More than eight million tons of plastic end up in the oceans every
year—a serious danger for the environment and health. Biodegradable
bioplastics could provide an alternative. In the journal Angewandte Chemie,
a research team has now introduced a new method for the production of
protein-based plastics that are easily processable, biodegradable, and
biocompatible, as well as having favorable mechanical properties.
© Wiley-VCH, re-use with credit to 'Angewandte Chemie' and a link to the original article.
Whether as packaging or toys, mulch films or cars, plastics based on
petrochemicals are ubiquitous—demand is rising, and so are the piles of
garbage. Bioplastics based on natural materials like starch, or
synthetic biomaterials like polylactic acid, have exhibited inadequate
durability, biocompatibility, and/or biodegradability in most cases. In
addition, they often require complex, energy-intensive processing
methods and toxic chemicals.
A team led by Jingjing Li and Yawei Liu (Chinese Academy of Sciences,
Changchun, China), as well as Bo Wei (First Medical Center of PLA
General Hospital) have now introduced novel bioplastics with properties
that can be tailored according to need. To do this they developed two
lysine-rich proteins and produced them in bacterial cultures: “ELP” is a
polypeptide similar to the connective tissue protein elastin. It does
not have defined folding, which leads to toughness and elasticity. “SRT”
consists of ELP plus crystalline segments of a squid protein with a
β-sheet structure.
ELP (or SRT) is crosslinked with a polyethylene glycol (PEG)
derivative by way of its lysine amino side-groups. (PEG is used in
pharmaceuticals, among other things.) If the crosslinking occurs in
water, the material can then simply be dried in a mold. The result is a
tough, transparent, solvent-resistant bioplastic. Its mechanical
properties can be varied by changing the proportion of PEG. This allows
for the production of bioplastics with high mechanical strength at room
temperature in any shape desired, and without toxic chemicals or complex
processing steps such as liquefaction, extrusion, or blow molding.
Their breaking stress exceeds those of many commercial plastics. One
problem left is that they swell in water.
If ELP is crosslinked in a water/glycerol solution, the material gels
into soft, elastic bioplastics. The team also used wet spinning to
produce biofibers that are as strong as some biotechnological spider
silks. The natural enzyme elastase completely degrades all of the new
protein-based bioplastics.
It is conceivable to make toys with this new, nontoxic bioplastic
that can be dyed with food coloring. This material may also be used to
seal wounds as it has hemostatic effects. Implants were completely
broken down within a few weeks.
To store information, ELP could be polymerized together with peptides
that have been programmed with codes by means of their specific amino
acid sequences. The information could be read back through sequencing.
This would allow for higher information density than is possible with
DNA data storage.
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About the Author
Dr. Yawei Liu is an
assistant research scientist at the Changchun Institute of Applied
Chemistry, Chinese Academy of Sciences. Her main specialty is
biomaterials technology, and the materials design to broaden the
application of biomaterials, especially engineered proteins.
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