3D printing
Post date: Sep 09, 2015 3:5:9 PM
Thoughts on "You can print your own guns at home. Next it will be nuclear weapons. Really." by D. C. Tirone and J. Gilley (accessed 9/9/2015, 10 am)
This piece combines vastly different types of additive manufacturing with a misunderstanding of the science involved. As a result the authors take a large and overly optimistic logical leap that lands in unwarranted alarmism.
It is inarguable that people have used 3D printing to print guns that have worked. In these examples, guns have been printed plastic "ink" with features on relatively large length scales (mm-cm). The authors take this as a starting point and then take examples from other areas where additive manufacturing techniques have been used to formulate other supports or scaffolds (guns are essentially supports for the containment and delivery of bullets) as a starting point for speculation about the development of unsupported materials.
The examples chosen all describe the use of 3D printing techniques for the preparation of The printed medications described in the link are 3D-printed tablets designed to dissolve more rapidly when swallowed. The printing here is at the processing level. The drug (leviteracetam) delivered has been used in other formulations for some time; it is not changed (or shouldn't be changed) by the 3D printing process. The organ printing paper described is similar to the other examples in that additive manufacturing is used to print a support for the growth of cells, in this case into an ear with some embedded electronics, which is very cool but again involves the printing of existing stable materials into functional large-scale assemblies. The hamburger example is cute, but the actual existing examples of 3D printed food begin with liquified food that is printed into desired shapes.
From these examples, the authors then state that "bacteria and chemicals aren't far behind." First, there is a huge difference between claiming that one might be able to print a bacterium, an exquisitely complex and squishy assemblage of proteins, nucleic acids, salts, fatty acids, and many other molecules, from scratch (impossible to envision happening in any of our lifetimes or our great-great-great-great grandchildren's lifetimes), and that one might be able use 3D printing techniques to place existing bacteria within a three-dimensional scaffold. While the latter scenario is quite feasible, it presupposes the possession of the bacteria to be printed, so if someone is going to use the bacteria to cause trouble they will be able to do so regardless of their access to additive manufacturing facilities.
The work of Marty Burke's group at the University of Illinois to develop automated processes for the iterative synthesis of specific complex molecules is linked to as an example of the printing of chemicals (http://dx.doi.org/10.1126/science.aaa5414). The key problem here seems to be that the authors have relied upon a news report from the Calvin College newspaper that inaccurately conflates Burke's synthesizer with 3D printing. Iterative synthesis methods have been known for a long time, with Bruce Merrifield (Nobel Prize 1984; 1965 Science paper (free!)) the most famous proponent. Smaller molecules are sequentially strung together into larger molecules through judicious choices of chemical functional groups that allow the desired connections between molecules to be made rather than unwanted connections. This is a much more limited process than the 3D printing it is compared to: specific stable molecules must first be designed and synthesized, and the structure and variety in these molecules limits the range of possible structures that can be prepared. Proteins and nucleic acids have been made by these methods for a long time. The cost and time required to make quantities of dangerous materials by these methods are likely so prohibitive that there have been no reported examples of people even considering these methods as reasonable route.
Finally, the authors make an overly imaginative leap into the possibility of printing atoms from subatomic components and the likelihood that this will enable the printing of nuclear materials. Conceptually, all additive manufacturing methods require stable starting materials. On their own, subatomic components are highly reactive, unstable, unisolable, and generally uncontainable. The combination of these components is highly energetic (e.g., nuclear fusion). To make nuclear weapons, you need a critical mass of radioactive uranium or plutonium. How the bomb is assembled and how the different components are placed relative to one another (things that could be potentially be addressed by additive manufacturing) is not as important as having the radioactive uranium. "Printing" uranium-235 (143 neutrons, 92 protons, 92 electrons, etc.) or even smaller radioactive nuclei from subatomic components, even in trace amounts, is completely implausible. Esoteric individuals have long sought routes to convert base metals into more precious ones--this would be a much bigger deal than the authors seem to appreciate.
There are plenty of good chemists and physicists at LSU who would be able to provide helpful and constructive feedback on the authors' pending article. There are important issues related to additive manufacturing and 3D printing that should be considered at the governmental level. If alarmist arguments are made upon a misunderstanding of the underlying science, it is too likely that the important issues within the arguments will be ignored and obscured.