Using a small block of aluminum with a tiny groove carved in
it (Fig. 1), a team of researchers from the National Institute
of Standards and Technology (NIST) and the
Polytechnic Institute of New York University is developing an
improved green chemistry method for making
biodegradable polymers. Their recently published work is a
prime example of the value of microfluidics, a technology more commonly associated
with inkjet printers and medical diagnostics, to process
modeling and development for industrial chemistry.
1. Typical NIST microreactor plate for
studying enzyme-catalyzed polymerization.
Photo courtesy of Kundu, NIST.
We basically developed a
microreactor that lets us monitor continuous polymerization
using enzymes, explained Kathryn Beers, a NIST materials
scientist. These enzymes are an alternate green technology for making these types of
polymers. We looked at a polyester, but the processes
arent really industrially competitive yet. Data
from the microreactor, a sort of zig-zag channel about a
millimeter deep crammed with hundreds of tiny beads, shows how
the process could be made much more efficient. The team
believes it to be the first example of the observation of
polymerization with a solid-supported enzyme in a
The group studied the synthesis of PCL, a biodegradable
polyester used in applications ranging from medical devices to
disposable tableware. PCL, Ms. Beers said, is most commonly
synthesized using an organic tin-based catalyst to stitch the
base chemical rings together into the long polymer chains. The
catalyst is highly toxic, however, and has to be disposed
Modern biochemistry has found a more environmentally friendly substitute
in an enzyme produced by the yeast strain Candida antartica,
Ms. Beers said, but standard batch processesin which the
raw material is dumped into a vat, along with tiny beads that
carry the enzyme, and stirredis too inefficient to be
commercially competitive. It also has problems with enzyme
residue contaminating and degrading the product.
By contrast, Ms. Beers said, the microreactor is a
continuous flow process. The feedstock chemical flows through the
narrow channel, around the enzyme-coated beads, and polymerized
out the other end. The arrangement allows precise control of
temperature and reaction time, so that detailed data on the
chemical kinetics of the process can be recorded to develop an
accurate model to scale the process.
The small-scale flow reactor allows us to monitor
polymerization and look at the performance recyclability and
recovery of these enzymes, Ms. Beers said. With
this process-engineering approach, weve shown that
continuous flow really benefits these reactors. Not only does
it dramatically accelerate the rate of reaction, but it
improves your ability to recover the enzyme and reduce
contamination of the product.
A forthcoming follow-up paper will present a full kinetic
model of the reaction that could serve as the basis for
designing an industrial scale process.
While this study focused on a specific type of
enzyme-assisted polymer reactions, the authors observe,
it is evident that similar microreactor-based platforms
can readily be extended to other systems; for example,
high-throughput screening of new enzymes and to processes where
continuous flow mode is preferred.