Literature Review: Developing Alternative Bioplastics with Biomimicry and Biotechnology-Based Solutions

Past studies finding alternative solutions to the consumption of plastics have been favored to replace items like straws, plates, eating utensils, and bags with alternatives like paper, bamboo, or wood-like materials. Corporations like Starbucks have tried promoting sustainability in their business models by integrating paper straws into their drinks. However, most of the containers for their drinks mainly consist of plastic materials.

Large corporations thrive off the cheaply manufactured material applicable to any one-time consumed product, which is relevant mainly in food or wrapping markets. Annually, one million plastic water bottles are used every minute, and 5 trillion plastic bags are produced in factories. Of all single-use plastics, 85% are in poorly managed waste systems or landfills, primarily in developing and poorer countries that “stockholder” this waste. In America, only 9% of all plastic gets recycled from 400 million tons, presenting a problem in managing this material.

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Following a feedback loop of detrimental consequences to societal and environmental health, the poor sustainability of plastic makes it hazardous for long-term consumption. Certain plastics can take up to 500 years for the plastic to degrade, which means the build-up of such existing plastic has easy potential to be in landfills. Decomposition of this plastic is expensive and most likely to be carried through photodegradation, but this takes a long time to get rid of the material. Hence, a negative cycle of plastic is created and sent to various sectors of the environment. For instance, we see a correlation between a lack of waste management and decreased human health:

• Animals may damage plastic that is transported to landfills in developing countries in the nearby area.
• The toxic pollutants and liquids from burning or melting plastic may leak into waterways infecting river steams and other drinking water sources for local communities.
• Nearby residents who depend on these waterways may now be infected with these new diseases and illnesses that get passed by the contamination leading to deaths, shorter lifespans, or maternal-related illnesses or deaths.

Around 400,000 to one million deaths occur in developing countries from the lack of such waste management and lack of funding for proper regulation.

Other examples include the impact on ecosystem health: animals that are searching for food eating microplastic material or eating plastic from poorly discarded plastic waste; this harms the health of the ecosystem from quaternary consumers or tertiary consumers and through the rest of the food chain as microplastic and other hazardous chemicals are ingested and passed down. Burning the material or manufacturing it in factories releases pollutants not only through the soil or water but also through the atmosphere.

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Alginate-Gelatin Hydrogels

The macromolecule form of alginate, a derivative of algae, and the material gelatin can be used to make a new water-based material allowing a particular consistency for plastic. The initial idea behind the new material was to have the macromolecules of the two substances react in a water-based environment to form a hydrogel chemically. The hydrogel would form a transparent, flexible material that could be molded into any 3D-dimensional shape desired when taken out of its water environment and dried. A high biocapacity, making it flexible with liquid and soft objects, allows the hydrogel to be used for material reasons (A Physically Cross-Linked Sodium Alginate–Gelatin).

Alginate is used primarily to make hydrogels because it retains water (Łabowska, Magdalena B, 2021). Although it is favorable in the biomedical sense, it could lead to water scarcity problems if mass-produced. Alginate is a very flexible structure commonly used with gels; however, it also has a very loose structure. This flaw is counteracted with gelatin, which gives the material more rigidity. The problem is that gelatin has environmental issues. It is usually sourced from farm animals’ bones, tendons, and skin. Using this material could further incentivize animal slaughtering, correlating with increases in greenhouse gas emissions. There is also the problem of durability. Gelatin is bacteria-prone, which could lead to safety problems — incompatibility with food materials that could lead to health risks.

Why is plastic so relevant? Plastic packaging is lightweight and can take up less space than alternatives, which means lighter loads for planes and trucks and lower emissions. However, when it comes to alginate-gelatin hydrogels, they do not provide or make up for the properties that plastic has. This is mainly why the majority of people around the world continue using plastic. Environmentally friendly straws, utensils, and many more still need to amount to the number of plastic objects that are being used, and this is because they all lack the properties of plastic. Although it is important to revisit that alginate-hydrogels hold similar properties to living tissue and are not as durable as the materials themselves, they have high elasticity and are incredibly flexible for shaping.

