Hi Patrik,
I had that very same idea independently a few weeks ago, agree it would be fantastic, and have been working on researching alternatives, as I'm also interested in 3D printing and trained in molecular biology. I have tried some initial experiments with commercially available enzymes (e.g. proteinase K from the above-mentioned Tritirachium) and some biological detergent mixtures (see the interesting comment in the linked thread about dishwasher tablets!), but haven't seen significant degradation of 3 mm filament yet over several days. The problem with these enzymes is that while they do degrade plastic, it is usually measured over the course of weeks or months - the specific activity is usually really low. My guess is some serious mutagenesis work will be necessary to get the rate up to where it would be useful. Then there is the type of enzyme - the hydrolases and lipases have broad specificity, but have problems with solid plastic due to adsorption issues (most experiments are done with thin PLA film). Some of the more PLA-specific proteases have potential for higher rates of reaction but tend to require tailoring to a specific formulation of plastic. Recombinant production of a synthetic gene for the enzyme might yield plenty of product, but they commonly end up in the periplasmic space or in inclusion bodies in E. coli, which is annoying. Also, several mg of protein would be needed per litre of bathing solution, so we're talking fermenter-size enzyme production to get enough, so cell-free translation systems are out. Are there any diybio solutions yet for producing several mg of synthetic protein?
I haven't given up quite yet though; Stratasys already sells their 'WaveWash' system for their FDM printers which looks suspiciously like an enzyme-based solution, so I think it's possible, but the question is whether it is possible using the bulk plastic most of us currently print with at home.
Best,
Dave
On Thu, Aug 8, 2013 at 6:13 AM, Patrik D'haeseleer <patrikd@gmail.com> wrote:
So I was soaking the print nozzle of our 3D printer in acetone to get it unclogged. Problem is, we've printed both ABS and PLA plastic with it, and I know PLA doesn't dissolve in acetone. In fact, there's very little in terms of relatively safe solvents that will dissolve PLA. Which is rather ironic, since PLA is supposed to be biodegradable and stuff.
So here's a very interesting suggestion I stumbled upon while googling for a solution, by "Kevin R" on the Ultimaker forum:https://groups.google.com/d/msg/ultimaker/8s1bq_9LsRM/VXz40PTjJq8J
"I've actually been looking into using PLA and PCL for a product I'm going to launch in the new year, so I've been learning about the biochemistry for their decomposition because... well... I'm a nerd. The problem with PLA is that really isn't as biodegradable as one might think, but it can be none the less (which is a far cry that what ABS can claim). To make a truly safe and environmentally friendly method of removing PLA supports, you would want to use a combination of a hydrolase (either/or a lipase and protease... protease seems to be best) and a polymerase to break down the polymer. These are the enzymes that fungi and bacteria use to catalyze the decomposition of the PLA into to its base units. At best PLA isn't overly biodegradable, so using the fungi alone would take a while. You could isolate and separate the hydrolase and polymerase, disperse them in water at relatively concentrated levels and use them as a bath (in theory they should last forever if you don't denature them). The best fungi for this (and seemingly the only fungi that can completely breakdown PLA) seems to be Tritirachium album but aside from a couple of us, who around here could get their hands on that? Here's a fun fact though: the second best fungi for PLA decomposition is Penicillin roqueforti which is your friendly neighborhood bread mold! This is the same fuzzy stuff that grows on your bread if you leave it too long and is what makes blue cheese blue. If there is a biologist in our midst with some free time, they might be able to get a culture to pump out the polymerase and protease into a solution that we could dip our parts into (heated up to the right activation temperature of course). If you feed the culture gelatin you might be able to spur the secretion of the polymerase."
That sounds entirely feasible, and an enzyme cocktail to dissolve PLA plastic might even be commercializeable, given the exponential growth in 3D printing these days. Would make for a wonderful synergy between two of the hottest nerd topics of the century - DIY 3D printing and DIYbio!
Patrik
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