Controlled degradation with 3D-printed enzyme-embedded plastics
Enzymes embedded into plastic objects can be triggered to break down the plastic at the end of the object’s life.
This enzymatic technology offers a new way to ensure that compostable plastics biodegrade quickly in an environmentally friendly way.
Scion materials scientists have been working on the problem of developing cost-effective ways for mass producing enzyme-embedded plastics. The challenges include the use of heat during plastic processing. Many enzymes are denatured at higher temperatures and lose their activity. And the enzymes need to be embedded into the plastic, which up to now has been accomplished by encasing the enzyme and plastic using toxic solvents or the use of additional protective layers around the enzyme.
The solution developed by the team is deceptively simple. They mixed solid enzyme with finally ground polycaprolactone (PCL), a biodegradable polyester with a low melting point, and used 3D printing techniques to mimic industrial thermoplastic processing where plastic is heated to or past its melting point then shaped (extruded, moulded or blown).
The chosen enzyme, in its solid state, was found to be very heat stable. During testing, samples heated to 130°C for two hours retained most of their activity.
Printed films made by the research team broke down in aqueous conditions with the rate of degradation dependent on the amount of enzyme added to the plastic. After one week, 400 mm thick plastic films containing 1% by weight of the enzyme had lost 70% of their original weight.
The possibility of using controlled breakdown for drug delivery in a biomedical application was shown through the slow release of an added dye as the plastic degraded.
The researchers were also able to demonstrate how controlled degradation could be used for 4D printing, where 3D printed objects respond to their environments and change over time. A kiwi printed from polylactic acid (PLA) was encapsulated in an egg made of enzyme-containing PCL. After eight days ‘incubation’ in a buffer solution at 37°C, the kiwi ‘hatched’.
The kiwi-in-egg object shows how 4D printed materials could also be used in biomedical implants, for example, where one part of the system needs to absorb into the body before another part.
Looking to the future
Thermoplastic processing of solid state enzymes combined with bioplastics is a practical, solvent-free and scalable way to produce plastics that degrade in a controlled way. While this work focussed on biomedical applications, replacing non-biodegradable polymers with biobased plastics that degrade quickly and predictably is one possible way to tackle the world’s plastic waste problem. The next step for Scion’s research is to work with companies that are interested in embedding this technology into their compostable products.
We would love to hear from anyone interested in working on this together.
For more information on controlled degradation contact
Angelique F. Greene, Alankar Vaidya, Christophe Collet, Kelly R. Wade, Meeta Patel, Marc Gaugler, Mark West, Miruna Petcu, and Kate Parker (2021). 3D-Printed Enzyme-Embedded Plastics, Biomacromolecules. https://doi.org/10.1021/acs.biomac.1c00105