Biodegradable bioplastics could provide an alternative to the eight million tons of plastic that end up in the oceans every year. As packaging demands rise, so is the waste generated by plastics based on petrochemicals. Unfortunately, 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.
In the journal Angewandte Chemie, a research 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) 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.
The innovative bioplastics’ properties can be tailored according to need. To do so, 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. If the attachment 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 bioplastics to be produced at room temperature in any shape desired, and without toxic chemicals or complex processing steps. Their breaking stress exceeds those of many commercial plastics. However, one problem left is that they swell in water.
When 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.
This new nontoxic bioplastic can be used in the production of toys, and even 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.