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E. Coli Inspired Aquaplastics

E.coli can also be utilized to produce a type of aqua plastic. The basic principle is rooted in the biomimicry of living cells and their properties. E.coli build matrices, or “nests,” to surround themselves with. The outermost of these layers is called the extracellular matrix, and it is made up of protein curli nanofibres (CSA). E.coli is first cultured in a tube of water. Once the growth is sufficient, the E. Coli is separated through a filter, separating the water and bacteria from the extracellular matrix (Duraj-Thatte, 2021). This matrix will serve as the primary material to make these aqua plastics. The water that this matrix retains supports the frame of the hydrogel. Once these cellular matrices are concentrated into hydrogels, they are dried under ambient conditions to produce the new plastic.

These aqua plastics present unique abilities: aqua wielding — a process that allows two different aqua plastics to be glued together using microliters of water, and aqua healing — a process that allows the material to self-heal (like skin cells) with the use of microliters of water, and aqua molding — the use of 2D or 3D molds to give hydrogels their rigid shape. This new plastic is very resistant to solvents. However, it still possesses biodegradability skills that constitute it sustainable (it loses 90% of its mass in 45 days once in contact with natural conditions/solvents). It should also be noted that there is no concern with bacterial infections, as the material is made of bacteria.

In an example of using genetically modified E. coli, a study team from South Korea’s KAIST University showed they could produce aromatic polyesters from feedstock carbohydrates. Plastic that is both strong and light is made using these aromatic polyesters. This product would use a microbially-based biomanufacturing strategy with the lab or environmentally grown E. Coli. Research developing these types of aqua plastics was studied at the Center for Nanoscale Systems at Harvard. A limitation noted was that when there was an absence of CsgA fusions, a significant protein of curli fibers assembled by E. Coli, and SDS-induced gelation proteins, the consistency of the aqua plastic became brittle during the drying process (Anna, Duraj-Thatte). Results from the study noted that a protein-coding gene called TFF2 or the presence of SDS was needed for the moldable properties of the hydrogels. More insights into biomaterial tech for production in bacterial-based bioplastics need to be looked into for more efficiency in the material.

There are a few limitations and implications on the production of aqua plastic from e. Coli. When looking a journal, Water-Processable, Biodegradable and Coatable Aquaplastic from Engineered Biofilms, the paper states that although the aqua plastics are biodegradable, the curli fibers that they are made from are resistant to “disassembly in the presence of solvents, harsh pH values, and detergents” (Duraj-Thatte, 2021). It was also found that aqua plastics remained stable in non-polar solvents such as n-hexane, even after incubating them for 24 hours. They also remained stable in chloroform, which helps other substances dissolve, including rubber, plastics, and coatings. The weight of the aqua plastics did not change appreciably after incubation in the organic solvents; surprisingly, both aqua plastics remained intact and unchanged after 24 h in 18 M sodium hydroxide.

Moreover, Jeffrey S. Moore, a professor of chemistry at the University of Illinois, stated that some obstacles need to be overcome when making aqua plastic commercially available and in competition with traditional plastic (Schlossberg, Tatiana). An example of an obstacle was that aqua plastic is not water-resistant. In order to compete with traditional plastic, it needs to match its characteristics of it, one of them being protection and the ability to protect food and other sterile objects. Because of their lack of specific characteristics, Moore says that “aqua plastic still has a long way to go” (Schlossberg, Tatiana, 2021).

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Chitin Mixtures

Crab, shrimp, lobster, or any chitin-based waste is collected and ground in chitin mixtures. The chitosan is separated and blended with vinegar to form a mixture. This mixture is then heated and molded to fit the product’s shape (Varun, Tarun Kumar, 2017). This product has excellent durability and moldability and is very cheap to produce. Although specific durability is unknown, the use of chitosan gives it comparable strength to that of crustacean shells.

