chuck Hull: the father of 3D printing who shaped technology. The Guardian, 2014-06-22, 2014. http://www.theguardian.com/business/2014/jun/22/chuck-hull-father-3d-printing-shaped-technology.
3. Y, T.; C, C.; X, X.; J, W.; X, H.; K, L.; X, L.; H, S.; ES, L.; HB, J. A Review of 3D Printing in Dentistry: Technologies, Affecting Factors, and Applications. Scanning 2021, 2021. DOI: 10.1155/2021/9950131.
4. Helmenstine, A. What Is a Micron? Definition and Examples. Science Notes, 2020. https://sciencenotes.org/what-is-a-micron-definition-and-examples/ (accessed.
5. D, F.; Y, L.; X, W.; T, Z.; Q, W.; H, C.; W, L.; Y, T.; Z, L. Progressive 3D Printing Technology and Its Application in Medical Materials. Frontiers in pharmacology 2020, 11. DOI: 10.3389/fphar.2020.00122.
6. Griffin, M. SLA Printing: Is 3D Printer Resin Toxic? all3dp, 2022. https://all3dp.com/2/sla-3d-printing-is-3d-printer-resin-toxic/ (accessed 2022 6/16/2022).
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8. Kondo, H. SLA vs FDM: Is Resin 3D Printing Faster? @all3dp, 2020. https://all3dp.com/2/sla-vs-fdm-is-resin-3d-printing-faster/ (accessed.
9. Dvorak, K. 3D model preparing for rapid prototyping by FDM method. In 8th International Conference on Mechanical and Aerospace Engineering, Prague, Czech Republic; 2017.
10. Carpenter, S. 3D Printing in Construction – How Long Does it Take to Print a House? all3dp, 2019. https://all3dp.com/2/3d-printing-in-construction-how-long-does-it-take-to-print-a-house/ (accessed 2022 6/16/2022).
11. Greguric, L. How Much Does a 3D Printed House Cost? all3dp, 2021. https://all3dp.com/2/3d-printed-house-cost/ (accessed 2022 6/16/2022).
12. Chiusoli, A. The first 3D printed House with earth | Gaia – 3D Printers | WASP. 2022. https://www.3dwasp.com/en/3d-printed-house-gaia/ (accessed 2022 6/24/2022).