Mass production, in which identical products are manufactured cost-effectively on a large scale, has been a mainstay of the global economy since the industrial revolution. Now, however, three dimensional printing is helping to usher in a brand new era of mass customisation, in which unique, bespoke items are produced cheaply to order. But 3D printing won’t stop at just revolutionising traditional manufacturing – it could also transform the way that chemicals are made in the laboratory.
In 3D printing, a computer-generated design is built up layer-by-layer. This can be done by depositing successive layers of a plastic or metal powder that are then heated with a laser to solidify them, known as laser sintering, or by depositing layers of molten plastic that harden on cooling. Already, a whole host of wild and wonderful products have being produced by 3D printing, including jewellery, lampshades, medical implants, batteries and clothing.
Using lots of 3D printers, these products can easily be manufactured on a large scale, but they can also easily be adapted and customised by simply altering the computer-generated design. Not only does this mean that manufacturers can now cost-effectively create products specifically designed for particular customers or uses, such as football boots made for the shape of individual feet, but it also opens up the possibility of using less material (see box: Lightening the load).
With the cost of 3D printers falling in price, such that a build-it-yourself 3D printer is now available for less than $1000, this kind of advanced manufacturing technology is now open to almost anybody, even scientists. So rather than paying for expensive scientific equipment, it becomes possible for scientists to fabricate their own versions at a fraction of the cost, as Joshua Pearce, an associate professor of materials science at Michigan Technological University, US, has shown.
Pearce’s primary research interest is solar photovoltaic technology and one of his projects involved helping a team of undergraduates develop a solar photovoltaic charger for the low-cost laptops given out by the One Laptop Per Child initiative. ‘They came up with a clever design that both looked good and would help young users orient the cells to the sun using a pencil,’ explains Pearce. ‘[Initially] we used the university’s professional rapid prototyper to make the plastic case [for the charger], which even using student rates was 10 times more expensive than the solar cells! It was absurd, we were paying over $100 for plastic that could not have been worth more than $1.’
That was when Pearce discovered the RepRap, an open-source, build-it-yourself 3D printer that could print the case for merely the cost of the plastic. Since then he has used the printer to fabricate many other photovoltaic components. ‘We have developed an open-source optics library of printable components that you can use to do everything from simple experiments on an optical rail to more complicated systems like those that test photoluminescence.’
As he explained in a recent article in Science (2012, 337, 1303), he has also used the printer to fabricate several other pieces of scientific equipment, including a rotor for a centrifuge and an automated filter wheel. A commercial filter wheel costs around $2500 to buy, whereas Pearce produced his for less than $50. ‘We have saved tens of thousands of dollars of research funds, and get to have complete control of our tools and use equipment that is exactly what we want,’ he says.
But this is likely to be only the beginning, as 3D printing offers the possibility of fabricating entirely novel scientific equipment that couldn’t be produced by other means. ‘I have just started to look at complicated geometries for optimising chemical reactionware that would be exceptionally difficult if not impossible to manufacture using conventional subtractive technologies,’ Pearce says. In this, he has been inspired by work conducted by Lee Cronin, a professor of chemistry at the University of Glasgow, UK.
In a ground-breaking study published in Nature Chemistry in April (2012, 4, 349), Cronin reported using another build-it-yourself 3D printer called Fab@Home to fabricate plastic reaction vessels from a quick-drying silicone polymer, otherwise known as bathroom sealant. These vessels comprise two separate solution-holding chambers above a larger mixing and reaction chamber.
To perform chemical reactions in this reaction vessel, or reactionware, Cronin and his colleagues simply deposit two different chemical solutions into the two solution-holding chambers. Using a needle attached to a vacuum source, they then suck these two solutions into the larger chamber, where they react together.
Trying this process out with both organic and inorganic chemicals, Cronin was able to produce an organic heterocycle and two inorganic nanoclusters that had never been seen before. By inserting electrodes into the reaction vessel, he was also able to perform electrochemical reactions and even turn the vessel into a working electrochemical cell.
What Cronin did next, however, was truly revolutionary, because he printed versions of these vessels that could play an active role in the reaction process. One way of doing this is simply to incorporate catalytic particles into the polymer ink, which then become embedded in the walls of the vessels. Cronin did this with particles of palladium on carbon, which can catalyse hydrogenation reactions, and showed that the resultant vessels could convert styrene into ethylbenzene within around 30 minutes at room temperature.
Even more impressively, Cronin also showed he could alter the progress of a reaction by simply changing the architecture of the reaction vessel. Using the same basic design, he and his colleagues produced two versions of the vessel with different size reaction chambers: one had a volume of 9.5ml, while the other had a volume of just 2ml.
They then added two different chemical solutions into the solution-holding chambers of each vessel, adding three times more of one solution than the other. The vessel with the large chamber could hold the entirety of both solutions, which thus mixed together in a ratio of three to one, reacting to produce a specific heterocycle. The vessel with the small chamber, on the other hand, could only hold 1ml of each solution, which thus mixed together in an equal ratio, producing a completely different heterocycle.
Cronin has since gone on to print other vessels with more complicated designs, including microfluidic devices, in which he has performed a whole range of different organic and inorganic reactions, such as polymerisation and protein synthesis reactions. ‘What we’re trying to do is to come up with credible avenues for molecular discovery that couldn’t be done any other way,’ he says.
Cronin has even been able to conduct the kind of multiple synthesis steps found in flow chemistry, which conventionally needs lots of expensive, automated equipment, in a single printed device. ‘I think that we can pretty much do what big pharma can do with very expensive robots, but very, very cheaply using 3D printers,’ he says, ‘and I think that’s a big development if it works.’
As early pioneers of 3D printing for scientific applications, Pearce and Cronin are now trying to convince others of the benefits of this approach, in the face of quite a bit of scepticism at times. ‘A lot of people say that 3D printing is just a gimmick, you can print lots of novelty items but it’s not going to allow you to do anything new.’ explains Cronin, ‘So it’s crucial to show what is possible, what is new.’
If Cronin and Pearce are able to do this, then the 3D printer may soon become a common, but still potentially revolutionary, sight in chemical laboratories.
Jon Evans is a freelance science writer based in Chichester, UK.
Lightening the load
Conventional manufacturing produces a lot of waste: metal products need to be hewn out of solid lumps, while even fabricating plastic products in moulds tends to generate quite a bit of waste plastic.
In contrast, 3D printers only use the amount of material needed to fabricate the product. Not only does this greatly reduce waste, but it also means the resultant products are much lighter, as their design is no longer constrained by the practicalities of the manufacturing process.
Lighter products and components are particularly sought after by car and aircraft manufacturers, because lighter cars and aircraft mean better fuel efficiency: a 1kg reduction in the weight of an airliner saves around $3000 of fuel per year. With this in mind, the European defence and aerospace company EADS is now using 3D printing to produce some of the titanium components in its aircraft. These printed components are often 60% lighter than the conventionally-produced versions.
Last year, the University of Southampton, UK, went one better and fabricated a whole aircraft by 3D printing, albeit a miniature one with a 2m wingspan. The entire structure was printed by laser sintering, including the elliptical, Spitfire-inspired wings, and then simply snapped together to produce the aircraft. Powered by an electric motor, this autopilot-controlled aircraft can travel at speeds of up to 100 miles/ hour (C&I, 2011, 16, 7).
Perhaps most excitingly, 3D printing can fabricate products that couldn’t be produced by conventional manufacturing technology, usually because the design is too complex. Thus, a British design consultancy firm called Within Technologies has used 3D printing to fabricate titanium medical implants with a similar structure to bone and heat exchangers shaped like fish gills.
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