Current chitin/chitosan research has the potential to be synthesized into reliable materials that can boast similar properties to plastic. After forming a mold using recycled seafood waste, the material has excellent flexibility and moldability to fit whatever application is necessary. The abundance of this seafood waste makes this material very economically viable, allowing it to expand to mass production. Shellworks, an alternative plastic packaging company, uses vegan and compostable materials for their biopolymers. Their Vivomer product uses the aid of microbes for packaging material. It can be used for shelf-storage reasons and co-exist with oil and water-based emulsions. As the product degrades, microbes eat the Vivomer material making it naturally degradable (“Materials,” Shellworks). Although chitin has excellent durability properties with the ability to be decomposed and used as a fertilizer after being used, the material is not transparent, possessing a brownish color displeasing to the eye. It has a very repulsive color that could draw away customers. Some research has been done on glycerol to achieve a more transparent look, but it still needs to be thoroughly tested, and tangible results still need to be identified. There are also some concerns about smell, as the bass polymer, chitosan, is derived directly from seafood waste. It could deviate from the pristine look of plastics and thus drive down production. The improvement of the mechanical properties of chitin bioplastics would have to be further researched to consider this material as an alternative.

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Keratin-based biocomposites

Keratin is commonly found in hair or nails, making it highly fibrous and full of protein. Chitin and keratin composites derived from cross-linking experiments were thought to have applications in biomedicine. A membrane derived from it would be a bandaid for healing wounds (Lin, Che-Wei, 2018). In another study, keratin extracted from chicken feathers was mixed with PVA/glycerol (commonly added with PVA material to make it softer and more flexible) to make protein-based plastics. The results of the study showed a “high structural strength” and a “morphology good crystallinity” for food packaging and manufacturing purposes and other biomedical uses (Alashwal, Basma, 2019). Although the technical process for manufacturing the material is very recyclable and clean, the resulting product is still a thin film, not a rigid plastic. This presents issues in terms of applications. Its poor mechanical properties, that deal with elasticity, strength, harness, or ability to be stretched, require it to be combined with other natural materials to improve the development of the gel films (Lin, Che-Wei, 2018). However, some chemical cross-linking methods to improve the gel consistency can be time-consuming in a lab.

To enhance the weak fiber proteins, keratin can be combined with a common biopolymer, specifically chitosan, increasing rigidity and bacterial resistance (Mututuvari, Tamutsiwa, 2015). A new ionic liquid: butyl methylimidazolium chloride ([BMIm+ Cl–]), can now be used as the sole solvent to synthesize composites, able to do so in a single and recyclable step. First, under an N2 atmosphere and vigorous stirring, chitosan and keratin are dissolved in ([BMIm+ Cl–]) by adding portions of these polymers in 0.5 wt % of the IL (Mututuvari, Tamutsiwa, 2015). The resulting solution can be cast onto molds and undergo gelatinization at room temperature to yield gel films. To complete the process, these wet gel films are dried at room temperature in a humidity-controlled chamber to obtain dry films.

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Amino Acids from Feathers

In addition to the other research studies, peacock feathers are structured with amino acids which correlate to high concentrations of glycine and serine (Gregg, Keith, 1986). Serine is a chemical component that acts as a building block for proteins which can be transformed into its composition through glycine. Glycine is an amino acid highly compatible with plastics, making them more flexible. Since it is an amino acid, it is desirable to bacteria that want to eat it. Amino acids found in feathers can be used as natural plasticizers to make a new plastic material. The potential of the acids can be used to make bioplastics for packaging materials that need elasticity. In one study by chemist Thomas M. Stein from the National Center for Agricultural Utilization Research in Illinois, he tested different plasticizers with those mixed with starch and amino acids like proline, glycine, and isoleucine. He found that the proline had the most flexibility among all the composites (Hardin, Ben, 1997). Although proline allows for a highly elastic material, it is expensive and becomes glassy and not flexible when placed in environments that are at humidities of about 20 percent. Experimentation with amino acids in the consistency of bioplastic can be tested to get the elastic properties that want to be seen for wrappers and bendable containers.

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Conclusion

Regarding approaching chitin mixtures, its lack of efficiency in mechanical properties, rigidness, and unappealing yellow-brown color make it inconvenient in the bioplastic market. Keratin solutions have a higher potential to be integrated for better gel consistency. On the other hand, the E. coli bacterium is relatively more expensive to test in trials as there needs to be a constant variable environment for the bacteria to survive within a lab. A more accessible approach to the hydrogels can be the experimentation of an existing idea, such as the Alginate-Gelatin hydrogels, as our materials are currently limited. A more viable proposition to approach the plastic waste problem would be to synthesize biowaste, similar to chitin mixtures, and prioritize water-based, ambient conditions like hydrogels.

Works Cited

1. Duraj-Thatte, Anna M., et al. “Water-Processable, Biodegradable and Coatable Aquaplastic from Engineered Biofilms.” Nature News, Nature Publishing Group, 18 March. 2021, https://www.nature.com/articles/s41589-021-00773-y.
2. A Physically Cross-Linked Sodium Alginate–Gelatin … — ACS Publications. https://pubs.acs.org/doi/10.1021/acsapm.1c00404.
3. Łabowska, Magdalena B, et al. “A Review on the Adaption of Alginate-Gelatin Hydrogels for 3D Cultures and Bioprinting.” Materials (Basel, Switzerland), MDPI, 10 Feb. 2021, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7916803/.
4. “Materials.” Shellworks, https://www.theshellworks.com/materials.
5. Lin, Che-Wei, et al. “Photo-Crosslinked Keratin/Chitosan Membranes as Potential Wound Dressing Materials.” Polymers, MDPI, 4 September 2018, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6403811/.
6. Alashwal, Basma Y., et al. “Improved Properties of Keratin-Based Bioplastic Film Blended with Microcrystalline Cellulose: A Comparative Analysis.” Science, Elsevier, 28 Mar. 2019, https://www.sciencedirect.com/science/article/pii/S1018364718321001.
7. Schlossberg, Tatiana. “Scientists Say This E. Coli Will not Make You Sick and Could Be Good for the Planet.” The Washington Post, WP Company, 12 May 2021, https://www.washingtonpost.com/climate-solutions/2021/05/12/plastic-waste-ecoli/.
8. Keratinization of Sheath and Calamus Cells in Developing and … https://www.researchgate.net/publication/5770588_Keratinization_of_sheath_and_calamus_cells_in_developing_and_regenerating_feathers.
9. Gregg, Keith, and George E. Rogers. “Feather Keratin: Composition, Structure and Biogenesis.” SpringerLink, Springer Berlin Heidelberg, 1 Jan. 1986, https://link.springer.com/chapter/10.1007/978-3-662-00989-5_33.
10. Hardin, Ben. “Plastic made more flexible, more degradable.” Agricultural Research, vol. 45, no. 4, Apr. 1997, p. 21. Gale Academic OneFile, link.gale.com/apps/doc/A19547872/AONE?u=ever01909&sid=googleScholar&xid=05216852. Accessed 23 September 2022.
11. Mututuvari, Tamutsiwa, and Tran, Chieu. “Cellulose, Chitosan, and Keratin Composite Materials. Controlled Drug Release.” ACSPublications 30 December 2014, https://pubs.acs.org/doi/10.1021/la5034367#
12. Łabowska, Magdalena B, et al. “A Review on the Adaption of Alginate-Gelatin Hydrogels for 3D Cultures and Bioprinting.” Materials (Basel, Switzerland), MDPI, 10 Feb. 2021, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7916803/
13. Varun, Tarun Kumar, et al. “Extraction of Chitosan and Its Oligomers from Shrimp Shell Waste, Their Characterization, and Antimicrobial Effect.” Veterinary World, Veterinary World, Feb. 2017